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Thomas Kuhn
Luleå University of Technology (LTU). Department of Computer Science, Electrical and Space Engineering. Division of Space Technology, 98 128, Kiruna, Sweden

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Journal article
Published: 18 May 2021 in Atmospheric Chemistry and Physics
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Improved snowfall predictions require accurate knowledge of the properties of ice crystals and snow particles, such as their size, cross-sectional area, shape, and fall speed. The fall speed of ice particles is a critical parameter for the representation of ice clouds and snow in atmospheric numerical models, as it determines the rate of removal of ice from the modelled clouds. Fall speed is also required for snowfall predictions alongside other properties such as ice particle size, cross-sectional area, and shape. For example, shape is important as it strongly influences the scattering properties of these ice particles and thus their response to remote sensing techniques. This work analyzes fall speed as a function of particle size (maximum dimension), cross-sectional area, and shape using ground-based in situ measurements. The measurements for this study were done in Kiruna, Sweden, during the snowfall seasons of 2014 to 2019, using the ground-based in situ instrument Dual Ice Crystal Imager (D-ICI). The resulting data consist of high-resolution images of falling hydrometeors from two viewing geometries that are used to determine particle size (maximum dimension), cross-sectional area, area ratio, orientation, and the fall speed of individual particles. The selected dataset covers sizes from about 0.06 to 3.2 mm and fall speeds from 0.06 to 1.6 m s−1. Relationships between particle size, cross-sectional area, and fall speed are studied for different shapes. The data show in general low correlations to fitted fall speed relationships due to large spread observed in fall speed. After binning the data according to size or cross-sectional area, correlations improve, and we can report reliable parameterizations of fall speed vs. particle size or cross-sectional area for part of the shapes. For most of these shapes, the fall speed is better correlated with cross-sectional area than with particle size. The effects of orientation and area ratio on the fall speed are also studied, and measurements show that vertically oriented particles fall faster on average. However, most particles for which orientation can be defined fall horizontally.

ACS Style

Sandra Vázquez-Martín; Thomas Kuhn; Salomon Eliasson. Shape dependence of snow crystal fall speed. Atmospheric Chemistry and Physics 2021, 21, 7545 -7565.

AMA Style

Sandra Vázquez-Martín, Thomas Kuhn, Salomon Eliasson. Shape dependence of snow crystal fall speed. Atmospheric Chemistry and Physics. 2021; 21 (10):7545-7565.

Chicago/Turabian Style

Sandra Vázquez-Martín; Thomas Kuhn; Salomon Eliasson. 2021. "Shape dependence of snow crystal fall speed." Atmospheric Chemistry and Physics 21, no. 10: 7545-7565.

Preprint content
Published: 16 March 2021
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Meteorological forecast and climate models require good knowledge of the microphysical properties of hydrometeors and the atmospheric snow and ice crystals in clouds. For instance, their size, cross-sectional area, shape, mass, and fall speed. Especially shape is an important parameter in that it strongly affects the scattering properties of ice particles, and consequently their response to remote sensing techniques. The fall speed and mass of ice particles are other important parameters both for numerical forecast models and for the representation of snow and ice clouds in climate models. In the case of fall speed, it is responsible for the rate of removal of ice from these models. The particle mass is a key quantity that connects the cloud microphysical properties to radiative properties. Using an empirical relationship between the dimensionless Reynolds and Best numbers, fall speed and mass can be derived from each other if particle size and cross-sectional area are also known. In this work, ground-based in-situ measurements of snow particle microphysical properties are used to analyse mass as a function of shape and the other properties particle size, cross-sectional area, and fall speed. The measurements for this study were done in Kiruna, Sweden during snowfall seasons of 2014 to 2019 and using the ground-based in-situ instrument Dual Ice Crystal Imager (D-ICI), which takes high-resolution side- and top-view images of natural hydrometeors. From these images, particle size (maximum dimension), cross-sectional area, and fall speed of individual particles are determined. The particles are shape classified according to the scheme presented in our previous work, in which particles sort into 15 different shape groups depending on their shape and morphology. Particle masses of individual ice particles are estimated from measured particle size, cross-sectional area, and fall speed. The selected dataset covers sizes from about 0.1 mm to 3.2 mm, fall speeds from 0.1 m s−1 to 1.6 m s−1, and masses from close to 0.2 μg to 320 μg. In our previous work, the fall speed relationships between particle size and cross-sectional area were studied. In this work, the same dataset is used to determine the particle mass, and consequently, the mass relationships between particle size, cross-sectional area, and fall speed are studied for these 15 shape groups. Furthermore, the mass relationships presented in this study are compared with the previous studies.

ACS Style

Sandra Vázquez-Martín; Thomas Kuhn; Salomon Eliasson. Mass of different snow crystal shapes derived from fall speed measurements. 2021, 2021, 1 -24.

AMA Style

Sandra Vázquez-Martín, Thomas Kuhn, Salomon Eliasson. Mass of different snow crystal shapes derived from fall speed measurements. . 2021; 2021 ():1-24.

Chicago/Turabian Style

Sandra Vázquez-Martín; Thomas Kuhn; Salomon Eliasson. 2021. "Mass of different snow crystal shapes derived from fall speed measurements." 2021, no. : 1-24.

