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The Impact of Sea Surface Temperature Anomalies on the Rainfall over Northeast Brazil

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  • 1 Department of Atmospheric Sciences, University of California, Los Angeles, Los Angeles. California
  • | 2 Department of Meteorology. Texas A&M University, College Station, Texas
  • | 3 Department of Atmospheric Sciences, University of California, Los Angeles, Los Angeles, California
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Abstract

The response of the tropical atmosphere to the sea surface temperature (SST) anomalies in the Northern Hemisphere spring of 1984 is investigated. The methodology for investigation consists of comparing simulations with and without the global distribution of SST anomalies in the boundary conditions of the UCLA General Circulation Model (GCM). At low levels, the response includes weaker southeast trade winds over the Atlantic, increased precipitation off the northeast coast of Brazil, and reduced precipitation west of this region. The increased precipitation is due to enhanced convergence of moisture advected by the southeast trade winds, although the trades themselves are weaker. The results for the western equatorial Atlantic am in apparent agreement with the observed anomalous southern migration of the ITCZ in years with warm SST anomalies in the southern tropical Atlantic. There are strong anomalous trade winds over the Pacific extending east of the date line and weak wind anomalies over the maritime continent, in broad agreement with the observed.

The sensitivity of the simulated atmospheric response over an ocean basin to using the SST anomalies confined to the basin or in the global ocean is analyzed. It is found that there can be notable local differences in the results obtained using those procedures. In particular, the simulation with the SST anomalies confined to the Pacific shows weak anomalous trade winds over the western part of this ocean basin and strong westerly anomalies over the maritime continent unlike that with the anomalies in the global ocean.

Abstract

The response of the tropical atmosphere to the sea surface temperature (SST) anomalies in the Northern Hemisphere spring of 1984 is investigated. The methodology for investigation consists of comparing simulations with and without the global distribution of SST anomalies in the boundary conditions of the UCLA General Circulation Model (GCM). At low levels, the response includes weaker southeast trade winds over the Atlantic, increased precipitation off the northeast coast of Brazil, and reduced precipitation west of this region. The increased precipitation is due to enhanced convergence of moisture advected by the southeast trade winds, although the trades themselves are weaker. The results for the western equatorial Atlantic am in apparent agreement with the observed anomalous southern migration of the ITCZ in years with warm SST anomalies in the southern tropical Atlantic. There are strong anomalous trade winds over the Pacific extending east of the date line and weak wind anomalies over the maritime continent, in broad agreement with the observed.

The sensitivity of the simulated atmospheric response over an ocean basin to using the SST anomalies confined to the basin or in the global ocean is analyzed. It is found that there can be notable local differences in the results obtained using those procedures. In particular, the simulation with the SST anomalies confined to the Pacific shows weak anomalous trade winds over the western part of this ocean basin and strong westerly anomalies over the maritime continent unlike that with the anomalies in the global ocean.

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