scholarly journals Microphysical sensitivity of coupled springtime Arctic stratocumulus to modelled primary ice over the ice pack, marginal ice, and ocean

2017 ◽  
Vol 17 (6) ◽  
pp. 4209-4227 ◽  
Author(s):  
Gillian Young ◽  
Paul J. Connolly ◽  
Hazel M. Jones ◽  
Thomas W. Choularton
Keyword(s):  
Sea Ice ◽  
Liquid Water ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
The Arctic ◽  
Ice Formation ◽  
Large Eddy ◽  
Break Up ◽  
Mixed Phase Clouds ◽  
Ice Pack

Abstract. This study uses large eddy simulations to test the sensitivity of single-layer mixed-phase stratocumulus to primary ice number concentrations in the European Arctic. Observations from the Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign are considered for comparison with cloud microphysics modelled using the Large Eddy Model (LEM, UK Met. Office). We find that cloud structure is very sensitive to ice number concentrations, Nice, and small increases can cause persisting mixed-phase clouds to glaciate and break up.Three key dependencies on Nice are identified from sensitivity simulations and comparisons with observations made over the sea ice pack, marginal ice zone (MIZ), and ocean. Over sea ice, we find deposition–condensation ice formation rates are overestimated, leading to cloud glaciation. When ice formation is limited to water-saturated conditions, we find microphysics comparable to aircraft observations over all surfaces considered. We show that warm supercooled (−13 °C) mixed-phase clouds over the MIZ are simulated to reasonable accuracy when using both the DeMott et al.(2010) and Cooper(1986) primary ice nucleation parameterisations. Over the ocean, we find a strong sensitivity of Arctic stratus to Nice. The Cooper(1986) parameterisation performs poorly at the lower ambient temperatures, leading to a comparatively higher Nice (2.43 L−1 at the cloud-top temperature, approximately −20 °C) and cloud glaciation. A small decrease in the predicted Nice (2.07 L−1 at −20 °C), using the DeMott et al.(2010) parameterisation, causes mixed-phase conditions to persist for 24 h over the ocean. However, this representation leads to the formation of convective structures which reduce the cloud liquid water through snow precipitation, promoting cloud break-up through a depleted liquid phase. Decreasing the Nice further (0.54 L−1, using a relationship derived from ACCACIA observations) allows mixed-phase conditions to be maintained for at least 24 h with more stability in the liquid and ice water paths. Sensitivity to Nice is also evident at low number concentrations, where 0.1  ×  Nice predicted by the DeMott et al.(2010) parameterisation results in the formation of rainbands within the model; rainbands which also act to deplete the liquid water in the cloud and promote break-up.

scholarly journals Microphysical sensitivity of coupled springtime Arctic stratocumulus to modelled primary ice over the ice pack, marginal ice, and ocean

2016 ◽  
Author(s):  
Gillian Young ◽  
Paul J. Connolly ◽  
Hazel M. Jones ◽  
Thomas W. Choularton
Keyword(s):  
Sea Ice ◽  
Liquid Water ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
The Arctic ◽  
Ice Formation ◽  
Large Eddy ◽  
Break Up ◽  
Mixed Phase Clouds ◽  
Ice Pack

Abstract. This study uses large eddy simulations to test the sensitivity of single-layer mixed-phase stratocumulus to primary ice number concentrations in the European Arctic. Observations from the Aerosol-Cloud Coupling and Climate Interactions in the Arctic (ACCACIA) campaign are considered for comparison with cloud microphysics modelled using the Large Eddy Model (LEM, UK Met. Office). We find that cloud structure is very sensitive to ice number concentrations, N_ice , and small increases can cause persisting mixed-phase clouds to glaciate and break up. Three key sensitivities are identified with comparison to in situ cloud observations over the sea ice pack, marginal ice zone (MIZ), and ocean. Over sea ice, we find deposition-condensation ice formation rates are overestimated, leading to cloud glaciation. When ice formation is limited to water-saturated conditions, we find microphysics comparable to the aircraft observations over all surfaces considered. We show that warm supercooled (−13 °C) mixed-phase clouds over the MIZ are simulated to reasonable accuracy when using both the DeMott et al. (2010) and Cooper (1986) parameterisations. Over the ocean, we find a strong sensitivity of Arctic stratus to ice number concentrations. Cooper (1986) performs poorly at the lower ambient temperatures, leading to comparatively higher ice number concentrations (2.43 L−1 at the cloud top temperature, approximately −20 °C) and cloud glaciation. A small decrease in the predicted Nice (2.07 L−1 at −20 °C), using the DeMott et al. (2010) parameterisation, causes mixed-phase conditions to persist for 24 h over the ocean. However, this representation leads to the formation of convective structures which reduce the cloud liquid water through snow precipitation, promoting cloud break up. Decreasing the ice crystal number concentration further (0.54 L−1, using a relationship derived from ACCACIA observations) allows mixed-phase conditions to be maintained for at least 24 h with more stability in the liquid and ice water paths. Sensitivity to Nice is also evident at low number concentrations, where 0.1×Nice predicted by the DeMott et al. (2010) parameterisation results in the formation of rainbands within the model; rainbands which also act to deplete the liquid water in the cloud and promote break up.

