A revised conceptual model of the tropical marine boundary layer. Part I: Statistical characterization of the variability inherent in the wintertime trade wind regime over the Western Tropical Atlantic

Jennifer L. Davison, Robert M. Rauber, Larry Di Girolamo, Margaret A. Lemone

Research output: Contribution to journalArticlepeer-review

Abstract

This paper investigates wintertime tropicalmarine boundary layer (TMBL) statistical characteristics over the western North Atlantic using the complete set of island-launched soundings fromthe Rain in Cumulus over the Ocean (RICO) experiment. The soundings are subdivided into undisturbed and disturbed classifications using two discriminators: 1) dates chosen by Global Energy and Water Cycle Experiment (GEWEX) Cloud System Studies (GCSS) investigators to construct the mean RICO sounding and 2) daily average rain rates. A wide range of relative humidity (RH) values was observed between the surface and 8.0 km. At 2.0 km, half theRHvalues were within 56%-89%; at 4.0 km, half were within 13%-61%. The rain-ratemethod of separating disturbed and undisturbed soundings appears more meaningful than the GCSS method. The median RH for disturbed conditions using the rain-rate method showed moister conditions from the surface to 8.0km, with maximumRHdifferences of 30%-40%.Moist air generally extended higher on disturbed than undisturbed days. Based on equivalent potential temperature, wind direction, and RH analyses, the most common altitude marking the TMBL top was about 4.0 km. Temperature inversions (over both 50-and 350-m intervals) were observed at every altitude above 1.2 km; there were no dominant inversion heights and most of the inversions were weak. Wind direction analyses indicated that winds within the TMBL originated from more tropical latitudes on disturbed days. The analyses herein suggest that the RICO profile used to initialize many model simulations of this environment represents only a small subset of the broad range of possible conditions characterizing thewintertime trades.

Original languageEnglish (US)
Pages (from-to)3005-3024
Number of pages20
JournalJournal of the Atmospheric Sciences
Volume70
Issue number10
DOIs
StatePublished - Oct 24 2013

ASJC Scopus subject areas

  • Atmospheric Science

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