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  • 1.
    Achtert, Peggy
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Birmili, W.
    Nowak, A.
    Wehner, B.
    Wiedensohler, A.
    Takegawa, N.
    Kondo, Y.
    Miyazaki, Y.
    Hu, M.
    Zhu, T.
    Hygroscopic growth of tropospheric particle number size distributions over the North China Plain2009In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 114, D00G07- p.Article in journal (Refereed)
    Abstract [en]

    The hygroscopic growth of atmospheric submicrometer particle size distributions (diameter D-p ranging from 22 to 900 nm) was studied at a rural/suburban site in the North China Plain within the framework of the international Campaigns of Air Quality Research in Beijing and Surrounding Region 2006 (CAREBeijing-2006) research project. The goal was to characterize the regional aerosol in the polluted northeastern plain in China. Size descriptive hygroscopic growth factors (DHGFs) were determined as a function of relative humidity (RH) by relating the particle number size distribution at a dry condition ( 100 nm), the DHGF are substantially higher than in the Aitken particle mode (D-p < 100 nm) as a result of different chemical composition. The size-dependent behavior of the DHGF highlights the relevance of particulate sulfate production over the North China Plain, accomplished by secondary formation from the gas phase and, potentially, liquid phase processes in convective clouds. Furthermore, all results concerning the DHGF show a significant dependency on meteorological air masses. The hygroscopic growth of accumulation mode particles correlates significantly with the PM1-mass fraction of sulfate ions determined by chemical analysis. Finally, this investigation provides a parameterization of the hygroscopic growth of 250-nm particles, which might be useful when predicting visibility and radiative forcing and performing atmospheric aerosol model validations.

  • 2.
    Achtert, Peggy
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Khosrawi, Farahnaz
    Stockholm University, Faculty of Science, Department of Meteorology .
    Blum, U.
    Fricke, K. H.
    Investigation of polar stratospheric clouds in January 2008 by means of ground-based and spaceborne lidar measurements and microphysical box model simulations2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, D07201- p.Article in journal (Refereed)
    Abstract [en]

    Polar stratospheric clouds (PSCs) play a key role in heterogeneous chemistry and ozone depletion in the lower stratosphere. The type of PSC as well as their temporal and spatial extent are important for the occurrence of heterogeneous reactions and, thus, ozone depletion. In this study a combination of ground-based and spaceborne lidar measurements were used together with microphysical box model simulations along back trajectories to investigate the formation and alteration of Arctic PSCs. The measurements were made by the Rayleigh/Mie/Raman lidar system at Esrange and by the Cloud-Aerosol Lidar with Orthogonal Polarization aboard the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation (CALIPSO) satellite. Between 20 and 23 January 2008 PSCs composed of liquid particles were observed by CALIPSO between Greenland and the western side of the Scandinavian Mountains. Between 21 and 23 January 2008 the Esrange lidar observed a PSC composed of distinct layers of liquid and solid particles on the eastern side of the mountain range. Microphysical box model simulations along air parcel back trajectories indicate that liquid particles had formed at least 40 h before the observation at Esrange. Furthermore, the model indicates a high HNO(3) uptake into the liquid layer between 10 and 20 h before the observation. The PSC was formed when the air mass was over Greenland. On two occasions during these 20 h, CALIPSO observed PSCs when its measurement tracks crossed the air parcel back trajectory ending at the location of the Esrange lidar. Backscatter ratios calculated from the output of the box model simulation indicate good agreement with the values observed with the Esrange lidar and by CALIPSO. The box model simulations along the back trajectories from Esrange to the CALIPSO ground track and beyond provide us with the unique opportunity to relate ground-based and spaceborne lidar measurements that were not performed at the same spatial location and time. Furthermore, possible differences in the observations from ground and space can be traced to temporal and/or geographically induced changes in particle microphysics within the measured PSCs.

  • 3. Adriani, O.
    et al.
    Barbarino, G.
    Bazilevskaya, G. A.
    Bellotti, R.
    Boezio, M.
    Bogomolov, E. A.
    Bonechi, L.
    Bongi, M.
    Bonvicini, V.
    Borisov, S. V.
    Bottai, S.
    Bruno, A.
    Cafagna, F. S.
    Campana, D.
    Carbone, R.
    Carlson, Per
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Casolino, M.
    Castellini, G.
    Consiglio, L.
    De Pascale, M. P.
    De Santis, C.
    De Simone, N.
    Di Felice, V.
    Galper, A. M.
    Gillard, William
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Grishantseva, L. A.
    Jerse, G.
    Hofverberg, Petter
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Karelin, A. V.
    Koldashov, S. V.
    Krutkov, S. Y.
    Kvashnin, A. N.
    Leonov, A. A.
    Malakhov, V. V.
    Malvezzi, V.
    Marcelli, L.
    Mayorov, A. G.
    Menn, W.
    Mikhailov, V. V.
    Mocchiutti, E.
    Monaco, A.
    Mori, N.
    Nikonov, N. N.
    Osteria, G.
    Papini, P.
    Pearce, Mark
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Picozza, P.
    Pizzolotto, C.
    Ricci, M.
    Ricciarini, S. B.
    Rossetto, Laura
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Ritabrata, S.
    Runtso, M. F.
    Simon, M.
    Sparvoli, R.
    Spillantini, P.
    Stozhkov, Y. I.
    Vacchi, A.
    Vannuccini, E.
    Vasilyev, G. I.
    Voronov, S. A.
    Wu, Juan
    KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
    Yurkin, Y. T.
    Zampa, G.
    Zampa, N.
    Zverev, V. G.
    Measurements of quasi-trapped electron and positron fluxes with PAMELA2009In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 114, A12218- p.Article in journal (Refereed)
    Abstract [en]

    This paper presents precise measurements of the differential energy spectra of quasi-trapped secondary electrons and positrons and their ratio between 80 MeV and 10 GeV in the near-equatorial region (altitudes between 350 km and 600 km). Latitudinal dependences of the spectra are analyzed in detail. The results were obtained from July until November 2006 onboard the Resurs-DK satellite by the PAMELA spectrometer, a general purpose cosmic ray detector system built around a permanent magnet spectrometer and a silicon-tungsten calorimeter.

  • 4. Agapitov, Oleksiy
    et al.
    Krasnoselskikh, Vladimir
    de Wit, Thierry Dudok
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Pickett, Jolene S.
    Santolik, Ondrej
    Rolland, Guy
    Multispacecraft observations of chorus emissions as a tool for the plasma density fluctuations' remote sensing2011In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 116, A09222- p.Article in journal (Refereed)
    Abstract [en]

    Discrete ELF/VLF chorus emissions are the most intense electromagnetic plasma waves that are observed in the radiation belts and in the outer magnetosphere of the Earth. They are assumed to propagate approximately along the magnetic field lines and are generated in source regions in the vicinity of the magnetic equator and in minimum B pockets in the dayside outer zone of the magnetosphere. The presence of plasma density irregularities along the raypath causes a loss of phase coherence of the chorus wave packets. These irregularities are often present around the plasmapause and in the radiation belts; they occur at scales ranging from a few meters up to several hundred kilometers and can be highly anisotropic. Such irregularities result in fluctuations of the dielectric permittivity, whose statistical properties can be studied making use of intersatellite correlations of whistler waves' phases and amplitudes. We demonstrate how the whistler-mode wave properties can be used to infer statistical characteristics of the density fluctuations. The analogy between weakly coupled oscillators under the action of uncorrelated random forces and wave propagation in a randomly fluctuating medium is used to determine the wave phase dependence on the duration of signal recording time. We study chorus whistler-mode waves observed by the Cluster WBD instrument and apply intersatellite correlation analysis to determine the statistical characteristics of the waveform phases and amplitudes. We then infer the statistical characteristics of the plasma density fluctuations and evaluate the spatial distribution of the irregularities using the same chorus events observed by the four Cluster spacecraft.

  • 5. Agren, Anneli
    et al.
    Buffam, Ishi
    Bishop, Kevin
    Department of Aquatic Sciences and Assessment, Swedish University of Agricultural Sciences, Uppsala, Sweden.
    Laudon, Hjalmar
    Modeling stream dissolved organic carbon concentrations during spring flood in the boreal forest: A simple empirical approach for regional predictions2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, no G1, G01012- p.Article in journal (Refereed)
    Abstract [en]

    Changes in dissolved organic carbon (DOC) concentration are clearly seen for streams in which chemistry is measured on a high-frequency/episode basis, but these high-frequency data are not available in long-term monitoring programs. Here we develop statistical models to predict DOC concentrations during spring flood from easily available geographic information system data and base flow chemistry. Two response variables were studied, the extreme DOC concentration and the concentration during peak flood. Ninety-seven streams in boreal Scandinavia in two different ecoregions with substantially different mean water chemistry and landscape characteristics (covering a large climatic gradient) were used to construct models where 56% of the extreme DOC concentration and 63% of the concentration during peak flood were explained by altitude. This highlights important regional drivers (gradients in altitude, runoff, precipitation, temperature) of material flux. Spring flood extreme DOC concentration could be predicted from only base flow chemistry (r(2) = 0.71) or from landscape data (r(2) = 0 .74) but combining them increased the proportion of explained variance to 87%. The "best" model included base flow DOC (positive), mean annual runoff (negative), and wetland coverage (positive). The root mean square error was 1.18 mg L-1 for both response variables. The different ecoregions were successfully combined into the same regression models, yielding a single approach that works across much of boreal Scandinavia.

