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  • 1.
    Barabash, Victoria
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ejemalm, Johnny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Milz, Mathias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Molin, Sven
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Johansson, Jonny
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Westerberg, Lars-Göran
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Fluid and Experimental Mechanics.
    Masters Programs in Space Science and Engineering in Northern Sweden2017Conference paper (Refereed)
  • 2.
    Earle, M.E.
    et al.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Khalizov, A.F.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Sloan, J.J.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Volume nucleation rates for homogeneous freezing in supercooled water microdroplets: results from a combined experimental and modelling approach2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 16, 7945-7961 p.Article in journal (Refereed)
    Abstract [en]

    Temperature-dependent volume nucleation rate coefficients for supercooled water droplets, JV(T), are derived from infrared extinction measurements in a cryogenic laminar aerosol flow tube using a microphysical model. The model inverts water and ice aerosol size distributions retrieved from experimental extinction spectra by considering the evolution of a measured initial droplet distribution via homogeneous nucleation and the exchange of vapour-phase water along a well-defined temperature profile. Experiment and model results are reported for supercooled water droplets with mean radii of 1.0, 1.7, and 2.9 μ1/4m. Values of mass accommodation coefficients for evaporation of water droplets and vapour deposition on ice particles are also determined from the model simulations. The coefficient for ice deposition was found to be 0.031 ± 0.001, while that for water evaporation was 0.054 ± 0.012. Results are considered in terms of the applicability of classical nucleation theory to the freezing of micrometre-sized droplets in cirrus clouds, with implications for the parameterization of homogeneous ice nucleation in numerical models.

  • 3.
    Earle, M.E.
    et al.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Khalizov, A.F.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Sloan, J.J.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Volume nucleation rates for homogeneous freezing in supercooled water microdroplets: results from a combined experimental and modelling approach2009In: Atmospheric Chemistry and Physics Discussions, ISSN 1680-7367, E-ISSN 1680-7375, Vol. 9, no 5, 22883-22927 p.Article in journal (Refereed)
    Abstract [en]

    Temperature-dependent volume nucleation rate coefficients for supercooled water droplets, JV(T), are derived from infrared extinction measurements in a cryogenic laminar aerosol flow tube using a microphysical model. The model inverts water and ice aerosol size distributions retrieved from experimental extinction spectra by considering the evolution of a measured initial droplet distribution via homogeneous nucleation and the exchange of vapour-phase water along a well-defined temperature profile. Experiment and model results are reported for supercooled water droplets with mode radii of 1.0, 1.7, and 2.9 α1/4m. Values of mass accommodation coefficients for evaporation of water droplets and vapour deposition on ice particles are also determined from the model simulations. The coefficient for ice deposition was found to be approximately 0.031, while that for water evaporation was 0.054. Results are considered in terms of the applicability of classical nucleation theory to the freezing of micrometre-sized droplets in cirrus clouds, with implications for the parameterization of homogeneous ice nucleation in numerical models.

  • 4.
    Ekman, Jonas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Embedded Internet Systems Lab.
    Antti, Marta-Lena
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Martin-Torres, Javier
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Emami, Reza
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Törlind, Peter
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nilsson, Hans
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Minami, Ichiro
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Öhrwall Rönnbäck, Anna
    Gustafsson, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Zorzano Mier, Maria-Paz
    Milz, Mathias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Grahn, Mattias
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Chemical Engineering.
    Parida, Vinit
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Behar, Etienne
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering.
    Wolf, Veronika
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Dordlofva, Christo
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Mendaza de Cal, Maria Teresa
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Jamali, Maryam
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Roos, Tobias
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Ottemark, Rikard
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nieto, Chris
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Soria Salinas, Álvaro Tomás
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Vázquez Martín, Sandra
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Nyberg, Erik
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Machine Elements.
    Neikter, Magnus
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Lindwall, Angelica
    Luleå University of Technology, Department of Business Administration, Technology and Social Sciences, Innovation and Design.
    Fakhardji, Wissam
    Luleå University of Technology, Department of Engineering Sciences and Mathematics, Material Science.
    Projekt: Rymdforskarskolan2015Other (Other (popular science, discussion, etc.))
    Abstract [en]

    The Graduate School of Space Technology

  • 5.
    Eliasson, Salomon
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Holl, Gerrit
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Stengel, M.
    Iturbe-Sanchez, F.
    Johnston, M.
    Systematic and random errors between collocated satellite ice water path observations2013In: Journal of Geophysical Research, ISSN 0148-0227, E-ISSN 2156-2202, Vol. 118, no 6, 2629-2642 p.Article in journal (Refereed)
    Abstract [en]