scholarly journals The Vertical Profile of Liquid and Ice Water Content in Midlatitude Mixed-Phase Altocumulus Clouds

2008 ◽  
Vol 47 (9) ◽  
pp. 2487-2495 ◽  
Author(s):  
Lawrence D. Carey ◽  
Jianguo Niu ◽  
Ping Yang ◽  
J. Adam Kankiewicz ◽  
Vincent E. Larson ◽  
...  
Keyword(s):  
Water Content ◽  
Liquid Water ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
The Arctic ◽  
Cloud Base ◽  
Ice Water Content ◽  
Mixed Phase Clouds ◽  
Ice Water ◽  
Water Contents

Abstract The microphysical properties of mixed-phase altocumulus clouds are investigated using in situ airborne measurements acquired during the ninth Cloud Layer Experiment (CLEX-9) over a midlatitude location. Approximately ⅔ of the sampled profiles are supercooled liquid–topped altocumulus clouds characterized by mixed-phase conditions. The coexistence of measurable liquid water droplets and ice crystals begins at or within tens of meters of cloud top and extends down to cloud base. Ice virga is found below cloud base. Peak liquid water contents occur at or near cloud top while peak ice water contents occur in the lower half of the cloud or in virga. The estimation of ice water content from particle size data requires that an assumption be made regarding the particle mass–dimensional relation, resulting in potential error on the order of tens of percent. The highest proportion of liquid is typically found in the coldest (top) part of the cloud profile. This feature of the microphysical structure for the midlatitude mixed-phase altocumulus clouds is similar to that reported for mixed-phase clouds over the Arctic region. The results obtained for limited cases of midlatitude mixed-phase clouds observed during CLEX-9 may have an implication for the study of mixed-phase cloud microphysics, satellite remote sensing applications, and the parameterization of mixed-phase cloud radiative properties in climate models.

Intercomparison of Bulk Cloud Microphysics Schemes in Mesoscale Simulations of Springtime Arctic Mixed-Phase Stratiform Clouds

2006 ◽  
Vol 134 (7) ◽  
pp. 1880-1900 ◽  
Author(s):  
H. Morrison ◽  
J. O. Pinto
Keyword(s):  
Boundary Layer ◽  
Liquid Water ◽  
Heat Budget ◽  
Cloud Microphysics ◽  
Ice Nucleation ◽  
Mixed Phase ◽  
Precipitation Rate ◽  
The Arctic ◽  
Ice Clouds ◽  
Complex Scheme

Abstract A persistent, weakly forced, horizontally extensive mixed-phase boundary layer cloud observed on 4–5 May 1998 during the Surface Heat Budget of the Arctic Ocean (SHEBA)/First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment–Arctic Clouds Experiment (FIRE–ACE) is modeled using three different bulk microphysics parameterizations of varying complexity implemented into the polar version of the fifth-generation Pennsylvania State University–National Center for Atmospheric Research Mesoscale Model (MM5). The two simpler schemes predict mostly ice clouds and very little liquid water, while the complex scheme is able to reproduce the observed persistence and horizontal extent of the mixed-phase stratus deck. This mixed-phase cloud results in radiative warming of the surface, the development of a cloud-topped, surface-based mixed layer, and an enhanced precipitation rate. In contrast, the optically thin ice clouds predicted by the simpler schemes lead to radiative cooling of the surface, a strong diurnal cycle in the boundary layer structure, and very weak precipitation. The larger surface precipitation rate using the complex scheme is partly balanced by an increase in the turbulent flux of water vapor from the surface to the atmosphere. This enhanced vapor flux is attributed to changes in the surface and boundary layer characteristics induced by the cloud itself, although cloud–surface interactions appear to be exaggerated in the model compared with reality. The prediction of extensive mixed-phase stratus by the complex scheme is also associated with increased surface pressure and subsidence relative to the other simulations. Sensitivity tests show that the detailed treatment of ice nucleation and prediction of snow particle number concentration in the complex scheme suppresses ice particle concentration relative to the simpler schemes, reducing the vapor deposition rate (for given values of bulk ice mass and ice supersaturation) and leading to much greater amounts of liquid water and mixed-phase cloudiness. These results suggest that the treatments of ice nucleation and the snow intercept parameter in the simpler schemes, which are based upon midlatitude observations, are inadequate for simulating the weakly forced mixed-phase clouds endemic to the Arctic.