  • 6. Aikio, A T
    et al.
    Blomberg, Lars
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Yamauchi, M
    On the origin of the high-altitude electric field fluctuations in the auroral zone1996In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 101, no A12, 27157-27170 p.Article in journal (Refereed)
    Abstract [en]

    Intense fluctuations in the electric field at high altitudes in the auroral zone are frequently measured by the Viking satellite. We have made an analysis of the origin of electric and magnetic fluctuations in the frequency range of 0.1 - 1 Hz by assuming four different sources for the signals: (I) spatial structures, (2) spatial structures with a parallel potential drop below the satellite, (3) traveling; shear Alfven waves, and (4) interfering shear Alfven waves. We will shaw that these different sources of the signals may produce similar amplitude ratios and phase differences between the perpendicular electric and magnetic fields. Since the different sources have different frequency dependencies, this can be used as an additional test if the signals are broadband. In other cases, additional information is needed, for example, satellite particle measurements or ground; magnetic measurements. The ideas presented in the theory were tested for one Viking eveningside pass over Scandinavia, where ground-based magnetometer and EISCAT radar measurements were available. The magnetic conditions were active during this pass and several interfering shear Alfven waves were found. Also, a spatial structure with a parallel potential drop below the satellite was identified. The magnitude of the 10-km-wide potential drop was at least 2 kV and the upward field-aligned current 26 mu A m(-2) (value mapped to the ionospheric level). The held-aligned conductance was estimated as 1.3 - 2.2x10(-8) S m(-2).

  • 7.
    Alm, Love
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Electron density and parallel electric field distribution of the auroral density cavity2015In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 120, no 11, 9428-9441 p.Article in journal (Refereed)
    Abstract [en]

    We present an event study in which Cluster satellites C1 and C3 encounters the flux tube of a stable auroral arc in the pre-midnight sector. C1 observes the mid cavity, while C3 enters the flux tube of the auroral arc at an altitude which is below the acceleration region, before crossing into the top half of the acceleration region. This allows us to study the boundary between the ionosphere and the density cavity, as well as large portion of the upper density cavity. The position of the two satellites, in relation to the acceleration region, is described using a pseudo altitude derived from the distribution of the parallel potential drop above and below the satellites.The electron density exhibits an anti-correlation with the pseudo altitude, indicating that the lowest electron densities are found near the top of the density cavity. Over the entire pseudo altitude range, the electron density distribution is similar to a planar sheath, formed out of a plasma sheet dominated electron distribution, in response to the parallel electric field of the acceleration region. This indicates that the parallel electric fields on the ionosphere-cavity boundary, as well as the mid cavity parallel electric fields, are part of one unified structure rather than two discrete entities.The results highlight the strong connection between the auroral density cavity and auroral acceleration as well as the necessity of studying them in a unified fashion.

  • 8.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Burlini, Luigi
    Mainprice, David
    Hirt, Ann
    Elastic properties of anisotropic synthetic calcite-muscovite aggregates2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115Article in journal (Refereed)
  • 9.
    Almqvist, Bjarne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Mainprice, David
    Madonna, Claudio
    Burlini, Luigi
    Hirt, Ann
    Application of differential effective medium, magnetic pore fabric analysis, and X-ray microtomography to calculate elastic properties of porous and anisotropic rock aggregates2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116Article in journal (Refereed)
  • 10. Al-Wardy, W
    et al.
    Zimmerman, Robert W
    Dept. of Earth Science/Engineering, Imperial Coll. of Sci. Technol./Med., London .
    Effective stress law for the permeability of clay-rich sandstones2004In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 109, no 4, 1-10 p.Article in journal (Refereed)
    Abstract [en]

    Two models of clay-rich sandstones are analyzed to explain the relative sensitivity ofpermeability to pore pressure and confining pressure. In one model the clay lines the entire pore wall in a layer of uniform thickness, and in the second model the clay is distributed in the form of particles that are only weakly coupled to the pore walls. Equations of elasticity and fluid flow are solved for both models, giving expressions for theeffective stress coefficients in terms of clay content and the elastic moduli of the rock andclay. Both models predict that the permeability will be much more sensitive to changes in pore pressure than to changes in confining pressure. The clay particle model gives somewhat better agreement with data from the literature and with new data on a Staintonsandstone having a solid volume fraction of 8% clay. 

  • 11. Amanda Collaboration, -
    et al.
    Pohl, Arvid
    University of Kalmar, School of Pure and Applied Natural Sciences.
    Optical Properties of Deep Glacial Ice at the South Pole2006In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 111, no D13, D13203- p.Article in journal (Refereed)
    Abstract [en]

    We have remotely mapped optical scattering and absorption in glacial ice at the South Pole for wavelengths between 313 and 560 nm and depths between 1100 and 2350 m. We used pulsed and continuous light sources embedded with the AMANDA neutrino telescope, an array of more than six hundred photomultiplier tubes buried deep in the ice. At depths greater than 1300 m, both the scattering coefficient and absorptivity follow vertical variations in concentration of dust impurities, which are seen in ice cores from other Antarctic sites and which track climatological changes. The scattering coefficient varies by a factor of seven, and absorptivity (for wavelengths less than ∼450 nm) varies by a factor of three in the depth range between 1300 and 2300 m, where four dust peaks due to stadials in the late Pleistocene have been identified. In our absorption data, we also identify a broad peak due to the Last Glacial Maximum around 1300 m. In the scattering data, this peak is partially masked by scattering on residual air bubbles, whose contribution dominates the scattering coefficient in shallower ice but vanishes at ∼1350 m where all bubbles have converted to nonscattering air hydrates. The wavelength dependence of scattering by dust is described by a power law with exponent −0.90 ± 0.03, independent of depth. The wavelength dependence of absorptivity in the studied wavelength range is described by the sum of two components: a power law due to absorption by dust, with exponent −1.08 ± 0.01 and a normalization proportional to dust concentration that varies with depth; and a rising exponential due to intrinsic ice absorption which dominates at wavelengths greater than ∼500 nm.

  • 12. Anderson, L. G.
    et al.
    Björk, G.
    Holby, O.
    Jones, E. P.
    Kattner, G.
    Kolterman, K. P.
    Liljeblad, B.
    Lindegren, R.
    Rudels, B.
    Swift, J.
    Water masses and circulation in the Eurasian basin. Results from the Oden-91 expedition1994In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 99, no C2, 3273-3283 p.Article in journal (Refereed)
  • 13. Anderson, L G
    et al.
    Jones, E P
    Swift, J H
    Export production in the central Arctic Ocean evaluated from phosphate deficits2003In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 108, no C6Article in journal (Refereed)
    Abstract [en]

    [1] Primary productivity in the central Arctic Ocean has recently been reported as being much higher than earlier thought. If a significant fraction of this primary production were exported from the immediate surface region, present estimates of the carbon budget for the Arctic Ocean would have to be reassessed. Using the deficit of phosphate in the central Arctic Ocean, we show that the export production is very low, on an average less than 0.5 gC m(-2) yr(-1). This is at least an order of magnitude lower than the total production as measured or estimated from oxygen data, thus indicating extensive recycling of nutrients in the upper waters of the central Arctic Ocean and very little export production.

  • 14.
    Andersson, Camilla
    et al.
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Engardt, Magnuz
    European ozone in a future climate: The importance of changes in dry deposition and isoprene emissions2010In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 115, D02303- p.Article in journal (Refereed)
    Abstract [en]

    [1] Using a regional chemistry transport model (CTM) driven with meteorological data from a regional climate model (A2 emission scenario) we have investigated important processes for determining surface ozone concentration across Europe in a future climate. Anthropogenic ozone precursor emissions were kept constant (year 2000) to isolate the effect of climate change from 1961-1990 to 2021-2050 and 2071-2100. Biogenic isoprene emissions were calculated on-line. The results point to substantial increase in daily mean and daily maximum surface ozone over central and southern Europe. The importance of changes in natural isoprene emissions and dry deposition were investigated especially.[2] The isoprene emissions increased by a factor of about 1.8 from the current to the second future period. However, a sensitivity study using a sophisticated rescaling of isoprene emissions shows that the large increase in isoprene emission is of moderate importance in southern Europe for the strong increase in surface ozone (it can explain up to 30% of the change in central, southern and western Europe).[3] The soil-moisture dependent ozone dry deposition formulation and changes in snow cover, affecting the dry deposition, are more important processes: soil moisture dependence explains up to 80% of the change in Spain. Therefore it is vital to include soil moisture dependence in a model study of this type. Isoprene emissions are of less importance (0-30% in central and southern Europe), but not dismissible and should definitely be emitted on-line in climate-ozone projection studies.

  • 15. Andersson, L
    et al.
    Ivchenko, Nickolay
    KTH, Superseded Departments, Alfvén Laboratory.
    Clemmons, J
    Namgaladze, A
    Gustavsson, B
    Wahlund, E
    Eliasson, L
    Yurik, Y
    Electron signatures and Alfven waves2002In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 107, no A9Article in journal (Refereed)
    Abstract [en]

    [1] We identify two distinct electron populations associated with Alfven waves in the Freja data set using the high time resolution state of the art electron detector. One of the populations, detected together with an Alfven wave, is field-aligned and can be seen as trapped within the wave. The other electron population is detected before the wave and consists of electrons which have left the wave at a point with a velocity higher than the local Alfven speed. In the paper, the electrons leaving wave are modeled for different density profiles and are compared with the observed data. Depending on the density profile, the model can produce the same energy-time and pitch angle-time dispersion that is observed in the Freja data. The conclusion of the paper is that the Alfven wave can explain the observed particle signatures. It is shown that the Alfven wave acceleration can create electron signatures similar to inverted-V structures. The density distribution along a flux tube has an important role in the type of particle signatures that can be detected at low altitudes.

  • 16. Andreeova, K.
    et al.
    Pulkkinen, T. I.
    Laitinen, Tiera V.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Prech, L.
    Shock propagation in the magnetosphere: Observations and MHD simulations compared2008In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 113, no A9, A09224- p.Article in journal (Refereed)
    Abstract [en]

    We examine the propagation of disturbances in the Earth's magnetosphere caused by fast forward shock interaction with the magnetopause. Our statistical study and event analyses show that the propagation speeds are larger in the magnetosphere than in the solar wind and are larger in the nightside magnetosphere than in the dayside magnetosphere. A case study of a double shock during 9 November 2002 is examined both observationally and using the GUMICS-4 global MHD simulation. Tracing the disturbance propagation allows us to confirm that the MHD simulation results are in good agreement with the in situ observations. The simulation results show that the propagation of the disturbance occurs in the antisunward direction at all clock angles simultaneously. However, changes in the magnetosheath are largest at high latitudes, while in the magnetotail the largest variations are seen in the plasma sheet.