Journal article
Published: 02 November 2020 in Atmospheric Chemistry and Physics
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This study presents airborne in situ and satellite remote sensing climatologies of cirrus clouds and humidity. The climatologies serve as a guide to the properties of cirrus clouds, with the new in situ database providing detailed insights into boreal midlatitudes and the tropics, while the satellite-borne data set offers a global overview. To this end, an extensive, quality-checked data archive, the Cirrus Guide II in situ database, is created from airborne in situ measurements during 150 flights in 24 campaigns. The archive contains meteorological parameters, ice water content (IWC), ice crystal number concentration (Nice), ice crystal mean mass radius (Rice), relative humidity with respect to ice (RHice), and water vapor mixing ratio (H2O) for each of the flights. Depending on the parameter, the database has been extended by about a factor of 5–10 compared to earlier studies. As one result of our investigation, we show that the medians of Nice, Rice, and RHice have distinct patterns in the IWC–T parameter space. Lookup tables of these variables as functions of IWC and T can be used to improve global model cirrus representation and remote sensing retrieval methods. Another outcome of our investigation is that across all latitudes, the thicker liquid-origin cirrus predominate at lower altitudes, while at higher altitudes the thinner in situ-origin cirrus prevail. Further, examination of the radiative characteristics of in situ-origin and liquid-origin cirrus shows that the in situ-origin cirrus only slightly warm the atmosphere, while liquid-origin cirrus have a strong cooling effect. An important step in completing the Cirrus Guide II is the provision of the global cirrus Nice climatology, derived by means of the retrieval algorithm DARDAR-Nice from 10 years of cirrus remote sensing observations from satellite. The in situ measurement database has been used to evaluate and improve the satellite observations. We found that the global median Nice from satellite observations is almost 2 times higher than the in situ median and increases slightly with decreasing temperature. Nice medians of the most frequently occurring cirrus sorted by geographical regions are highest in the tropics, followed by austral and boreal midlatitudes, Antarctica, and the Arctic. Since the satellite climatologies enclose the entire spatial and temporal Nice occurrence, we could deduce that half of the cirrus are located in the lowest, warmest (224–242 K) cirrus layer and contain a significant amount of liquid-origin cirrus. A specific highlight of the study is the in situ observations of cirrus and humidity in the Asian monsoon anticyclone and the comparison to the surrounding tropics. In the convectively very active Asian monsoon, peak values of Nice and IWC of 30 cm−3 and 1000 ppmv are detected around the cold point tropopause (CPT). Above the CPT, ice particles that are convectively injected can locally add a significant amount of water available for exchange with the stratosphere. We found IWCs of up to 8 ppmv in the Asian monsoon in comparison to only 2 ppmv in the surrounding tropics. Also, the highest RHice values (120 %–150 %) inside of clouds and in clear sky are observed around and above the CPT. We attribute this to the high H2O mixing ratios (typically 3–5 ppmv) observed in the Asian monsoon compared to 1.5 to 3 ppmv found in the tropics. Above the CPT, supersaturations of 10 %–20 % are observed in regions of weak convective activity and up to about 50 % in the Asian monsoon. This implies that the water available for transport into the stratosphere might be higher than the expected saturation value.

ACS Style

Martina Krämer; Christian Rolf; Nicole Spelten; Armin Afchine; David Fahey; Eric Jensen; Sergey Khaykin; Thomas Kuhn; Paul Lawson; Alexey Lykov; Laura L. Pan; Martin Riese; Andrew Rollins; Fred Stroh; Troy Thornberry; Veronika Wolf; Sarah Woods; Peter Spichtinger; Johannes Quaas; Odran Sourdeval. A microphysics guide to cirrus – Part 2: Climatologies of clouds and humidity from observations. Atmospheric Chemistry and Physics 2020, 20, 12569 -12608.

AMA Style

Martina Krämer, Christian Rolf, Nicole Spelten, Armin Afchine, David Fahey, Eric Jensen, Sergey Khaykin, Thomas Kuhn, Paul Lawson, Alexey Lykov, Laura L. Pan, Martin Riese, Andrew Rollins, Fred Stroh, Troy Thornberry, Veronika Wolf, Sarah Woods, Peter Spichtinger, Johannes Quaas, Odran Sourdeval. A microphysics guide to cirrus – Part 2: Climatologies of clouds and humidity from observations. Atmospheric Chemistry and Physics. 2020; 20 (21):12569-12608.

Chicago/Turabian Style

Martina Krämer; Christian Rolf; Nicole Spelten; Armin Afchine; David Fahey; Eric Jensen; Sergey Khaykin; Thomas Kuhn; Paul Lawson; Alexey Lykov; Laura L. Pan; Martin Riese; Andrew Rollins; Fred Stroh; Troy Thornberry; Veronika Wolf; Sarah Woods; Peter Spichtinger; Johannes Quaas; Odran Sourdeval. 2020. "A microphysics guide to cirrus – Part 2: Climatologies of clouds and humidity from observations." Atmospheric Chemistry and Physics 20, no. 21: 12569-12608.