scholarly journals Hemispheric contrasts in ice formation in stratiform mixed-phase clouds: disentangling the role of aerosol and dynamics with ground-based remote sensing

2021 ◽  
Vol 21 (23) ◽  
pp. 17969-17994
Author(s):  
Martin Radenz ◽  
Johannes Bühl ◽  
Patric Seifert ◽  
Holger Baars ◽  
Ronny Engelmann ◽  
...  
Keyword(s):  
Remote Sensing ◽  
Boundary Layer ◽  
Gravity Wave ◽  
Detection Threshold ◽  
Cloud Microphysics ◽  
Mixed Phase ◽  
Ice Formation ◽  
Absolute Difference ◽  
Optical Parameters ◽  
Mixed Phase Clouds

Abstract. Multi-year ground-based remote-sensing datasets were acquired with the Leipzig Aerosol and Cloud Remote Observations System (LACROS) at three sites. A highly polluted central European site (Leipzig, Germany), a polluted and strongly dust-influenced eastern Mediterranean site (Limassol, Cyprus), and a clean marine site in the southern midlatitudes (Punta Arenas, Chile) are used to contrast ice formation in shallow stratiform liquid clouds. These unique, long-term datasets in key regions of aerosol–cloud interaction provide a deeper insight into cloud microphysics. The influence of temperature, aerosol load, boundary layer coupling, and gravity wave motion on ice formation is investigated. With respect to previous studies of regional contrasts in the properties of mixed-phase clouds, our study contributes the following new aspects: (1) sampling aerosol optical parameters as a function of temperature, the average backscatter coefficient at supercooled conditions is within a factor of 3 at all three sites. (2) Ice formation was found to be more frequent for cloud layers with cloud top temperatures above -15∘C than indicated by prior lidar-only studies at all sites. A virtual lidar detection threshold of ice water content (IWC) needs to be considered in order to bring radar–lidar-based studies in agreement with lidar-only studies. (3) At similar temperatures, cloud layers which are coupled to the aerosol-laden boundary layer show more intense ice formation than decoupled clouds. (4) Liquid layers formed by gravity waves were found to bias the phase occurrence statistics below -15∘C. By applying a novel gravity wave detection approach using vertical velocity observations within the liquid-dominated cloud top, wave clouds can be classified and excluded from the statistics. After considering boundary layer and gravity wave influences, Punta Arenas shows lower fractions of ice-containing clouds by 0.1 to 0.4 absolute difference at temperatures between −24 and -8∘C. These differences are potentially caused by the contrast in the ice-nucleating particle (INP) reservoir between the different sites.

scholarly journals The Effect of Ice Nuclei Efficiency on Arctic Mixed-Phase Clouds from Large-Eddy Simulations

2017 ◽  
Vol 74 (12) ◽  
pp. 3901-3913 ◽  
Author(s):  
Shizuo Fu ◽  
Huiwen Xue
Keyword(s):  
Simulation Analysis ◽  
Mixed Phase ◽  
Ice Formation ◽  
Microphysics Scheme ◽  
Large Eddy Simulation Model ◽  
Eddy Simulation ◽  
Ice Nuclei ◽  
Large Eddy ◽  
Bin Microphysics ◽  
Mixed Phase Clouds

