Change search
Refine search result
12 1 - 50 of 82
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 1.
    Ahmad, Mohd Riduan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mohd Esa, Mona Riza
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baharudin, Zikri Abadi
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity. Universiti Teknikal Malaysia Melaka.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Latitude Dependence of Narrow Bipolar Pulse Emissions2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 128, p. 40-45Article in journal (Refereed)
  • 2.
    Ahmad, Noor Azlinda
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Baharudin, Z. A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Saleh, Ziad
    Dwyer, Joseph R.
    Rassoul, Hamid K.
    The first electric field pulse of cloud and cloud-to-ground lightning discharges2010In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, no 2-3, p. 143-150Article in journal (Refereed)
    Abstract [en]

    In this study, the first electric field pulse of cloud and cloud-to-ground discharges were analyzed and compared with other pulses of cloud discharges. Thirty eight cloud discharges and 101 cloud-to-ground discharges have been studied in this analysis. Pulses in cloud discharges were classified as [`]small', [`]medium' and [`]large', depending upon the value of their relative amplitude with respect to that of the average amplitude of the five largest pulses in the flash. We found that parameters, such as pulse duration, rise time, zero crossing time and full-width at half-maximum (FWHMs) of the first pulse of cloud and cloud-to-ground discharges are similar to small pulses that appear in the later stage of cloud discharges. Hence, we suggest that the mechanism of the first pulse of cloud and cloud-to-ground discharges and the mechanism of pulses at the later stage of cloud discharges could be the same.

  • 3.
    Ahmad, Noor Azlinda
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, Mahendra
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Baharudin, Zikri A.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ahmad, H.
    Malek, Z. Abdul
    Characteristics of narrow bipolar pulses observed in Malaysia2010In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, no 5-6, p. 534-540Article in journal (Refereed)
    Abstract [en]

    Narrow bipolar pulses (NBPs) are considered as isolated intracloud events with higher peak amplitude and strong high frequency emission compared to the first return strokes and other intracloud discharges. From 182 NBPs recorded in Malaysia in the tropic, 75 were narrow negative bipolar pulses (NNBPs) while 107 were narrow positive bipolar pulses (NPBPs). The mean duration of NNBPs was 24.6 +/- 17.1 mu s, while 30.2 +/- 12.3 mu s was observed for NPBPs. The mean full-width at half-maximum (FVVHM) was 2.2 +/- 0.7 and 2.4 +/- 1.4 mu s for NNBPs and NPBPs, respectively. The mean peak amplitude of NPBPs normalized to 100 km was 22.7 V/m, a factor of 1.3 higher than that of NNBPs which is 17.6 V/m. In contrast to the previous studies, it was observed that the electric field change was characterized by a bipolar pulse with a significant amount of fine structures separated by a few tens of nanoseconds intervals, embedded on it. (C) 2010 Elsevier Ltd. All rights reserved.

  • 4. Asmus, H.
    et al.
    Robertson, S.
    Dickson, S.
    Friedrich, M.
    Megner, Linda
    Stockholm University, Faculty of Science, Department of Meteorology .
    Charge balance for the mesosphere with meteoric dust particles2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 127, p. 137-149Article in journal (Refereed)
    Abstract [en]

    An aerosol particle charging model initially developed for noctilucent cloud ice particles has been extended in several steps in order to better explain the data for charged meteoric smoke particles (MSPs) obtained by the nighttime and daytime CHAMPS rockets launched from Andoya, Norway, in October 2011. Addition of photodetachment to the model shows that this process reduces the number density of positively charged MSPs as well as the number density of negatively charged MSPs as a consequence of the photodetached electrons neutralizing the positively charged MSPs. In addition, the model shows that the ionization rate can be deduced from the electron number density and the electron-ion recombination rate only at the highest altitudes (those with ionization rates above 20 cm(-3) s(-1)) as a consequence of recombination on the MSPs being dominant at lower altitudes. The differences between the daytime and the nighttime rocket data suggest a photodetachment rate between 0.1 and 0.01 s(-1). A further extension of the model to include the formation of negative ions and their destruction helps explain the ledge seen in the number density of the lightest negatively charged particles. The MSP number densities that are the inputs to the charging model are taken from the CARMA/CHEM2D model. The CHAMPS data are more consistent with number densities generated with an assumed input flux from ablation of 4 t d(-1) than with 44 t d(-1) assumed previously.

  • 5.
    Baharudin, Zikri A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ahmad, Noor Azlinda
    Makela, J. S.
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Negative cloud-to-ground lightning flashes in Malaysia2014In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 108, p. 61-67Article in journal (Refereed)
    Abstract [en]

    The characteristics of the negative cloud-to-ground lightning flashes in Malaysia are studied by analyzing the electric fields generated by the whole flash in nanosecond resolution. A total of 405 strokes obtained from 100 successive negative cloud-to-ground lightning flashes were analyzed, which were recorded from seven convective thunderstorms during the southwest monsoon period, i.e. from April to June 2009. It was found that the total number of interstroke intervals has an arithmetic mean value of 86 ms, a geometric mean value of 67 ms and does not depend on the return stroke order. Of the 100 negative ground flashes, 38 flashes (38%) have at least one subsequent return-stroke (SRS) whose electric field peak was greater than that of the first return-stroke (RS). Furthermore, 58 (19%) out of 305 SRS have electric field peak larger than those of the first RS. The arithmetic and geometric mean ratio between the peak electric field of the SRS and the peak electric field of the first RS are 0.7 and 0.6, respectively. The percentage of single-stroke flashes was 16% while the mean number of strokes per flash and maximum number of stroke per flash were 4 and 14, respectively.

  • 6.
    Baharudin, Zikri A.
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Fernando, M.
    Dept of Physics, University of Colombo, Sri Lanka.
    Ahmad, Noor Azlinda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Mäkelä, J. S.
    Nokia OY, Salo, Finland.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Electric field changes generated by the preliminary breakdown for the negative cloud-to-ground lightning flashes in Malaysia and Sweden2012In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 84-85, p. 15-24Article in journal (Refereed)
    Abstract [en]

    We present the study of the electric field changes generated by the preliminary breakdown for negative cloud-to-ground lightning flashes in Malaysia and Sweden concerning the association of slow field changes associated in preliminary breakdown process. We examined the total of 1685 negative cloud-to-ground lightning flashes from the total of 39 thunderstorms by recording the slow electric field, fast electric field and narrowband radiation field at 3 and 30 MHz signals simultaneously. Our results show that there is a pre-starting time, i.e. the duration between the first preliminary breakdown pulse and slow field changes starting point, which is found to be after the first preliminary breakdown pulse. The pre-starting time has the arithmetic and geometric mean range from 1.4-6.47 and 1-3.36 ms, respectively. The mean values of pre-starting time in Malaysia are greater than the values observed in Sweden by more than a factor of 3. From the two data sets it shows that the slow field changes never start before the preliminary breakdown. Furthermore, the use of single-station electric fields measurement with high resolutions of 12 bits transient recorder with several nanosecond accuracy allow one to distinguish the slow field changes generated by preliminary breakdown, which preceded the negative first return stroke, between tens to hundreds of milliseconds of pre-return stroke duration.

  • 7.
    Baharudin, Zikri Abadi
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Hettiarachchi, Pasan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ahmad, Noor Azlinda
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the characteristics of positive lightning ground flashes in Sweden2016In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 138, p. 106-111Article in journal (Refereed)
    Abstract [en]

    In this study the stroke characteristics of positive cloud-to-ground flashes in Sweden were obtained from the electric field records measured from 14 thunderstorms. The electric fields were measured with nanosecond resolution. Together with the fast and the slow electric field records, the narrowband radiation field at 3 and 30 MHz signals were also measured simultaneously. Out of a total of 107 flashes, 30 flashes had two strokes, 7 had three strokes and 3 flashes had four strokes. The arithmetic and geometric means of the interstroke intervals were found to be 116 and 70 ms, respectively. The arithmetic and geometric mean ratio between the peak electric field of the Subsequent Return Stroke (SRS) and the first Return Stroke (RS) were 0.48 and 0.36, respectively. Of the 40 positive multiple-stroke ground flashes, 5% have at least one SRS with field peak higher than the first RS. The percentage of SRS with field peaks greater than the first RS was 6%. In our best of our knowledge, this is the first time a large sample of positive return strokes in Sweden was analysed. It was found to be statistically more significant than the previous studies.

