scholarly journals Vertical Motions in Arctic Mixed-Phase Stratiform Clouds

2008 ◽  
Vol 65 (4) ◽  
pp. 1304-1322 ◽  
Author(s):  
Matthew D. Shupe ◽  
Pavlos Kollias ◽  
P. Ola G. Persson ◽  
Greg M. McFarquhar
Keyword(s):  
Liquid Water ◽  
Single Layer ◽  
Water Layer ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Remote Sensors ◽  
Microphysical Properties ◽  
Stratiform Clouds ◽  
Dynamical Properties

Abstract The characteristics of Arctic mixed-phase stratiform clouds and their relation to vertical air motions are examined using ground-based observations during the Mixed-Phase Arctic Cloud Experiment (MPACE) in Barrow, Alaska, during fall 2004. The cloud macrophysical, microphysical, and dynamical properties are derived from a suite of active and passive remote sensors. Low-level, single-layer, mixed-phase stratiform clouds are typically topped by a 400–700-m-deep liquid water layer from which ice crystals precipitate. These clouds are strongly dominated (85% by mass) by liquid water. On average, an in-cloud updraft of 0.4 m s−1 sustains the clouds, although cloud-scale circulations lead to a variability of up to ±2 m s−1 from the average. Dominant scales-of-variability in both vertical air motions and cloud microphysical properties retrieved by this analysis occur at 0.5–10-km wavelengths. In updrafts, both cloud liquid and ice mass grow, although the net liquid mass growth is usually largest. Between updrafts, nearly all ice falls out and/or sublimates while the cloud liquid diminishes but does not completely evaporate. The persistence of liquid water throughout these cloud cycles suggests that ice-forming nuclei, and thus ice crystal, concentrations must be limited and that water vapor is plentiful. These details are brought together within the context of a conceptual model relating cloud-scale dynamics and microphysics.

scholarly journals Falling Mixed-Phase Ice Virga and their Liquid Parent Cloud Layers as Observed by Ground-Based Lidars

2020 ◽  
Vol 12 (13) ◽  
pp. 2094
Author(s):  
Chong Cheng ◽  
Fan Yi
Keyword(s):  
Local Maximum ◽  
Water Layer ◽  
Supercooled Liquid ◽  
Mixed Phase ◽  
Ice Crystals ◽  
Cloud Base ◽  
Depolarization Ratio ◽  
Ice Crystal ◽  
Liquid Drops ◽  
The Mean

Falling mixed-phase virga from a thin supercooled liquid layer cloud base were observed on 20 occasions at altitudes of 2.3–9.4 km with ground-based lidars at Wuhan (30.5 °N, 114.4 °E), China. Polarization lidar profile (3.75-m) analysis reveals some ubiquitous features of both falling mixed-phase virga and their liquid parent cloud layers. Each liquid parent cloud had a well-defined base height where the backscatter ratio R was ~7.0 and the R profile had a clear inflection point. At an altitude of ~34 m above the base height, the depolarization ratio reached its minimum value (~0.04), indicating a liquid-only level therein. The thin parent cloud layers tended to form on the top of a broad preexisting aerosol/liquid water layer. The falling virga below the base height showed firstly a significant depolarization ratio increase, suggesting that most supercooled liquid drops in the virga were rapidly frozen into ice crystals (via contact freezing). After reaching a local maximum value of the depolarization ratio, both the values of the backscatter ratio and depolarization ratio for the virga exhibited an overall decrease with decreasing height, indicating sublimated ice crystals. The diameters of the ice crystals in the virga were estimated based on an ice particle sublimation model along with the lidar and radiosonde observations. It was found that the ice crystal particles in these virga cases tended to have smaller mean diameters and narrower size distributions with increasing altitude. The mean diameter value is 350 ± 111 µm at altitudes of 4–8.5 km.

scholarly journals Arctic Mixed-Phase Cloud Properties from AERI Lidar Observations: Algorithm and Results from SHEBA

