Spectral dependence of backscattering coefficient of mixed phase clouds over West Africa measured with two-wavelength Raman polarization lidar: Features attributed to ice-crystals corner reflection

2017 ◽  
Vol 202 ◽  
pp. 74-80 ◽  
Author(s):  
I. Veselovskii ◽  
P. Goloub ◽  
T. Podvin ◽  
D. Tanre ◽  
A. Ansmann ◽  
...  
Keyword(s):  
West Africa ◽  
Spectral Dependence ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Backscattering Coefficient ◽  
Mixed Phase Clouds

scholarly journals Study of mixed phase clouds over west Africa: Ice-crystal corner reflection effects observed with a two-wavelength polarization lidar

2018 ◽  
Vol 176 ◽  
pp. 05004
Author(s):  
Igor Veselovskii ◽  
Philippe Goloub ◽  
Thierry Podvin ◽  
Didier Tanre ◽  
Albert Ansmann ◽  
...  
Keyword(s):  
West Africa ◽  
Zenith Angle ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Raman Lidar ◽  
Lidar Sounding ◽  
Ångström Exponent ◽  
Mixed Phase Clouds ◽  
532 Nm

Lidar sounding is used for the analysis of possible contribution of the corner reflection (CR) effect to the total backscattering in case of ice crystals. Our study is based on observations of mixed phase clouds performed during the SHADOW campaign in Senegal. Mie-Raman lidar allows measurements at 355 nm and 532 nm at 43 dg. off-zenith angle, so the extinction and backscattering Ångström exponents can be evaluated. In some measurements we observed the positive values of backscattering Ångström exponent, which can be attributed to the corner reflection by horizontally oriented ice plates.

scholarly journals Some effects of ice crystals on the FSSP measurements in mixed phase clouds

2012 ◽  
Vol 12 (19) ◽  
pp. 8963-8977 ◽  
Author(s):  
G. Febvre ◽  
J.-F. Gayet ◽  
V. Shcherbakov ◽  
C. Gourbeyre ◽  
O. Jourdan
Keyword(s):  
Particle Size ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Crystal Surfaces ◽  
Hexagonal Ice ◽  
Ice Particles ◽  
Second Mode ◽  
Ice Production ◽  
Bulk Parameters ◽  
Mixed Phase Clouds

Abstract. In this paper, we show that in mixed phase clouds, the presence of ice crystals may induce wrong FSSP 100 measurements interpretation especially in terms of particle size and subsequent bulk parameters. The presence of ice crystals is generally revealed by a bimodal feature of the particle size distribution (PSD). The combined measurements of the FSSP-100 and the Polar Nephelometer give a coherent description of the effect of the ice crystals on the FSSP-100 response. The FSSP-100 particle size distributions are characterized by a bimodal shape with a second mode peaked between 25 and 35 μm related to ice crystals. This feature is observed with the FSSP-100 at airspeed up to 200 m s−1 and with the FSSP-300 series. In order to assess the size calibration for clouds of ice crystals the response of the FSSP-100 probe has been numerically simulated using a light scattering model of randomly oriented hexagonal ice particles and assuming both smooth and rough crystal surfaces. The results suggest that the second mode, measured between 25 μm and 35 μm, does not necessarily represent true size responses but corresponds to bigger aspherical ice particles. According to simulation results, the sizing understatement would be neglected in the rough case but would be significant with the smooth case. Qualitatively, the Polar Nephelometer phase function suggests that the rough case is the more suitable to describe real crystals. Quantitatively, however, it is difficult to conclude. A review is made to explore different hypotheses explaining the occurrence of the second mode. However, previous cloud in situ measurements suggest that the FSSP-100 secondary mode, peaked in the range 25–35 μm, is likely to be due to the shattering of large ice crystals on the probe inlet. This finding is supported by the rather good relationship between the concentration of particles larger than 20 μm (hypothesized to be ice shattered-fragments measured by the FSSP) and the concentration of (natural) ice particles (CPI data). In mixed cloud, a simple estimation of the number of ice crystals impacting the FSSP inlet shows that the ice crystal shattering effect is the main factor in observed ice production.

scholarly journals Effects of Entrainment and Mixing on the Wegener–Bergeron–Findeisen Process

2020 ◽  
Vol 77 (6) ◽  
pp. 2279-2296
Author(s):  
Fabian Hoffmann
Keyword(s):  
Molecular Diffusion ◽  
Scale Effects ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Small Scale ◽  
Liquid Droplets ◽  
Ice Crystal ◽  
Slowing Down ◽  
Linear Eddy Model ◽  
Mixed Phase Clouds