  • 8. Belova, E.
    et al.
    Kirkwood, S.
    Latteck, R.
    Zecha, M.
    Pinedo, H.
    Hedin, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Multi-radar observations of polar mesosphere summer echoes during the PHOCUS campaign on 20-22 July 20112014In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 118, p. 199-205Article in journal (Refereed)
    Abstract [en]

    During the PHOCUS rocket campaign, on 20-22 July 2011, the observations of polar mesosphere summer echoes (PMSE) were made by three mesosphere-stratosphere-troposphere radars, operating at about 50 MHz. One radar, ESRAD is located at Esrange in Sweden, where the rocket was launched, two other radars, MAARSY and MORRO, are located 250 km north-west and 200 km north of the ESRAD, respectively, on the other side of the Scandinavian mountain ridge. We compared PMSE as measured by these three radars in terms of their strength, spectral width and wave modulation. Time-altitude maps of PMSE strength look very similar for all three radars. Cross-correlations with maximum values 0.5-0.6 were found between the signal powers over the three days of observations for each pair of radars. By using cross-spectrum analysis of PMSE signals, we show that some waves with periods of a few hours were observed by all three radars. Unlike the strengths, simultaneous values of PMSE spectral width, which is related to turbulence, sometimes differ significantly between the radars. For interpretation of the results we suggested that large-scale fields of neutral temperature, ice particles and electron density, which are more or less uniform over 150-250 km horizontal extent were 'modulated' by waves and smaller patches of turbulence.

  • 9.
    Benze, Susanne
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology . University of Colorado, USA.
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Randall, Cora E.
    Karlsson, Bodil
    Stockholm University, Faculty of Science, Department of Meteorology .
    Hultgren, Kristoffer
    Stockholm University, Faculty of Science, Department of Meteorology .
    Lumpe, Jerry D.
    Baumgarten, Gerd
    Making limb and nadir measurements comparable: A common volume study of PMC brightness observed by Odin OSIRIS and AIM CIPS2018In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 167, p. 66-73Article in journal (Refereed)
    Abstract [en]

    Combining limb and nadir satellite observations of Polar Mesospheric Clouds (PMCs) has long been recognized as problematic due to differences in observation geometry, scattering conditions, and retrieval approaches. This study offers a method of comparing PMC brightness observations from the nadir-viewing Aeronomy of Ice in the Mesosphere (AIM) Cloud Imaging and Particle Size (CIPS) instrument and the limb-viewing Odin Optical Spectrograph and InfraRed Imaging System (OSIRIS). OSIRIS and CIPS measurements are made comparable by defining a common volume for overlapping OSIRIS and CIPS observations for two northern hemisphere (NH) PMC seasons: NH08 and NH09. We define a scattering intensity quantity that is suitable for either nadir or limb observations and for different scattering conditions. A known CIPS bias is applied, differences in instrument sensitivity are analyzed and taken into account, and effects of cloud inhomogeneity and common volume definition on the comparison are discussed. Not accounting for instrument sensitivity differences or inhomogeneities in the PMC field, the mean relative difference in cloud brightness (CIPS - OSIRIS) is -102 +/- 55%. The differences are largest for coincidences with very inhomogeneous clouds that are dominated by pixels that CIPS reports as non-cloud points. Removing these coincidences, the mean relative difference in cloud brightness reduces to -6 +/- 14%. The correlation coefficient between the CIPS and OSIRIS measurements of PMC brightness variations in space and time is remarkably high, at 0.94. Overall, the comparison shows excellent agreement despite different retrieval approaches and observation geometries.

  • 10.
    Blomberg, Lars G.
    et al.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Eriksson, Stefan
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Cumnock, Judy A.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Yamauchi, M.
    Clemmons, J. H.
    Marklund, Göran T.
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lindqvist, Per-Arne
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Karlsson, Tomas
    KTH, Superseded Departments, Alfvén Laboratory. KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lundin, R.
    Solar windmagnetosphere-ionosphere coupling: an event study based on Freja data2004In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 66, no 5, p. 375-380Article in journal (Refereed)
    Abstract [en]

    Freja data are used to study the relative contributions from the high-latitude (reconnection/direct entry) and low-latitude (viscous interaction) dynamos to the cross-polar potential drop. Convection streamlines which are connected to the high-latitude dynamo may be identified from dispersed magnetosheath ions not only in the cusp/cleft region itself but also several degrees poleward of it. This fact, together with Freja's orbital geometry allows us to infer the potential drop from the high-latitude dynamo as well as to obtain a lower limit to the potential drop from the low-latitude dynamo for dayside Freja passes. All cases studied here are for active magnetospheric conditions. The Freja data suggest that under these conditions at least one third of the potential is generated in the low-latitude dynamo. These observations are consistent with earlier observations of the potential across the low-latitude boundary layer if we assume that the low-latitude dynamo region extends over several tens of Earth radii in the antisunward direction along the tail flanks, and that the majority of the potential drop derives from the sun-aligned component of the electric field rather than from its cross-boundary component, or equivalently, that the centre of the dynamo region is located quite far down tail. A possible dynamo geometry is illustrated.

  • 11. Bodhika, J. A. P.
    et al.
    Dharmarathna, W. G. D.
    Fernando, Mahendra
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Reconstruction of lightning channel geometry by localizing thunder sources2013In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 102, p. 81-90Article in journal (Refereed)
    Abstract [en]

    Thunder is generated as a result of a shock wave created by sudden expansion of air in the lightning channel due to high temperature variations. Even though the highest amplitudes of thunder signatures are generated at the return stroke stage, thunder signals generated at other events such as preliminary breakdown pulses also can be of amplitudes which are large enough to record using a sensitive system. In this study, it was attempted to reconstruct the lightning channel geometry of cloud and ground flashes by locating the temporal and spatial variations of thunder sources. Six lightning flashes were reconstructed using the recorded thunder signatures. Possible effects due to atmospheric conditions were neglected. Numerical calculations suggest that the time resolution of the recorded signal and 10 ms(-1)error in speed of sound leads to 2% and 3% errors, respectively, in the calculated coordinates. Reconstructed channel geometries for cloud and ground flashes agreed with the visual observations. Results suggest that the lightning channel can be successfully reconstructed using this technique.

  • 12.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    A return stroke model based purely on the current dissipation concept2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 136, no Part A, p. 61-65Article in journal (Refereed)
    Abstract [en]

    A return stroke model based purely on the current dissipation concept is introduced. With three model parameters the model is capable of generating electric and magnetic fields that are in reasonable agreement with experimentally observed electromagnetic fields.

  • 13.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the mimimum length of leader channel and the minimum volume of space charge concentration necessary to initiate lightning flashes in thunderclouds2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 136, no Part A, p. 39-45Article in journal (Refereed)
    Abstract [en]

    Minimum length to which a leader channel has to grow before it can propagate continuously as a stable leader as a function of the background electric field inside a thundercloud is estimated. For electric field magnitudes comparable to the values measured inside thunderclouds, the minimum length of the leader channel that is required for it to propagate continuously is about 3-5 m. In other words, a leader discharge that originated inside a thundercloud has to grow to a length of 3-5 m before it can culminate in a stable and continuously propagating leader discharge that can give rise to a lightning flash. The minimum size of charge concentrations that can make this event possible have radii in the range of 2-4 m and should carry about 300-900 mu C of electric charge, respectively. This in turn shows that the high field regions inside the cloud where electrical discharges that can culminate in stable leader discharges, and hence in lightning discharges, may be confined to volumes which are no larger than a few meters in radius.

