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

F. Tornow, A. S. Ackerman, A. M. Fridlind, B. Cairns, E. C. Crosbie, S. Kirschler, R. H. Moore, D. Painemal, C. E. Robinson, C. Seethala, M. A. Shook, C. Voigt, E. L. Winstead, L. D. Ziemba, P. Zuidema, A. Sorooshian

Research output: Contribution to journalArticlepeer-review

Abstract

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.

Original languageEnglish (US)
Article numbere2022GL098444
JournalGeophysical Research Letters
Volume49
Issue number11
DOIs
StatePublished - Jun 16 2022

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)

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