Preprint content
Published: 26 October 2020
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Improved snowfall predictions require accurate knowledge of the properties of ice crystals and snow particles, such as their size, cross-sectional area, shape, and fall speed. In particular, the shape is an important parameter as it strongly influences the scattering properties of these ice particles, and thus their response to remote sensing techniques such as radar measurements. The fall speed of ice particles is a critical parameter for the representation of ice clouds and snow in atmospheric numerical models, as it determines the rate of removal of ice from the modelled clouds. They are also required for snowfall predictions alongside other properties such as ice particle size, cross-sectional area, and shape. For example, shape is important as it strongly influences the scattering properties of these ice particles, and thus their response to remote sensing techniques. This work analyses fall speed as a function of shape and other properties using ground-based in-situ measurements. The measurements for this study were done in Kiruna, Sweden during the snowfall seasons of 2014 to 2019, using the ground-based in-situ instrument Dual Ice Crystal Imager (D-ICI). The resulting data consist of high-resolution images of falling hydrometeors from two viewing geometries that are used to determine size (maximum dimension), cross-sectional area, area ratio, orientation, and the fall speed of individual particles. The selected dataset covers sizes from about 0.06 to 3.2 mm and fall speeds from 0.06 to 1.6 m s−1. The particles are shape-classified into 15 different shape groups depending on their shape and morphology. For these 15 shape groups relationships are studied, firstly, between size and cross-sectional area, then between fall speed and size or cross-sectional area. The data show in general low correlations to fitted fall-speed relationships due to large spread observed in fall speed. After binning the data according to size or cross-sectional area, correlations improve and we can report reliable parameterizations of fall speed vs. size or cross-sectional area for part of the shapes. The effects of orientation and area ratio on the fall speed are also studied, and measurements show that vertically orientated particles fall faster on average. However, most particles for which orientation can be defined fall horizontally.

ACS Style

Sandra Vázquez-Martín; Thomas Kuhn; Salomon Eliasson. Shape dependence of snow crystal fall speed. 2020, 2020, 1 -31.

AMA Style

Sandra Vázquez-Martín, Thomas Kuhn, Salomon Eliasson. Shape dependence of snow crystal fall speed. . 2020; 2020 ():1-31.

Chicago/Turabian Style

Sandra Vázquez-Martín; Thomas Kuhn; Salomon Eliasson. 2020. "Shape dependence of snow crystal fall speed." 2020, no. : 1-31.

Journal article
Published: 04 May 2020 in Applied Sciences
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This paper studies the specifications of balloons for the exploration of bodies with different atmospheric conditions. Three types of balloons, i.e., zero-pressure, super-pressure, and over-pressurized, with four different shapes, i.e., sphere, oblate, prolate, and airship, were analysed. First, the development of a simulation tool is described, which was used for analysing the behaviour of balloons for different exploration missions. Next, the developed software was verified by comparing its output with recorded data from a set of flights at the Esrange Space Center. Based on the simulation results, recommendations are given for different balloon types and shapes for operation on Mars, Venus, and Titan.

ACS Style

Kanika Garg; Thomas Kuhn. Balloon Design for Mars, Venus, and Titan Atmospheres. Applied Sciences 2020, 10, 3204 .

AMA Style

Kanika Garg, Thomas Kuhn. Balloon Design for Mars, Venus, and Titan Atmospheres. Applied Sciences. 2020; 10 (9):3204.

Chicago/Turabian Style

Kanika Garg; Thomas Kuhn. 2020. "Balloon Design for Mars, Venus, and Titan Atmospheres." Applied Sciences 10, no. 9: 3204.

Journal article
Published: 16 March 2020 in Atmospheric Measurement Techniques
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Accurate predictions of snowfall require good knowledge of the microphysical properties of the snow ice crystals and particles. Shape is an important parameter as it strongly influences the scattering properties of the ice particles, and thus their response to remote sensing techniques such as radar measurements. The fall speed of ice particles is another important parameter for both numerical forecast models as well as representation of ice clouds and snow in climate models, as it is responsible for the rate of removal of ice from these models. We describe a new ground-based in situ instrument, the Dual Ice Crystal Imager (D-ICI), to determine snow ice crystal properties and fall speed simultaneously. The instrument takes two high-resolution pictures of the same falling ice particle from two different viewing directions. Both cameras use a microscope-like setup resulting in an image pixel resolution of approximately 4 µm pixel−1. One viewing direction is horizontal and is used to determine fall speed by means of a double exposure. For this purpose, two bright flashes of a light-emitting diode behind the camera illuminate the falling ice particle and create this double exposure, and the vertical displacement of the particle provides its fall speed. The other viewing direction is close-to-vertical and is used to provide size and shape information from single-exposure images. This viewing geometry is chosen instead of a horizontal one because shape and size of ice particles as viewed in the vertical direction are more relevant than these properties viewed horizontally, as the vertical fall speed is more strongly influenced by the vertically viewed properties. In addition, a comparison with remote sensing instruments that mostly have a vertical or close-to-vertical viewing geometry is favoured when the particle properties are measured in the same direction. The instrument has been tested in Kiruna, northern Sweden (67.8∘ N, 20.4∘ E). Measurements are demonstrated with images from different snow events, and the determined snow ice crystal properties are presented.