  • 17.
    Andrews, David J.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cowley, S. W. H.
    Dougherty, M. K.
    Lamy, L.
    Provan, G.
    Southwood, D. J.
    Planetary period oscillations in Saturn's magnetosphere: Evolution of magnetic oscillation properties from southern summer to post-equinox2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, A04224- p.Article in journal (Refereed)
    Abstract [en]

    We investigate the evolution of the properties of planetary period magnetic field oscillations observed by the Cassini spacecraft in Saturn's magnetosphere over the interval from late 2004 to early 2011, spanning equinox in mid-2009. Oscillations within the inner quasi-dipolar region (L <= 12) consist of two components of close but distinct periods, corresponding essentially to the periods of the northern and southern Saturn kilometric radiation (SKR) modulations. These give rise to modulations of the combined amplitude and phase at the beat period of the two oscillations, from which the individual oscillation amplitudes and phases (and hence periods) can be determined. Phases are also determined from northern and southern polar oscillation data when available. Results indicate that the southern-period amplitude declines modestly over this interval, while the northern-period amplitude approximately doubles to become comparable with the southern-period oscillations during the equinox interval, producing clear effects in pass-to-pass oscillation properties. It is also shown that the periods of the two oscillations strongly converge over the equinox interval, such that the beat period increases significantly from similar to 20 to more than 100 days, but that they do not coalesce or cross during the interval investigated, contrary to recent reports of the behavior of the SKR periods. Examination of polar oscillation data for similar beat phase effects yields a null result within a similar to 10% upper limit on the relative amplitude of northern-period oscillations in the south and vice versa. This result strongly suggests a polar origin for the two oscillation periods.

  • 18.
    Arvidson, R. E.
    et al.
    Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, United States.
    Ashley, J. W.
    School of Earth and Space Exploration, Mars Space Flight Facility, Arizona State University, Tempe, AZ 85287, United States.
    Bell III, J. F.
    Department of Astronomy, Cornell University, Ithaca, NY 14853, United States.
    Chojnacki, M.
    Planetary Geosciences Institute, Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, TN 37996, United States.
    Cohen, J.
    Honeybee Robotics Spacecraft Mechanisms Corporation, 460 W. 34th St., New York, NY 10001, United States.
    Economou, T. E.
    Laboratory for Astrophysics and Space Research, Enrico Fermi Institute, University of Chicago, Chicago, IL 60637, United States.
    Farrand, W. H.
    Space Science Institute, 4750 Walnut St., Boulder, CO 80301, United States.
    Fergason, R.
    U.S. Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001, United States.
    Fleischer, I.
    Institut für Anorganische und Analytische Chemie, Johannes Gutenberg-Universität, D-55099 Mainz, Germany.
    Geissler, P.
    U.S. Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001, United States.
    Gellert, R.
    Department of Physics, University of Guelph, Guelph, ON N1G 2W1, Canada.
    Golombek, M. P.
    Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, United States.
    Grotzinger, J. P.
    Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, United States.
    Guinness, E. A.
    Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, United States.
    Haberle, R. M.
    NASA Ames Research Center, Moffett Field, CA 94035, United States.
    Herkenhoff, K. E.
    U.S. Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001, United States.
    Herman, J. A.
    Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, United States.
    Iagnemma, Karl
    MIT, USA.
    Jolliff, B. L.
    Department of Earth and Planetary Sciences, Washington University, St. Louis, MO 63130, United States.
    Johnson, J. R.
    U.S. Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001, United States.
    Klingelhöfer, G.
    Institut für Anorganische und Analytische Chemie, Johannes Gutenberg-Universität, D-55099 Mainz, Germany.
    Knoll, A. H.
    Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, United States.
    Knudson, A. T.
    Planetary Science Institute, 1700 East Fort Lowell, Tucson, AZ 85719, United States.
    Li, R.
    Department of Civil and Environmental Engineering and Geodetic Science, Ohio State University, Columbus, OH 43210, United States.
    McLennan, S. M.
    Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY 11794, United States.
    Mittlefehldt, D. W.
    NASA Johnson Space Center, Houston, TX 77058, United States.
    Morris, R. V.
    NASA Johnson Space Center, Houston, TX 77058, United States.
    Parker, T. J.
    Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, United States.
    Rice, M. S.
    Department of Astronomy, Cornell University, Ithaca, NY 14853, United States.
    Schröder, C.
    Department of Hydrology, University of Bayreuth, Bayreuth, Germany.
    Soderblom, L. A.
    U.S. Geological Survey, 2255 N. Gemini Dr., Flagstaff, AZ 86001, United States.
    Squyres, S. W.
    Department of Astronomy, Cornell University, Ithaca, NY 14853, United States.
    Sullivan, R. J.
    Department of Astronomy, Cornell University, Ithaca, NY 14853, United States.
    Wolff, M. J.
    Space Science Institute, 4750 Walnut St., Boulder, CO 80301, United States.
    Opportunity Mars Rover mission: Overview and selected results from Purgatory ripple to traverses to Endeavour crater2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 116, E00F15- p.Article in journal (Refereed)
    Abstract [en]

    Opportunity has been traversing the Meridiani plains since 25 January 2004 (sol 1), acquiring numerous observations of the atmosphere, soils, and rocks. This paper provides an overview of key discoveries between sols 511 and 2300, complementing earlier papers covering results from the initial phases of the mission. Key new results include (1) atmospheric argon measurements that demonstrate the importance of atmospheric transport to and from the winter carbon dioxide polar ice caps; (2) observations showing that aeolian ripples covering the plains were generated by easterly winds during an epoch with enhanced Hadley cell circulation; (3) the discovery and characterization of cobbles and boulders that include iron and stony-iron meteorites and Martian impact ejecta; (4) measurements of wall rock strata within Erebus and Victoria craters that provide compelling evidence of formation by aeolian sand deposition, with local reworking within ephemeral lakes; (5) determination that the stratigraphy exposed in the walls of Victoria and Endurance craters show an enrichment of chlorine and depletion of magnesium and sulfur with increasing depth. This result implies that regional-scale aqueous alteration took place before formation of these craters. Most recently, Opportunity has been traversing toward the ancient Endeavour crater. Orbital data show that clay minerals are exposed on its rim. Hydrated sulfate minerals are exposed in plains rocks adjacent to the rim, unlike the surfaces of plains outcrops observed thus far by Opportunity. With continued mechanical health, Opportunity will reach terrains on and around Endeavour's rim that will be markedly different from anything examined to date. Copyright 2011 by the American Geophysical Union.

  • 19.
    Arvidson, R. E.
    et al.
    Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, United States.
    Bell III, J. F.
    Department of Astronomy, Cornell University, Ithaca, NY, United States.
    Bellutta, P.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
    Cabrol, N. A.
    NASA Ames Research Center, Moffett Field, CA, United States.
    Catalano, J. G.
    Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, United States.
    Cohen, J.
    Honeybee Robotics Spacecraft Mechanisms Corporation, New York, NY, United States.
    Crumpler, L. S.
    New Mexico Museum of Natural History and Science, Albuquerque, United States.
    Marais, D. J. Des
    NASA Ames Research Center, Moffett Field, CA, United States.
    Estlin, T. A.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
    Farrand, W. H.
    Space Science Institute, Boulder, CO, United States.
    Gellert, R.
    Department of Physics, University of Guelph, Guelph, ON, Canada.
    Grant, J. A.
    Center for Earth and Planetary Studies, Smithsonian Institution, Washington, DC, United States.
    Greenberger, R. N.
    Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, United States.
    Guinness, E. A.
    Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, United States.
    Herkenhoff, K. E.
    U.S. Geological Survey, Flagstaff, AZ, United States.
    Herman, J. A.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
    Iagnemma, Karl
    Department of Mechanical Engineering, Massachusetts Institute of Technology, Cambridge, MA, United States.
    Johnson, J. R.
    U.S. Geological Survey, Flagstaff, AZ, United States.
    Klingelhöfer, G.
    Institut für Anorganische und Analytische Chemie, Johannes Gutenberg-Universität, Mainz, Germany.
    Li, R.
    Department of Civil and Environmental Engineering and Geodetic Science, Ohio State University, Columbus, OH, United States.
    Lichtenberg, K. A.
    Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, United States.
    Maxwell, S. A.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
    Ming, D. W.
    NASA Johnson Space Center, Houston, TX, United States.
    Morris, R. V.
    NASA Johnson Space Center, Houston, TX, United States.
    Rice, M. S.
    Department of Astronomy, Cornell University, Ithaca, NY, United States.
    Ruff, S. W.
    School of Earth and Space Exploration, Arizona State University, Tempe, AZ, United States.
    Shaw, A.
    Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, United States.
    Siebach, K. L.
    Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, United States.
    de Souza, P. A.
    Information and Communication Technologies Centre, CSIRO, Hobart, Australia.
    Stroupe, A. W.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
    Squyres, S. W.
    Department of Astronomy, Cornell University, Ithaca, NY, United States.
    Sullivan, R. J.
    Department of Astronomy, Cornell University, Ithaca, NY, United States.
    Talley, K. P.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
    Townsend, J. A.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
    Wang, A.
    Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO, United States.
    Wright, J. R.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
    Yen, A. S.
    Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, United States.
    Spirit Mars Rover Mission: Overview and selected results from the northern Home Plate Winter Haven to the side of Scamander crater2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, no 9, E00F03- p.Article in journal (Refereed)
  • 20.
    Asokan, Shilpa M.
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Jarsjö, Jerker
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Vapor flux by evapotranspiration: effects of changes in climate, land-use and water-use2010In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 115, no D24Article in journal (Refereed)
    Abstract [en]

    Enhanced evapotranspiration (ET) over irrigated land and associated latent heat flux change can modify the climate. Model studies of such climate change effects of irrigation are commonly based on land use parameterizations, in terms of irrigated land area, or land area equipped for irrigation. Actual ET change, however, may also be driven by water use change in addition to land use change. This study quantifies and compares ET changes due to changes in climate, land use, and water use from the preirrigation period 1901–1955 to the recent period 1990–2000 (with irrigation) for the example case of Mahanadi River Basin (MRB) in India. The results show that actual water use per unit area of irrigated land may vary greatly over a hydrological drainage basin. In MRB, much higher water use per irrigated land unit in the downstream humid basin parts leads to higher vapor flux by ET, and irrigation‐induced ET flux change, than in the upstream, water‐stressed basin parts. This is consistent with water supply limitations in water‐stressed basins. In contrast, the assumption in land use−based models that irrigation maintains high soil moisture contents can imply higher modeled water use and therefore also higher modeled ET fluxes under dry conditions than under humid conditions. The present results indicate water use as an important driver of regional climate change, in addition to land use and greenhouse gas‐driven changes.

