Alexandria Digital Research Library

The South Atlantic Coupled Variability and the South Atlantic Convergence Zone

Author:
Bombardi, Rodrigo Jose
Degree Grantor:
University of California, Santa Barbara. Geography
Degree Supervisor:
Leila MV Carvalho
Place of Publication:
[Santa Barbara, Calif.]
Publisher:
University of California, Santa Barbara
Creation Date:
2013
Issued Date:
2013
Topics:
Atmospheric Sciences and Meteorology
Keywords:
SST
South America
ENSO
Cyclones
South Atlantic Dipole
Precipitation
Genres:
Dissertations, Academic and Online resources
Dissertation:
Ph.D.--University of California, Santa Barbara, 2013
Description:

The dominant mode of coupled variability over the South Atlantic Ocean is known as "South Atlantic Dipole" (SAD) and is characterized by a dipole in sea surface temperature (SST) anomalies with centers over the tropical and the extratropical South Atlantic. Previous studies have shown that variations in SST related to SAD modulate large-scale patterns of precipitation over the Atlantic Ocean. Here we show that variations in the South Atlantic SST are associated with changes in daily precipitation over eastern South America. This study is based on observational and regional atmospheric modeling. Rain gauge precipitation, satellite derived sea surface temperature and reanalysis data are used to investigate the variability of the subtropical and tropical South Atlantic and impacts on precipitation. SAD phases are assessed by performing Singular Value Decomposition (SVD) analysis of sea level pressure and SST anomalies.

We show that during neutral El Nino-Southern Oscillation (ENSO) events, SAD plays an important role in modulating cyclogenesis and the characteristics of the South Atlantic Convergence Zone (SACZ). Positive SST anomalies over the extratropical South Atlantic (SAD negative phase) are related to increased cyclogenesis near southeast Brazil as well as the migration of extratropical cyclones further north. As a consequence, these systems organize convection and increase precipitation over eastern South America. Numerical experiments forced with prescribed SST anomalies showed that even though the Atlantic SST affects the position of the cyclone associated with the SACZ, the atmospheric response and precipitation patters over land were opposite from the observational results.

On the other hand, experiments forced with prescribed anomalous driving fields showed that the atmospheric component of SAD plays a significant role for the right position and intensity of precipitation associated with the SACZ. SAD negative anomalies provide the low-level and upper-level atmospheric support for the intensification of the cyclone at surface and for the increase in precipitation over the land portion of the SACZ. Therefore, the numerical experiments suggest that, during ENSO neutral conditions, the SACZ precipitation variability associated with SAD is largely dependent on the atmospheric variability rather than the underlying SST.

Physical Description:
1 online resource (125 pages)
Format:
Text
Collection(s):
UCSB electronic theses and dissertations
ARK:
ark:/48907/f3j38qh7
ISBN:
9781303537721
Catalog System Number:
990040924130203776
Rights:
Inc.icon only.dark In Copyright
Copyright Holder:
Rodrigo Bombardi
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