ACS Style

Thomas Kuhn; Sandra Vázquez-Martín. Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI). Atmospheric Measurement Techniques 2020, 13, 1273 -1285.

AMA Style

Thomas Kuhn, Sandra Vázquez-Martín. Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI). Atmospheric Measurement Techniques. 2020; 13 (3):1273-1285.

Chicago/Turabian Style

Thomas Kuhn; Sandra Vázquez-Martín. 2020. "Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI)." Atmospheric Measurement Techniques 13, no. 3: 1273-1285.

Preprint content
Published: 09 March 2020
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Particle size distributions (PSDs) for cirrus clouds are important for both climate models as well as many remote sensing retrieval methods. Therefore, PSD parametrizations are required. This study presents parametrizations of Arctic cirrus PSDs. The dataset used for this purpose originates from balloon-borne measurements carried out during winter above Kiruna (Sweden), i.e. north of the Arctic circle. The observations are sorted into two types of cirrus cloud origin, either in-situ or liquid. The cloud origin describes the formation pathway of the ice particles. At temperatures below −38 °C, ice particles form in-situ from solution or ice nucleating-aerosol particles. Liquid origin ice particles have formed at temperatures warmer than or equal to −38 °C, either via ice-nucleating particles embedded in liquid drops or via homogeneous drop freezing, and are then further uplifted to the cirrus temperature regime.

In order to derive parametrizations for each cloud origin, the observed PSDs are represented by gamma functions. The gamma coefficients exhibit large differences with regard to cloud origin. Functions describing the relationships in between the gamma coefficients and with temperature are fitted. These functions for Arctic cirrus confirm established parametrizations for continental cirrus sorted by two particle size modes but differ from others depending only on temperature. We suppose that the agreement between the parametrizations of the geographically different cirrus is because in-situ and liquid origin cirrus also distinguish by particle size modes. Since cloud sorting by their origin is based on physical processes that are independent of geographical region, we further hypothesize that these cloud-type-based parametrizations might be generally valid for use in global models and satellite retrievals, given the distribution of the cloud types is known.

ACS Style

Thomas Kuhn; Veronika Wolf; Martina Krämer. On the Dependence of Cirrus Parametrizations on the Cloud Origin. 2020, 1 .

AMA Style

Thomas Kuhn, Veronika Wolf, Martina Krämer. On the Dependence of Cirrus Parametrizations on the Cloud Origin. . 2020; ():1.

Chicago/Turabian Style

Thomas Kuhn; Veronika Wolf; Martina Krämer. 2020. "On the Dependence of Cirrus Parametrizations on the Cloud Origin." , no. : 1.

Journal article
Published: 09 February 2020 in Applied Sciences
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We present ground-based in situ snow measurements in Kiruna, Sweden, using the ground-based in situ instrument Dual Ice Crystal Imager (D-ICI). D-ICI records dual high-resolution images from above and from the side of falling natural snow crystals and other hydrometeors with particle sizes ranging from 50 μ m to 4 mm. The images are from multiple snowfall seasons during the winters of 2014/2015 to 2018/2019, which span from the beginning of November to the middle of May. From our images, the microphysical properties of individual particles, such as particle size, cross-sectional area, area ratio, aspect ratio, and shape, can be determined. We present an updated classification scheme, which comprises a total of 135 unique shapes, including 34 new snow crystal shapes. This is useful for other studies that are using previous shape classification schemes, in particular the widely used Magono–Lee classification. To facilitate the study of the shape dependence of the microphysical properties, we further sort these individual particle shapes into 15 different shape groups. Relationships between the microphysical properties are determined for each of these shape groups.

ACS Style

Sandra Vázquez-Martín; Thomas Kuhn; Salomon Eliasson. Shape Dependence of Falling Snow Crystals’ Microphysical Properties Using an Updated Shape Classification. Applied Sciences 2020, 10, 1163 .

AMA Style

Sandra Vázquez-Martín, Thomas Kuhn, Salomon Eliasson. Shape Dependence of Falling Snow Crystals’ Microphysical Properties Using an Updated Shape Classification. Applied Sciences. 2020; 10 (3):1163.

Chicago/Turabian Style

Sandra Vázquez-Martín; Thomas Kuhn; Salomon Eliasson. 2020. "Shape Dependence of Falling Snow Crystals’ Microphysical Properties Using an Updated Shape Classification." Applied Sciences 10, no. 3: 1163.

Preprint content
Published: 04 February 2020
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ACS Style

Thomas Kuhn. Response to Referee Comment, RC1. 2020, 1 .

AMA Style

Thomas Kuhn. Response to Referee Comment, RC1. . 2020; ():1.

Chicago/Turabian Style

Thomas Kuhn. 2020. "Response to Referee Comment, RC1." , no. : 1.