  • 14.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Propagation effects on radiation field pulses generated by cloud lightning flashes2007In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 69, no 12, p. 1397-1406Article in journal (Refereed)
    Abstract [en]

    As the electromagnetic fields propagate over finitely conducting ground, selective attenuation of the high frequencies takes place. As a result. the signatures of broad-band electromagnetic radiation fields generated by lightning flashes change as they; propagate over such ground. In addition to being a function of the electrical parameters of the ground over which the electromagnetic fields propagate, these propagation effects depend on the height of their source above ground level. This makes the propagation effects on radiation fields from cloud flashes differ from those on the radiation fields generated by return strokes in ground flashes. In this paper the propagation effects on radiation field pulses of cloud flashes are illustrated and it is shown that these effects are not as severe as those of return strokes in ground flashes.

  • 15.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Arevalo, Liliana
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dwyer, Joseph
    Rassoul, Hamid
    On the possible origin of X-rays in long laboratory sparks2009In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, no 17-18, p. 1890-1898Article in journal (Refereed)
  • 16.
    Cooray, Vernon
    et al.
    Division for Electricity, Uppsala University.
    Becerra Garcia, Marley
    Division for Electricity, Uppsala University.
    Rakov, Vladimir
    Department of Electrical and Computer Engineering, University of Florida.
    On the electric field at the tip of dart leaders in lightning flashes2009In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, no 12, p. 1397-1404Article in journal (Refereed)
    Abstract [en]

    The results obtained in this study show that as the dart leader tip passes a given point on the defunct return stroke channel the electric field increases within a fraction of a microsecond to values larger than the critical electric field necessary for the initiation of cold electron runaway in low-density air comprising the channel. These results are in support of the hypothesis that cold runaway electron breakdown may play a role in the emission of X-ray bursts by dart leaders. The calculations also show that the peak power dissipated by a typical dart leader is about 300–500 MW/m and the energy dissipated within the first 10 μs or so is about 500–600 J/m. Furthermore, the minimum resistance and the maximum radius of the core of a typical dart leader are estimated to be about 3 Ω/m and 0.003 m, respectively.

  • 17.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Becerra, Marley
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rakov, Vladimir
    On the electric field at the tip of dart leaders in lightning flashes2009In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, no 12, p. 1397-1404Article in journal (Refereed)
    Abstract [en]

    The results obtained in this study show that as the dart leader tip passes a given point on the defunct return stroke channel the electric field increases within a fraction of a microsecond to values larger than the critical electric field necessary for the initiation of cold electron runaway in low-density air comprising the channel. These results are in support of the hypothesis that cold runaway electron breakdown may play a role in the emission of X-ray bursts by dart leaders. The calculations also show that the peak power dissipated by a typical dart leader is about 300-500 MW/m and the energy dissipated within the first 10 [mu]s or so is about 500-600 J/m. Furthermore, the minimum resistance and the maximum radius of the core of a typical dart leader are estimated to be about 3 [Omega]/m and 0.003 m, respectively.

  • 18.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Gerald K.
    Karolinska Univ Hosp, Dept Clin Neurosci, Stockholm, Sweden..
    Cooray, Charith
    Karolinska Univ Hosp, Dept Clin Neurosci, Stockholm, Sweden..
    On the possible mechanism of keraunographic markings on lightning victims2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 136, no Part A, p. 119-123Article in journal (Refereed)
    Abstract [en]

    During a lightning strike to a human the high electric field that exists at the point of contact of the lightning flash can generate electrical discharges known as streamer discharges along the skin. Previous research work has shown that the electric field at the head of these streamer discharges are large enough to accelerate electrons to relativistic speeds. In this paper it is shown that the streamers propagating along the skin will bombard the skin with energetic electrons. In this paper an estimation of the energy dissipated by these energetic electrons on the skin is estimated. Since beta radiation generated by radioactive substances consists of energetic electrons the effects of the energetic electrons generated by streamer discharges would be similar to the effects caused by low level beta radiation. It is suggested that the feather like marks, called keraunographical marks, that is sometimes observed on the skin of lightning victims is a result of superficial radiation injury with following inflammation in the epidermis and superficial layers of the dermis caused by energetic electrons.

  • 19.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dwyer, Joseph
    Rakov, V.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    On the mechanism of X-ray production by dart leaders of lightning flashes2010In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, p. 848-855Article in journal (Refereed)
  • 20.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rachidi, Farhad
    Ecole Polytech Fed Lausanne, Swiss Fed Inst Technol, Lausanne, Switzerland..
    Advances in lightning research2017In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 154, p. 181-181Article in journal (Refereed)
  • 21.
    Cooray, Vernon
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rakov, Vladimir
    On the NOx production by laboratory electrical discharges and lightning2009In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, p. 1877-1889Article in journal (Refereed)
  • 22.
    Dahlgren, Hanna
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Aikio, Anita
    Department of physical sciences, University of Oulu.
    Kaila, Kari
    Department of physical sciences, University of Oulu.
    Ivchenko, Nickolay
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lanchester, Betty
    Space Environment Physics Group, University of Southampton.
    Whiter, Daniel
    Space Environment Physics Group, University of Southampton.
    Marklund, Göran
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Simultaneous observations of small multi-scale structures in an auroral arc2010In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 72, p. 633-637Article in journal (Refereed)
    Abstract [en]

    Auroral arcs can develop small-scale distortions known as vortex streets or curls. Other common and somewhat larger spatially periodic distortions are auroral folds. In this event study we present simultaneous wide and narrow field imager observations of a third kind of structuring, on even smaller spatial scales. Boundary undulations, or “ruffs”, have been observed to form on the edge of an auroral arc and they occur superimposed on curls, folds or at times of auroral shear. The undulations typically have wavelengths of less than 3 km and amplitudes of less than 800 m. They are observed to move on the edge of the arc, with velocities of about 11 km/s. These observations, with multi-scale deformations, reveal a much more intricate structuring of auroral arcs than previously found.

  • 23.
    Dahlgren, Hanna
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ivchenko, Nickolay V.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Lanchester, B. S.
    School of Physics and Astronomy, University of Southampton.
    Ashrafi, M.
    School of Physics and Astronomy, University of Southampton.
    Whiter, D.
    School of Physics and Astronomy, University of Southampton.
    Marklund, Göran T.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Sullivan, J.
    School of Physics and Astronomy, University of Southampton.
    First direct optical observations of plasma flows using afterglow of O+ in discrete aurora2009In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, no 2, p. 228-238Article in journal (Refereed)
    Abstract [en]

    Imaging of active structured aurora in the forbidden O+ ion line at 732.0 nm provides a possibility of direct observation of plasma drifts in the topside ionosphere. The metastable O+ P-2 state has a radiative lifetime of 5 s, so the oxygen ions can be detected after the precipitation creating them has ceased. The decay time of the O+ emission is studied and modelled with a time-dependent electron transport and ion chemistry model. Four examples are given of O+ afterglow observed with the multi-spectral imager, auroral structure and kinetics (ASK), which was located near Tromso, Norway, in 2006. Estimates are given of drift velocities resulting from the analysis of the afterglow motions. Bulk plasma velocities of 340 and 720 m/s directed eastwards were found for two afterglowing arc filaments, corresponding to southward electric fields of 18 and 40 mV/m, respectively.

  • 24. Ekeberg, J.
    et al.
    Stasiewicz, Kristof
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Wannberg, G.
    Sergienko, T.
    Eliasson, L.
    Incoherent scatter ion line enhancements and auroral arc-induced Kelvin-Helmholtz turbulence2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 122, p. 119-128Article in journal (Refereed)
    Abstract [en]

    We present two cases of incoherent-scatter ion line enhancements in conjunction with auroral arcs drifting through the radar beam. The up- and downshifted ion line shoulders as well as the spectral region between them are enhanced equally and simultaneously. The power enhancements are one order of magnitude above the thermal level and are concentrated in less than 15 km wide altitude ranges at the ionospheric F region peak. The auroral arc passages are preceded by significantly enhanced ion temperatures in the E region, assumed to be caused by transient electric fields associated with velocity shears. We use a Hall MHD model of velocity shears perpendicular to the geomagnetic field and show that a Kelvin-Helmholtz instability will grow for the two presented cases.

