[Eoas-seminar] Monday, July 10th, 11:00AM - Meteorology Master's Defense - Thomas Vaughan - 353 LOV

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Fri Jul 7 15:25:06 EDT 2017

Meteorology Seminar

Thomas Vaughan

M.S. Meteorology Candidate

Title:  “An Examination of El Niño and La Niña Teleconnections to Sahel and Guinea Coast Rainfall in the Context of the 1968 Rainfall Regime Change.”

Major Professor:  Dr. Sharon Nicholson
Date:   Monday, July 10th                  Time: 11:00 AM

Location: Werner A. Baum Seminar Room (353 Love Building)
(Please join us for refreshments served outside room 353 Love @ 10:30 AM)


The Sahel and Guinea Coast regions of Africa have long been the subject of studies on interannual and intraseasonal rainfall variability. The unique geography, monsoon circulation regime, and a variety of climatic teleconnections produce large variations in year-to-year rainfall across the region. These large fluctuations in rainfall can have devastating effects on the inhabitants of West Africa, who rely on the rainfall for both agriculture and human consumption. Thus, a better understanding of the nature of rainfall variability in the area is warranted.

The El Niño/Southern Oscillation (ENSO), one of the most studied climate phenomena, is known to have far-reaching impacts on weather across the globe. This study provides one of the most comprehensive and complete analyses of the relationship between ENSO and rainfall across the Sahel and Guinea Coast to date. Several previous studies have found little connection between Sahel rainfall and ENSO phase, while others have suggested that ENSO can result in changes within the monsoon circulation and cause a reduction in Sahel rainfall during El Niño years. By utilizing the largest and longest dataset of rainfall gauge data available, this study provides an analysis of rainfall anomalies experienced during El Niño and La Niña years from 1921-2012 in the context of a major shift in the rainfall regime that occurred around the year 1968.

This research finds that before 1968, rainfall during the peak Sahel rainy season in El Niño years was below normal, but above normal in the Guinea Coast. The same is observed after 1968, but the anomalies are of stronger magnitude than before 1968, suggesting an increased ENSO-Sahel rainfall teleconnection after 1968. Similar intensifications of the El Niño signal are observed in other seasons as well. In general, opposite rainfall anomalies were observed during La Niña years when compared to El Niño years. An increase in La Niña influence in more recent years is also detected. An analysis of the consistency of the ENSO signal suggests that the ENSO rainfall response is most consistent in areas of the Sahel during the JAS (-1), OND (-1), JAS, and OND seasons. Evidence also suggests that there was a weakening of the Sahel/Guinea Coast dipole after 1968. Finally, an analysis of upper air circulations shows few differences in zonal winds during El Niño and La Niña years versus non-ENSO years, suggesting the relationship between ENSO and Sahel rainfall may be fairly weak. There are some subtle differences seen, however, when comparing years before 1968 to years afterwards that were consistent with the observed rainfall anomalies in certain seasons.

This study concludes that the rainfall response to El Niño and La Niña events in the Sahel and Guinea Coast as a whole is relatively inconsistent, but there was some meaningful connection found between ENSO and rainfall in the Sahel during certain seasons outlined above. This relationship intensified after the 1968 rainfall regime change, consistent with findings from previous studies.

Paige Phillips

Academic Program Specialist - Meteorology  I  Earth, Ocean, & Atmospheric Science (EOAS)  I  Florida State University  I  410 Love Building  I  1017 Academic Way, Tallahassee, Florida 32306  I  (850) 644-8582  I  www.eoas.fsu.edu
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