The spectral signature of mixed-phase clouds composed of non-spherical ice crystals and spherical liquid droplets in the terrestrial window region

2003 ◽  
Vol 79-80 ◽  
pp. 1171-1188 ◽  
Author(s):  
Ping Yang ◽  
He-Li Wei ◽  
Bryan A Baum ◽  
Hung-Lung Huang ◽  
Andrew J Heymsfield ◽  
...  
Keyword(s):  
Mixed Phase ◽  
Ice Crystals ◽  
Spectral Signature ◽  
Liquid Droplets ◽  
Window Region ◽  
Mixed Phase Clouds

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.

scholarly journals Classification of Arctic, Mid-Latitude and Tropical Clouds in the Mixed-Phase Temperature Regime

2017 ◽  
Author(s):  
Anja Costa ◽  
Jessica Meyer ◽  
Armin Afchine ◽  
Anna Luebke ◽  
Gebhard Günther ◽  
...  
Keyword(s):  
Temperature Regime ◽  
Mixed Phase ◽  
Ice Crystals ◽  
The Arctic ◽  
Liquid Droplets ◽  
Tropical Regions ◽  
Theory Of Evolution ◽  
Phase Temperature ◽  
Cloud Particles ◽  
Mixed Phase Clouds

Abstract. The degree of glaciation of mixed-phase clouds constitutes one of the largest uncertainties in climate prediction. In order to better understand cloud glaciation, cloud spectrometer observations are presented in this paper that were made in the mixed-phase temperature regime between 0 °C and −38 °C, where cloud particles can either be frozen or liquid. The extensive dataset covers four airborne field campaigns providing a total of 139,000 1 Hz data points (38.6 hours within clouds) over Arctic, mid-latitude and tropical regions. We develop algorithms combining the information on number concentration, size and asphericity of the observed cloud particles to classify four cloud types associated with liquid clouds, clouds where liquid droplets and ice crystals coexist, fully glaciated clouds after the Wegener-Bergeron-Findeisen process, and clouds where secondary ice formation occurred. We quantify the occurrence of these cloud groups depending on the geographical region and temperature and find that liquid clouds dominate in our measurements during the Arctic spring, while clouds dominated by the Wegener-Bergeron-Findeisen process are most common in mid-latitude spring. Coexistence of liquid water and ice crystals is found over the whole mixed-phase temperature range in tropical convective towers in the dry season. Secondary ice is found at mid-latitudes at −5 °C to −10 °C and at higher altitudes, i.e. lower temperatures in the tropics. The distribution of the cloud types with decreasing temperatures is shown to be consistent with the theory of evolution of mixed-phase clouds. With this study, we aim to contribute to a large statistical database on cloud types in the mixed-phase temperature regime.

scholarly journals The Ice Selective Inlet: a novel technique for exclusive extraction of pristine ice crystals in mixed-phase clouds

2015 ◽  
Vol 8 (8) ◽  
pp. 3087-3106 ◽  
Author(s):  
P. Kupiszewski ◽  
E. Weingartner ◽  
P. Vochezer ◽  
M. Schnaiter ◽  
A. Bigi ◽  
...  
Keyword(s):  
Field Measurements ◽  
Droplet Evaporation ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Saharan Dust ◽  
Liquid Droplets ◽  
Mixed Phase Clouds ◽  
Evaporation Unit