  • 25.
    Ekeberg, Jonas
    et al.
    Umeå University, Faculty of Science and Technology, Department of Physics. ABB Schweiz AG, Corporate Research, CH-5405 Baden-Dättwil, Switzerland.
    Stasiewicz, Kristof
    Swedish Institute of Space Physics, P.O. Box 537, SE-751 21 Uppsala, Sweden.
    Wannberg, Gudmund
    Swedish Institute of Space Physics, P.O. Box 812, SE-981 28 Kiruna, Sweden.
    Sergienko, Tima
    Swedish Institute of Space Physics, P.O. Box 812, SE-981 28 Kiruna, Sweden.
    Eliasson, Lars
    Swedish Institute of Space Physics, P.O. Box 812, SE-981 28 Kiruna, Sweden.
    Incoherent scatter ion line enhancements and auroral arc-induced Kelvin-Helmholtz turbulence2015In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 122, p. 119-128Article in journal (Refereed)
    Abstract [en]

    We present two cases of incoherent-scatter ion line enhancements in conjunction with auroral arcs drifting through the radar beam. The up- and downshifted ion line shoulders as well as the spectral region between them are enhanced equally and simultaneously. The power enhancements are one order of magnitude above the thermal level and are concentrated in less than 15 km wide altitude ranges at the ionospheric F region peak. The auroral arc passages are preceded by significantly enhanced ion temperatures in the E region, which are shown to generate high velocity shears. We use a Hall MHD model of velocity shears perpendicular to the geomagnetic field and show that a Kelvin-Helmholtz instability will grow for the two presented cases. We assess the possibility that the subsequently generated low frequency turbulence can explain the observed spectrally uniform ion line power enhancements.

  • 26. Enell, Carl-Fredrik
    et al.
    Hedin, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Stegman, Jacek
    Stockholm University, Faculty of Science, Department of Meteorology .
    Witt, Georg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Friedrich, Martin
    Singer, Werner
    Baumgarten, Gerd
    Kaifler, Bernd
    Hoppe, Ulf-Peter
    Gustavsson, Björn
    Brandström, Urban
    Khaplanov, Mikhail
    Stockholm University, Faculty of Science, Department of Meteorology .
    Kero, Antti
    Ulich, Thomas
    Turunen, Esa
    The Hotel Payload 2 campaign: Overview of NO, O and electron density measurements in the upper mesosphere and lower thermosphere2011In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 73, no 14-15, p. 2228-2236Article in journal (Refereed)
    Abstract [en]

    The ALOMAR eARI Hotel Payload 2 (HotPay 2) rocket campaign took place at Andoya Rocket Range, Norway, in January 2008. The rocket was launched on January 31, 2008 at 19:14 UT, when auroral activity appeared after a long geomagnetically quiet period. In this paper we present an overview of the HotPay 2 measurements of upper mesospheric and lower thermospheric (UMLT) electron, atomic oxygen (O) and nitric oxide (NO) densities. [O] and [NO] were retrieved from a set of three photometers, Night-Time Emissions from the Mesosphere and Ionosphere (NEMI). Faraday rotation receivers on the rocket and the EISCAT UHF incoherent scatter radar provided simultaneous electron density profiles, whereas the ALOMAR Na lidar and meteor radar measured the temperature profile and wind. The aurora was also observed with ground-based imagers. The retrieved oxygen number density profile has a maximum at 89 km, some 10 km lower than expected from earlier measurements and modelled profiles based on climatological averages (such as the MSIS model), and the retrieved NO densities are also lower than the expected. Satellite measurements indicate that subsidence over the winter pole controlled the densities. Quantitative chemistry model results based on climatological average atmospheric density and temperature profiles were, therefore, not in good agreement with the measured profiles. The Hotel Payload 2 measurements thus confirm the importance of downward transport from the thermosphere into the winter polar vortex.

  • 27.
    Esa, Mona Riza Binti Mohd
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Ahmad, Mohd Riduan
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Distinctive features of radiation pulses in the very first moment of lightning events2014In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 109, p. 22-28Article in journal (Refereed)
    Abstract [en]

    This paper investigates the existence of distinctive features between 4 different types of lightning discharges, namely negative cloud to ground discharge (-CG), positive cloud to ground discharge (+ CG), cloud discharge (IC) and isolated breakdown discharge (IB). A total of 110 very fine structure waveforms of 44 CG, 16 +CG, 39 IC, and 11 IB discharges have been selected from a collection of 885 waveforms measured using fast electric field broadband antenna system. The measurements were carried out in Uppsala, Sweden from May to August 2010. We found that there are significant distinctions within the first 1 ms among different types of lightning discharges (-CG, +CG, IC, and IB). For example, the pulses in -CG discharges are more frequent than other discharges; the pulses in +CG discharges have the highest intensity and the IC discharge pulses tend to have shorter duration. o 2014 Elsevier Ltd. All rights reserved.

  • 28. Fernandoa, Mahendra
    et al.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Division for Electricity and Lightning Research.
    Propagation effects on the electric field time derivatives generated by return strokes in lightning flashes2007In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 69, no 12, p. 1388-1396Article in journal (Refereed)
    Abstract [en]

    The effects of propagation over finitely conducting ground on the features of radiation component of the electric field time derivatives are investigated. The results show that the peak, the half-width and the risetime of the electric field time derivative change significantly in propagating over finitely conducting ground. Furthermore, any correlation that may exist between various parameters could also change significantly due to propagation effects. Consequently, in return stroke model validations using experimentally measured fields, remote sensing of return stroke current time derivatives using measured electric field time derivatives and in the calculation of induced voltages generated by lightning flashes in electrical installations the distortions caused by propagation effects on the electric field time derivatives cannot be neglected.

  • 29.
    Friedman, Jonathan S.
    et al.
    National Astronomy and Ionosphere Center, Arecibo Observatory.
    Teplay, Carig A.
    National Astronomy and Ionosphere Center, Arecibo Observatory.
    Raizada, Shikira
    National Astronomy and Ionosphere Center, Arecibo Observatory.
    Zhou, Qihou H.
    Manufacturing and Mechanical Engineering Department, Miami University.
    Hedin, Jonas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Delgado, Ruben
    University of Puerto Rico, Department of Chemistry.
    Potassium Doppler-resonance lidar for the study of the mesosphere and lower thermosphere at the Arecibo Observatory2003In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 65, no 16-18, p. 1411-1424Article in journal (Refereed)
    Abstract [en]

    We have developed a lidar to study the temperature structure of the nighttime mesopause region over the Arecibo Observatory (18.35°N, 66.75°W) by measuring the lineshape of the fluorescence spectrum of atomic potassium that is deposited in the mesosphere and lower thermosphere (MLT) by meteors. To demonstrate how the potassium lidar can enhance MLT studies at Arecibo, we show recent results for: (1) comparisons with airglow temperature measurements; (2) simultaneous operations with stratospheric and mesospheric temperature profiling by Rayleigh lidar; (3) simultaneous observations of K, Ca+, and E-region electron density profiles; and (4) occurrences of sporadic K layers, and relationships to sporadic E layers.

