Potential evaporation (Ep) and actual evapotranspiration (E A ) values for 84 East Africanstations were estimated and mapped using Morton [12, 13,14] model. The data used in the study were tong term averages up to and including 1974.The Ep and EA distributions for the months of January, April, and July and October; and annual are discussed. High Ep values exist in the semi-arid/arid areas of northern and northeastern Kenya and central Tanzania. Low Ep values dominate on the highland areas. High EA values are observed over the East African rainfall favoured and thickly vegetated areas whereas the lowest EA values are predominantly observed during all months in semi-arid/arid areas. Both Ep and EA values show a good agreement with. the north/south movement of the rain belts across East Africa. Zusammenfassung Werte der Verdunstung in Ost-AfrikaEs werden ftir 84 Stationen in Ost-Afrika nach der Methode yon Morton [12, 13,14] die Werte der potentiellen Verdunstung Ep und der aktuellen Evapotranspiration EA bestimmt und ihre Verteitungen in Kartendarstellungen wiedergegeben. Als Beobachtungsdaten wurden langzeitige Mittelwerte bis einschlieNich 1974 verwendet. Die Verteilung yon Ep und EA wird fiir die Monate Januar, April, Juli, Oktober und ftir das Jahr besprochen. Hohe Ep-Werte kommen in den semiariden und ariden Gebieten von Nord-und Nordost-Kenya und yon Zentral-Tanzania vor. Niedrige Ep-Werte sind in Hochlandgebieten vorherrschend. Hohe EA -Werte werden in Ost-Afrika in den von Regen be~stigten und dicht mit Vegetation bewachsenen Gebieten beobachtet, w~ihrend die niedrigsten EA -Werte vorwiegend in allen Monaten in semiariden und ariden Gebieten festgestellt werden. Die Epund EA-Werte zeigen eine gute Obereinstimmung mit der Nord-Stid-Verlagerung der Regengiirtel tiber Ost-Afrika.

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SummaryIn this study an iterative initialization scheme suitable for tropical regions is designed, tested and used as an initialization vehicle in an experiment involving real tropical data. The model equations for the initialization scheme are the so called shallow water equations bounded by rigid walls at the north and south boundaries. The advective terms of the model equations are evaluated using the quasi-lagrangian scheme. This advective scheme was modified following Kanamitsu [18] so as to prevent the occurrence of the so called two grid distance waves. Time differencing scheme in the time integration (10 time steps forward ans 10 time steps backward) of the model equations is the Euler-backward type. The initialization scheme is found to conserve mean total energy, mean potential vorticity and mean square potential vorticity following an air parcel. The designed initialization scheme was used in an initialization experiment involving real tropical wind data. In this experiment, we started with observed wind field (rotational plus irrotational component) and the geopotential computed from non linear balance equation. The results from this experiment show that the initially imbalanced motion and mass fields tend to settle down to some form of balance during the initialization process. It is further noted that the "initialized" motion fields have more organized streamline pattern than the original wind field. Also, the streamline patterns shown that the difference between the initialized and original motion fields is small. This is desirable for any initialization scheme. Zusammenfassung

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