Abstract. Climate predictions are affected by high uncertainties partially due to an insufficient knowledge of aerosol–cloud interactions. One of the poorly understood processes is formation of mixed-phase clouds (MPCs) via heterogeneous ice nucleation. Field measurements of the atmospheric ice phase in MPCs are challenging due to the presence of much more numerous liquid droplets. The Ice Selective Inlet (ISI), presented in this paper, is a novel inlet designed to selectively sample pristine ice crystals in mixed-phase clouds and extract the ice residual particles contained within the crystals for physical and chemical characterization. Using a modular setup composed of a cyclone impactor, droplet evaporation unit and pumped counterflow virtual impactor (PCVI), the ISI segregates particles based on their inertia and phase, exclusively extracting small ice particles between 5 and 20 μm in diameter. The setup also includes optical particle spectrometers for analysis of the number size distribution and shape of the sampled hydrometeors. The novelty of the ISI is a droplet evaporation unit, which separates liquid droplets and ice crystals in the airborne state, thus avoiding physical impaction of the hydrometeors and limiting potential artefacts. The design and validation of the droplet evaporation unit is based on modelling studies of droplet evaporation rates and computational fluid dynamics simulations of gas and particle flows through the unit. Prior to deployment in the field, an inter-comparison of the optical particle size spectrometers and a characterization of the transmission efficiency of the PCVI was conducted in the laboratory. The ISI was subsequently deployed during the Cloud and Aerosol Characterization Experiment (CLACE) 2013 and 2014 – two extensive international field campaigns encompassing comprehensive measurements of cloud microphysics, as well as bulk aerosol, ice residual and ice nuclei properties. The campaigns provided an important opportunity for a proof of concept of the inlet design. In this work we present the setup of the ISI, including the modelling and laboratory characterization of its components, as well as field measurements demonstrating the ISI performance and validating the working principle of the inlet. Finally, measurements of biological aerosol during a Saharan dust event (SDE) are presented, showing a first indication of enrichment of bio-material in sub-2 μm ice residuals.

scholarly journals Scavenging of black carbon in mixed phase clouds at the high alpine site Jungfraujoch

2007 ◽  
Vol 7 (7) ◽  
pp. 1797-1807 ◽  
Author(s):  
J. Cozic ◽  
B. Verheggen ◽  
S. Mertes ◽  
P. Connolly ◽  
K. Bower ◽  
...  
Keyword(s):  
Black Carbon ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Research Station ◽  
Liquid Droplets ◽  
Cloud Droplets ◽  
Mixed Phase Clouds

Abstract. The scavenging of black carbon (BC) in liquid and mixed phase clouds was investigated during intensive experiments in winter 2004, summer 2004 and winter 2005 at the high alpine research station Jungfraujoch (3580 m a.s.l., Switzerland). Aerosol residuals were sampled behind two well characterized inlets; a total inlet which collected cloud particles (droplets and ice particles) as well as interstitial (unactivated) aerosol particles; an interstitial inlet which collected only interstitial aerosol particles. BC concentrations were measured behind each of these inlets along with the submicrometer aerosol number size distribution, from which a volume concentration was derived. These measurements were complemented by in-situ measurements of cloud microphysical parameters. BC was found to be scavenged into the condensed phase to the same extent as the bulk aerosol, which suggests that BC was covered with soluble material through aging processes, rendering it more hygroscopic. The scavenged fraction of BC (FScav,BC), defined as the fraction of BC that is incorporated into cloud droplets and ice crystals, decreases with increasing cloud ice mass fraction (IMF) from FScav,BC=60% in liquid phase clouds to FScav,BC~5–10% in mixed-phase clouds with IMF>0.2. This can be explained by the evaporation of liquid droplets in the presence of ice crystals (Wegener-Bergeron-Findeisen process), releasing BC containing cloud condensation nuclei back into the interstitial phase. In liquid clouds, the scavenged BC fraction is found to decrease with decreasing cloud liquid water content. The scavenged BC fraction is also found to decrease with increasing BC mass concentration since there is an increased competition for the available water vapour.

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

2018 ◽  
Vol 18 (11) ◽  
pp. 7843-7862 ◽  
Author(s):  
Lukas Pfitzenmaier ◽  
Christine M. H. Unal ◽  
Yann Dufournet ◽  
Herman W. J. 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 supercooled liquid droplets represents the most important process for precipitation formation in the mid-latitudes. However, such mixed-phase interaction processes remain relatively 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 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 3-D 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 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 and their contribution to rain production using fall streak rearranged radar data.

scholarly journals Scavenging of black carbon in mixed phase clouds at the high alpine site Jungfraujoch