  • 30. Friedman, Jonathan S.
    et al.
    Tepley, C. A.
    Raizada, S
    Zhou, Q. H.
    Hedin, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Delgado, R
    Potassium Doppler-resonance lidar for the study of the mesosphere and lower thermosphere at Arecibo Obsevatory2003In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 65, p. 1411-1424Article in journal (Refereed)
  • 31.
    Fu, Huishan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Physics, Swedish Institute of Space Physics, Uppsala Division.
    Cao, J. B.
    Zong, Q-G
    Lu, H. Y.
    Huang, S. Y.
    Wei, X. H.
    Ma, Y. D.
    The role of electrons during chorus intensification: Energy source and energy loss2012In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 80, p. 37-47Article in journal (Refereed)
    Abstract [en]

    The role of electrons during the shock-induced chorus intensification observed by THEMIS D on 19 November 2007 is investigated in detail. First, the electrons are accelerated through the local betatron acceleration and radial diffusion, which are primarily in the perpendicular direction and result in the positive anisotropy (T-perpendicular to > T-//) of electrons; then they are scattered through the pitch-angle diffusion, during which the electron energies are partially transferred to amplify the chorus. In the case of interest, the energy loss is more efficient for the lower-energy (15 key) electrons because they have larger density gradient along the diffusion curves. The energetic electrons act as the intermediate in this scenario. They transfer the energies carried by the interplanetary shock to the chorus. The energetic electrons injected from magnetotail are not observed; they have no contributions to the energy source in this event.

  • 32.
    Fälthammar, Carl-Gunne
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    The Discovery of Magnetohydrodynamic waves2007In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 69, no 14, p. 1604-1608Article in journal (Refereed)
    Abstract [en]

    The discovery of magnetohydrodynamic waves was a major breakthrough in plasma physics and its applicationsto space physics and fusion research. The waves were discovered by Hannes Alfve´n and are therefore also calledAlfve´n Waves. The discovery was typical of Alfve´n’s outstanding ability to derive results of great generality fromanalysis of specific problems—in this case, the sunspots and the sunspot cycle. It was also typical of his electrodynamicapproach to astrophysical problems. It took a long time before his discovery was generally accepted,partly because of the contemporary lack of means to verify the waves experimentally. The experimental verificationof the magnetohydrodynamic waves came gradually many years later, beginning with experiments in liquid metals. It wasnot until the end of the 1950s that experiments were performed in plasmas. These clearly and conclusively demonstratedthe existence and properties of magnetohydrodynamic waves, in excellent agreement with the theoretical prediction ofAlfve´n. The discovery of the magnetohydrodynamic waves opened a whole new field of physics—magnetohydrodynamics,which is of profound importance especially, but not only, in plasma physics. At the same time as themagnetohydrodynamic waves, Hannes Alfve´n also discovered another magnetohydrodynamic concept, the frozen-inmagnetic field.

  • 33.
    Gherm, VE
    et al.
    Univ Leeds, Inst Integrated Informat Syst, Sch Elect & Elect Engn, Leeds LS2 9JT, W Yorkshire, England FOI, Linkoping, Sweden St Petersburg State Univ, St Petersburg, Russia.
    Zernov, VV
    Univ Leeds, Inst Integrated Informat Syst, Sch Elect & Elect Engn, Leeds LS2 9JT, W Yorkshire, England FOI, Linkoping, Sweden St Petersburg State Univ, St Petersburg, Russia.
    Lundborg, B
    Univ Leeds, Inst Integrated Informat Syst, Sch Elect & Elect Engn, Leeds LS2 9JT, W Yorkshire, England FOI, Linkoping, Sweden St Petersburg State Univ, St Petersburg, Russia.
    Darnell, M
    Univ Leeds, Inst Integrated Informat Syst, Sch Elect & Elect Engn, Leeds LS2 9JT, W Yorkshire, England FOI, Linkoping, Sweden St Petersburg State Univ, St Petersburg, Russia.
    Strangeways, HJ
    Univ Leeds, Inst Integrated Informat Syst, Sch Elect & Elect Engn, Leeds LS2 9JT, W Yorkshire, England FOI, Linkoping, Sweden St Petersburg State Univ, St Petersburg, Russia.
    Wideband scattering functions for HF ionospheric propagation channels2001In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 63, no 14, p. 1489-1497Article in journal (Refereed)
    Abstract [en]

    A physically based method has been developed to simulate the wideband HF ionospheric propagation channel relevant to the case of wideband spread spectrum HF communications and also other HF applications such as digital broadcasting and over-the-horizon radar, It is based on the consideration and solution of the equations governing pulse signal propagation through a fluctuating time varying random ionosphere. The wideband scattering function has been constructed as the appropriate Fourier transform of the correlation function of a channel impulse response. Numerical codes have been written, which allow numerical simulation of the wideband scattering function of the HF sky wave ionospheric fluctuation channel for any given model of the background ionosphere and time varying ionospheric turbulence with an anisotropic inverse power law spatial spectrum and frozen drift of the ionospheric inhomogeneitics. When employed in the simulation of the scattering function for real conditions of propagation, the method provides the possibility of analysing the propagation effects for different relative bandwidths of the background channel, fluctuating channel and transmitted pulse. The effects of the transmitted pulse bandwidth and anisotropy of the irregularities have been studied. The numerical results have been obtained and presented, which demonstrate the contribution of the effects enumerated in the wideband scattering function of the HF ionospheric channel. (C) 2001 Elsevier Science Ltd. All rights reserved.

  • 34.
    Gumbel, Jörg
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Körnich, Heiner
    Stockholm University, Faculty of Science, Department of Meteorology .
    Bailey, S. M.
    Lubken, F. -J
    Morris, R.
    Special issue on layered phenomena in the mesopause region Foreword2011In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 73, no 14-15, p. 2045-2048Article in journal (Refereed)
  • 35.
    Gumbel, Jörg
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Megner, Linda
    Stockholm University, Faculty of Science, Department of Meteorology .
    Charged meteoric smoke as ice nuclei in the mesosphere. Part 1: A review of basic concepts2009In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, no 12, p. 1225-1235Article in journal (Refereed)
    Abstract [en]

    The role of meteoric smoke as condensation nuclei for mesospheric ice has recently been challenged by model simulations on the global transport of meteoric material. At the same time a considerable fraction of smoke particles is charged in the mesosphere. This has significant effects on nucleation processes as it can remove the Kelvin barrier. We suggest that in particular nucleation on negatively charged smoke is likely to be a dominant mechanism for mesospheric ice formation. This is in contrast to nucleation on positive ion clusters as the latter is largely hampered by efficient ion/electron recombination. Surprisingly, the large potential of nucleation on charged smoke has so far not been considered in mesospheric ice models. A challenging question concerns the fraction of mesospheric smoke that is actually charged. An improved understanding of mesospheric charging and nucleation will require laboratory experiments on nuclei in the transition regime between molecular and particulate sizes.

  • 36.
    Gunasekara, T. A. L. N.
    et al.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka..
    Fernando, M.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka..
    Sonnadara, U.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka..
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Characteristics of Narrow Bipolar Pulses observed from lightning in Sri Lanka2016In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 138, p. 66-73Article in journal (Refereed)
    Abstract [en]

    A detailed study on electric field characteristics of Narrow Bipolar Pulses (NBP) observed in Sri Lanka is presented here. NBP5 analyzed in this work were recorded at a coastal location in the Southern part of Sri Lanka (Matara: 5.95 degrees N, 8.53 degrees E), from five highly active consecutive thunderstorm days during the month of May in 2013. The waveforms were recorded with a 10 ns resolution within a 100 ms time window. Both positive and negative NBP5 were observed in this study with the negative type being the most frequent. Parameters presented in this study were the rise time (Tr), zero crossing time (Tz), the duration of slow front (Ts), the full width of half maximum (FWHM), the pulse duration and the ratio of amplitude of overshoot to the corresponding peak amplitude (Os/Pa). The corresponding average values of negative NBP5 for these parameters were found to be 0.58 mu s, 3.01 mu s, 0.20 mu s, 138 mu s, 19.21 mu s and 0.19 respectively. Similarly, for positive events corresponding values were 1.38 mu s, 4.66 mu s, 0.48 mu s, 1.93 mu s, 16.42 mu s and 0.37 respectively. The above values conforms to a much narrower bipolar events when compared to previously reported values which is considered to be caused by the propagation effects of signals captured by the apparatus.