  • 21. Auriac, A.
    et al.
    Spaans, K. H.
    Sigmundsson, F.
    Hooper, A.
    Schmidt, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Lund, Björn
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
    Iceland rising: Solid Earth response to ice retreat inferred from satellite radar interferometry and visocelastic modeling2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 4, 1331-1344 p.Article in journal (Refereed)
    Abstract [en]

    A broad uplift occurs in Iceland in response to the retreat of ice caps, which began circa 1890. Until now, this deformation signal has been measured primarily using GPS at points some distance away from the ice caps. Here, for the first time we use satellite radar interferometry (interferometric synthetic aperture radar) to constrain uplift of the ground all the way up to the edge of the largest ice cap, Vatnajokull. This allows for improved constraints on the Earth rheology, both the thickness of the uppermost Earth layer that responds only in an elastic manner and the viscosity below it. The interferometric synthetic aperture radar velocities indicate a maximum displacement rate of 24 +/- 4 and 31 +/- 4 mm/yr at the edge of Vatnajokull, during 1995-2002 and 2004-2009, respectively. The fastest rates occur at outlet glaciers of low elevation where ice retreat is high. We compare the observations with glacial isostatic adjustment models that include the deglaciation history of the Icelandic ice caps since 1890 and two Earth layers. Using a Bayesian approach, we derived probability density functions for the average Earth model parameters for three satellite tracks. Based on our assumptions, the three best fit models give elastic thicknesses in the range of 15-40 km, and viscosities ranging from 4-10x1018 Pa s.

  • 22. Austin, John
    et al.
    Struthers, Hamish
    Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Scinocca, J.
    Plummer, D. A.
    Akiyoshi, H.
    Baumgaertner, A. J. G.
    Bekki, S.
    Bodeker, G. E.
    Braesicke, P.
    Bruehl, C.
    Butchart, N.
    Chipperfield, M. P.
    Cugnet, D.
    Dameris, M.
    Dhomse, S.
    Frith, S.
    Garny, H.
    Gettelman, A.
    Hardiman, S. C.
    Joeckel, P.
    Kinnison, D.
    Kubin, A.
    Lamarque, J. F.
    Langematz, U.
    Mancini, E.
    Marchand, M.
    Michou, M.
    Morgenstern, O.
    Nakamura, T.
    Nielsen, J. E.
    Pitari, G.
    Pyle, J.
    Rozanov, E.
    Shepherd, T. G.
    Shibata, K.
    Smale, D.
    Teyssedre, H.
    Yamashita, Y.
    Chemistry-climate model simulations of spring Antarctic ozone2010In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 115, D00M11- p.Article in journal (Refereed)
    Abstract [en]

    Coupled chemistry-climate model simulations covering the recent past and continuing throughout the 21st century have been completed with a range of different models. Common forcings are used for the halogen amounts and greenhouse gas concentrations, as expected under the Montreal Protocol (with amendments) and Intergovernmental Panel on Climate Change A1b Scenario. The simulations of the Antarctic ozone hole are compared using commonly used diagnostics: the minimum ozone, the maximum area of ozone below 220 DU, and the ozone mass deficit below 220 DU. Despite the fact that the processes responsible for ozone depletion are reasonably well understood, a wide range of results is obtained. Comparisons with observations indicate that one of the reasons for the model underprediction in ozone hole area is the tendency for models to underpredict, by up to 35%, the area of low temperatures responsible for polar stratospheric cloud formation. Models also typically have species gradients that are too weak at the edge of the polar vortex, suggesting that there is too much mixing of air across the vortex edge. Other models show a high bias in total column ozone which restricts the size of the ozone hole (defined by a 220 DU threshold). The results of those models which agree best with observations are examined in more detail. For several models the ozone hole does not disappear this century but a small ozone hole of up to three million square kilometers continues to occur in most springs even after 2070.

  • 23.
    Axell, Lars
    SMHI, Research Department, Oceanography.
    Wind-driven internal waves and Langmuir circulations in a numerical ocean model of the southern Baltic Sea2002In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 107, no C11, 3204Article in journal (Refereed)
    Abstract [en]

    [1] A one-dimensional numerical ocean model of the southern Baltic Sea is used to investigate suitable parameterizations of unresolved turbulence and compare with available observations. The turbulence model is a k-epsilon model that includes extra source terms P-IW and P-LC of turbulent kinetic energy (TKE) due to unresolved, breaking internal waves and Langmuir circulations, respectively. As tides are negligible in the Baltic Sea, topographic generation of internal wave energy (IWE) is neglected. Instead, the energy for deepwater mixing in the Baltic Sea is provided by the wind. At each level the source term P-IW is assumed to be related to a vertically integrated pool of IWE, E-0, and the buoyancy frequency N at the same level, according to P-IW (z) proportional to E0Ndelta (z). This results in vertical profiles of epsilon (the dissipation rate of TKE) and K-h (the eddy diffusivity) according to epsilon proportional to N-delta and K-h proportional to Ndelta-2 below the main pycnocline. Earlier observations are inconclusive as to the proper value of delta, and here a range of values of delta is tested in hundreds of 10-year simulations of the southern Baltic Sea. It is concluded that delta = 1.0 +/- 0.3 and that a mean energy flux density to the internal wave field of about (0.9 +/- 0.3) x 10(-3) W m(-2) is needed to explain the observed salinity field. In addition, a simple wind-dependent formulation of the energy flux to the internal wave field is tested, which has some success in describing the short- and long-term variability of the deepwater turbulence. The model suggests that similar to16% of the energy supplied to the surface layer by the wind is used for deepwater mixing. Finally, it is also shown that Langmuir circulations are important to include when modeling the oceanic boundary layer. A simple parameterization of Langmuir circulations is tuned against large-eddy simulation data and verified for the Baltic Sea.

  • 24.
    Ayarza, P
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
    Juhlin, Christopher
    Brown, D
    Beckholmen, M
    Kimbell, G
    Pechnig, R
    Pevzner, L
    Pevzner, R
    Ayala, C
    Bliznetsov, M
    Glushkov, A
    Rybalka, A
    Integrated geological and geophysical studies in the SG4 borehole area, Tagil Volcanic Arc, Middle Urals: Location of seismic reflectors and source of the reflectivity2000In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 105, no B9, 21333-21352 p.Article in journal (Refereed)
    Abstract [en]

    Near-vertical incidence reflection seismic data acquired in the Tagil Volcanic Arc (Middle Urals) show the upper crust to be highly reflective. Two intersecting seismic lines located near the ongoing ∼5400 m deep SG4 borehole show that the main reflectivity strikes approximately N-S and dips ∼35°–55° to the east. Prominent reflections intercept the borehole at ∼1000, ∼1500, 2800–2900, ∼3400, and between ∼4000 and 5400 m, which correspond to intervals of low velocity/low density/low resistivity. The surface projections of these reflections lie parallel to the strike of magnetic anomaly trends. Multioffset vertical seismic profile (VSP) data acquired in the SG4 borehole show a seismic response dominated by P to S reflected converted waves from the moderately east dipping reflectivity and from a set of very steep east dipping reflectors not imaged by the surface data. Modeling of the VSP data constrains the depth at which reflectors intercept the borehole and suggests that the P to S conversions are best explained by low-velocity porous intervals rather than higher-velocity mafic material. The most prominent east dipping reflection on the surface seismic data is only imaged on VSP shots that sample the crust closer to the E-W seismic line. This discrepancy between the VSP and the surface seismic data is attributed to rapid lateral changes in the physical properties of the reflector. Surface and borehole data suggest that the low-velocity/low-density/low-resistivity intervals are the most important source of reflectivity in the SG4 borehole area, although lithological contrasts may also play a role. Drill cores from the these zones contain hydrothermal alteration minerals indicating interaction with fluids. Tectonic criteria suggest that they might represent imbricated fracture zones often bounding different lithologies and/or intrusions. Some of them might also represent high-porosity lava flows or pyroclastic units, common in island arc environments.

  • 25.
    Backstrand, K.
    et al.
    Stockholm University.
    Crill, P. M.
    Stockholm University.
    Mastepanov, M.
    Lund University.
    Christensen, T. R.
    Lund University.
    Bastviken, D.
    Stockholm University.
    Total hydrocarbon flux dynamics at a subarctic mire in northern Sweden2008In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 113, no G3Article in journal (Refereed)
    Abstract [en]

    This is a study of the spatial and temporal variability of total hydrocarbon (THC) emissions from vegetation and soil at a subarctic mire, northern Sweden. THCs include methane (CH4) and nonmethane volatile organic compounds (NMVOCs), both of which are atmospherically important trace gases and constitute a significant proportion of the carbon exchange between biosphere and atmosphere. Reliable characterization of the magnitude and the dynamics of the THC fluxes from high latitude peatlands are important when considering to what extent trace gas emissions from such ecosystems may change and feed back on climate regulation as a result of warmer climate and melting permafrost. High frequency measurements of THC and carbon dioxide (CO2) were conducted during four sequential growing seasons in three localities representing the trophic range of plant communities at the mire. The magnitude of the THC flux followed the moisture gradient with increasing emissions from a dry Palsa site (2.2 +/- 0.1 mgC m(-2) d(-1)), to a wet intermediate melt feature with Sphagnum spp. (28 +/- 0.3 mgC m(-2) d(-1)) and highest emissions from a wet Eriophorum spp. site (122 +/- 1.4 mgC m(-2) d(-1)) (overall mean +/- 1 SE, n = 2254, 2231 and 2137). At the Palsa site, daytime THC flux was most strongly related to air temperature while daytime THC emissions at the Sphagnum site had a stronger relation to ground temperature. THC emissions at both the wet sites were correlated to net ecosystem exchange of CO2. An overall spatial correlation indicated that areas with highly productive vegetation communities also had high THC emission potential.