    There remains large disagreement between IWP in observational datasets, largely because the sensors observe different parts of the ice particle size distribution. A detailed comparison of retrieved IWP from satellite observations in the Tropics ({plus minus}30{degree sign} latitude) in 2007 is made using collocated measurements. The DARDAR IWP dataset, based on combined Radar/Lidar measurements, is used as a reference as it provides arguably the best estimate of the total column IWP. For each dataset, usable IWP dynamic ranges are inferred from this comparison. IWP retrievals based on solar reflectance measurements, MODIS, and AVHRR-based CMSAF, and PATMOS-x, were found to be correlated with DARDAR over a large IWP range (~20-7000 g/m-2;). The random errors of the collocated datasets have a close to log-normal distribution, and the combined random error of MODIS and DARDAR is less than a factor of 2, which also sets the upper limit for MODIS alone. In the same way the upper limit for the random error of all considered datasets is determined. Datasets based on passive microwave measurements,MSPPS, MiRS, and CMO, are largely correlated with DARDAR for IWP values larger than approximately 700 g/m². The combined uncertainty between these datasets and DARDAR in this range is slightly less MODIS-DARDAR, but the systematic bias is nearly an order of magnitude.

  • 6.
    Gultepe, Ismail
    et al.
    Cloud Physics and Severe Weather Research Section, Environment Canada.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Pavolonis, Michael J.
    NOAA, NESDIS, Madison, WI.
    Calvert, C.
    CIMSS, University of Wisconsin-Madison, Madison, WI.
    Gurka, James J.
    NOAA, NESDIS, Greenbelt, MD.
    Heymsfield, Andrew J.
    NCAR, Boulder, Colorado.
    Liu, P.S.K.
    Cloud Physics and Severe Weather Research Section, Environment Canada.
    Zhou, B.
    I.M. Systems Group, NOAA/NWS/NCEP, Camp Springs, MD.
    Ware, Randolph H.
    Radiometrics Corporation, CIRES, University of Colorado, Boulder, CO.
    Ferrier, Brad Schoenberg
    I.M. Systems Group, NOAA/NWS/NCEP, Camp Springs, MD.
    Milbrandt, Jason A.
    RPN, CMC, Environment Canada.
    Bernstein, Ben C.
    Leading Edge Atmospherics, Boulder, CO.
    Ice fog in arctic during fram-ice fog project aviation and nowcasting applications2014In: Bulletin of The American Meteorological Society - (BAMS), ISSN 0003-0007, E-ISSN 1520-0477, Vol. 95, no 2, 211-226 p.Article in journal (Refereed)
    Abstract [en]

    Increased understanding of ice fog microphysics can improve frost and ice fog prediction using forecast models and remote-sensing retrievals, thereby reducing potential hazards to aviation

  • 7.
    Gultepe, Ismail
    et al.
    Cloud Physics and Severe Weather Research Section, Environment Canada.
    Zhou, B.
    I.M. Systems Group, NOAA/NWS/NCEP, Camp Springs, MD.
    Milbrandt, Jason A.
    RPN, CMC, Environment Canada.
    Bott, A.
    Meteorolooieches lnstitut, University of Bonn.
    Li, Y.
    Institute of Atmospheric Physics, Chinese Academy of Sciences, Beijing.
    Heymsfield, Andrew J.
    National Center for Atmospheric Research, Boulder, Colorado.
    Ferrier, Brad Schoenberg
    I.M. Systems Group, NOAA/NWS/NCEP, Camp Springs, MD.
    Ware, Randolph H.
    Radiometrics Corporation, CIRES, University of Colorado, Boulder, CO.
    Pavolonis, Michael J.
    NOAA, NESDIS, Madison, WI.
    Kuhn, Thomas
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Gurka, James J.
    NOAA, NESDIS, Greenbelt, MD.
    Liu, P.
    Cloud Physics and Severe Weather Research Section, Environment Canada.
    Cermak, J.
    Ruhr-Universität Bochum, Department of Geography.
    A review on ice fog measurements and modeling2015In: Atmospheric research, ISSN 0169-8095, E-ISSN 1873-2895, Vol. 151, 2-19 p.Article in journal (Refereed)
    Abstract [en]