2006 ◽  
Vol 6 (6) ◽  
pp. 11877-11912 ◽  
Author(s):  
J. Cozic ◽  
B. Verheggen ◽  
S. Mertes ◽  
P. Connolly ◽  
K. Bower ◽  
...  
Keyword(s):  
Black Carbon ◽  
Cloud Condensation Nuclei ◽  
Aerosol Particles ◽  
Liquid Water Content ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Research Station ◽  
Liquid Droplets ◽  
Cloud Droplets ◽  
Mixed Phase Clouds

Abstract. The scavenging of black carbon (BC) in liquid and mixed phase clouds was investigated during intensive experiments in winter 2004, summer 2004 and winter 2005 at the high alpine research station Jungfraujoch (3580 m a.s.l., Switzerland). Aerosol residuals were sampled behind two well characterized inlets; a total inlet which collected cloud particles (drops and ice particles) as well as interstitial aerosol particles; an interstitial inlet which collected only interstitial (unactivated) aerosol particles. BC concentrations were measured behind each of these inlets along with the submicrometer aerosol number size distribution, from which a volume concentration was derived. These measurements were complemented by in-situ measurements of cloud microphysical parameters. BC was found to be scavenged into the cloud phase to the same extent as the bulk aerosol, which suggests that BC was covered with soluble material through aging processes, rendering it more hygroscopic. The scavenged fraction of BC (FScav,BC), defined as the fraction of BC that is incorporated into cloud droplets and ice crystals, decreases with increasing cloud ice mass fraction (IMF) from FScav,BC=60% in liquid phase clouds to FScav,BC~10% in mixed-phase clouds with IMF>0.2. This is explained by the evaporation of liquid droplets in the presence of ice crystals (Wegener-Bergeron-Findeisen process), releasing BC containing cloud condensation nuclei back into the interstitial phase. In liquid clouds, the scavenged BC fraction is found to decrease with decreasing cloud liquid water content. The scavenged BC fraction is also found to decrease with increasing BC mass concentration since there is an increased competition for the available water vapour.

scholarly journals The Ice Selective Inlet: a novel technique for exclusive extraction of pristine ice crystals in mixed-phase clouds

2014 ◽  
Vol 7 (12) ◽  
pp. 12481-12515 ◽  
Author(s):  
P. Kupiszewski ◽  
E. Weingartner ◽  
P. Vochezer ◽  
A. Bigi ◽  
B. Rosati ◽  
...  
Keyword(s):  
Field Measurements ◽  
Supercooled Liquid ◽  
Droplet Evaporation ◽  
Transmission Efficiency ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Liquid Droplets ◽  
Mixed Phase Clouds ◽  
Evaporation Unit

Abstract. Climate predictions are affected by high uncertainties partially due to an insufficient knowledge of aerosol-cloud interactions. One of the poorly understood processes is formation of mixed-phase clouds (MPCs) via heterogeneous ice nucleation. Field measurements of the atmospheric ice phase in MPCs are challenging due to the presence of supercooled liquid droplets. The Ice Selective Inlet (ISI), presented in this paper, is a novel inlet designed to selectively sample pristine ice crystals in mixed-phase clouds and extract the ice residual particles contained within the crystals for physical and chemical characterisation. Using a modular setup composed of a cyclone impactor, droplet evaporation unit and pumped counterflow virtual impactor (PCVI), the ISI segregates particles based on their inertia and phase, exclusively extracting small ice particles between 5 and 20 μm in diameter. The setup also includes optical particle spectrometers for analysis of the number size distribution and shape of the sampled hydrometeors. The novelty of the ISI is a droplet evaporation unit, which separates liquid droplets and ice crystals in the airborne state, thus avoiding physical impaction of the hydrometeors and limiting potential artifacts. The design and validation of the droplet evaporation unit is based on modelling studies of droplet evaporation rates and computational fluid dynamics simulations of gas and particle flows through the unit. Prior to deployment in the field, an inter-comparison of the WELAS optical particle size spectrometers and a characterisation of the transmission efficiency of the PCVI was conducted in the laboratory. The ISI was subsequently deployed during the Cloud and Aerosol Characterisation Experiment (CLACE) 2013 – an extensive international field campaign encompassing comprehensive measurements of cloud microphysics, as well as bulk aerosol, ice residual and ice nuclei properties. The campaign provided an important opportunity for a proof of concept of the inlet design. In this work we present the setup of the ISI, including the modelling and laboratory characterisation of its components, as well as a case study demonstrating the ISI performance in the field during CLACE 2013.