Preprint content
Published: 27 January 2020
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This study presents airborne in-situ and satellite remote sensing climatologies of cirrus clouds and humidity. The climatologies serve as a guide to the properties of cirrus clouds, with the new in-situ data base providing detailed insights into boreal mid-latitudes and the tropics, while the satellite-borne data set offers a global overview. To this end, an extensive, quality checked data archive, the Cirrus Guide II in-situ data base, is created from airborne in-situ measurements during 150 flights in 24 campaigns. The archive contains meteorological parameters, IWC, Nice, Rice, RHice and H2O for each of the flights (IWC: ice water content, Nice: number concentration of ice crystals, Rice: ice crystal mean mass radius, RHice: relative humidity with respect to ice, H2O: water vapor mixing ratio). Depending on the specific parameter, the data base has extended by about a factor of 5–10 compared to the previous studies of Schiller et al. (2008), JGR, and Krämer et al. (2009), ACP. One result of our investigations is, that across all latitudes, the thicker liquid origin cirrus predominate at lower altitudes, while at higher altitudes the thinner in-situ cirrus prevail. Further, exemplary investigations of the radiative characteristics of in-situ and liquid origin cirrus show that the in-situ origin cirrus only slightly warm the atmosphere, while liquid origin cirrus have a strong cooling effect. An important step in completing the Cirrus Guide II is the provision of the global cirrus Nice climatology, derived by means of the retrieval algorithm DARDAR-Nice from ten years of cirrus remote sensing observations from satellite. The in-situ data base has been used to evaluate and adjust the satellite observations. We found that the global median Nice from satellite observations is almost two times higher than the in-situ median and increases slightly with decreasing temperature. Nice medians of the most frequentl occuring cirrus sorted by geographical regions are highest in the tropics, followed by austral/boreal mid-latitudes, Antarctica and the Arctic. Since the satellite climatologies enclose the entire spatial and temporal Nice occurrence, we could deduce that half of the cirrus are located in the lowest, warmest cirrus layer and contain a significant amount of liquid origin cirrus. A specific highlight of the study is the in-situ observations of tropical tropopause layer (TTL) cirrus and humidity in the Asian monsoon anticyclone and the comparison to the surrounding tropics. In the convectively very active Asian monsoon, peak values of Nice and IWC of 30 ppmv and 1000 ppmv are detected around the cold point tropopause (CPT). Above the CPT, ice particles that are convectively injected can locally add a significant amount of water available for exchange with the stratosphere. We found IWCs of up to 8 ppmv in the Asian monsoon in comparison to only 2 ppmv in the surrounding tropics. Also, the highest RHice inside of the clouds as well as in clear sky (120–150 %) are observed around and above the CPT. We attribute this to the high amount of H2O (3–5 ppmv) in comparison to 1.5–3 ppmv in other tropical regions. The supersaturations above the CPT suggest that the water exchange with the stratosphere is 10–20 % higher than expected in regions of weak convective activity and up to about 50 % in the Asian monsoon.

ACS Style

Martina Krämer; Christian Rolf; Nicole Spelten; Armin Afchine; David Fahey; Eric Jensen; Sergey Khaykin; Thomas Kuhn; Paul Lawson; Alexey Lykov; Laura L. Pan; Martin Riese; Andrew Rollins; Fred Stroh; Troy Thornberry; Veronika Wolf; Sarah Woods; Peter Spichtinger; Johannes Quaas; Odran Sourdeval. A Microphysics Guide to Cirrus – Part II: Climatologies of Clouds and Humidity from Observations. 2020, 2020, 1 -63.

AMA Style

Martina Krämer, Christian Rolf, Nicole Spelten, Armin Afchine, David Fahey, Eric Jensen, Sergey Khaykin, Thomas Kuhn, Paul Lawson, Alexey Lykov, Laura L. Pan, Martin Riese, Andrew Rollins, Fred Stroh, Troy Thornberry, Veronika Wolf, Sarah Woods, Peter Spichtinger, Johannes Quaas, Odran Sourdeval. A Microphysics Guide to Cirrus – Part II: Climatologies of Clouds and Humidity from Observations. . 2020; 2020 ():1-63.

Chicago/Turabian Style

Martina Krämer; Christian Rolf; Nicole Spelten; Armin Afchine; David Fahey; Eric Jensen; Sergey Khaykin; Thomas Kuhn; Paul Lawson; Alexey Lykov; Laura L. Pan; Martin Riese; Andrew Rollins; Fred Stroh; Troy Thornberry; Veronika Wolf; Sarah Woods; Peter Spichtinger; Johannes Quaas; Odran Sourdeval. 2020. "A Microphysics Guide to Cirrus – Part II: Climatologies of Clouds and Humidity from Observations." 2020, no. : 1-63.

Preprint content
Published: 27 January 2020
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ACS Style

Martina Krämer; Christian Rolf; Nicole Spelten; Armin Afchine; David Fahey; Eric Jensen; Sergey Khaykin; Thomas Kuhn; Paul Lawson; Alexey Lykov; Laura L. Pan; Martin Riese; Andrew Rollins; Fred Stroh; Troy Thornberry; Veronika Wolf; Sarah Woods; Peter Spichtinger; Johannes Quaas; Odran Sourdeval. Supplementary material to "A Microphysics Guide to Cirrus – Part II: Climatologies of Clouds and Humidity from Observations". 2020, 1 .