  • 37.
    Gunasekara, T. A. L. N.
    et al.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka.
    Fernando, M.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka.
    Sonnadara, U.
    Univ Colombo, Dept Phys, Colombo 3, Sri Lanka.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Horizontal electric fields of lightning return strokes and narrow bipolar pulses observed in Sri Lanka2018In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 173, p. 57-65Article in journal (Refereed)
    Abstract [en]

    Simultaneous measurement of both vertical and horizontal electric field signatures of lightning was carried out in an elevated location in Colombo, Sri Lanka. The experimental setup used in this work was similar to an earlier study carried out by a different group in the late 1980s. To our knowledge, this is the first instance that such a study is conducted in this region. Data were acquired during the active months (April-May) of the southwest monsoon period in 2014. Lightning flashes from the most active thunderstorm was analyzed by selecting 65 Return Strokes (RS), 50 Negative Narrow Bipolar Pulses (NNBP) and 40 Positive Narrow Bipolar Pulses (PNBP). The wave shapes were initially validated against results of a previous study and subsequently via a theoretical method as well. Since the direction and the distance information was not available, rather than the amplitudes, ratios of the peak amplitudes of vertical electric field (Ev) and corresponding horizontal electric field (Eh) were compared. The average ratio for the return stroke was 0.024 +/- 0.008. The same for the NNBP was 0.041 +/- 0.004. The PNBP had a ratio of 0.031 +/- 0.006. The average 10%-90% rise times (Tr) for Ev for RS, NNBP and PNBP was 2.124 +/- 1.088 mu s, 0.734 +/- 0.077 is and 1.141 +/- 0.311 mu s respectively. The Tr values for Eh for RS, NNBP and PNBP were 1.865 +/- 1.200 mu s, 0.538 +/- 0.061 mu s and 1.086 +/- 0.423 mu s.

  • 38.
    Gunasekara, T.A.L.N.
    et al.
    Department of Physics, University of Colombo, Sri Lanka.
    Jayalal, S.N
    Department of Physics, University of Colombo, Sri Lanka.
    Fernando, Mahendra
    Department of Physics, University of Colombo, Sri Lanka.
    Sonnadara, Upul
    Department of Physics, University of Colombo, Sri Lanka.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Time-Frequency Analysis of vertical and horizontal electric field changes of lightning negative return strokes observed in Sri Lanka2018In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 179, p. 34-39Article in journal (Refereed)
    Abstract [en]

    Simultaneously captured vertical and horizontal (total) electric field signatures of lightning negative Return Strokes (RS) were analyzed to obtain Time-Frequency (TF) variation using Stockwell Transformation (ST). In the study, ST was utilized since it is known to possess comparatively better time resolution at high frequency regions compared to other available TF methods. The data were obtained during the monsoon season of April–May 2014. The vertical and horizontal component of fifty negative RSs was utilized in the study. The resultant ST spectrum was analyzed and the regions of interest were demarcated based on the color which represented their relative power output intensities for different frequency components of the signal. The spread area was identified as the region of frequencies which consisted of power intensity equal or above 90th percentile when compared to the maximum possible value. The spectral area was identified as the area of frequencies in the borderline to the natural background noise. The spread region for the vertical E field had a range between 10 kHz and 650 kHz. Its average values were in between 126 kHz and 331 kHz. The spectral region of the vertical electric field change spanned from 1 kHz to 1020 kHz. Its average distribution was 44 kHz–660 kHz. Horizontal electric fields had a range of 20 kHz–1940 kHz in the spectral region. The same for the spread region was 80 kHz–910 kHz. The averages of the horizontal E field's spectral region were 46–1112 kHz and its spread region varied between 227 and 599 kHz. The results display a higher frequency range for all aspects of the horizontal E field changes which implies that its influence on the high frequency radiation is much higher than its vertical counterpart.

  • 39. Havnes, O.
    et al.
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Antonsen, T.
    Hedin, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    La Hoz, C.
    On the size distribution of collision fragments of NLC dust particles and their relevance to meteoric smoke particles2014In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 118, p. 190-198Article in journal (Refereed)
    Abstract [en]

    We present the results from a new dust probe MUDD on the PHOCUS payload which was launched in July 2011. In the interior of MUDD all the incoming NLC/PMSE icy dust particles will collide, at an impact angle similar to 70 degrees to the surface normal, with a grid constructed such that no dust particles can directly hit the bottom plate of the probe. Only collision fragments will continue down towards the bottom plate. We determine an energy distribution of the charged fragments by applying a variable electric field between the impact grid and the bottom plate of MUDD. We find that similar to 30% of the charged fragments have kinetic energies less than 10 eV, similar to 20% have energies between 10 and 20 eV while similar to 50% have energies above 20 eV. The transformation of limits in kinetic energy for ice or meteoric smoke particles (MSP) to radius is dependent on many assumptions, the most crucial being fragment velocity. We find, however, that the sizes of the charged fragments most probably are in the range of 1 to 2 nm if meteoric smoke particles (MSP), and slightly higher if ice particles. The observed high charging fraction and the dominance of fragment sizes below a few nm makes it very unlikely that the fragments can consist mainly of ice but that they must be predominantly MSP as predicted by Havnes and N ae sheim (2007) and recently observed by Hervig et al. (2012). The MUDD results indicate that MSP are embedded in NLC/PMSE ice particles with a minimum volume filling factor of similar to.05% in the unlikely case that all embedded MSP are released and charged. A few % volume filling factor (Hervig et al., 2012) can easily be reached if similar to 10% of the MSP are released and that their charging probability is similar to 0.1.

  • 40.
    Hedin, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Giovane, Frank
    Waldemarsson, Tomas
    Stockholm University, Faculty of Science, Department of Meteorology . Naval Research Laboratory, USA.
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Blum, Jürgen
    Stroud, Rhonda M.
    Marlin, Layne
    Moser, John
    Siskind, David E.
    Jansson, Kjell
    Stockholm University, Faculty of Science, Department of Materials and Environmental Chemistry (MMK).
    Saunders, Russell W.
    Summers, Michael E.
    Reissaus, Philipp
    Stegman, Jacek
    Stockholm University, Faculty of Science, Department of Meteorology .
    Plane, John M. C.
    Horanyi, Mihaly
    The MAGIC meteoric smoke particle sampler2014In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 118, p. 127-144Article in journal (Refereed)
    Abstract [en]

    Between a few tons to several hundred tons of meteoric material enters the Earth's atmosphere each day, and most of this material is ablated and vaporized in the 70-120 km altitude region. The subsequent chemical conversion, re-condensation and coagulation of this evaporated material are thought to form nanometre sized meteoric smoke particles (MSPs). These smoke particles are then subject to further coagulation, sedimentation and global transport by the mesospheric circulation. MSPs have been proposed as a key player in the formation and evolution of ice particle layers around the mesopause region, i.e. noctilucent clouds (NLC) and polar mesosphere summer echoes (PMSE). MSPs have also been implicated in mesospheric heterogeneous chemistry to influence the mesospheric odd oxygen/odd hydrogen (O-x/HOx) chemistry, to play an important role in the mesospheric charge balance, and to be a significant component of stratospheric aerosol and enhance the depletion of O-3. Despite their apparent importance, little is known about the properties of MSPs and none of the hypotheses can be verified without direct evidence of the existence, altitude and size distribution, shape and elemental composition. The aim of the MAGIC project (Mesospheric Aerosol - Genesis, Interaction and Composition) was to develop an instrument and analysis techniques to sample for the first time MSPs in the mesosphere and return them to the ground for detailed analysis in the laboratory. MAGIC meteoric smoke particle samplers have been flown on several sounding rocket payloads between 2005 and 2011. Several of these flights concerned non-summer mesosphere conditions when pure MSP populations can be expected. Other flights concerned high latitude summer conditions when MSPs are expected to be contained in ice particles in the upper mesosphere. In this paper we present the MAGIC project and describe the MAGIC MSP sampler, the measurement procedure and laboratory analysis. We also present the attempts to retrieve MSPs from these flights, the challenges inherent to the sampling of nanometre sized particles and the subsequent analysis of the sampled material, and thoughts for the future. Despite substantial experimental efforts, the MAGIC project has so far failed to provide conclusive results. While particles with elemental composition similar to what is to be expected from MSPs have been found, the analysis has been compromised by challenges with different types of contamination and uncertainties in the sticking efficiency of the particles on the sampling surfaces.