2005 ◽  
Vol 44 (4) ◽  
pp. 427-444 ◽  
Author(s):  
D. D. Turner
Keyword(s):  
Liquid Water ◽  
Heat Budget ◽  
Single Layer ◽  
Precipitable Water ◽  
Mixed Phase ◽  
The Arctic ◽  
Retrieval Algorithm ◽  
Cloud Optical Depth ◽  
Microphysical Properties ◽  
Ice Particles

Abstract A new approach to retrieve microphysical properties from mixed-phase Arctic clouds is presented. This mixed-phase cloud property retrieval algorithm (MIXCRA) retrieves cloud optical depth, ice fraction, and the effective radius of the water and ice particles from ground-based, high-resolution infrared radiance and lidar cloud boundary observations. The theoretical basis for this technique is that the absorption coefficient of ice is greater than that of liquid water from 10 to 13 μm, whereas liquid water is more absorbing than ice from 16 to 25 μm. MIXCRA retrievals are only valid for optically thin (τvisible < 6) single-layer clouds when the precipitable water vapor is less than 1 cm. MIXCRA was applied to the Atmospheric Emitted Radiance Interferometer (AERI) data that were collected during the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment from November 1997 to May 1998, where 63% of all of the cloudy scenes above the SHEBA site met this specification. The retrieval determined that approximately 48% of these clouds were mixed phase and that a significant number of clouds (during all 7 months) contained liquid water, even for cloud temperatures as low as 240 K. The retrieved distributions of effective radii for water and ice particles in single-phase clouds are shown to be different than the effective radii in mixed-phase clouds.

scholarly journals Vertical distribution of microphysical properties of Arctic springtime low-level mixed-phase clouds over the Greenland and Norwegian seas

2017 ◽  
Vol 17 (20) ◽  
pp. 12845-12869 ◽  
Author(s):  
Guillaume Mioche ◽  
Olivier Jourdan ◽  
Julien Delanoë ◽  
Christophe Gourbeyre ◽  
Guy Febvre ◽  
...  
Keyword(s):  
Liquid Water ◽  
Crystal Size ◽  
Ice Crystals ◽  
Vertical Profiles ◽  
Liquid Droplets ◽  
Ice Crystal ◽  
Mean Values ◽  
Microphysical Properties ◽  
Ice Crystal Size ◽  
Mixed Phase Clouds

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 (MPCs). We compiled and analyzed cloud in situ measurements from four airborne spring campaigns (representing 18 flights and 71 vertical profiles in MPCs) over the Greenland and Norwegian seas mainly in the vicinity of the Svalbard archipelago. Cloud phase discrimination and representative vertical profiles of the number, size, mass and shape of ice crystals and liquid droplets are established. The results show that the liquid phase dominates the upper part of the MPCs. High concentrations (120 cm−3 on average) of small droplets (mean values of 15 µm), with an averaged liquid water content (LWC) of 0.2 g m−3 are measured at cloud top. The ice phase dominates the microphysical properties in the lower part of the cloud and beneath it in the precipitation region (mean values of 100 µm, 3 L−1 and 0.025 g m−3 for diameter, particle concentration and ice water content (IWC), respectively). The analysis of the ice crystal morphology shows that the majority of ice particles are irregularly shaped or rimed particles; the prevailing regular habits found are stellars and plates. We hypothesize that riming and diffusional growth processes, including the Wegener–Bergeron–Findeisen (WBF) mechanism, are the main growth mechanisms involved in the observed MPCs. The impact of larger-scale meteorological conditions on the vertical profiles of MPC properties was also investigated. Large values of LWC and high concentration of smaller droplets are possibly linked to polluted situations and air mass origins from the south, which can 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 studies 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.

scholarly journals Arctic Mixed-Phase Stratiform Cloud Properties from Multiple Years of Surface-Based Measurements at Two High-Latitude Locations

