TITLE:
The Response of Geopotential Height Anomalies to El Niño and La Niña Conditions and Their Implications to Seasonal Rainfall Variability over the Horn of Africa
AUTHORS:
Solomon Gunta, Hejamady Gangadhara Bhat, Busnur Rachotappa Manjunatha
KEYWORDS:
Geopotential Height, Composite Analysis, ENSO, Atmospheric Circulations, NCEP Reanalysis, Tropical SST Anomalies, Teleconnections, Belg, Kiremt
JOURNAL NAME:
Atmospheric and Climate Sciences,
Vol.12 No.2,
April
28,
2022
ABSTRACT:
In this study, we unveil
atmospheric circulation anomalies associated with the
large-scale tropical teleconnections using National Center for Environmental Prediction
(NCEP) reanalysis dataset. Composite analyses have been performed to know the
impact of large-scale tropical circulations on the Horn of Africa. The
composite analysis performed at the geopotential height of 850 Mb and 200 Mb,
and precipitation rate (mm/day) during six strong El Niño and La Niña episodes revealed that the large-scale tropical
variability induced climate anomalies in space and time. A substantial decrease in
upper-level height (200 Mb) has been observed in the study area during El Niño
composite years as compared to the La Niña years. During El Niño conditions,
the upper-level divergence initiates low-level vertical motion, thereby
enhancing convection, however, during La Niña composite years, nearly
contrasting situations are noticed in Belg (February to May) season in
Ethiopia. However, geopotential height anomalies at 850 Mb are above-normal
during the strong El Niño years, suggesting suppressed convection due to
vertical shrinking and enhancement of divergence at the lower level. Compared
to the Belg (February to May), geopotential anomalies were generally positive
during the Kiremt (June to September) season, thereby suppressing the rainfall,
particularly in Southern Ethiopia and Northern Part of Kenya. In contrast, an
increase in rainfall was observed during the Belg season (February to May).