    The rate of weather-related aviation accident occurrence in the northern latitudes is likely 25 times higher than the national rate of Canada. If only cases where reduced visibility was a factor are considered, the average rate of occurrence in the north is about 31 times higher than the Canadian national rate. Ice fog occurs about 25% of the time in the northern latitudes and is an important contributor to low visibility. This suggests that a better understanding of ice fog prediction and detection is required over the northern latitudes. The objectives of this review are the following: 1) to summarize the current knowledge of ice fog microphysics, as inferred from observations and numerical weather prediction (NWP) models, and 2) to describe the remaining challenges associated with measuring ice fog properties, remote sensing microphysical retrievals, and simulating/predicting ice fog within numerical models. Overall, future challenges related to ice fog microphysics and visibility are summarized and current knowledge is emphasized.

  • 8.
    Kuhn, Thomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Damoah, R.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Bacak, A.
    School of Earth, Atmospheric and Environmental Sciences, University of Manchester.
    Sloan, J.J.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Characterising aerosol transport into the Canadian high Arctic using aerosol mass spectrometry and Lagrangian modelling2010In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 10, no 21, 10489-10502 p.Article in journal (Refereed)
    Abstract [en]

    We report the analysis of measurements made using an aerosol mass spectrometer (AMS; Aerodyne Research Inc.) that was installed in the Polar Environment Atmospheric Research Laboratory (PEARL) in summer 2006. PEARL is located in the Canadian high Arctic at 610 m above sea level on Ellesmere Island (80° N 86° W). PEARL is unique for its remote location in the Arctic and because most of the time it is situated within the free troposphere. It is, therefore, well suited as a receptor site to study the long-range tropospheric transport of pollutants into the Arctic. Some information about the successful year-round operation of an AMS at a high Arctic site such as PEARL will be reported here, together with design considerations for reliable sampling under harsh low-temperature conditions. Computational fluid dynamics calculations were made to ensure that sample integrity was maintained while sampling air at temperatures that average 40 °C in the winter and can be as low as 55 °C. Selected AMS measurements of aerosol mass concentration, size and chemical composition recorded during the months of August, September and October 2006 will be reported. The air temperature was raised to about 20 deg;C during sampling, but the short residence time in the inlet system (∼25 s) ensured that less than 10% of semivolatiles such as ammonium nitrate were lost. During this period, sulfate was, at most times, the predominant aerosol component with on average 0.115 μg-3 (detection limit 0.003mg-3). The second most abundant component was undifferentiated organic aerosol, with on average 0.11 Î1/4g mg3 (detection limit 0.04 I1/4g mg3). The nitrate component, which averaged 0.007 mg-3, was above its detection limit (0.002 Î1/4g mg3), whereas the ammonium ion had an apparent average concentration of 0.02 g mg-3, which was approximately equal to its detection limit. A few episodes, having increased mass concentrations and lasting from several hours to several days, are apparent in the data. These were investigated further using a statistical analysis to determine their common characteristics. High correlations among some of the components arriving during the short-term episodes provide evidence for common sources. Lagrangian methods were also used to identify the source regions for some of the episodes. In all cases, these coincided with the arrival of air that had contacted the surface at latitudes below about 60° N. Most of these lower-latitude footprints were on land, but sulfate emissions from shipping in the Atlantic were also detected. The Lagrangian results demonstrate that there is direct transport of polluted air into the high Arctic (up to 80° N) from latitudes down to 40° N on a time scale of 2-3 weeks. The polluted air originates in a wide variety of industrial, resource extraction and petroleum-related activity as well as from large population centres

  • 9.
    Kuhn, Thomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Earle, M.E.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Khalizov, A.F.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Sloan, J.J.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Size dependence of volume and surface nucleation rates for homogeneous freezing of supercooled water droplets2011In: Atmospheric Chemistry And Physics, ISSN 1680-7316, E-ISSN 1680-7324, Vol. 11, no 6, 2853-2861 p.Article in journal (Refereed)
    Abstract [en]

    The relative roles of volume and surface nucleation were investigated for the homogeneous freezing of pure water droplets. Experiments were carried out in a cryogenic laminar aerosol flow tube using supercooled water aerosols with maximum volume densities at radii between 1 and 3 Î1/4m. Temperature-and size-dependent values of volume-and surface-based homogeneous nucleation rates between 234.8 and 236.2 K were derived using a microphysical model and aerosol phase compositions and size distributions determined from infrared extinction measurements in the flow tube. The results show that the contribution from nucleation at the droplet surface increases with decreasing droplet radius and dominates over nucleation in the bulk droplet volume for droplets with radii smaller than approximately 5 Î1/4m. This is interpreted in terms of a lowered free energy of ice germ formation in the surface-based process. The implications of surface nucleation for the parameterization of homogeneous ice nucleation in numerical models are considered

