| dc.description.abstract | Logarithmic wind profile equations account for the
aerodynamics within the lower atmosphere. This paper employs
logarithmic equations in various forms while incorporating
changes in atmospheric stability to simulate the spatial and
temporal structure of both the planetary boundary layer depth
and the field of flow within it. Turbulent fluxes of sensible
heat and momentum as a result of the impact of the synoptic
flow on the frictionally active surface are assumed to be the
only means of modifying the mixing heights. Cumulus
convection, moisture flux, and the associated effects of
latent heat change are ignored. As a case study, the
procedure is designed to investigate diurnal/nocturnal and
seasonal change by modelling using monthly time averages
over a year s period, 1986, in Nairobi. To this end, a threet
dimensional simple Eulerian model is attained in the
analyses.
Results show a reasonable resemblance between the
nocturnal-diurnal and seasonal cycles of the computed mixing
,
"
heights and the observed surface weather parameters,
particularly wind speed and insolation. Seasonal variations
were noticed for the estimated mixing heights during
daytime only. The inversion strengths of 12~7 were comparable
with those at the sinking arm of the Hadley cell of the
general circulation. The inversion strengths however vary
seasonally with the highest values in the period from June to
August, and the lowest in the rainy months of April and
October. The elevated inversions, though, are not responsible
in determining ·the model depths of the planetary
-xiil-·
boundary layer owing to the lofty heights at which they
occur. The inversions are substantially influenced by the
upper level trade wind regime in addition to surface
processes. Low ground heat storage, being just 10% to 0.5% of
the global radiation, is due to the nature of the soil within
the region. Horizontal and vertical variations in the wind
field seem to be a consequence of the influence of the large
forests, altered surface fabric, urbanisation and terrain
undulations as they alter the synoptic flow. | en |
