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University of Tokyo (2014)

Decadal Shifts and their Impact on Climate of East and Southern Africa

Desmond, Manatsa

Titre : Decadal Shifts and their Impact on Climate of East and Southern Africa

Auteur : Desmond, Manatsa

Université de soutenance : University of Tokyo

Grade : Doctoral Thesis 2014

Présentation The low frequency modulation of the interannual variability of East African rainfall and the surface air temperature (SAT) of southern Africa for the October to December period is statistically explored. Observations and reanalysis data dating from the late 19th to the early 20th century are used in this study. It is revealed that there exist three statistically significant shifts in the years 1917, 1961 and 1997 in the Indian Ocean basin manifesting not only in the Indian Ocean Dipole (IOD)’s temporal characteristics but also the Mascarene High (MH)’s equatorward and eastward epochal displacement of the northern and eastern ridges respectively. Hence by virtue of the dominant portion of the climate variability of East and southern Africa being controlled by circulation patterns originating from the Indian Ocean basin, this phenomenon is seen to be translated as abrupt changes in the climate of East and southern Africa. It is intriguing to note the close similarities in the shift development during each of these three shifts. The occurrence of the shift appears to be initiated when a moderate negative IOD event intensifies to an extreme negative IOD event in the succeeding year but reverses to a positive extreme IOD event in the subsequent year (the shift year). The last two extreme IOD events reach record breaking magnitudes during their respective occurrence since 1900. This implies epochal intensification of the shift process as the occurrences progress towards the end of the 20th century. The observation that this three year shift process is unique within the entire IOD time series used from 1870, irrespective of the sea surface temperature dataset used, entails that the identification of a similar phenomenon in the future may imply a new existence of a basinwide shift. The fortunate aspect is that this conclusion can be reached with some reasonable degree of confidence even before data will have accumulated long enough to confirm the occurrence as a statistically significant shift in the Indian Ocean basin.

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