| dc.description.abstract | A two-dimensional, hydrostatic, primitive
equation model is used to describe the initiation and
evolutfon of the lake and sea breezes over Kenya as
a function of surface heat and momentum fluxes. The
model has 12 vertical levels and 45 grid points in
the horizontal. In the soil, 12 levels with a constant
spacing of 2.5 cm are used. The horizontal minimum
resolution is 20 km except near the lateral boundaries
where a coarser resolution is employed. The vertical
resolution is variable with a fine resolution near
the ground along~ith-areasonably regular transition
to 1 km spacing used higher up.
The model is used to study the mesoscale circulations
which develop over a mountain barrier and a flat
terrain and to discuss the effects of these circulations
on the thunderstorm and hailstorm formations over the
Kenya highlands.
At the start of the integration, the atmosphere
is assumed to be at rest. Orography is given corres-
.
ponding to the Kenyan topographical map.
The equations of motion are solved by a semiimplicit
forward-upstream differencing technique.
Vertical velocity is diagnosed by vertical integration.
One of the main features of the model is the inclusion
of the parameterisation of the surface heat budget,
and shortwave and longwave radiative fluxes. Results
show that the mesoscale flows in the form of the Lake
Victoria breeze, the upslope winds, and the Indian
Ocean breeze converge above the Kenya highlands where
serious hailstorms are observed almost daily. The
results further show that the combined lake/land and
sea/land breezes and upslope and downslope winds
produce a more intense circulation during both day
and night than the lake/land and sea/land breezes
over a flat terrain.
The predicted convergence patterns qualitatively
agree with ·ari the existing observational studies of
cumulus convection organisation over the Kenya highlands
during daytime and over Lake Victoria at night.
The model simulations show that the lake-land and sealand
breezes and upslope and downslope flows have an
important influence on the formation and movement of
hailstorms/thunderstorms over the tea-growing areas
of the Kenya highlands during day and over the lake
during the night respectively.
The results of this study have an important
bearing on the energy and water budget over Kenya and
for the cloud modification program over the Kenya
highlands. | en |