2009 ◽  
Vol 66 (9) ◽  
pp. 2874-2887 ◽  
Author(s):  
Gijs de Boer ◽  
Edwin W. Eloranta ◽  
Matthew D. Shupe
Keyword(s):  
Liquid Water ◽  
Microwave Radiometer ◽  
Single Layer ◽  
Mixed Phase ◽  
Cloud Base ◽  
Microphysical Properties ◽  
Cloud Properties ◽  
Arctic Change ◽  
Mixed Phase Clouds ◽  
Water Contents

Abstract Macro- and microphysical properties of single-layer stratiform mixed-phase clouds are derived from multiple years of lidar, radar, and radiosonde observations. Measurements were made as part of the Mixed-Phase Arctic Clouds Experiment (MPACE) and the Study of Environmental Arctic Change (SEARCH) in Barrow, Alaska, and Eureka, Nunavut, Canada, respectively. Single-layer mixed-phase clouds occurred between 4% and 26% of the total time observed, varying with season and location. They had mean cloud-base heights between ∼700 and 2100 m and thicknesses between ∼200 and 700 m. Seasonal mean cloud optical depths ranged from 2.2 up. The clouds existed at temperatures of ∼242–271 K and occurred under different wind conditions, depending on season. Utilizing retrievals from a combination of lidar, radar, and microwave radiometer, mean cloud microphysical properties were derived, with mean liquid effective diameters estimated from 16 to 49 μm, mean liquid number densities on the order of 104–105 L−1, and mean water contents estimated between 0.07 and 0.28 g m−3. Ice precipitation was shown to have mean ice effective diameters of 50–125 μm, mean ice number densities on the order of 10 L−1, and mean water contents estimated between 0.012 and 0.031 g m−3. Mean cloud liquid water paths ranged from 25 to 100 g m−2. All results are compared to previous studies, and potential retrieval errors are discussed. Additionally, seasonal variation in macro- and microphysical properties was highlighted. Finally, fraction of liquid water to ice mass was shown to decrease with decreasing temperature.

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.

scholarly journals Microphysical properties and fall speed measurements of snow ice crystals using the Dual Ice Crystal Imager (D-ICI)

2020 ◽  
Vol 13 (3) ◽  
pp. 1273-1285 ◽  
Author(s):  
Thomas Kuhn ◽  
Sandra Vázquez-Martín
Keyword(s):  
Remote Sensing ◽  
Vertical Direction ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Double Exposure ◽  
Shape Information ◽  
Microphysical Properties ◽  
Ice Particles ◽  
Crystal Properties ◽  
Fall Speed

Abstract. 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.

scholarly journals First Look at the Occurrence of Horizontally Oriented Ice Crystals over Summit, Greenland

2017 ◽  
Author(s):  
Sebastian Cole ◽  
Ryan R. Neely III. ◽  
Robert A. Stillwell
Keyword(s):  
Ground Level ◽  
Cirrus Clouds ◽  
Ice Crystals ◽  
Wind Speeds ◽  
Microphysical Properties ◽  
Stratiform Clouds ◽  
Monthly Changes ◽  
Microphysical Processes ◽  
Monthly Variations

Abstract. The microphysical properties of clouds play a significant role in determining their radiative effect; one of these properties is the orientation of ice crystals. A source of error in current microphysical retrievals and model simulations is the assumption that clouds are composed of only randomly oriented ice crystals (ROIC). This assumption is frequently not true, as evidenced by optical phenomena such as parhelia (commonly referred to as sundogs). Here, observations from the Cloud, Aerosol and Polarization Backscatter Lidar (CAPABL) at Summit, Greenland are utilized along with instruments that are part of the Integrated Characterization of Energy, Clouds, Atmospheric state and Precipitation at Summit (ICECAPS) project in order to determine when, where and under what conditions horizontally oriented ice crystals (HOIC) occur at Summit, Greenland. Between July 2015 and May 2016, HOIC are observed on 86 days of the 335-day study. HOIC occurred within stratiform clouds on 48 days, in precipitation on 32 days and in cirrus clouds on 14 days. Analysis of all of the cases found that, on average, in comparison to ROIC, HOIC occur at higher temperatures, higher wind speeds and lower heights above ground level. Differences were also present in the relative humidities (RHs) at which HOIC and ROIC occurred in stratiform clouds and precipitation but not in cirrus clouds. Analysis over the whole study period revealed monthly variations in the abundance of HOIC with the number of detections peaking in April and October. Monthly changes were also present in the number of days containing HOIC. The results presented here aim to be the first step towards a comprehensive climatology and understanding of the microphysical processes that lead to the formation of HOIC at Summit, Greenland.

