(Pohl and
Camberlin 2011) indicated that both inter-annual variability and intraseasonal variability
over equatorial East Africa are strongly controlled by zonal wind shear (the difference between 850 hPa and 150 hPa winds)
over the central equatorial Indian Ocean. They concluded that it holds for all
seasons except boreal summer when the
winds at both levels are relatively constant. They also found out that the
shear is more closely correlated with ENSO than with the IOZM in all seasons except
boreal summer.

 (Gong et al., 2016) analyzed the inter-annual linkage between
the boreal winter Arctic Oscillation (AO) and East African early short rains.
When the Indian Ocean Dipole and El Nino/ Southern Oscillation variance were
excluded by linear regression, the boreal winter AO index was significantly correlated
with the October East African precipitation, whereby the upper ocean heat
content likely acts as a medium that links the AO and East African
precipitation. It was also concluded that there was a significant inter-annual
relationship between East African early short rains and boreal winter Arctic
Oscillation which induces anomalous wind stress curl in the tropical Indian Ocean and generates oceanic
Rossby waves, whereby the d own welling Rossby waves lead to anomalous upper
ocean heat content which enhance precipitation over East Africa in October.

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In general,
precipitation events during the long rains (MAM) season tends to be heavier and
longer in duration, with less inter-annual variability, and are more likely
associated with local factors. In contrast, precipitation events during the
short rains (SON) season are less intense with shorter duration and stronger
intra-seasonal and inter-annual variability that mirrors large-scale phenomena
such as ElNino-Southern Oscillation (ENSO) and the varying intensity of the
zonal circulation cell along the equatorial Indian Ocean (Chan et al.,
2008) and citations there in.

In this study
the main objective is to investigate the variation
of precipitation in East Africa during the SON season and the major effects
from the North Atlantic Oscillation, which has not been undertaken before save
for (Shilenje et al., 2015) with a study to investigate the relationship
between the North Atlantic Ocean Oscillation Index (NAOI) and October –December
(OND) rainfall variability over Kenya, and found out that the correlation
between NAOI and OND rainfall over Kenya is generally low and highly variable
in space ranging from negative to positive correlation. The results show that a
very small area in the western part of Kenya exhibits a significant correlation
between NAOI and OND rainfall.

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