  • 26. Bais, A F
    et al.
    Gardiner, B G
    Slaper, H
    Blumthaler, M
    Bernhard, G
    McKenzie, R
    Webb, A R
    Seckmeyer, G
    Kjeldstad, B
    Koskela, T
    Kirsch, P J
    Grobner, J
    Kerr, J B
    Kazadzis, S
    Leszczynski, K
    Wardle, D
    Josefsson, Weine
    SMHI, Research Department, Atmospheric remote sensing.
    Brogniez, C
    Gillotay, D
    Reinen, H
    Weihs, P
    Svenoe, T
    Eriksen, P
    Kuik, F
    Redondas, A
    SUSPEN intercomparison of ultraviolet spectroradiometers2001In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 106, no D12, 12509-12525 p.Article in journal (Refereed)
    Abstract [en]

    Results from an intercomparison campaign of ultraviolet spectroradiometers that was organized at Nea Michaniona, Greece July, 1-13 1997, are presented. Nineteen instrument systems from 15 different countries took part and provided spectra of global solar UV irradiance for two consecutive days from sunrise to sunset every half hour. No data exchange was allowed between participants in order to achieve absolutely independent results among the instruments. The data analysis procedure included the determination of wavelength shifts and the application of suitable corrections to the measured spectra, their standardization to common spectral resolution of 1 nm full width at half maximum and the application of cosine corrections. Reference spectra were calculated for each observational time, derived for a set of instruments which were objectively selected and used as comparison norms for the assessment of the relative agreement among the various instruments. With regard to the absolute irradiance measurements, the range of the deviations from the reference for all spectra was within +/- 20%. About half of the instruments agreed to within +/-5%, while only three fell outside the +/- 10% agreement limit. As for the accuracy of the wavelength registration of the recorded spectra, for most of the spectroradiometers (14) the calculated wavelength shifts were smaller than 0.2 nm. The overall outcome of the campaign was very encouraging, as it was proven that the agreement among the majority of the instruments was good and comparable to the commonly accepted uncertainties of spectral UV measurements. In addition, many of the instruments provided consistent results relative to at least the previous two intercomparison campaigns, held in 1995 in Ispra, Italy and in 1993 in Garmisch-Partenkirchen, Germany. As a result of this series of intercomparison campaigns, several of the currently operating spectroradiometers operating may be regarded as a core group Of instruments, which with the employment of proper operational procedures are capable of providing quality spectral solar UV measurements.

  • 27.
    Bastviken, D.
    et al.
    Stockholm University.
    Cole, J. J.
    Institute of Ecosystem Studies, Millbrook.
    Pace, M. L.
    Institute of Ecosystem Studies, Millbrook.
    Van de Bogert, M. C.
    University of Wisconsin.
    Fates of methane from different lake habitats: Connecting whole-lake budgets and CH4 emissions2008In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 113, no G2Article in journal (Refereed)
    Abstract [en]

    Methane (CH4) represents a major product of organic matter decomposition in lakes. Once produced in the sediments, CH4 can be either oxidized or emitted as a greenhouse gas to the atmosphere. Lakes represent an important source of atmospheric CH4, but the relative magnitudes of the internal pathways that lead to CH4 emissions are not yet clear. We quantified internal cycling and methane emissions in three lakes during summer stratification. These methane budgets included: sediment release of CH4 at different depths; water column transport patterns and methane oxidation; methane storage in the water column; and methane emissions to the atmosphere by diffusion and ebullition. The contribution of CH4 carbon, via oxidation by methanotrophic bacteria, to pelagic food webs was also estimated. Despite the very low concentration of CH4 in surface waters, shallow, epilimnetic sediments were major contributors of CH4 to the atmosphere. While 51 - 80% of the CH4 produced in deep sediments was oxidized in the water column, most of the CH4 released from shallow sediment escaped oxidation and reached the atmosphere. Epilimnetic sediments accounted for 100% of CH4 emitted during summer stratification, and 14 - 76% considering the release of CH4 stored in deep water layers during lake circulation after the stratification period; diffusive emission accounted for 26 - 48% and ebullition the remainder. These results indicate that it is important to address transport rates of CH4 from the shallow sediment along with the production-consumption processes when trying to understand methane dynamics and the regulation of lake methane emissions.

  • 28. Bavassano Cattaneo, M. Bice
    et al.
    Marcucci, M. Federica
    Retinò, Alessandro
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Pallocchia, G.
    Rème, H.
    Dandouras, I.
    Kistler, L. M.
    Klecker, B.
    Carlson, C. W.
    Korth, A.
    McCarthy, M.
    Lundin, Rickard
    Balogh, A.
    Kinetic signatures during a quasi-continuous lobe reconnection event: Cluster Ion Spectrometer (CIS) observations2006In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 111, no A9, A09212- p.Article in journal (Refereed)
    Abstract [en]

    On 3 December 2001 the Cluster spacecraft observed a long-lasting lobe reconnection event in the southern high-latitude dusk magnetopause (MP) tailward of the cusp, during a 4 hour interval of mainly northward interplanetary magnetic field ( IMF) and of sub-Alfvenic magnetosheath flow. Almost all the MP encounters have accelerated flows ( for which the Walen test has been successfully verified by Retino et al. ( 2005)) as well as a large number of secondary populations related to reconnection, that is, ions of magnetosheath or magnetospheric origin which cross the MP either way. The detailed analysis of the distribution functions shows that the reconnection site frequently moves relative to the spacecraft, but simultaneous measurements by two spacecraft on opposite sides of the reconnection site indicate that the spacecraft's distance from the X line is small, i.e., below 3200 km. The vicinity to the X line throughout the event is probably the reason why the distribution functions characteristics agree with theoretical expectations on both sides of the reconnection site throughout this long event. Moreover, the detailed analysis of the distribution functions shows evidence, during a few time intervals, of dual reconnection, i.e., of reconnection simultaneously going on also in the northern hemisphere.

  • 29.
    Becerra Garcia, Marley
    et al.
    Division for Electricity, Uppsala University.
    Cooray, Vernon
    Division for Electricity, Uppsala University.
    Soula, S
    Laboratoire d’Ae´rologie, UMR CNRS, Universite´ Paul Sabatier, Toulouse, France.
    Chauzy, S
    Laboratoire d’Ae´rologie, UMR CNRS, Universite´ Paul Sabatier, Toulouse, France.
    Effect of the space charge layer created by corona at ground level on the inception of upward lightning leaders from tall towers2007In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 112, no 12Article in journal (Refereed)
    Abstract [en]

    Electric field measurements above ground have shown that the space charge layercreated by corona at ground level shields the background electric field produced by thethundercloud. Therefore it is expected that this space charge layer can also influence theconditions required to initiate upward lightning from tall objects. For this reason, anumerical model that describes the evolution of the main electrical parameters below athunderstorm is used to compute the space charge layer development. The time variationof the electric field measured at 600 m above ground during the 1989 rockettriggered lightning experiment at the Kennedy Space Center (Florida) is used to drive themodel. The obtained space charge density profiles are used to compute the conditionsrequired to initiate stable upward lightning positive leaders from tall towers. Corona at thetip of the tower is neglected. It is found that the space charge layer significantly affectsthe critical thundercloud electric fields required to initiate upward lightning leadersfrom tall objects. The neutral aerosol particle concentration is observed to have asignificant influence on the space charge density profiles and the critical thundercloudelectric fields, whereas the corona current density does not considerably affect the resultsfor the cases considered in the analysis. It is found that a lower thundercloud electric fieldis required to trigger a lightning flash from a tall tower or other tall slender groundedstructure in the case of sites with a high neutral aerosol particle concentration, like polluted areas or coastal regions.

  • 30.
    Becerra, Marley
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Soula, Serge
    Chauzy, Serge
    Effect of the space charge layer created by corona at ground level on the inception of upward lightning leaders from tall towers2007In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 112, no D12, D12205- p.Article in journal (Refereed)
    Abstract [en]

    Electric field measurements above ground have shown that the space charge layer created by corona at ground level shields the background electric field produced by the thundercloud. Therefore it is expected that this space charge layer can also influence the conditions required to initiate upward lightning from tall objects. For this reason, a numerical model that describes the evolution of the main electrical parameters below a thunderstorm is used to compute the space charge layer development. The time variation of the electric field measured at 600 m above ground during the 1989 rocket triggered lightning experiment at the Kennedy Space Center (Florida) is used to drive the model. The obtained space charge density profiles are used to compute the conditions required to initiate stable upward lightning positive leaders from tall towers. Corona at the tip of the tower is neglected. It is found that the space charge layer significantly affects the critical thundercloud electric fields required to initiate upward lightning leaders from tall objects. The neutral aerosol particle concentration is observed to have a significant influence on the space charge density profiles and the critical thundercloud electric fields, whereas the corona current density does not considerably affect the results for the cases considered in the analysis. It is found that a lower thundercloud electric field is required to trigger a lightning flash from a tall tower or other tall slender grounded structure in the case of sites with a high neutral aerosol particle concentration, like polluted areas or coastal regions.