scholarly journals Limitations of the Wegener–Bergeron–Findeisen Mechanism in the Evolution of Mixed-Phase Clouds

2007 ◽  
Vol 64 (9) ◽  
pp. 3372-3375 ◽  
Author(s):  
Alexei Korolev
Keyword(s):  
Phase Transformation ◽  
Limited Range ◽  
Mixed Phase ◽  
Ice Crystals ◽  
The Other ◽  
Liquid Droplets ◽  
Ice Particles ◽  
Mixed Phase Clouds ◽  
Precipitation Formation ◽  
Simultaneous Growth

Abstract Phase transformation and precipitation formation in mixed-phase clouds are usually associated with the Wegener–Bergeron–Findeisen (WBF) process in which ice crystals grow at the expense of liquid droplets. The evolution of mixed-phase clouds, however, is closely related to local thermodynamical conditions, and the WBF process is just one of three possible scenarios. The other two scenarios involve simultaneous growth or evaporation of liquid droplets and ice particles. Particle evolution in the other two scenarios differs significantly from that associated with the WBF process. Thus, during simultaneous growth, liquid droplets compete for the water vapor with the ice particle, which slows down the depositional growth of ice particles instead of promoting their growth at the expense of the liquid as in the WBF process. It is shown that the WBF process is expected to occur under a limited range of conditions and that ice particles and liquid droplets in mixed-phase clouds are not always processed in accordance with the WBF mechanism.

scholarly journals Characterization of Arctic mixed-phase cloud properties at small scale and coupling with satellite remote sensing

2017 ◽  
Author(s):  
Guillaume Mioche ◽  
Olivier Jourdan ◽  
Julien Delanoë ◽  
Christophe Gourbeyre ◽  
Guy Febvre ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Crystal Size ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Small Scale ◽  
Vertical Profiles ◽  
Liquid Droplets ◽  
Ice Crystal ◽  
High Concentration ◽  
Ice Crystal Size

Abstract. This study aims to characterize the microphysical and optical properties of ice crystals and supercooled liquid droplets within low-level Arctic mixed-phase clouds (MPC). We compiled and analyzed cloud in situ measurements from 4 airborne campaigns (18 flights, 71 vertical profiles in MPC) over the Greenland Sea and the Svalbard region. Cloud phase discrimination and representative vertical profiles of number, size, mass and shapes of ice crystals and liquid droplets are assessed. The results show that the liquid phase dominates the upper part of the MPC with high concentration of small droplets (120 cm−3, 15&tinsp;μm), and averaged LWC around 0.2 g m−3. The ice phase is found everywhere within the MPC layers, but dominates the properties in the lower part of the cloud and below where ice crystals precipitate down to the surface. The analysis of the ice crystal morphology highlights that irregulars and rimed are the main particle habit followed by stellars and plates. We hypothesize that riming and condensational growth processes (including the Wegener-Bergeron-Findeisein mechanism) are the main growth mechanisms involved in MPC. The differences observed in the vertical profiles of MPC properties from one campaign to another highlight that large values of LWC and high concentration of smaller droplets are possibly linked to polluted situations which lead to very low values of ice crystal size and IWC. On the contrary, clean situations with low temperatures exhibit larger values of ice crystal size and IWC. Several parameterizations relevant for remote sensing or modeling are also determined, such as IWC (and LWC) – extinction relationship, ice and liquid integrated water paths, ice concentration and liquid water fraction according to temperature. Finally, 4 flights collocated with active remote sensing observations from CALIPSO and CloudSat satellites are specifically analyzed to evaluate the cloud detection and cloud thermodynamical phase DARDAR retrievals. This comparison is valuable to assess the sub-pixel variability of the satellite measurements as well as their shortcomings/performance near the ground.

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