AMA Style

Martina Krämer, Christian Rolf, Nicole Spelten, Armin Afchine, David Fahey, Eric Jensen, Sergey Khaykin, Thomas Kuhn, Paul Lawson, Alexey Lykov, Laura L. Pan, Martin Riese, Andrew Rollins, Fred Stroh, Troy Thornberry, Veronika Wolf, Sarah Woods, Peter Spichtinger, Johannes Quaas, Odran Sourdeval. Supplementary material to "A Microphysics Guide to Cirrus – Part II: Climatologies of Clouds and Humidity from Observations". . 2020; ():1.

Chicago/Turabian Style

Martina Krämer; Christian Rolf; Nicole Spelten; Armin Afchine; David Fahey; Eric Jensen; Sergey Khaykin; Thomas Kuhn; Paul Lawson; Alexey Lykov; Laura L. Pan; Martin Riese; Andrew Rollins; Fred Stroh; Troy Thornberry; Veronika Wolf; Sarah Woods; Peter Spichtinger; Johannes Quaas; Odran Sourdeval. 2020. "Supplementary material to "A Microphysics Guide to Cirrus – Part II: Climatologies of Clouds and Humidity from Observations"." , no. : 1.

Research letter
Published: 09 November 2019 in Geophysical Research Letters
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Parametrizations of Arctic cirrus particle size distributions (PSD) are presented depending on the cloud origin, either in situ or liquid. The data set used originate from balloon‐borne measurements above Kiruna during winter. The observed PSDs are represented by gamma functions. The gamma coefficients exhibit large differences with regard to cloud origin. The functions for Arctic cirrus confirm established parametrizations for continental cirrus sorted by two particle size modes, but differ from others depending only on temperature. We suppose that the agreement between the parametrizations of the geographically different cirrus is because in situ and liquid origin cirrus also distinguish by particle size modes. Since cloud sorting by their origin is based on physical processes which are independent of geographical region, we further hypothesise that these cloud‐type‐based parametrizations might be generally valid for use in global models and satellite retrievals, given the distribution of the cloud types is known.

ACS Style

Veronika Wolf; Thomas Kuhn; Martina Krämer. On the Dependence of Cirrus Parametrizations on the Cloud Origin. Geophysical Research Letters 2019, 46, 12565 -12571.

AMA Style

Veronika Wolf, Thomas Kuhn, Martina Krämer. On the Dependence of Cirrus Parametrizations on the Cloud Origin. Geophysical Research Letters. 2019; 46 (21):12565-12571.

Chicago/Turabian Style

Veronika Wolf; Thomas Kuhn; Martina Krämer. 2019. "On the Dependence of Cirrus Parametrizations on the Cloud Origin." Geophysical Research Letters 46, no. 21: 12565-12571.

Preprint content
Published: 04 November 2019
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Accurate predictions of snowfall require good knowledge of the microphysical properties of the snow ice crystals and particles. Shape is an important parameter as it influences strongly the scattering properties of the ice particles, and thus their response to remote sensing techniques such as radar measurements. The fall speed of ice particles is another important parameter for both numerical forecast models as well as representation of ice clouds and snow in climate models, as it is responsible for the rate of removal of ice from these models. We describe a new ground-based in-situ instrument, the Dual Ice Crystal Imager (D-ICI), to determine snow ice crystal properties and fall speed simultaneously. The instrument takes two high-resolution pictures of the same falling ice particle from two different viewing directions. Both cameras use a microscope-like set-up resulting in an image pixel resolution of approximately 4 μm/pixel. One viewing direction is horizontal and is used to determine fall speed by means of a double exposure. For this purpose, two bright flashes of a light emitting diode behind the camera illuminate the falling ice particle and create this double exposure and the vertical displacement of the particle provides its fall speed. The other viewing direction is close to vertical and is used to provide size and shape information from single-exposure images. This viewing geometry is chosen instead of a horizontal one because shape and size of ice particles as viewed in the vertical direction are more relevant than these properties viewed horizontally as the vertical fall speed is more strongly influenced by the vertically viewed properties. In addition, a comparison with remote sensing instruments that mostly have a vertical or close to vertical viewing geometry is favoured when the particle properties are measured in the same direction. The instrument has been tested in Kiruna, northern Sweden (67.8° N, 20.4° E). Measurements are demonstrated with images from different snow events, and the determined snow ice crystal properties are presented.

ACS Style

Thomas Kuhn; Sandra Vázquez-Martín. Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI). 2019, 1 .

AMA Style

Thomas Kuhn, Sandra Vázquez-Martín. Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI). . 2019; ():1.

Chicago/Turabian Style

Thomas Kuhn; Sandra Vázquez-Martín. 2019. "Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI)." , no. : 1.