  • 31.
    Becher, Marina
    et al.
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Olid, Carolina
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Klaminder, Jonatan
    Umeå University, Faculty of Science and Technology, Department of Ecology and Environmental Sciences.
    Buried soil organic inclusions in non-sorted circles fields in northern Sweden: Age and Paleoclimatic context2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 1, 104-111 p.Article in journal (Refereed)
    Abstract [en]

    Although burial of surface organic soil horizons into deeper mineral soil layers helps drive the long-term buildup of carbon in arctic soils, when and why buried horizons formed as result of cryoturbation in northern Sweden remain unclear. In this study, we used C-14 and Pb-210 dating to assess when organic matter was buried within non-sorted circles fields near Abisko in northern Sweden. In addition, we used aerial photos from 1959 and 2008 to detect eventual trends in cryogenic activities during this period. We found that organic matter from former organic horizons (stratigraphically intact or partly fragmented) corresponds to three major periods: 0-100 A. D., 900-1250 A. D., and 1650-1950 A. D. The latter two periods were indicated by several dated samples, while the extent of the oldest period is more uncertainty (indicated by only one sample). The aerial photos suggest a net overgrowth by shrub vegetation of previously exposed mineral soil surfaces since 1959. This overgrowth trend was seen in most of the studied fields (92 out of 137 analyzed fields), indicating that the cryogenic activity has mainly decreased in studied non-sorted circles fields since the 1950s. This latter interpretation is also supported by the absence of buried organic layers formed during the last decades. We suggest that the organic matter was buried during the transition from longer cold periods to warmer conditions. We believe these climatic shifts could have triggered regional scale burial of soil organic matter and thus affected how these soils sequestered carbon.

  • 32.
    Becher, Marina
    et al.
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Olid, Carolina
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Klaminder, Jonatan
    Umeå universitet, Institutionen för ekologi, miljö och geovetenskap.
    Buried soil organic inclusions in non-sorted circles fields in northern Sweden: Age and Paleoclimatic context2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 1, 104-111 p.Article in journal (Refereed)
    Abstract [en]

    Although burial of surface organic soil horizons into deeper mineral soil layers helps drive the long-term buildup of carbon in arctic soils, when and why buried horizons formed as result of cryoturbation in northern Sweden remain unclear. In this study, we used C-14 and Pb-210 dating to assess when organic matter was buried within non-sorted circles fields near Abisko in northern Sweden. In addition, we used aerial photos from 1959 and 2008 to detect eventual trends in cryogenic activities during this period. We found that organic matter from former organic horizons (stratigraphically intact or partly fragmented) corresponds to three major periods: 0-100 A. D., 900-1250 A. D., and 1650-1950 A. D. The latter two periods were indicated by several dated samples, while the extent of the oldest period is more uncertainty (indicated by only one sample). The aerial photos suggest a net overgrowth by shrub vegetation of previously exposed mineral soil surfaces since 1959. This overgrowth trend was seen in most of the studied fields (92 out of 137 analyzed fields), indicating that the cryogenic activity has mainly decreased in studied non-sorted circles fields since the 1950s. This latter interpretation is also supported by the absence of buried organic layers formed during the last decades. We suggest that the organic matter was buried during the transition from longer cold periods to warmer conditions. We believe these climatic shifts could have triggered regional scale burial of soil organic matter and thus affected how these soils sequestered carbon.

  • 33. Benze, Susanne
    et al.
    Randall, Cora E.
    Karlsson, Bodil
    Stockholm University, Faculty of Science, Department of Meteorology .
    Harvey, V. Lynn
    DeLand, Matthew T.
    Thomas, Gary E.
    Shettle, Eric P.
    On the onset of polar mesospheric cloud seasons as observed by SBUV2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, D07104- p.Article in journal (Refereed)
    Abstract [en]

    This paper describes an investigation using data from the Solar Backscatter Ultraviolet (SBUV) satellite instruments to explore and understand variations in the timing of the onset of Polar Mesospheric Cloud (PMC) seasons. Previous work has shown that for several recent southern hemisphere (SH) seasons, the PMC season onset was controlled by the timing of the shift from winter to summer zonal wind flow in the SH stratosphere. We extend the analysis of PMC season onset to 28 years of SBUV observations, including both hemispheres. A multiple linear regression analysis of SBUV data from 1984 to 2011 suggests that the SH PMC season onset is delayed by one day for every day that the zonal wind at 65 degrees S and 50 hPa (similar to 20 km) remains in a winter-like state. In addition, we find that the solar cycle plays a role: The SH season onset is delayed by about ten days at solar maximum compared to solar minimum. In the NH, the PMC season onset is delayed by similar to 7 days at solar maximum compared to solar minimum; variations in the NH stratospheric wind, however, are not correlated with the NH onset date. On the other hand, inter-hemispheric teleconnections are important in the NH; a one-day shift in the NH season onset corresponds to a shift of similar to 1.4 m/s in the SH stratospheric wind at 60.0 degrees S and 20 hPa (similar to 26 km). Neither the NH nor the SH season onset date is correlated with the Quasi-Biennial Oscillation, North Atlantic Oscillation, Arctic Oscillation, or El Nino Southern Oscillation.

  • 34. Björnsson, H.
    et al.
    Magnusson, Sverker
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Optimization and Systems Theory.
    Arason, P.
    Petersen, G. N.
    Velocities in the plume of the 2010 Eyjafjallajökull eruption2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 20, 11698-11711 p.Article in journal (Refereed)
    Abstract [en]

    The eruption of the Icelandic volcano Eyjafjallajökull in the spring of 2010 lasted for 39 days with an explosive phase (14-18 April), an effusive phase (18 April to 4 May) and a phase with renewed explosive activity (5-17 May). Images every 5 s from a camera mounted 34 km from the volcano are available for most of the eruption. Applying the maximum cross-correlation method (MCC) on these images, the velocity structure of the eruption cloud has been mapped in detail for four time intervals covering the three phases of the eruption. The results show that on average there are updrafts in one part of the cloud and lateral motion or downdrafts in another. Even within the updraft part, there are alternating motions of strong updrafts, weak updrafts, and downward motion. These results show a highly variable plume driven by intermittent explosions. The results are discussed in the context of integral plume models and in terms of elementary parcel theory. Key Points Velocities in a volcanic cloud based on analysis of image data from the eruption Velocities in the eruption cloud are inhomogeneous and updrafts intermittent Intermittent updrafts are important for the dynamics and the lofting of ash.

  • 35.
    Block, Lars P
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    The Role of Magnetic-Field-Aligned Electric Fields in Auroral Acceleration1990In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 95, 5877-5888 p.Article in journal (Refereed)
  • 36.
    Bosson, Emma
    et al.
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology. Swedish Nuclear Fuel and Waste Management Company, Stockholm, Sweden.
    Sabel, Ulrika
    Gustafsson, Lars-Göran
    Sassner, Mona
    Destouni, Georgia
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Influences of shifts in climate, landscape, and permafrost on terrestrial hydrology2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, D05120Article in journal (Refereed)
    Abstract [en]

    This study has simulated the terrestrial hydrology associated with different climate, landscape, and permafrost regime scenarios for the field case example of the relatively well characterized coastal catchment of Forsmark, Sweden. The regime scenarios were selected from long-term simulation results of climate, topographical, shoreline, and associated Quaternary deposit and vegetation development in this catchment with a time perspective of 100,000 years or more and were used as drivers for hydrological simulations with the three-dimensional model MIKE SHE. The hydrological simulations quantify the responses of different water flow and water storage components of terrestrial hydrology to shifts from the present cool temperate climate landscape regime in Forsmark to a possible future Arctic periglacial landscape regime with or without permafrost. The results show complexity and nonlinearity in the runoff responses to precipitation changes due to parallel changes in evapotranspiration, along with changes in surface and subsurface water storage dynamics and flow pathways through the landscape. The results further illuminate different possible perspectives of what constitutes wetter/drier landscape conditions, in contrast to the clearer concept of what constitutes a warmer/colder climate.

  • 37.
    Brenning, Nils
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Axnas, I.
    Raadu, Michael A.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tennfors, E.
    Koepke, M.
    Radiation from an electron beam in a magnetized plasma: Whistler mode wave packets2006In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 111, no A11Article in journal (Refereed)
    Abstract [en]

    Experimental studies are reported of oscillations and radiation that is spontaneously excited by an electron beam which is shot along a diverging magnetic field into a plasma from a hot cathode. In the present study we focus on oscillations below the electron gyrofrequency, where we find that whistler mode radiation appears in the form of bursts, or wave packets, each with typically 0.1-1 mu s time duration, and which together cover typically a few percent of the full time. Wave packets are found in a broad frequency range of 7-40 MHz, while each individual wave packet is dominated by a single frequency. There is propagation along two routes: at the group velocity resonance cone angle, away from the central channel where the waves are excited, and in a channel along the magnetic field. Features of the whistler mode wave packets that are studied include (1) the statistics of amplitudes, frequencies, and time durations; (2) the propagation and decay of wave packets with different frequencies; (3) the group and phase velocities; and (4) how the wave packet production varies with the energy, and the current density, in the electron beam.

  • 38.
    Brenning, Nils
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Fälthammar, Carl-Gunne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Haerendel, G.
    Kelley, M.C.
    Marklund, Göran
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Pfaff, R.
    Providakes, J.
    Stenbaek-Nielsen, H.C.
    Swenson, C.
    Torbert, R.
    Wescott, E.M.
    Interpretation of the Electric Fields Measured in an Ionospheric Critical Ionization Velocity Experiment1991In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 96, 9719-9733 p.Article in journal (Refereed)
    Abstract [en]

    This paper deals with the quasi-dc electric fields measured in the CRIT I ionospheric release experiment, which was launched from Wallops Island on May 13, 1986. The purpose of the experiment was to study the critical ionization velocity (CIV) mechanism in the ionosphere. Two identical barium shaped charges were fired from distances of 1.99 km and 4.34 km towards a main payload, which made full three-dimensional measurements of the electric field inside the streams. There was also a subpayload separated from the main payload by a couple of kilometers along the magnetic field. The relevance of earlier proposed mechanisms for electron heating in CIV is investigated in the light of the CRIT I results. It is concluded that both the “homogeneous” and the “ionizing front” models probably apply, but in different parts of the stream. It is also possible that electrons are directly accelerated by a magnetic-field-aligned component of the electric field; the quasi-dc electric field observed within the streams had a large magnetic-field-aligned component, persisting on the time scale of the passage of the streams. The coupling between the ambient ionosphere and the ionized barium stream in CRIT I was more complicated than is usually assumed in CIV theories, with strong magnetic-field-aligned electric fields and probably current limitation as important processes. One interpretation of the quasi-dc electric field data is that the internal electric fields of the streams were not greatly modified by magnetic-field-aligned currents, i.e., a state was established where the transverse currents were to a first approximation divergence-free. It is argued that this interpretation can explain both a reversal of the strong explosion-directed electric field in burst 1 and the absence of such a reversal in burst 2.

