Flying into the Cold: First Results from the NSF Cold-Air outbreak Experiment in the Sub-ARctic (CAESAR)

Le résumé fourni par la source

Abstract The National Science Foundation-sponsored Cold-Air outbreak Experiment over the Sub-Arctic Region (CAESAR) is motivated by hypotheses in how dynamical, aerosol and cloud microphysical processes influence cold-air outbreak development and the accompanying spatial organization of clouds and precipitation, including in polar lows. CAESAR characterized the aerosol, thermodynamic and dynamic environment occupied by mixed-phase clouds within air masses moving southward off the Arctic sea ice over the Greenland/Norwegian Seas in the spring of 2024. The aircraft campaign supported a suite of remote sensing and in situ measurements below, within and above the mostly shallow convective clouds. Three flights reached the Greenland Marginal Ice Zone. A golden-case cold-air outbreak, sampled from its origin in clear skies over 100% sea ice, revealed a boundary layer containing anthropogenically-modified air, with the first-detected in situ cloud particles being ice polycrystals, within -25 °C air. Two flights sampled polar lows, and another flight characterized a closed-to-open cell transition occurring under high aerosol loading originating from Siberia and strong surface fluxes. The transition occurred after drizzle-sized drops developed within a boundary layer deepening under a weakening inversion. Combined ice particle and ice nucleating particle concentrations suggest most ice production is primary at cloud temperatures < -20 °C, with secondary ice production evident at cloud temperatures > -20 °C. Overall these first observations already reveal a diversity of CAO cloud structures.

Ce résumé expose les affirmations des auteurs. BNTIC ne l’interprète pas comme une validation indépendante des résultats.