Microphysics and mesoscale dynamics of marine boundary-layer clouds in cold air over open water

Abstract:

The Arctic is arguably the region on planet Earth that is warming the most rapidly, with rapid sea ice loss and warming air temperatures reinforcing each other. Decreasing ice cover implies potentially more hazardous Arctic winter weather effects upon coastal communities and local transportation. A key question is how the high-latitude changes in both hemispheres connect to those in the mid-latitude and the global climate system. One particularly poorly-understood regime is that of cold-air-outbreaks. Outbreaks of cold air streaming over open ocean water encourage strong surface fluxes of moisture and heat, supporting shallow, but highly convective clouds. These occasionally spawn intense ``polar lows”, and both are difficult to forecast. Cold-air outbreaks have an significant impact on the global energy and water cycles, including the ocean circulation. Despite the impacts on weather and climate, cold-air-outbreaks remain difficult to model. This is in part because of the range of scales involved, with this cloud regime occupying a ‘grey-zone’ where typical weather or climate models fail to capture or parameterize the relevant cloud and dynamical processes. In addition, little is known about the cloud properties, their rain and snowfall amounts, the accompanying boundary layer structure and circulations, interactions with meteorology, and surface fluxes. Very little is known about these clouds. Recently several field campaigns have explored cold-air outbreaks over the marine BL: DOE ARM conducted the MARCUS campaign over the Southern Ocean, and the COMBLE campaign on the edge of the Norwegian Sea, and an airborne field campaign - CAESAR - is planned for early 22 to gather the necessary measurements with which to support modeling improvements of this mysterious cloud regime. Here, some key findings are summarized based on observations in MARCUS and COMBLE.