  • 39. Bromley, T.
    et al.
    Allan, W.
    Martin, R.
    Fletcher, S. E. Mikaloff
    Lowe, D. C.
    Struthers, Hamish
    Stockholm University, Faculty of Science, Department of Meteorology . Stockholm University, Faculty of Science, Department of Applied Environmental Science (ITM).
    Moss, R.
    Shipboard measurements and modeling of the distribution of CH4 and (CH4)-C-13 in the western Pacific2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, D04307- p.Article in journal (Refereed)
    Abstract [en]

    We present observations of methane (CH4) mixing ratio and C-13/C-12 isotopic ratios in CH4 (delta C-13) data from a collaborative shipboard project using bulk carrier ships sailing between Nelson, New Zealand, and Osaka, Japan, in the western Pacific Ocean. Measurements of the CH4 mixing ratio and delta C-13 in CH4 were obtained from large clean-air samples collected in each 2.5 degrees to 5 degrees of latitude between 30 degrees S and 30 degrees N on eight voyages from 2004 to 2007. The data show large variations in CH4 mixing ratio in the tropical western Pacific, and data analysis suggests that these large variations are related to the positions and strengths of the South Pacific Convergence Zone and the Intertropical Convergence Zone, with variability in the sources playing a much smaller role. These measurements are compared with results from a modified version of the Unified Model (UMeth) general circulation model along two transects, one similar to the ship transects and another 18.75 degrees to the east. Although UMeth was run to a steady state with the same sources and sinks each year, the gradient structures varied considerably from year to year, supporting our conclusion that variability in transport is a major driver for the observed variations in CH4. Simulations forced with an idealized representation of the El Nino-Southern Oscillation (ENSO) suggest that a large component of the observed variability in latitudinal gradients of CH4 and its delta C-13 arises from intrinsic variability in the climate system that does not occur on ENSO time scales.

  • 40.
    Bruneton, M.
    et al.
    Laboratoire de Ge´ophysique Interne et Tectonophysique, Observatoire des Sciences de l’Univers de Grenoble, Grenoble, France..
    et, al. Shomali, Z.H.
    Svekalapko working group.
    Complex lithospheric structure under the central Baltic Shield from surface wave tomography2004In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 109, no B10303, 1-15 p.Article in journal (Refereed)
  • 41.
    Buehler, Stefan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Courcoux, N.
    Universität Bremen, Institute of Environmental Physics.
    John, Viju Oommen
    University of Miami, Rosenstiel School of Marine and Atmospheric Sciences, Miami.
    Radiative transfer calculations for a passive microwave satellite sensor: comparing a fast model and a line-by-line model2006In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 111, no 20, 20304- p.Article in journal (Refereed)
    Abstract [en]

    [1] A comparison between the fast radiative transfer model Radiative Transfer for the TIROS Operational Vertical Sounder (RTTOV-7) and the physical radiative transfer model Atmospheric Radiative Transfer Simulator ( ARTS) was carried out. Radiances were simulated for the sounding channels of the Advanced Microwave Sounding Unit B (AMSU-B) for the whole globe for a single time of a single day ( 1 January 2000, 0000 UT). Temperature, pressure, and specific humidity profiles from the reanalysis data set ERA-40 of the European Centre for Medium-Range Weather Forecasts (ECMWF) were used as input for both models; geopotential height profiles were also used but only as input for ARTS. The simulations were made for two different surface emissivities, 0.60 and 0.95. The low surface emissivity case exhibits the larger radiance differences. Although the global values of the mean difference and standard deviation are small ( for example, the global mean difference for channel 18 is 0.014 K and the standard deviation is 0.232 K), the examination of the geographical distribution of the differences shows that large positive or negative values are observed over dry regions of high northern and southern latitudes and over dry elevated regions. The origin of these differences was found to be due to errors introduced by the transmittance parametrization used in RTTOV.

  • 42. Buehler, Stefan
    et al.
    John, V. O.
    Universität Bremen, Institute of Environmental Physics.
    A simple method to relate microwave radiances to upper tropospheric humidity2005In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 110, no 2, D02110- p.Article in journal (Refereed)
    Abstract [en]

    A brightness temperature (BT) transformation method can be applied to microwave data to retrieve Jacobian weighted upper tropospheric relative humidity (UTH) in a broad layer centered roughly between 6 and 8 km altitude. The UTH bias is below 4% RH, and the relative UTH bias below 20%. The UTH standard deviation is between 2 and 6.5% RH in absolute numbers, or between 10 and 27% in relative numbers. The standard deviation is dominated by the regression noise, resulting from vertical structure not accounted for by the simple transformation relation. The UTH standard deviation due to radiometric noise alone has a relative standard deviation of approximately 7% for a radiometric noise level of 1 K. The retrieval performance was shown to be of almost constant quality for all viewing angles and latitudes, except for problems at high latitudes due to surface effects. A validation of AMSU UTH against radiosonde UTH shows reasonable agreement if known systematic differences between AMSU and radiosonde are taken into account. When the method is applied to supersaturation studies, regression noise and radiometric noise could lead to an apparent supersaturation even if there were no supersaturation. For a radiometer noise level of 1 K the drop-off slope of the apparent supersaturation is 0.17% RH−1, for a noise level of 2 K the slope is 0.12% RH−1. The main conclusion from this study is that the BT transformation method is very well suited for microwave data. Its particular strength is in climatological applications where the simplicity and the a priori independence are key advantages.

  • 43. Buehler, Stefan
    et al.
    Kuvatov, M.
    Universität Bremen, Institute of Environmental Physics.
    John, V. O.
    Universität Bremen, Institute of Environmental Physics.
    Leiterer, U.
    Meteorological Observatory Lindenberg, German Weather Service, Lindenberg.
    Dier, H.
    Meteorological Observatory Lindenberg, German Weather Service, Lindenberg.
    Comparison of microwave satellite humidity data and radiosonde profiles: a case study2004In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 109, no 13, S13103- p.Article in journal (Refereed)
    Abstract [en]

    This article documents a case study comparing radiosonde humidity data to Advanced Microwave Sounding Unit (AMSU) satellite humidity data. The study had two goals: first, to develop a robust method for such a comparison, and second, to check the quality and mutual consistency of radiosonde data, radiative transfer model, and AMSU data. The radiosonde data used are Vaisala RS80 data from the station Lindenberg of the German Weather Service (DWD), which have been subject to several corrections compared to the standard data processing. The radiative transfer model is the Atmospheric Radiative Transfer Simulator ( ARTS), and the AMSU data are those of the satellites NOAA 15 and 16 for the time periods 2001 and 2002. The comparison was done in radiance space, using a radiative transfer model to simulate AMSU radiances from the radiosonde data. The overall agreement is very good, with radiance biases below 1.5 K and standard deviations below 2 K. The main source of "noise'' in the comparison is atmospheric inhomogeneity on the 10-km scale. While the radiosonde correction performed at Lindenberg significantly reduces the bias between simulated and measured AMSU radiance, there still remains a slope in the radiance difference. Possible reasons for this were investigated. Most likely, the radiosondes underestimate the relative humidity under extremely dry conditions, showing 0 % RH when the true value is 2 - 4 % RH.

  • 44.
    Buehler, Stefan
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kuvatov, M.
    Institut für Umweltphysik (Institute for Environmental Physics) (IUP), University of Bremen.
    John, V. O.
    Meteorology and Physical Oceanography, Rosenstiel School for Marine and Atmospheric Science (RSMAS), University of Miami.
    Milz, Mathias
    Soden, B.J.
    Meteorology and Physical Oceanography, Rosenstiel School for Marine and Atmospheric Science (RSMAS), University of Miami.
    Jackson, D.L.
    Cooperative Institute for Research in Environmental Science (CIRES), University of Colorado, NOAA Earth System Research Laboratory.
    Norholt, J.
    Institut für Umweltphysik (Institute for Environmental Physics) (IUP), University of Bremen.
    An upper tropospheric humidity data set from operational satellite microwave data2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no 14, D14110- p.Article in journal (Refereed)
    Abstract [en]

    183.31 GHz observations from the Advanced Microwave Sounding Unit B (AMSUB) instruments onboard the NOAA 15, 16, and 17 satellites were used to derive a new data set of Upper Tropospheric Humidity (UTH). The data set consist of monthly median and mean data on a 1.5 degrees latitude-longitude grid between 60 degrees S and 60 degrees N, and covers the time period of January 2000 to February 2007. The data from all three instruments are very consistent, with relative difference biases of less than 4% and relative difference standard deviations of 7%. Radiometric contributions by high ice clouds and by the Earth's surface affect the measurements in certain areas. The uncertainty due to clouds is estimated to be up to approximately 10%RH in areas with deep convection. The uncertainty associated with contamination from surface emission can exceed 10%RH in midlatitude winter, where the data therefore should be regarded with caution. Otherwise the surface influence appears negligible. The paper also discusses the UTH median climatology and seasonal cycle, which are found to be broadly consistent with UTH climatologies from other sensors. Finally, the paper presents an initial validation of the new data set against IR satellite data and radiosonde data. The observed biases of up to 9%RH (wet bias relative to HIRS) were found to be broadly consistent with expectations based on earlier studies. The observed standard deviations against all other data sets were below 6%RH. The UTH data are available to the scientific community on http://www.sat.ltu.se.