Research article
Published: 07 December 2018 in Atmospheric Chemistry and Physics
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Ice particle and cloud properties such as particle size, particle shape and number concentration influence the net radiation effect of cirrus clouds. Measurements of these features are of great interest for the improvement of weather and climate models, especially for the Arctic region. In this study, balloon-borne in situ measurements of Arctic cirrus clouds have been analysed for the first time with respect to their origin. Eight cirrus cloud measurements have been carried out in Kiruna (68∘ N), Sweden, using the Balloon-borne Ice Cloud particle Imager (B-ICI). Ice particle diameters between 10 and 1200 µm have been found and the shape could be recognized from 20 µm upwards. Great variability in particle size and shape is observed. This cannot simply be explained by local environmental conditions. However, if sorted by cirrus origin, wind and weather conditions, the observed differences can be assessed. Number concentrations between 3 and 400 L−1 have been measured, but the number concentration has reached values above 100 L−1 only for two cases. These two cirrus clouds are of in situ origin and have been associated with waves. For all other measurements, the maximum ice particle concentration is below 50 L−1 and for one in situ origin cirrus case only 3 L−1. In the case of in situ origin clouds, the particles are all smaller than 350 µm diameter. The PSDs for liquid origin clouds are much broader with particle sizes between 10 and 1200 µm. Furthermore, it is striking that in the case of in situ origin clouds almost all particles are compact (61 %) or irregular (25 %) when examining the particle shape. In liquid origin clouds, on the other hand, most particles are irregular (48 %), rosettes (25 %) or columnar (14 %). There are hardly any plates in cirrus regardless of their origin. It is also noticeable that in the case of liquid origin clouds the rosettes and columnar particles are almost all hollow.

ACS Style

Veronika Wolf; Thomas Kuhn; Mathias Milz; Peter Voelger; Martina Krämer; Christian Rolf. Arctic ice clouds over northern Sweden: microphysical properties studied with the Balloon-borne Ice Cloud particle Imager B-ICI. Atmospheric Chemistry and Physics 2018, 18, 17371 -17386.

AMA Style

Veronika Wolf, Thomas Kuhn, Mathias Milz, Peter Voelger, Martina Krämer, Christian Rolf. Arctic ice clouds over northern Sweden: microphysical properties studied with the Balloon-borne Ice Cloud particle Imager B-ICI. Atmospheric Chemistry and Physics. 2018; 18 (23):17371-17386.

Chicago/Turabian Style

Veronika Wolf; Thomas Kuhn; Mathias Milz; Peter Voelger; Martina Krämer; Christian Rolf. 2018. "Arctic ice clouds over northern Sweden: microphysical properties studied with the Balloon-borne Ice Cloud particle Imager B-ICI." Atmospheric Chemistry and Physics 18, no. 23: 17371-17386.

Preprint content
Published: 23 August 2018
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Thomas Kuhn. Author comment in response to Referee comment RC1. 2018, 1 .

AMA Style

Thomas Kuhn. Author comment in response to Referee comment RC1. . 2018; ():1.

Chicago/Turabian Style

Thomas Kuhn. 2018. "Author comment in response to Referee comment RC1." , no. : 1.

Preprint content
Published: 02 May 2018
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Ice particle and cloud properties such as particle size, particle shape and number concentration influence the net radiation effect of cirrus clouds. Measurements of these features are of great interest for the improvement of weather and climate models, especially for the Arctic region. In this study, balloon-borne in-situ measurements of Arctic cirrus clouds have been analysed for the first time with respect to their origin. Eight cirrus cloud measurements were carried out in Kiruna (68° N), Sweden. Ice particle diameters between 10 μm and 1200 μm were found and the shape could be recognised from 20 μm upwards. Great variability in particle size and shape was observed. This cannot simply be explained by local environmental conditions. However, if sorted by cirrus origin, wind, and weather conditions, the observed differences can be assessed. Number concentrations between 3/L and 400/L were measured, but only for two cases the number concentration reached values above 100/L. These two cirrus clouds were of in-situ origin and were caused by gravity and mountain lee-waves. For all other measurements, the maximum ice particle concentration was below 50/L and for one in-situ origin cirrus case only 3/L. In the case of in-situ origin clouds, the particles were all smaller than 350 μm diameter. The number size distribution for liquid origin clouds was much broader with particle sizes between 10 μm and 1200 μm. Furthermore, it is striking that in the case of in-situ origin clouds almost all particles were compact (61 %) or irregular (25 %) when examining the particle shape. In liquid origin clouds, on the other hand, most particles were irregular (48 %), rosettes (25 %) or columnar (14 %). There were hardly any plates in cirrus regardless of their origin. It is also noticeable that in the case of liquid origin clouds the rosettes and columnar particles were almost all hollow.

ACS Style

Veronika Wolf; Thomas Kuhn; Mathias Milz; Peter Voelger; Martina Krämer; Christian Rolf. Ice particle properties of Arctic cirrus. 2018, 2018, 1 -18.

AMA Style

Veronika Wolf, Thomas Kuhn, Mathias Milz, Peter Voelger, Martina Krämer, Christian Rolf. Ice particle properties of Arctic cirrus. . 2018; 2018 ():1-18.

Chicago/Turabian Style

Veronika Wolf; Thomas Kuhn; Mathias Milz; Peter Voelger; Martina Krämer; Christian Rolf. 2018. "Ice particle properties of Arctic cirrus." 2018, no. : 1-18.

Journal article
Published: 11 July 2016 in Pure and Applied Geophysics
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Thomas Kuhn; Ismail Gultepe. Ice Fog and Light Snow Measurements Using a High-Resolution Camera System. Pure and Applied Geophysics 2016, 173, 3049 -3064.