Abstract The growth of ice crystals at the expense of water droplets, the Wegener–Bergeron–Findeisen (WBF) process, is of major importance for the production of precipitation in mixed-phase clouds. The effects of entrainment and mixing on WBF, however, are not well understood, and small-scale inhomogeneities in the thermodynamic and hydrometeor fields are typically neglected in current models. By applying the linear eddy model, a millimeter-resolution representation of turbulent deformation and molecular diffusion, we investigate these small-scale effects on WBF. While we show that entrainment is accelerating WBF by contributing to the evaporation of liquid droplets, entrainment may also cause aforementioned inhomogeneities, particularly regions filled with exclusively ice or liquid hydrometeors, which tend to decelerate WBF if the ice crystal concentration exceeds 100 L−1. At lower ice crystal concentrations, even weak turbulence can homogenize hydrometeor and thermodynamic fields sufficiently fast so as to not affect WBF. Independent of the ice crystal concentration, it is shown that a fully resolved entrainment and mixing process may delay the nucleation of entrained aerosols to ice crystals, thereby delaying the uptake of water vapor by the ice phase, further slowing down WBF. All in all, this study indicates that, under specific conditions, small-scale inhomogeneities associated with entrainment and mixing counteract the accelerated WBF in entraining clouds. However, further research is required to assess the importance of the newly discovered processes more broadly in fully coupled, evolving mixed-phase cloud systems.

scholarly journals Observing ice particle growth along fall streaks in mixed-phase clouds using spectral polarimetric radar data

2018 ◽  
Author(s):  
Lukas Pfitzenmaier ◽  
Christine M. H. Unal ◽  
Yann Dufournet ◽  
Herman J. W. Russchenberg
Keyword(s):  
Particle Growth ◽  
Supercooled Liquid ◽  
Radar Data ◽  
Detection Algorithm ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Liquid Droplets ◽  
Growth Processes ◽  
Retrieval Technique ◽  
Mixed Phase Clouds

Abstract. The growth of ice crystals in presence of super-cooled liquid droplets represents the most important process for precipitation formation in the mid-latitudes. Such mixed-phase interaction processes remain however pretty much unknown, as capturing the complexity in cloud dynamics and microphysical variabilities turns to be a real observational challenge. Ground-based radar systems equipped with fully polarimetric and Doppler capabilities in high temporal and spatial resolutions 5 such as the S-band Transportable Atmospheric Radar (TARA) are best suited to observe mixed-phase growth processes. In this paper, measurements are taken with the TARA radar during the ACCEPT campaign (Analysis of the Composition of Clouds with Extended Polarization Techniques). Besides the common radar observables, the 3D wind field is also retrieved due to TARA unique three beam configuration. The novelty of this paper is to combine all these observations with a particle evolution detection algorithm based on a new fall streak retrieval technique in order to study ice particle growth within complex 10 precipitating mixed-phased cloud systems. In the presented cases, three different growth processes of ice crystals, plate-like crystals, and needles, are detected and related to the presence of supercooled liquid water. Moreover, TARA observed signatures are assessed with co-located measurements obtained from a cloud radar and radiosondes. This paper shows that it is possible to observe ice particle growth processes within complex systems taking advantage of adequate technology and state of the art retrieval algorithms. A significant improvement is made towards a conclusive interpretation of ice particle growth processes 15 and their contribution to rain production using fall streak rearranged radar data.

The microphysical characters of wintertime mixed-phase clouds in North China.

2021 ◽  
Author(s):  
Xuexu Wu ◽  
Minghuai Wang ◽  
Daniel Rosenfeld ◽  
Delong Zhao ◽  
Deping Ding
Keyword(s):  
Water Content ◽  
North China ◽  
Particle Number ◽  
Number Concentration ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Particle Number Concentration ◽  
Aggregation Process ◽  
Higher Temperature ◽  
Mixed Phase Clouds

