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State University of New York at Albany (2012)

Analysis of intraseasonal convective variability modes over West Africa during the monsoon season

Ceratto, Jeffrey

Titre : Analysis of intraseasonal convective variability modes over West Africa during the monsoon season

Auteur : Ceratto, Jeffrey

Université de soutenance : State University of New York at Albany

Grade : Master of Science (MS) 2012

Résumé
Intraseasonal variability of rainfall within the West African Monsoon has been shown to be an important factor in the weather of this region. Multiple factors have been found to contribute to variability at this timescale. Mounier, et al (2008) use EOF analysis to uncover and describe a quasi-stationary dipole of precipitation between the West African Monsoon system and the West Atlantic/Caribbean Sea. This mode, termed the Quasi Biweekly Zonal Dipole mode, operates on timescales of roughly 13 days. The stationary nature of this dipole is focused upon in their work, while the role of Kelvin waves in the mode are considered secondary. In this work, the role of Kelvin waves in the dipole mode is considered. Regression analyses are performed with time lags to observe how the dipole evolves with time. Kelvin waves are observed to dominate the timing and the phase of the dipole mode. Dynamical regressions indicate a possible source region for these Kelvin waves, over the South American continent, as well as the effects the Kelvin waves have on the West African Monsoon system as they enter and exit the region. Impacts on the strength of the Saharan Heat Low and on African Easterly Wave activity are observed. A case study highlighting Kelvin wave activity in relation to the QBZD is also considered. The second EOF pattern is also examined with lagged regressions ; a relationship is found between it and the first EOF pattern.

Mots clés : Intraseasonal, West Africa, Monsoon, Atmospheric sciences, Kelvin wave, Meteorology Earth sciences, Sahel

Présentation

Page publiée le 13 février 2015, mise à jour le 12 juillet 2018