AMA Style

Thomas Kuhn, Ismail Gultepe. Ice Fog and Light Snow Measurements Using a High-Resolution Camera System. Pure and Applied Geophysics. 2016; 173 (9):3049-3064.

Chicago/Turabian Style

Thomas Kuhn; Ismail Gultepe. 2016. "Ice Fog and Light Snow Measurements Using a High-Resolution Camera System." Pure and Applied Geophysics 173, no. 9: 3049-3064.

Journal article
Published: 17 June 2016 in Pure and Applied Geophysics
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Thomas Kuhn; Andrew J. Heymsfield. In Situ Balloon-Borne Ice Particle Imaging in High-Latitude Cirrus. Pure and Applied Geophysics 2016, 173, 3065 -3084.

AMA Style

Thomas Kuhn, Andrew J. Heymsfield. In Situ Balloon-Borne Ice Particle Imaging in High-Latitude Cirrus. Pure and Applied Geophysics. 2016; 173 (9):3065-3084.

Chicago/Turabian Style

Thomas Kuhn; Andrew J. Heymsfield. 2016. "In Situ Balloon-Borne Ice Particle Imaging in High-Latitude Cirrus." Pure and Applied Geophysics 173, no. 9: 3065-3084.

Review
Published: 13 May 2014 in Atmospheric Research
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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.

ACS Style

I. Gultepe; B. Zhou; J. Milbrandt; A. Bott; Ying Li; A.J. Heymsfield; B. Ferrier; R. Ware; M. Pavolonis; Thomas Kuhn; J. Gurka; P. Liu; J. Cermak. A review on ice fog measurements and modeling. Atmospheric Research 2014, 151, 2 -19.

AMA Style

I. Gultepe, B. Zhou, J. Milbrandt, A. Bott, Ying Li, A.J. Heymsfield, B. Ferrier, R. Ware, M. Pavolonis, Thomas Kuhn, J. Gurka, P. Liu, J. Cermak. A review on ice fog measurements and modeling. Atmospheric Research. 2014; 151 ():2-19.

Chicago/Turabian Style

I. Gultepe; B. Zhou; J. Milbrandt; A. Bott; Ying Li; A.J. Heymsfield; B. Ferrier; R. Ware; M. Pavolonis; Thomas Kuhn; J. Gurka; P. Liu; J. Cermak. 2014. "A review on ice fog measurements and modeling." Atmospheric Research 151, no. : 2-19.

Journal article
Published: 01 February 2014 in Bulletin of the American Meteorological Society
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Ice fog and frost occur commonly (at least 26% of the time) in the northern latitudes and Arctic regions during winter at temperatures usually less than about –15°C. Ice fog is strongly related to frost formation—a major aviation hazard in the northern latitudes. In fact, it may be considered a more dangerous event than snow because of the stronger aircraft surface adhesion compared to snow particles. In the winter of 2010/11, the Fog Remote Sensing and Modeling–Ice Fog (FRAM-IF) project was organized near Yellowknife International Airport, Northwest Territories, Canada, with the main goals of advancing understanding of ice fog microphysical and visibility characteristics, and improving its prediction using forecast models and remotesensing retrievals. Approximately 40 different sensors were used to measure visibility, precipitation, ice particle spectra, vertical thermodynamic profiles, and ceiling height. Fog coverage and visibility parameters were estimated using both Geostationary Operational Environmental Satellites (GOES) and Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. During this project, the inversion layer usually was below a height of 1.5 km. High humidity typically was close to the ground, frequently producing ice fog, frost, and light snow precipitation. At low temperatures, snow crystals can be swept away by a very low wind speed (∼1 m s−1). Ice fog during the project was not predicted by any forecast model. These preliminary results in the northern latitudes suggest that ice fog and frost studies, over the Arctic regions, can help us to better understand ice microphysical processes such as ice nucleation, visibility, and parameterizations of ice fog.

ACS Style

I. Gültepe; T. Kuhn; Mike Pavolonis; C. Calvert; J. Gurka; A. J. Heymsfield; P. S. K. Liu; B. Zhou; R. Ware; B. Ferrier; J. Milbrandt; B. Bernstein. Ice Fog in Arctic During FRAM–Ice Fog Project: Aviation and Nowcasting Applications. Bulletin of the American Meteorological Society 2014, 95, 211 -226.

AMA Style

I. Gültepe, T. Kuhn, Mike Pavolonis, C. Calvert, J. Gurka, A. J. Heymsfield, P. S. K. Liu, B. Zhou, R. Ware, B. Ferrier, J. Milbrandt, B. Bernstein. Ice Fog in Arctic During FRAM–Ice Fog Project: Aviation and Nowcasting Applications. Bulletin of the American Meteorological Society. 2014; 95 (2):211-226.

Chicago/Turabian Style

I. Gültepe; T. Kuhn; Mike Pavolonis; C. Calvert; J. Gurka; A. J. Heymsfield; P. S. K. Liu; B. Zhou; R. Ware; B. Ferrier; J. Milbrandt; B. Bernstein. 2014. "Ice Fog in Arctic During FRAM–Ice Fog Project: Aviation and Nowcasting Applications." Bulletin of the American Meteorological Society 95, no. 2: 211-226.