  • 10. Kuhn, Thomas
    et al.
    Grishin, Igor
    Department of Earth and Environmental Sciences, University of Waterloo.
    Sloan, James J.
    Department of Earth and Environmental Sciences, University of Waterloo.
    Improved imaging and image analysis system for application to measurement of small ice crystals2012In: Journal of Atmospheric and Oceanic Technology, ISSN 0739-0572, E-ISSN 1520-0426, Vol. 29, no 12, 1811-1824 p.Article in journal (Refereed)
    Abstract [en]

    Accurate knowledge of ice particle size and shape distribution is required for understanding of atmospheric microphysical processes. While larger ice particles are easily measured with a variety of sensors, the measurement of small ice particles with sizes down to a few micrometers remains challenging. Here the authors report the development of a system that measures the size and shape of small ice particles using a novel combination of high-resolution imaging and high-speed automated image classification. The optical system has a pixel resolution of 0.2 μm and a resolving power of approximately 1 μm. This imaging instrument is integrated into a cryogenic flow tube that allows precise control of experimental conditions.This study also describes an automated method for the high-speed analysis of high-resolution particle images. Each particle is located in the image using a Sobel edge detector, the border is vectorized, and a polygon representing the border is found. The vertices of this polygon are expressed in complex coordinates, and an analytic implementation of Fourier shape descriptors is used for piecewise integration along the edges of the polygon.The authors demonstrate the capabilities of this system in a study of the early-stage growth of ice particles, which are grown for approximately 1 min at fixed temperature and saturated water vapor concentrations in the cryogenic flowtube. Ice particle shapes and size distributions are reported and compared with habit diagrams found in the literature. The capability of the shape recognition system is verified by comparison with manual classification.

  • 11.
    Kuhn, Thomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Gultepe, Ismail
    Cloud Physics and Severe Weather Research Section, Environment Canada.
    Ice Fog and Light Snow Measurements Using a High-Resolution Camera System2016In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 173, no 9, 3049-3064 p.Article in journal (Refereed)
    Abstract [en]

    Ice fog, diamond dust, and light snow usually form over extremely cold weather conditions, and they affect both visibility and Earth’s radiative energy budget. Prediction of these hydrometeors using models is difficult because of limited knowledge of the microphysical properties at the small size ranges due to measurement issues. These phenomena need to be better represented in forecast and climate models; therefore, in addition to remote sensing accurate measurements using ground-based instrumentation are required. An imaging instrument, aimed at measuring ice fog and light snow particles, has been built and is presented here. The ice crystal imaging (ICI) probe samples ice particles into a vertical, tapered inlet with an inlet flow rate of 11 L min−1. A laser beam across the vertical air flow containing the ice crystals allows for their detection by a photodetector collecting the scattered light. Detected particles are then imaged with high optical resolution. An illuminating LED flash and image capturing are triggered by the photodetector. In this work, ICI measurements collected during the fog remote sensing and modeling (FRAM) project, which took place during Winter of 2010–2011 in Yellowknife, NWT, Canada, are summarized and challenges related to measuring small ice particles are described. The majority of ice particles during the 2-month-long campaign had sizes between 300 and 800 μm. During ice fog events the size distribution measured had a lower mode diameter of 300 μm compared to the overall campaign average with mode at 500 μm.

  • 12.
    Kuhn, Thomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Heymsfield, Andrew J.
    National Center for Atmospheric Research, Boulder, Colorado.
    In Situ Balloon-Borne Ice Particle Imaging in High-Latitude Cirrus2016In: Pure and Applied Geophysics, ISSN 0033-4553, E-ISSN 1420-9136, Vol. 173, no 9, 3065-3084 p.Article in journal (Refereed)
    Abstract [en]

