Trajectory analysis shows that the COMBLE COA air mass sources to be in the Central Arctic.
The Arctic air typically flows from the sea ice in Fram Strait and to the east of Greenland over the Greenland and Norwegian Seas, and can reach SSTs of 6 C within 15 h.
As the sea ice edge retreats due to warming of the Arctic, such COAs will become more extensive.
Ground-based vertically pointing cloud radar observations made during COMBLE on the coast of Norway show that the associated convective cloud tops often reach altitudes of 4 km and sometimes exceed 5 km.
MODIS visible imagery and CloudSat radar profiles show that
the clouds associated with these COAs evolve from closed cell, shallow stratocumulus near the sea ice edge to open cell, deep mesoscale convective clouds near the Norwegian coast.
Our scientific objectives are to (1) increase our understanding of how microphysical processes determine macrophysical cloud properties of marine CAOs, (2) document and understand the life cycle of the large, deep, and long-lived mesoscale cells observed in COMBLE CAOs which appear to be a result of a new type of convective aggregation.
We will perform and analyze high-resolution Lagrangian simulations based on observed trajectories, and with a variety of microphysical schemes.
The marine cold air outbreak (CAO) cloud systems in this region are
strongly forced, widespread, and long-lasting, with rather simple boundary and initial conditions, and are remarkably repeatable, (but with interesting variations from case to case). In other words, the COMBLE CAO events effectively provide an atmospheric laboratory. This is beneficial for both purely observational analyses of COMBLE CAO cases, and for using simulations to learn more about CAO macro- and microphysical processes.
Because of the dominant sensitivity of simulations of marine CAO clouds to mixed-phase microphysics parameterization assumptions, rather than to the large-scale forcing or high-resolution model dynamics, the repeatability of CAO events means that the conclusions drawn from observations and simulations will be more precise than would be possible from a single case study.
The graphic displays measurements from the ARM Mobile Facility during a COA on March 28, 2020, 06 to 07 UTC. Top panel: KAZR (Ka-band vertically pointing cloud radar) equivalent reflectivity (Ze) and the Cloud Base Best-estimate (CBBE, white) and “first radar top” (black), top height of lowest significant detection layer. Second panel: Hydrometeor particles detected at the surface by laser disdrometer. Third panel: LWP retrieved by MWR (microwave radiometer). Bottom panel: KAZR Doppler vertical velocity. The labels a, b, c, and d in the graphic indicate various cloud processes: At (a), convective updrafts are associated with liquid water in the column and low Ze. At (b), convective downdrafts are associated with snowfall at the surface and high Ze. At (c), moderate Ze, high CBBE, and weak updrafts above downdrafts suggest elevated convection. At (d), an elevated, low Ze cloud layer with a well-defined base, and little air motion, consists of small hydrometeors.
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