<p>We use aircraft observation data to investigate the microphysical characters of wintertime mixed-phase clouds in North China, including the cloud particle number concentration (N<sub>c</sub>), the liquid water content (LWC), the ice particle number concentration (N<sub>i</sub>), the ice water content (IWC), the particle spectrum distributions (PSDs) and the effective diameter (D<sub>e</sub>). For wintertime mixed-phase clouds, the average N<sub>c</sub> and N<sub>i</sub> were 170±154 cm<sup>-3</sup> and 26±39 L<sup>-1</sup>, respectively; the average LWC and IWC were 0.05±0.06 and 0.07±0.09g/m<sup>3</sup>, respectively; the D<sub>e</sub> for cloud particles was 10±4 μm. When compared to the results from other regions, including East Europe, North America, Southern Ocean and Tibetan Plateau, we found that the wintertime mixed-phase cloud in North China has larger N<sub>c</sub>, smaller LWC, IWC and D<sub>e</sub>, and narrower PSDs. The main reason might be the larger aerosol loading and smaller water content in the atmosphere in winter in North China. With increasing temperature, N<sub>c</sub> and LWC increased, but N<sub>i</sub> and D<sub>e</sub> decreased. The dominate physical processes in wintertime mixed-phase cloud were aggregation process and riming process. As the temperature increased, the peak concentration of ice PSD decreased, but N<sub>i</sub> increased and the ice PSD became wider, indicating more ice crystals and the ice crystals became larger at higher temperature. With temperature increasing, the ice habit also changed, and the amount of plates, irregular crystals and their aggregates increased. What’s more, with the existence of larger LWC at higher temperature, the ice crystals gradually tightened and their surface became more complicated as well. Therefore, both aggregation process and riming process were more active at higher temperature, but riming process changed much more. This work fills the gap in the observation of wintertime mixed-phase clouds in north China, and the results suggest that the wintertime mixed-phase clouds have some unique microphysical characters.</p><div> </div>

scholarly journals Implementation of a comprehensive ice crystal formation parameterization for cirrus and mixed-phase clouds in the EMAC model (based on MESSy 2.53)

2018 ◽  
Vol 11 (10) ◽  
pp. 4021-4041 ◽  
Author(s):  
Sara Bacer ◽  
Sylvia C. Sullivan ◽  
Vlassis A. Karydis ◽  
Donifan Barahona ◽  
Martina Krämer ◽  
...  
Keyword(s):  
Climate Model ◽  
Ice Nucleation ◽  
Cirrus Clouds ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Dust Particles ◽  
Crystal Formation ◽  
Ice Crystal ◽  
Upper Troposphere ◽  
Mixed Phase Clouds

Abstract. A comprehensive ice nucleation parameterization has been implemented in the global chemistry-climate model EMAC to improve the representation of ice crystal number concentrations (ICNCs). The parameterization of Barahona and Nenes (2009, hereafter BN09) allows for the treatment of ice nucleation taking into account the competition for water vapour between homogeneous and heterogeneous nucleation in cirrus clouds. Furthermore, the influence of chemically heterogeneous, polydisperse aerosols is considered by applying one of the multiple ice nucleating particle parameterizations which are included in BN09 to compute the heterogeneously formed ice crystals. BN09 has been modified in order to consider the pre-existing ice crystal effect and implemented to operate both in the cirrus and in the mixed-phase regimes. Compared to the standard EMAC parameterizations, BN09 produces fewer ice crystals in the upper troposphere but higher ICNCs in the middle troposphere, especially in the Northern Hemisphere where ice nucleating mineral dust particles are relatively abundant. Overall, ICNCs agree well with the observations, especially in cold cirrus clouds (at temperatures below 205 K), although they are underestimated between 200 and 220 K. As BN09 takes into account processes which were previously neglected by the standard version of the model, it is recommended for future EMAC simulations.

scholarly journals Cloud phase identification of low-level Arctic clouds from airborne spectral radiation measurements: test of three approaches

2008 ◽  
Vol 8 (4) ◽  
pp. 15901-15939 ◽  
Author(s):  
A. Ehrlich ◽  
E. Bierwirth ◽  
M. Wendisch ◽  
J.-F. Gayet ◽  
G. Mioche ◽  
...  
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Mixed Phase ◽  
Ice Crystals ◽  
The Arctic ◽  
Pure Liquid ◽  
Phase Identification ◽  
Ice Clouds ◽  
Mixed Phase Clouds