Abstract The effects of ice nuclei (IN) efficiency on the persistent ice formation in Arctic mixed-phase clouds (AMCs) are investigated using a large-eddy simulation model, coupled to a bin microphysics scheme with a prognostic IN formulation. In the three cases where the IN efficiency is high, ice formation and IN depletion are fast. When the IN concentration is 1 and 10 g−1, IN are completely depleted and the cloud becomes purely liquid phase before the end of the 24-h simulation. When the IN concentration is 100 g−1, the IN supply is sufficient but the liquid water is completely consumed so that the cloud dissipates quickly. In the three cases when the IN efficiency is low, ice formation is negligible in the first several hours but becomes significant as the temperature is decreased through longwave cooling. Before the end of the simulation, the cloud is in mixed phase when the IN concentration is 1 and 10 g−1 but dissipates when the IN concentration is 100 g−1. In the case where two types of IN are considered, ice formation persists throughout the simulation. Analysis shows that as the more efficient IN are continuously removed through ice formation, the less efficient IN gradually nucleate more ice crystals because the longwave cooling decreases the cloud temperature. This mechanism is further illustrated with a simple model. These results indicate that a spectrum of IN efficiency is necessary to maintain the persistent ice formation in AMCs.

scholarly journals Study of the Impact of Ice Formation in Leads upon the Sea Ice Pack Mass Balance Using a New Frazil and Grease Ice Parameterization

2015 ◽  
Vol 45 (8) ◽  
pp. 2025-2047 ◽  
Author(s):  
Alexander V. Wilchinsky ◽  
Harold D. B. S. Heorton ◽  
Daniel L. Feltham ◽  
Paul R. Holland
Keyword(s):  
Sea Ice ◽  
Mass Balance ◽  
Ice Crystals ◽  
The Arctic ◽  
Ice Formation ◽  
Frazil Ice ◽  
Marginal Seas ◽  
Ice Production ◽  
The Impact ◽  
Ice Pack

AbstractLeads are cracks in sea ice that often form because of deformation. During winter months, leads expose the ocean to the cold atmosphere, resulting in supercooling and the formation of frazil ice crystals within the mixed layer. Here the authors investigate the role of frazil ice formation in leads on the mass balance of the sea ice pack through the incorporation of a new module into the Los Alamos sea ice model (CICE). The frazil ice module considers an initial cooling of leads followed by a steady-state formation of uniformly distributed single size frazil ice crystals that precipitate to the ocean surface as grease ice. The grease ice is pushed against one of the lead edges by wind and water drag that the authors represent through a variable collection thickness for new sea ice. Simulations of the sea ice cover in the Arctic and Antarctic are performed and compared to a model that treats leads the same as the open ocean. The processes of ice formation in the new module slow down the refreezing of leads, resulting in a longer period of frazil ice production. The fraction of frazil-derived sea ice increases from 10% to 50%, corresponding better to observations. The new module has higher ice formation rates in areas of high ice concentration and thus has a greater impact within multiyear ice than it does in the marginal seas. The thickness of sea ice in the central Arctic increases by over 0.5 m, whereas within the Antarctic it remains unchanged.

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 Simulation of mixed-phase clouds with the ICON large-eddy model in the complex Arctic environment around Ny-Ålesund

2020 ◽  
Vol 20 (1) ◽  
pp. 475-485 ◽  
Author(s):  
Vera Schemann ◽  
Kerstin Ebell
Keyword(s):  
High Resolution ◽  
General Structure ◽  
Value Added ◽  
Mixed Phase ◽  
The Arctic ◽  
Radiative Energy ◽  
Liquid Water Path ◽  
Substantial Impact ◽  
Large Eddy ◽  
Mixed Phase Clouds

Abstract. Low-level mixed-phase clouds have a substantial impact on the redistribution of radiative energy in the Arctic and are a potential driving factor in Arctic amplification. To better understand the complex processes around mixed-phase clouds, a combination of long-term measurements and high-resolution modeling able to resolve the relevant processes is essential. In this study, we show the general feasibility of the new high-resolution icosahedral nonhydrostatic large-eddy model (ICON-LEM) to capture the general structure, type and timing of mixed-phase clouds at the Arctic site Ny-Ålesund and its potential and limitations for further detailed research. To serve as a basic evaluation, the model is confronted with data streams of single instruments including a microwave radiometer and cloud radar and also with value-added products like the CloudNet classification. The analysis is based on a 11 d long time period with selected periods studied in more detail focusing on the representation of particular cloud processes, such as mixed-phase microphysics. In addition, targeted statistical evaluations against observational data sets are performed to assess (i) how well the vertical structure of the clouds is represented and (ii) how much information is added by higher horizontal resolutions. The results clearly demonstrate the advantage of high resolutions. In particular, with the highest horizontal model resolution of 75 m, the variability of the liquid water path can be well captured. By comparing neighboring grid cells for different subdomains, we also show the potential of the model to provide information on the representativity of single sites (such as Ny-Ålesund) for a larger domain.

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