On trade wind cumulus cold pools

Paquita Zuidema, Zhujun Li, Reginald J. Hill, Ludovic Bariteau, Bob Rilling, Chris Fairall, W. Alan Brewer, Bruce Albrecht, Jeff Hare

Research output: Contribution to journalArticle

66 Scopus citations

Abstract

Shallow precipitating cumuli within the easterly trades were investigated using shipboard measurements, scanning radar data, and visible satellite imagery from 2 weeks in January 2005 of the Rain in Cumulus over the Ocean (RICO) experiment. Shipboard rainfall rates of up to 2 mm h -1 were recorded almost daily, if only for 10-30 min typically, almost always from clouds within mesoscale arcs. The precipitating cumuli, capable of reaching above 4 km, cooled surface air by 1-2 K, in all cases lowered surface specific humidities by up to 1.5 g kg -1, reduced surface equivalent potential temperatures by up to 6 K, and were often associatedwith shortlived increases in wind speed. Upper-level downdrafts were inferred to explain double-lobed moisture and temperature sounding profiles, as well as multiple inversions in wind profiler data. In two cases investigated further, the precipitating convection propagated fasterwestward than themean surfacewind by about 2-3 m s -1, consistentwith a density current of depth~200 m. In their cold pool recovery zones, the surface air temperatures equilibrated with time to the sea surface temperatures, but the surface air specific humidities stayed relatively constant after initial quick recoveries. This suggested that entrainment of drier air fromabove fully compensated themoistening fromsurface latent heat fluxes. Recovery zone surfacewind speeds and latent heat fluxeswere not higher than environmental values. Nonprecipitating clouds developed after the surface buoyancy had recovered (barring encroachment of other convection). The mesoscale arcs favored atmospheres with higher water vapor paths. These observations differed from those of stratocumulus and deep tropical cumulus cold pools.

Original languageEnglish (US)
Pages (from-to)258-280
Number of pages23
JournalJournal of the Atmospheric Sciences
Volume69
Issue number1
DOIs
StatePublished - Jan 1 2012

Keywords

  • Atmosphere-ocean interaction
  • Boundary layer
  • Cumulus clouds
  • Instrumentation/sensors
  • Mesoscale processes
  • Small scale processes

ASJC Scopus subject areas

  • Atmospheric Science

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    Zuidema, P., Li, Z., Hill, R. J., Bariteau, L., Rilling, B., Fairall, C., Brewer, W. A., Albrecht, B., & Hare, J. (2012). On trade wind cumulus cold pools. Journal of the Atmospheric Sciences, 69(1), 258-280. https://doi.org/10.1175/JAS-D-11-0143.1