Improved Convective Parametrization for Precipitation Modeling over the Horn of Africa
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Date
2011-06
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Addis Ababa University
Abstract
The study compared the performance of four di erent cumulus parametrization schemes
in the ICTP's Regional Climate Model RegCM4 for the period 1989-2008 over the
Horn of Africa. The Horn of Africa has been delineated in to 12 homogeneous region
based on clustering method that minimizes a sum of dissimilarities. Grell-FC scheme
best captured the mean climatology. Within the 12 clustered regions positive/negative
precipitation biases are obtained in Emanuel/Grell-AS and Kuo convective schemes
while intermediate values closer to zero are obtained in Grell-FC. Grell-FC scheme
is then selected for customization over the Horn of Africa. To improve the simulation
of rainfall using the selected Grell-FC scheme, several sensitivity experiments
are performed by adjusting the minimum and maximum precipitation e ciency, the
minimum and maximum shear e ect on precipitation e ciency, the minimum and
maximum convective heating and the available buoyant energy removal time scale.
Setting the minimum and maximum shear e ect on precipitation e ciency to 0.10
and 0.30 respectively improve the correlation, which implies a better simulation of
precipitation. Setting the minimum and maximum convective heating to -150 and
400 respectively minimize the positive bias over most of the regions. 17 years long
period run revealed that using the new values of shear e ect on precipitation e ciency
improve the correlation and representation of the inter-annual variability
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Modeling over the Horn of Africa