  • 41.
    Hedin, Jonas
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    The global mesospheric sodium layer observed by Odin/OSIRIS in 2004-20092011In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 73, no 14-15, p. 2221-2227Article in journal (Refereed)
    Abstract [en]

    The source of the mesospheric sodium layer is the daily ablation of 10-100 tons of meteoric material in Earth's atmosphere. Global studies of this layer yield important information about the chemistry and dynamics of Earth's mesosphere and lower thermosphere (MLT). For nine years the Optical Spectrograph and Infra-Red Imager System (OSIRIS) on-board the Odin satellite has observed Earth's middle atmosphere by limb measurements of scattered sunlight from the ultraviolet to the infrared. In its aeronomy mode, Odin performs limb scans during 15 near-polar sun-synchronous orbits each day. The current measurement programme provides scans up to 110 km on about 300 days per year. Above 70 km, Na D resonance scattering at 589 nm results in a strong limb signal. Retrievals from this dayglow feature have provided a global database of the mesospheric sodium layer. We present an updated sodium climatology from the Odin mission, including latitudinal and seasonal dependence, and interannual variability. We find a weak seasonal variation at low latitudes and an annual variation at mid- and high-latitudes with a clear summer minimum. An interesting feature is an interhemispheric asymmetry in the global dataset with larger sodium abundances during fall in the northern hemisphere and during spring in the southern hemisphere.

  • 42.
    Hettiarachchi, Pasan
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Rahman, Mahbubur
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Cooray, Vernon
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Electricity.
    Dwyer, Joseph
    Univ New Hampshire, Inst Study Earth Oceans & Space, Morse Hall,8 Coll Rd, Durham, NH 03824 USA..
    X-rays from negative laboratory sparks in air: Influence of the anode geometry2017In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 154, p. 190-194Article in journal (Refereed)
    Abstract [en]

    In this experimental work, the influence of the grounded anode geometry is studied on the X-ray production from the laboratory sparks in air at atmospheric pressure when a negative impulse voltage is applied to a high voltage rod which served as a cathode. The result shows that the smaller the diameter of the anode, the higher the energy of X-ray bursts. This observation can be explained by the mechanism that the encounter of negative and positive streamer fronts just before the final breakdown is the event that accelerates electrons to X-ray generating energies, but may not be the only mechanism that generates X-rays.

  • 43.
    Hultgren, Kristoffer
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Degenstein, Doug
    Bourassa, Adam
    Lloyd, Nick
    Stegman, Jacek
    Stockholm University, Faculty of Science, Department of Meteorology .
    First simultaneous retrievals of horizontal and vertical structures of Polar Mesospheric Clouds from Odin/OSIRIS tomography2013In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 104, p. 213-223Article in journal (Refereed)
    Abstract [en]

    Limb-scanning satellites can provide global information about the vertical structure of Polar Mesospheric Clouds. However, information about horizontal structures usually remains limited. In eighteen days during the northern hemisphere summers of 2010 and 2011, the Odin satellite was operated in a special mesospheric mode with short limb scans limited to the altitude range of Polar Mesospheric Clouds. For Odin's Optical Spectrograph and InfraRed Imager System (OSIRIS) this provides multiple views through a given cloud volume, which forms a basis for tomographic analyses of the vertical/horizontal cloud structures. Here we present an algorithm for a tomographic analysis of mesospheric clouds based on maximum probability techniques. We also present the first simultaneously retrieved vertical and horizontal Polar Mesospheric Cloud structures. The findings show that the tomographic algorithm is able to locate detailed structures such as tilts, stratifications, or holes that cannot be analyzed by other limb, nadir, or ground-based measurements. We find a mean peak altitude of the clouds to be 83.6 km. We identify horizontal patches down to sizes of 300 km, which corresponds to a horizontal resolution that is limited by the available number of limb scans.

  • 44.
    Hultgren, Kristoffer
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Kornich, Heiner
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Gerding, Michael
    Hoffmann, Peter
    Lossow, Stefan
    Megner, Linda
    What caused the exceptional mid-latitudinal Noctilucent Cloud event in July 2009?2011In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 73, no 14-15, p. 2125-2131Article in journal (Refereed)
    Abstract [en]

    Noctilucent Clouds (NLCs) are rarely observed at mid-latitudes. In July 2009, strong NLCs were recorded from both Paris and Nebraska, located at latitudes 48 degrees N and 41 degrees N, respectively. The main focus of this work is on the atmospheric conditions that have led to NLCs at these latitudes. We investigate to what extent these clouds may be explained by local formation or by transport from higher latitudes. The dynamical situation is analyzed in terms of wind fields created from Aura/MLS temperature data and measured by radar. We discuss possible tidal effects on the transport and examine the general planetary wave activity during these days. The winds do not seem sufficient to transport NLC particles long southward distances. Hence a local formation is rather likely. In order to investigate the possibility of local NLC formation, the CARMA microphysical model has been applied with temperature data from MLS as input. The results from the large-scale datasets are compared to NLC observations by Odin and to local NLC, temperature and wind measurements by lidar and radar. The reason for the exceptional NLC formation is most likely a combination of local temperature variations by diurnal tides, advantageously located large-scale planetary waves, and general mesospheric temperature conditions that were 5-10 K colder than in previous years. The results also point to that NLCs are very unlikely to occur at latitudes below 50 degrees N during daytime. This conclusion can be made from a tidal temperature mode with cold temperatures during nighttime and temperatures above the limit for NLC occurrence during daytime. The best time for observing mid-latitude NLCs is during the early morning hours.

  • 45.
    Jordanova, V. K.
    et al.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Delzanno, G. L.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Henderson, M. G.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Godinez, H. C.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Jeffery, C. A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Lawrence, E. C.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Morley, S. K.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Moulton, J. D.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Vernon, L. J.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Woodroffe, J. R.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Brito, T. V.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Engel, M. A.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Meierbachtol, C. S.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Svyatsky, D.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA..
    Yu, Y.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA.;Beihang Univ, Beijing, Peoples R China..
    Toth, G.
    Univ Michigan, Ann Arbor, MI 48109 USA..
    Welling, D. T.
    Univ Michigan, Ann Arbor, MI 48109 USA..
    Chen, Y.
    Univ Michigan, Ann Arbor, MI 48109 USA..
    Haiducek, J.
    Univ Michigan, Ann Arbor, MI 48109 USA..
    Markidis, Stefano
    KTH, School of Electrical Engineering and Computer Science (EECS), Computational Science and Technology (CST).
    Albert, J. M.
    Air Force Res Lab, Kirtland AFB, NM USA..
    Birn, J.
    Los Alamos Natl Lab, Los Alamos, NM 87545 USA.;Space Sci Inst, Boulder, CO USA..
    Denton, M. H.
    Space Sci Inst, Boulder, CO USA.;New Mexico Consortium, Los Alamos, NM USA..
    Horne, R. B.
    British Antarctic Survey, Cambridge, England..
    Specification of the near-Earth space environment with SHIELDS2018In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 177, p. 148-159Article in journal (Refereed)
    Abstract [en]

    Predicting variations in the near-Earth space environment that can lead to spacecraft damage and failure is one example of "space weather" and a big space physics challenge. A project recently funded through the Los Alamos National Laboratory (LANL) Directed Research and Development (LDRD) program aims at developing a new capability to understand, model, and predict Space Hazards Induced near Earth by Large Dynamic Storms, the SHIELDS framework. The project goals are to understand the dynamics of the surface charging environment (SCE), the hot (keV) electrons representing the source and seed populations for the radiation belts, on both macro and micro-scale. Important physics questions related to particle injection and acceleration associated with magnetospheric storms and substorms, as well as plasma waves, are investigated. These challenging problems are addressed using a team of world-class experts in the fields of space science and computational plasma physics, and state-of-the-art models and computational facilities. A full two-way coupling of physics-based models across multiple scales, including a global MHD (BATS-R-US) embedding a particle-in-cell (iPIC3D) and an inner magnetosphere (RAM-SCB) codes, is achieved. New data assimilation techniques employing in situ satellite data are developed; these provide an order of magnitude improvement in the accuracy in the simulation of the SCE. SHIELDS also includes a post-processing tool designed to calculate the surface charging for specific spacecraft geometry using the Curvilinear Particle-In-Cell (CPIC) code that can be used for reanalysis of satellite failures or for satellite design.