Modeling Ice Crystal Aspect Ratio Evolution during Riming: A Single-Particle Growth Model

2015 ◽  
Vol 72 (7) ◽  
pp. 2569-2590 ◽  
Author(s):  
Anders A. Jensen ◽  
Jerry Y. Harrington
Keyword(s):  
Wind Tunnel ◽  
Growth Model ◽  
Liquid Water ◽  
Single Particle ◽  
Liquid Drop ◽  
Ice Crystals ◽  
Ice Crystal ◽  
Vapor Growth ◽  
Wind Tunnel Data ◽  
Fall Speed

This paper describes and tests a single-particle ice growth model that evolves both ice crystal mass and shape as a result of vapor growth and riming. Columnar collision efficiencies in the model are calculated using a new theoretical method derived from spherical collision efficiencies. The model is able to evolve mass, shape, and fall speed of growing ice across a range of temperatures, and it compares well with wind tunnel data. The onset time of riming and the effects of riming on mass and fall speed between −3° and −16°C are modeled, as compared with wind tunnel data for a liquid water content of 0.4 g m−3. Under these conditions, riming is constrained to the more isometric habits near −10° and −4°C. It is shown that the mass and fall speed of riming dendrites depend on the liquid drop distribution properties, leading to a range of mass–size and fall speed–size relationships. Riming at low liquid water contents is shown to be sensitive to ice crystal habit and liquid drop size. Moreover, very light riming can affect the shape of ice crystals enough to reduce vapor growth and suppress overall mass growth, as compared with those same ice crystals if they were unrimed.

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 Impacts of Secondary Ice Production on Arctic Mixed-Phase Clouds based on ARM Observations and CESM2

2020 ◽  
Author(s):  
Xi Zhao ◽  
Xiaohong Liu ◽  
Vaughan T. J. Phillips ◽  
Sachin Patade
Keyword(s):  
Global Climate Model ◽  
Single Layer ◽  
Ice Nucleation ◽  
Number Concentration ◽  
Mixed Phase ◽  
Department Of Energy ◽  
Cloud Base ◽  
Ice Crystal ◽  
Ice Production ◽  
Mixed Phase Clouds

Abstract. For decades, measured ice crystal number concentrations have been found to be orders of magnitude higher than measured ice nucleating particles in moderately cold clouds. This observed discrepancy reveals the existence of secondary ice production (SIP) in addition to the primary ice nucleation. However, the importance of SIP relative to primary ice nucleation remains highly unclear. Furthermore, most weather and climate models do not represent well the SIP processes, leading to large biases in simulated cloud properties. This study demonstrates a first attempt to represent different SIP mechanisms (frozen raindrop shattering, ice-ice collisional break-up, and rime splintering) in a global climate model (GCM). The model is run in the single column mode to facilitate comparisons with the Department of Energy (DOE)'s Atmospheric Radiation Measurement (ARM) Mixed-Phase Arctic Cloud Experiment (M-PACE) observations. We show the SIP importance in the four types of clouds during M-PACE (i.e., multilayer, and single-layer stratus, transition, and front clouds), with the maximum enhancement in ice crystal number concentration by up to 4 orders of magnitude in the moderately-cold clouds. We reveal that SIP is the dominant source of ice crystals near the cloud base for the long-lived Arctic single-layer mixed-phase clouds. The model with SIP improves the occurrence and phase partitioning of the mixed-phase clouds, reverses the vertical distribution pattern of ice number concentration, and provides a better agreement with observations. The findings of this study highlight the importance of considering the SIP in GCMs.

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