Abstract. Boundary layer clouds were investigated with a complementary set of remote sensing and in situ instruments during the Arctic Study of Tropospheric Aerosol, Clouds and Radiation (ASTAR) campaign in March and April 2007. The clouds that formed in a cold air outbreak over the open Greenland sea showed a variety in their thermodynamic state. Beside the predominant mixed-phase clouds pure liquid and ice clouds were observed. Utilizing the measurements of solar radiation reflected by the clouds three methods to retrieve the thermodynamic phase of the cloud were defined and compared. Two ice indices IS and IP were obtained by analyzing the spectral pattern of the cloud top reflectance in the near infrared (1500–1800 nm wavelength) characterized by ice and water absorption. A third ice index IA is based on the different side scattering of spherical liquid water particles and nonspherical ice crystals which was recorded in simultaneous measurements of cloud albedo and reflectance. Radiative transfer simulations showed that IS, IP and IA range between 5 to 80, 0 to 20 and 1 to 1.25, respectively, with lowest values indicating pure liquid water clouds and highest values pure ice clouds. IS and IP were found to be strongly sensitive to the effective diameter of the ice crystals present in the cloud. Therefore the identification of mixed-phase clouds requires a priori knowledge of the ice crystal dimension. IA has the disadvantage that this index is mainly dominated by the uppermost cloud layer (τ<1.5). Typical boundary layer mixed-phase clouds with a liquid cloud top layer will be identified as pure liquid water clouds. All three methods were applied to measurements above a cloud field observed during ASTAR 2007. The comparison with independent in situ microphysical measurements showed a good agreement in identifying the dominant mixed-phase clouds and a pure ice cloud at the edge of the cloud field.

scholarly journals In-situ Observation of Riming in Mixed-Phase Clouds using the PHIPS probe

2021 ◽  
Author(s):  
Fritz Waitz ◽  
Martin Schnaiter ◽  
Thomas Leisner ◽  
Emma Järvinen
Keyword(s):  
Liquid Water ◽  
Prediction Models ◽  
Supercooled Liquid ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Ice Crystals ◽  
The Arctic ◽  
In Situ Observation ◽  
Cloud Particle ◽  
Mixed Phase Clouds

Abstract. Mixed-phase clouds consist of both supercooled liquid water droplets and solid ice crystals. Despite having a significant impact on Earth‘s climate, mixed-phase clouds are poorly understood and not well represented in climate prediction models. One piece of the puzzle is understanding and parameterizing riming of mixed-phase cloud ice crystals, which is one of the main growth mechanisms of ice crystals via the accretion of small, supercooled droplets. Especially the extent of riming on ice crystals smaller than 500 μm is often overlooked in studies – mainly because observations are scarce. Here, we investigated riming in mixed-phase clouds during three airborne campaigns in the Arctic, the Southern Ocean and US east coast. Riming was observed from stereo-microscopic cloud particle images recorded with the Particle Habit Imaging and Polar Scattering (PHIPS) probe. We show that riming is most prevalent at temperatures around −7 °C, where, on average, 43 % of the investigated particles in a size range from 100 ≤ D ≤ 700 μm showed evidence of riming. We discuss the occurrence and properties of rimed ice particles and show correlation of the occurrence and the amount of riming with ambient meteorological parameters. We show that riming fraction increases with ice particle size (< 20 % for D ≤ 200 μm, 35–40 % for D ≥ 400 μm) and liquid water content (25 % for LWC ≤ 0.05 g m−3, up to 60 % for LWC = 0.5 g m−3). We investigate the ageing of rimed particles and the difference between "normal" and "epitaxial" riming based on a case study.

scholarly journals Physical properties of High Arctic tropospheric particles during winter

2009 ◽  
Vol 9 (2) ◽  
pp. 7781-7823 ◽  
Author(s):  
L. Bourdages ◽  
T. J. Duck ◽  
G. Lesins ◽  
J. R. Drummond ◽  
E. W. Eloranta
Keyword(s):  
Boundary Layer ◽  
Inversion Layer ◽  
Lower Troposphere ◽  
High Arctic ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Blowing Snow ◽  
Ice Clouds ◽  
Arctic Conditions ◽  
Mixed Phase Clouds

Abstract. A climatology of particle properties in the wintertime High Arctic troposphere is constructed using measurements from a lidar and cloud radar located at Eureka, Nunavut Territory (80° N, 86° W). Four different particle groupings are considered: aerosols, mixed-phase clouds, ice clouds and boundary-layer ice crystals. Two-dimensional histograms of occurrence probabilities against depolarization and radar/lidar colour ratio, as well as their vertical distributions, are presented. The largest ice crystals originate from mixed-phase clouds, whereas the smallest are topographic blowing snow residuals in the boundary layer. Ice cloud crystals have depolarization and size decreasing with height. The depolarization trend is associated with the large ice crystal sub-population. Small crystals depolarize more than large ones in ice clouds at a given altitude, and show constant modal depolarization with height. Ice clouds in the mid-troposphere are sometimes observed to precipitate to the ground. Water clouds are constrained to the lower troposphere and are associated with the surface inversion layer depth. Aerosols are most abundant near the ground and are frequently mixed with the other particle types. The data are used to construct a classification chart for particle scattering in wintertime Arctic conditions.

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