Accession Number:

ADA355487

Title:

Global and Local Circulations Associated with South American Summer Precipitation

Descriptive Note:

Master's thesis

Corporate Author:

UTAH UNIV SALT LAKE CITY DEPT OF METEOROLOGY

Personal Author(s):

Report Date:

1998-06-01

Pagination or Media Count:

169.0

Abstract:

Precipitation regimes over South America involving variations of one to two weeks are documented using 15 years of gridded data, 20 years of outgoing longwave radiation OLR measurements obtained from satellites and 6 years of cloud data from the International Satellite Cloud Climatology Project ISCCP. The gridded data were produced by an assimilation system from the European Center for Medium-range Weather Forecasts ECMWF. Comparisons of assimilated OLR fields with those obtained from satellite observations show model skill in reproducing tropical patterns of convection. The 6-month atmospheric evolution of the austral summer is discussed, based on the ECMWF reanalysis, with a focus on circulations over South America. The South Atlantic Convergence Zone SACZ is a typical feature of summer convection over South America, and it appears well-described by the gridded data. Fourteen-year averages are used to define the seasonal evolution every 2 weeks, and averages are removed from individual times to define anomalies. Previous research has shown the existence of a meridional seesaw of alternating wet and dry events over tropical and subtropical South America. This investigation focuses on 2-week modulations of the SACZ with the goal of ascertaining the dependence of precipitation regimes over South America on convection over the Central Pacific Ocean. This is accomplished using empirical orthogonal function analyses of filtered OLR anomalies confined to two regions one includes the South Pacific Convergence Zone SPCZ, extending from the dateline eastward to 20 E the other extends from 100 W to 0 W, including South America and the SACZ. Four convective patterns are identified those with an enhancedsuppressed SACZ with a well-defined SPCZ referred to as with SPCZ, and those with an enhancedsuppressed SACZ without a clear composite signature in the SPCZ SACZ only.

Subject Categories:

  • Meteorology

Distribution Statement:

APPROVED FOR PUBLIC RELEASE