  • 46.
    Kaladze, T D
    et al.
    Tbilisi State University.
    Pokhotelov, O A
    Moscow.
    Shah, H A
    GC University.
    Khan, M I
    GC University.
    Stenflo, Lennart
    Linköping University, Department of Physics, Chemistry and Biology, Theoretical Physics . Linköping University, The Institute of Technology.
    Acoustic-gravity waves in the Earths ionosphere2008In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 70, no 13, p. 1607-1616Article in journal (Refereed)
    Abstract [en]

    Taking into account the existence of charged particles in the Earths ionosphere the propagation of acoustic-gravity waves is investigated. The influence of the Coriolis force is also taken into account. The weakly ionized ionospheric D, E, and F-layers are considered. The existence of a cut-off frequency at 2 Omega(0) (Omega(0) is the value of the angular velocity of the Earths rotation) is noted. It is shown that the linear waves are damped because of the Pedersen conductivity. When the acoustic-gravity waves are excited by external events (volcanic eruptions, earthquakes, lightning strikes, etc.) their amplitudes grow until self-organization of these waves into nonlinear vortex solitary structures is admitted. Taking into account the interaction of the induced ionospheric current with the geomagnetic field the governing nonlinear equations are deduced. The formation of dipole vortex solitary structures of low-frequency internal gravity waves is shown for the stable stratified ionosphere. The dynamic energy equation for such nonlinear structures is obtained. It is shown that nonlinear solitary vortical structures damp due to joule losses.

  • 47. Kaladze, T. D.
    et al.
    Pokhotelov, Oleg A.
    Shah, H.A.
    Khan, M.I.
    Stenflo, Lennart
    Umeå University, Faculty of Science and Technology, Physics.
    Acoustic-gravity waves in the Earth´s ionosphere2008In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 70, p. 1607-1616Article in journal (Refereed)
  • 48.
    Karlsson, Bodil
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    McLandress, Charles
    Shepherd, Theodore G.
    Inter-hemispheric mesospheric coupling in a comprehensive middle atmosphere model2009In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 71, no 3-4, p. 518-530Article in journal (Refereed)
    Abstract [en]

    Observations of noctilucent clouds have revealed a surprising coupling between the winter stratosphere and the summer polar mesopause region. In spite of the great distance involved, this inter-hemispheric link has been suggested to be the principal reason for both the year-to-year variability and the hemispheric differences in the frequency of occurrence of these high-altitude clouds. In this study, we investigate the dynamical influence of the winter stratosphere on the summer mesosphere using simulations from the vertically extended version of the Canadian Middle Atmosphere Model (CMAM). We find that for both Northern and Southern Hemispheres, variability in the summer polar mesopause region from one year to another can be traced back to the planetary-wave flux entering the winter stratosphere. The teleconnection pattern is the same for both positive and negative wave-flux anomalies. Using a composite analysis to isolate the events, it is argued that the mechanism for inter-hemispheric coupling is a feedback between summer mesosphere gravity-wave drag (GWD) and zonal wind, which is induced by an anomaly in mesospheric cross-equatorial flow, the latter arising from the anomaly in winter hemisphere GWD induced by the anomaly in stratospheric conditions.

  • 49. Knappmiller, S.
    et al.
    Rapp, M.
    Robertson, S.
    Gumbel, Jörg
    Stockholm University, Faculty of Science, Department of Meteorology .
    Charging of meteoric smoke and ice particles in the mesosphere including photoemission and photodetachment rates2011In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 73, no 14-15, p. 2212-2220Article in journal (Refereed)
    Abstract [en]

    Charge probability distributions and charge number densities are presented for three types of particles that occur in the polar summer mesosphere: NLC particles (ice particles), meteoric smoke particles (MSP), and MSP covered in ice. Charge probability distributions and charge number densities are found using a kinetic rate equation including photoemission and photodetachment rates. Due to the large workfunction of ice, photoemission rates for NLC particles are negligible. The electron affinity for ice is an order of magnitude lower than the workfunction, thus photodetachment is a significant charging process. In the absence of photo-charging effects, an NLC particle will charge negatively by electron collection, and a particle above 10 nm in radius will have a charge that increases approximately linearly with radius. However when photodetachment is included, the number of electrons that attach to an NLC particle above 10 nm in radius is limited. Metal oxides such as Fe(2)O(3) have been suggested as a primary constituent of MSP. Assuming that the optical properties of MSP can be represented by these metal oxides, photoemission and photodetachment rates are comparable to electron attachment rates resulting in positively charged MSP. Photoemission, therefore, may help explain the multiple observations of positive particles observed in the mesosphere. In addition, the existence of positively charged MSP has implications for the formation of NLC particles. NLC particles with a core of meteoric smoke have an increased photodetachment rate, making the mean charge of the particle less negative. NLC particles with densities larger than the electron and ion densities calculated both with and without photodetachment show the coexistence of positive and negative particles. Large number densities of NLC particles are another possible explanation for the simultaneous occurrence of positive and negative particles observed by rocket-borne instruments.

  • 50.
    Kuilman, Maartje
    et al.
    Stockholm University, Faculty of Science, Department of Meteorology .
    Karlsson, Bodil
    Stockholm University, Faculty of Science, Department of Meteorology .
    Benze, Susanne
    Stockholm University, Faculty of Science, Department of Meteorology .
    Megner, Linda
    Stockholm University, Faculty of Science, Department of Meteorology .
    Exploring noctilucent cloud variability using the nudged and extended version of the Canadian Middle Atmosphere Model2017In: Journal of Atmospheric and Solar-Terrestrial Physics, ISSN 1364-6826, E-ISSN 1879-1824, Vol. 164, p. 276-288Article in journal (Refereed)
    Abstract [en]

    Ice particles in the summer mesosphere-such as those connected to noctilucent clouds and polar mesospheric summer echoes-have since their discovery contributed to the uncovering of atmospheric processes on various scales ranging from interactions on molecular levels to global scale circulation patterns. While there are numerous model studies on mesospheric ice microphysics and how the clouds relate to the background atmosphere, there are at this point few studies using comprehensive global climate models to investigate observed variability and climatology of noctilucent clouds. In this study it is explored to what extent the large-scale inter-annual characteristics of noctilucent clouds are captured in a 30-year run-extending from 1979 to 2009-of the nudged and extended version of the Canadian Middle Atmosphere Model (CMAM30). To construct and investigate zonal mean inter-seasonal variability in noctilucent cloud occurrence frequency and ice mass density in both hemispheres, a simple cloud model is applied in which it is assumed that the ice content is solely controlled by the local temperature and water vapor volume mixing ratio. The model results are compared to satellite observations, each having an instrument-specific sensitivity when it comes to detecting noctilucent clouds. It is found that the model is able to capture the onset dates of the NLC seasons in both hemispheres as well as the hemispheric differences in NLCs, such as weaker NLCs in the SH than in the NH and differences in cloud height. We conclude that the observed cloud climatology and zonal mean variability are well captured by the model.

12 1 - 50 of 82
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf