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State University of New York at Albany (2015)

Modulation of East African Precipitation by the Indian Ocean Dipole (IOD) and ENSO

Shaaban, Ahmed A

Titre : Modulation of East African Precipitation by the Indian Ocean Dipole (IOD) and ENSO

Auteur : Shaaban, Ahmed A

Université de soutenance : State University of New York at Albany

Grade : Master of Science (MS) 2015

Résumé
Tropical East Africa is influenced by two main rainy seasons, during autumn and spring. During autumn, tropical East African precipitation is clearly influenced by Indian Ocean Dipole (IOD) and/or ENSO. During spring, there is no clear SST pattern in the Indian Ocean. The association between El Niño and positive IOD phases is much stronger than the association between La Niña and negative IOD during October and November. During October, the association between El Niño and wet condition over tropical eastern Africa is stronger than association between La Niña and dry conditions. During November, the association between positive IOD and eastern African precipitation is stronger than the association between La Niña and dry conditions. During short wet phases (such as autumn) over eastern Africa, two anticyclones form in the lower troposphere with upper baroclinic structure. These anticyclones decay rapidly by December. These anticyclones are responsible for supplying East Africa with increased moisture. Most strong positive IOD events are associated with wet outcomes over eastern Africa. Not all strong El Niño events lead to wet outcomes. It is well known that during northern spring, precipitation over eastern Africa is not connected to any inter-annual SST modes of variability. During northern spring, SST in Indian Ocean is nearly always sufficiently high to sustain convection, however, convection is not always active. We found that precipitation over eastern Africa during spring is associated with a dipole pattern of outgoing longwave radiation anomaly (OLRA) not associated with SST variability.

Mots clés : Atmospheric sciences, Earth sciences

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Page publiée le 24 octobre 2015, mise à jour le 23 décembre 2017