    Cirrus clouds reflect incoming solar radiation, creating a cooling effect. At the same time, these clouds absorb the infrared radiation from the Earth, creating a greenhouse effect. The net effect, crucial for radiative transfer, depends on the cirrus microphysical properties, such as particle size distributions and particle shapes. Knowledge of these cloud properties is also needed for calibrating and validating passive and active remote sensors. Ice particles of sizes below 100 µm are inherently difficult to measure with aircraft-mounted probes due to issues with resolution, sizing, and size-dependent sampling volume. Furthermore, artefacts are produced by shattering of particles on the leading surfaces of the aircraft probes when particles several hundred microns or larger are present. Here, we report on a series of balloon-borne in situ measurements that were carried out at a high-latitude location, Kiruna in northern Sweden (68N 21E). The method used here avoids these issues experienced with the aircraft probes. Furthermore, with a balloon-borne instrument, data are collected as vertical profiles, more useful for calibrating or evaluating remote sensing measurements than data collected along horizontal traverses. Particles are collected on an oil-coated film at a sampling speed given directly by the ascending rate of the balloon, 4 m s−1. The collecting film is advanced uniformly inside the instrument so that an always unused section of the film is exposed to ice particles, which are measured by imaging shortly after sampling. The high optical resolution of about 4 µm together with a pixel resolution of 1.65 µm allows particle detection at sizes of 10 µm and larger. For particles that are 20 µm (12 pixel) in size or larger, the shape can be recognized. The sampling volume, 130 cm3 s−1, is well defined and independent of particle size. With the encountered number concentrations of between 4 and 400 L−1, this required about 90- to 4-s sampling times to determine particle size distributions of cloud layers. Depending on how ice particles vary through the cloud, several layers per cloud with relatively uniform properties have been analysed. Preliminary results of the balloon campaign, targeting upper tropospheric, cold cirrus clouds, are presented here. Ice particles in these clouds were predominantly very small, with a median size of measured particles of around 50 µm and about 80 % of all particles below 100 µm in size. The properties of the particle size distributions at temperatures between −36 and −67 °C have been studied, as well as particle areas, extinction coefficients, and their shapes (area ratios). Gamma and log-normal distribution functions could be fitted to all measured particle size distributions achieving very good correlation with coefficients R of up to 0.95. Each distribution features one distinct mode. With decreasing temperature, the mode diameter decreases exponentially, whereas the total number concentration increases by two orders of magnitude with decreasing temperature in the same range. The high concentrations at cold temperatures also caused larger extinction coefficients, directly determined from cross-sectional areas of single ice particles, than at warmer temperatures. The mass of particles has been estimated from area and size. Ice water content (IWC) and effective diameters are then determined from the data. IWC did vary only between 1 × 10−3 and 5 × 10−3 g m−3 at temperatures below −40 °C and did not show a clear temperature trend. These measurements are part of an ongoing study.

  • 13.
    Kuhn, Thomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Heymsfield, Andrew J.
    NCAR, Boulder, Colorado.
    Vertical distributions of small cirrus cloud particles from balloon-borne in-situ measurements: Oral presentation2014Conference paper (Other academic)
    Abstract [en]

    Thin and cold ice clouds are important for the radiative budget, yet they are difficult to measure. They are often high in the troposphere where they reflect incoming sunlight, creating a cooling effect. At the same time these clouds absorb longwave radiation from Earth, creating a greenhouse effect. Knowledge of the net effect is crucial and depends on the microphysical properties of the clouds, which at these altitudes and temperatures are often composed of small particles of 100 μm or less in size. Most of in-situ data reported in the literature have been sampled with aircraft probes, which have known issues with such small particles due to sizing and shattering prob- lems, in addition to having also a small and size-dependent sampling volume for these particles.A series of balloon-borne in-situ measurements, currently being carried out from a high-latitude location in north- ern Sweden (Kiruna, 68N 21E), combined with previous balloon-borne measurements from other locations, are used to study properties of small cloud ice particles at a variety of temperatures and altitudes. Among other prop- erties, size distributions and concentrations are analysed as a function of height within the cloud layer. Results are compared to literature data from aircraft probes to shed more light on the uncertainties related to the difficulties of these probes in measuring small particles.