  • 45. Buffam, Ishi
    et al.
    Laudon, Hjalmar
    Temnerud, Johan
    Örebro University, Department of Natural Sciences.
    Morth, Carl-Magnus
    Bishop, Kevin
    Landscape-scale variability of acidity and dissolved organic carbon during spring flood in a boreal stream network2007In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 112, no G1, G01022- p.Article in journal (Refereed)
    Abstract [en]

    Acidity is well known to influence stream biota, but the less well-studied spatial and temporal distributions of acidity are likely to play a larger ecological role than average values. We present data on spatial variability of chemical parameters contributing to acidity during winter baseflow and spring flood periods in Krycklan, a fourth-order boreal stream network in northern Sweden. Fifteen stream sites were monitored in subcatchments spanning 3 orders of magnitude in size and representing a wide range of percent wetland. At baseflow, pH ranged from 3.9 to 6.5 at the different sites. Baseflow dissolved organic carbon (DOC) concentration varied by an order of magnitude and was positively correlated with subcatchment percent wetland, resulting in high spatial variability in dissociated organic acids (OA(-)). During spring flood, DOC and OA(-) increased in forested sites and decreased in wetland sites, resulting in reduced spatial variability in their concentrations. In contrast, base cations and strong acid anions diluted throughout the stream network, resulting in decreased acid neutralizing capacity (ANC) at all sites. The spatial variability of base cations increased slightly with high flow. As a result of the changes in OA(-) and ANC, pH dropped at all but the most acidic site, giving a slightly narrowed pH range during spring flood (4.2-6.1). The transition from winter to spring flood stream chemistry could largely be explained by: (1) a shift from mineral to upper riparian organic soil flow paths in forested catchments and (2) dilution of peat water with snowmelt in wetland catchments.

  • 46. Byrne, P.K.
    et al.
    Van Wyk de Vries, B.
    Murray, J.B.
    Troll, Valentin
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Solid Earth Geology.
    A Volcanotectonic Survey of Ascraeus Mons, Mars2011In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117Article in journal (Refereed)
    Abstract [en]

    Ascraeus Mons is one of the largest volcanoes on Mars. It is replete with well-preserved features that can be used to understand its volcanotectonic evolution. Previous studies of this volcano focused on specific features, and were limited by the quality and coverage of contemporary data. Our objective is to review and enhance the existing developmental model for Ascraeus by considering all endogenic surface features on the volcano. We surveyed the volcano's caldera complex, flank terraces, pit structures, sinuous rilles, arcuate grabens, and small vents. We report the spatial and temporal distributions of these features, appraise their proposed formation mechanisms in light of our mapping results, and propose a detailed geological history for Ascraeus Mons. An initial shield-building phase was followed by the formation of a summit caldera complex and small parasitic cones, while compression due to flexure of the supporting basement led to extensive terracing of the shield flanks. An eruptive hiatus followed, ending with the construction of expansive rift aprons to the northeast and southwest. Against later, extensive flank resurfacing in the late Amazonian, continued flexure formed arcuate grabens concentric to the edifice. Localized eruption and surface flow of a fluid agent (lava and/or water) from within the volcano then produced a population of rilles on the lower flanks. Finally, in a change of flank tectonic regime from compression to extension, pit crater chains and troughs developed on the main shield and rift aprons, eventually coalescing to form large embayments at the northeast and southwest base of the volcano.

  • 47.
    Campbell-Brown, Margaret
    et al.
    University of Western Ontario.
    Kero, Johan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Szasz, Csilla
    Institutet för rymdfysik.
    Pellinen-Wannberg, Asta
    Weryk, Rob
    University of Western Ontario.
    Photometric and ionization masses of meteors with simultaneous EISCAT UHF radar and intensified video observations2012In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 117, A09323- p.Article in journal (Refereed)
    Abstract [en]

    There are significant uncertainties in the calculation of photometric and ionization masses of meteors, particularly those derived from meteor head echoes observed by high power, large aperture radars. Simultaneous observations of meteors with the EISCAT UHF tristatic system and narrow field two-station intensified video were conducted in October 2007; 11 hours of data produced four useful meteors observed on all three radar receivers and both cameras. The positions and speeds calculated on the two systems generally agree to within the observational uncertainty. The photometric and ionization masses for each meteor were calculated using several values of luminous efficiency and ionization probability from literature, and all of these masses were found to agree to within the estimated error in the methods. More observations are required to select among the various values of ionization coefficient and luminous efficiency.

  • 48. Chaufray, J. Y.
    et al.
    Modolo, Ronan
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Leblanc, F.
    Chanteur, G.
    Johnson, R. E.
    Luhmann, J. G.
    Mars solar wind interaction: Formation of the Martian corona and atmospheric loss to space2007In: Journal of Geophysical Research, ISSN 0148-0227, Vol. 112, no E9, E09009- p.Article, review/survey (Refereed)
    Abstract [en]

    A three- dimensional ( 3- D) atomic oxygen corona of Mars is computed for periods of low and high solar activities. The thermal atomic oxygen corona is derived from a collisionless Chamberlain approach, whereas the nonthermal atomic oxygen corona is derived from Monte Carlo simulations. The two main sources of hot exospheric oxygen atoms at Mars are the dissociative recombination of O-2(+) between 120 and 300 km and the sputtering of the Martian atmosphere by incident O+ pickup ions. The reimpacting and escaping fluxes of pickup ions are derived from a 3- D hybrid model describing the interaction of the solar wind with our computed Martian oxygen exosphere. In this work it is shown that the role of the sputtering crucially depends on an accurate description of the Martian corona as well as of its interaction with the solar wind. The sputtering contribution to the total oxygen escape is smaller by one order of magnitude than the contribution due to the dissociative recombination. The neutral escape is dominant at both solar activities ( 1 x 10(25) s(-1) for low solar activity and 4 x 10(25) s(-1) for high solar activity), and the ion escape flux is estimated to be equal to 2 x 10(23) s(-1) at low solar activity and to 3.4 x 10(24) s(-1) at high solar activity. This work illustrates one more time the strong dependency of these loss rates on solar conditions. It underlines the difficulty of extrapolating the present measured loss rates to the past solar conditions without a better theoretical and observational knowledge of this dependency.

  • 49. Chen, Li-Jen
    et al.
    Bessho, N.
    Lefebvre, B.
    Vaith, H.
    Fazakerley, A.
    Bhattacharjee, A.
    Puhl-Quinn, P. A.
    Runov, A.
    Khotyaintsev, Yuri
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Vaivads, Andris
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Georgescu, E.
    Torbert, R.
    Evidence of an extended electron current sheet and its neighboring magnetic island during magnetotail reconnection2008In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 113, no A12, A12213- p.Article in journal (Refereed)
    Abstract [en]

    We have identified a spatially extended electron current sheet (ECS) and its adjacent magnetic island during a magnetotail reconnection event with no appreciable guide field. This finding is based on data from the four Cluster spacecraft and is enabled by detailed maps of electron distribution functions and DC electric fields within the diffusion region. The maps are developed using two-dimensional particle-in-cell simulations with a mass ratio m(i)/m(e) = 800. One spacecraft crossed the ECS earthward of the reconnection null and, together with the other three spacecraft, registered the following properties: (1) The ECS is colocated with a layer of bipolar electric fields normal to the ECS, pointing toward the ECS, and with a half width less than 8 electron skin depths. (2) In the inflow region up to the ECS and separatrices, electrons have a temperature anisotropy (Te-parallel to/Te-perpendicular to > 1), and the anisotropy increases toward the ECS. (3) Within about 1 ion skin depth (d(i)) above and below the ECS, the electron density decreases toward the ECS by a factor of 3-4, reaching a minimum at edges of the ECS, and has a local distinct maximum at the ECS center. (4) A di-scale magnetic island is attached to the ECS, separating it from another reconnection layer. Our simulations established that the electric field normal to the ECS is due to charge imbalance and is of the ECS scale, and ions exhibit electron-scale structures in response to this electric field.

  • 50. Chiacchio, Marc
    et al.
    Pausata, Fransesco S. R.
    Messori, Gabriele
    Hannachi, Abdel
    Chin, Mian
    Önskog, Thomas
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.), Mathematical Statistics.
    Ekman, Annica M. L.
    Barrie, Leonard
    On the links between meteorological variables, aerosols, and tropical cyclone frequency in individual ocean basins2017In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 122, 802-822 p.Article in journal (Refereed)
    Abstract [en]

    A generalized linear model based on Poisson regression has been used to assess the impact of environmental variables modulating tropical cyclone frequency in six main cyclone development areas: the East Pacific, West Pacific, North Atlantic, North Indian, South Indian, and South Pacific. The analysis covers the period 1980-2009 and focuses on widely used meteorological parameters including wind shear, sea surface temperature, and relative humidity from different reanalyses as well as aerosol optical depth for different compounds simulated by the Goddard Chemistry Aerosol Radiation and Transport model. Circulation indices are also included. Cyclone frequency is obtained from the International Best Track Archive for Climate Stewardship. A strong link is found between cyclone frequency and the relative sea surface temperature, Atlantic Meridional Mode, and wind shear with significant explained log likelihoods in the North Atlantic of 37%, 27%, and 28%, respectively. A significant impact of black carbon and organic aerosols on cyclone frequency is found over the North Indian Ocean, with explained log likelihoods of 27%. A weaker but still significant impact is found for observed dust aerosols in the North Atlantic with an explained log likelihood of 11%. Changes in lower stratospheric temperatures explain 28% of the log likelihood in the North Atlantic. Lower stratospheric temperatures from a subset of Coupled Model Intercomparison Project Phase 5 models properly simulate the warming and subsequent cooling of the lower stratosphere that follows a volcanic eruption but underestimates the cooling by about 0.5 degrees C.

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