Dilution of Boundary Layer Cloud Condensation Nucleus Concentrations by Free Tropospheric Entrainment During Marine Cold Air Outbreaks

Recent aircraft measurements over the northwest Atlantic enable an investigation of how entrainment from the free troposphere (FT) impacts cloud condensation nucleus (CCN) concentrations in the marine boundary layer (MBL) during cold-air outbreaks (CAOs), motivated by the role of CCN in mediating tr...

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Bibliographic Details
Published in:	Geophysical research letters Vol. 49; no. 11
Main Authors:	Tornow, F, Ackerman, A S, Fridlind, A M, Cairns, B, Crosbie, E C, Kirschler, S, Moore, R H, Painemal, D, Robinson, C E, Seethala, C, Shook, M A, Volgt, C, Winstead, E L, Ziemba, L D, Zuidema, P, Sorooshian, A
Format:	Journal Article
Language:	English
Published:	Goddard Space Flight Center American Geophysical Union 16-06-2022 John Wiley & Sons, Inc
Subjects:	Aerosols Air Air entrainment Aircraft Albedo Boundary layers Brightness Budgets Cloud albedo Cloud condensation nuclei Cloud droplet concentration Cloud droplets Clouds Coalescence Cold Cold air outbreaks Cold flow Condensation Condensation nuclei Dilution Droplets Dry intrusions Entrainment Flight Hydrometeors Meteorology And Climatology Nucleus Outbreaks Rain formation Remote sensing Satellite observation Satellites Surface fluxes Troposphere Boundary Layer Cloud Condensation Nucleus Concentrations
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Summary:	Recent aircraft measurements over the northwest Atlantic enable an investigation of how entrainment from the free troposphere (FT) impacts cloud condensation nucleus (CCN) concentrations in the marine boundary layer (MBL) during cold-air outbreaks (CAOs), motivated by the role of CCN in mediating transitions from closed to open-cell regimes. Observations compiled over eight flights indicate predominantly far lesser CCN concentrations in the FT than in the MBL. For one flight, a fetch-dependent MBL-mean CCN budget is compiled from estimates of sea-surface fluxes, entrainment of FT air, and hydrometeor collision-coalescence, based on in-situ and remote-sensing measurements. Results indicate a dominant role of FT entrainment in reducing MBL CCN concentrations, consistent with satellite-observed trends in droplet number concentration upwind of CAO cloud-regime transitions over the northwest Atlantic. Relatively scant CCN may widely be associated with FT dry intrusions, and should accelerate cloud-regime transitions where underlying MBL air is CCN-rich, thereby reducing regional albedo.
Bibliography:	GSFC Goddard Space Flight Center
ISSN:	0094-8276 1944-8007
DOI:	10.1029/2022GL098444