  • 14.
    Kuhn, Thomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Heymsfield, Andrew J.
    National Center for Atmospheric Research, Boulder, Colorado.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Balloon-Borne Measurements of Ice Particle Shape and Ice Water Content in the Upper Troposphere over Northern Sweden2013In: 21st ESA Symposium: ESA Symposium on European Rocket and Balloon Programmes and Related Research 2013, 9–13 June 2013, Noordwijk: European Space Agency, ESA , 2013, 93-97 p.Conference paper (Refereed)
    Abstract [en]

    Ice clouds play an important role in the energy budget of the atmosphere. They are at high altitudes, absorb long-wave radiation from below and, as they are cold, emit little infrared radiation. This greenhouse effect warms the Earth-atmosphere system. On the other hand, ice clouds have a cooling effect by reflecting incoming solar short wave radiation. The net effect is crucial for the atmosphere, but will depend highly on the cloud’s horizontal extent, vertical position, ice water content (IWC), and ice particle microphysical properties such as size and shape. Targeting these upper-tropospheric, cold ice clouds, a series of in-situ balloon-borne experiments has been started at Kiruna, Sweden, which is located at 68°N. Fewer mea- surements exist at these high latitudes compared to mid- or tropical latitudes. Also temperatures in the upper troposphere can be around -60 °C, a temperature range under-represented in available in-situ data. Experiments are launched from Esrange Space Center. Ice particles are collected with a balloon-borne replicator and also imaged in-situ, and measurements are complemented by a radiosonde added to the instrument. Particle shape and size as well as IWC are determined from the replicas and images. The data are analysed to reveal relationships between IWC and other measurements such as temperature and volume extinction coefficient. Such relationships can be used for validation and improvement of satellite retrievals of IWC from, for example, thin cirrus measurements with satellite-borne lidar, such as on the future EarthCARE mission.

  • 15.
    Kuhn, Thomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Heymsfield, Andrew J.
    National Center for Atmospheric Research, Boulder, Colorado.
    Buehler, Stefan
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    In-situ ice particle measurements over northern Sweden2012Conference paper (Other academic)
    Abstract [en]

    ce clouds play an important role in the energy budget of the atmosphere. They are at high altitudes, absorb longwave radiation from below and, as they are cold, emit little infrared radiation. This greenhouse effect warms the Earth-atmosphere system. On the other hand, ice clouds have a cooling effect by reflecting incoming solar short wave radiation. The net effect is crucial for the atmosphere, but will depend highly on the cloud’s horizontal extent, vertical position, ice water content (IWC), and ice particle microphysical properties such as size and shape. A series of in-situ balloon measurements has been started at Kiruna, Sweden, which is located at 68°N. Fewer in- situ ice cloud measurements exist at these high latitudes compared to mid- or tropical latitudes. Also temperatures in the upper troposphere can be around -60 °C, a temperature range under-represented in available in-situ data. Ice particles are collected with a balloon-borne replicator launched from Esrange Space Center (near Kiruna, Sweden). Measurements are complemented by a radiosonde added to the instrument. The shape and size as well as IWC are determined from the replicas. The data are analyzed to reveal relationships between IWC and other measurements such as temperature and volume extinction coefficient. Such relationships can be used for validation and improvement of satellite retrievals of IWC from, for example, thin cirrus measurements with satellite-borne lidar.

  • 16.
    Kuhn, Thomas
    et al.
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Wolf, Veronika
    Luleå University of Technology, Department of Computer Science, Electrical and Space Engineering, Space Technology.
    Völger, Peter
    The Swedish Institute of Space Physics (IRF).
    Stanev, Marin
    Stockholm University, Department of Meteorology (MISU).
    Gumbel, Jörg
    Stockholm University, Department of Meteorology (MISU).
    Comparison of In-Situ Balloon-Borne and Lidar Measurement of Cirrus Clouds2017In: Proceedings of the 23rd ESA Symposium on European Rocket and Balloon Programmes and Related Research, Noordwijk, The Netherlands, 2017, A-091kuhnConference paper (Other academic)
    Abstract [en]

    A series of in-situ balloon-borne experiments con- ducted at Kiruna, Sweden (68°N), is studying upper- tropospheric, cold ice clouds in arctic latitudes. Ex- periments are launched from Esrange Space Center and collect ice particles with an in-situ imaging instrument. One of the aims with these measurements is to improve satellite remote sensing of cold ice clouds. Such clouds can be observed by lidar. Therefore, when possible, concurrent ground-based lidar measurements have been carried out with two available lidar systems to accom- pany the balloon-borne measurements. The Esrange lidar is located at Esrange Space Center, approximately 500 m from the in-situ launch site on the balloon pad; the IRF lidar is located about 29 km to the west of Esrange Space Center (operated by the Swedish Institute of Space Physics, IRF). Here we present results from these lidar measurements and compare them to ice particle proper- ties determined during the in-situ measurements. 

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