Mixed phase boundary layer clouds observed from a tethered balloon platform in the Arctic

Abstract Observations of long-lived mixed-phase Arctic boundary layer clouds on 7 May 1998 during the First International Satellite Cloud Climatology Project (ISCCP) Regional Experiment (FIRE)–Arctic Cloud Experiment (ACE)/Surface Heat Budget of the Arctic Ocean (SHEBA) campaign provide a unique opportunity to test understanding of cloud ice formation. Under the microphysically simple conditions observed (apparently negligible ice aggregation, sublimation, and multiplication), the only expected source of new ice crystals is activation of heterogeneous ice nuclei (IN) and the only sink is sedimentation. Large-eddy simulations with size-resolved microphysics are initialized with IN number concentration NIN measured above cloud top, but details of IN activation behavior are unknown. If activated rapidly (in deposition, condensation, or immersion modes), as commonly assumed, IN are depleted from the well-mixed boundary layer within minutes. Quasi-equilibrium ice number concentration Ni is then limited to a small fraction of overlying NIN that is determined by the cloud-top entrainment rate we divided by the number-weighted ice fall speed at the surface υf. Because wc < 1 cm s−1 and υf > 10 cm s−1, Ni/NIN ≪ 1. Such conditions may be common for this cloud type, which has implications for modeling IN diagnostically, interpreting measurements, and quantifying sensitivity to increasing NIN (when we/υf < 1, entrainment rate limitations serve to buffer cloud system response). To reproduce observed ice crystal size distributions and cloud radar reflectivities with rapidly consumed IN in this case, the measured above-cloud NIN must be multiplied by approximately 30. However, results are sensitive to assumed ice crystal properties not constrained by measurements. In addition, simulations do not reproduce the pronounced mesoscale heterogeneity in radar reflectivity that is observed.

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Intercomparison of cloud model simulations of Arctic mixed-phase boundary layer clouds observed during SHEBA/FIRE-ACE

Journal of Advances in Modeling Earth Systems ◽

10.1029/2011ms000066 ◽

2011 ◽

Vol 3 (2) ◽

pp. n/a-n/a ◽

Cited By ~ 72

Author(s):

Hugh Morrison ◽

Paquita Zuidema ◽

Andrew S Ackerman ◽

Alexander Avramov ◽

Gijs de Boer ◽

...

Keyword(s):

Boundary Layer ◽

Phase Boundary ◽

Cloud Model ◽

Mixed Phase ◽

Model Simulations ◽

Boundary Layer Clouds

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

Monthly Weather Review ◽

10.1175/mwr3154.1 ◽

2006 ◽

Vol 134 (7) ◽

pp. 1880-1900 ◽

Cited By ~ 62

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.

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The Impact of Mixed-Phase Microphysical Processes on the Turbulence in Low-level Clouds in the Arctic

10.5194/egusphere-egu21-13693 ◽

2021 ◽

Author(s):

Jan Chylik ◽

Roel Neggers

Keyword(s):

Boundary Layer ◽

Climate Models ◽

Weather Forecast ◽

Mixed Phase ◽

The Arctic ◽

Contributing Factors ◽

Microphysics Scheme ◽

Low Level ◽

Microphysical Processes ◽

The Impact

The proper representation of Arctic mixed-phased clouds remains a challenge in both weather forecast and climate models. Amongst the contributing factors is the complexity of turbulent properties of clouds. While the effect of evaporating hydrometeors on turbulent properties of the boundary layer has been identified in other latitudes, the extent of similar studies in the Arctic has been so far limited.Our study focus on the impact of heat release from mixed-phase microphysical processes on the turbulent properties of the convective low-level clouds in the Arctic. We &#160;employ high-resolution simulations, properly constrained by relevant measurements. Semi-idealised model cases are based on convective clouds observed during the recent campaign in the Arctic: ACLOUD, which took place May--June 2017 over Fram Strait. The simulations are performed in Dutch Atmospheric Large Eddy Simulation (DALES) with double-moment mixed-phase microphysics scheme of Seifert & Beheng.The results indicate an enhancement of boundary layer turbulence is some convective regimes. Furthermore, results are sensitive to aerosols concentrations. Additional implications for the role of mixed-phase clouds in the Arctic Amplification will be discussed.

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Midwinter Arctic leads form and dissipate low clouds

Nature Communications ◽

10.1038/s41467-019-14074-5 ◽

2020 ◽

Vol 11 (1) ◽

Cited By ~ 1

Author(s):

Xia Li ◽

Steven K. Krueger ◽

Courtenay Strong ◽

Gerald G. Mace ◽

Sally Benson

Keyword(s):

Boundary Layer ◽

Heat Flux ◽

Sensible Heat Flux ◽

Three Dimensional ◽

The Arctic ◽

Substantial Contribution ◽

Boundary Layer Clouds ◽

Low Clouds ◽

Arctic Ice ◽

High Lead

AbstractLeads are a key feature of the Arctic ice pack during the winter owing to their substantial contribution to the surface energy balance. According to the present understanding, enhanced heat and moisture fluxes from high lead concentrations tend to produce more boundary layer clouds. However, described here in our composite analyses of diverse surface- and satellite-based observations, we find that abundant boundary layer clouds are associated with low lead flux periods, while fewer boundary layer clouds are observed for high lead flux periods. Motivated by these counterintuitive results, we conducted three-dimensional cloud-resolving simulations to investigate the underlying physics. We find that newly frozen leads with large sensible heat flux but low latent heat flux tend to dissipate low clouds. This finding indicates that the observed high lead fractions likely consist of mostly newly frozen leads that reduce any pre-existing low-level cloudiness, which in turn decreases downwelling infrared flux and accelerates the freezing of sea ice.

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