The Meteorology of Kilimanjaro from One Year of Atmospheric Modeling at Fine Grid Spacing

Global circulation models often utilize coarse grid spacing that is incapable of adequately resolving terrain generated circulation patterns. In this context, it is important to understand the relationship between differing large scale flow regimes and terrain generated weather and climate patterns. Such knowledge is important for Kilimanjaro, located in equatorial East Africa where the climate is highly reliant on oscillations of the Intertropical Convergence Zone. This study utilizes the Regional Atmospheric Modeling System to simulate meteorology of Kilimanjaro for the period of July 2007 through June 2008 at one kilometer grid spacing. Analysis of the simulation shows the dependence of local processes on synoptic fields as well as modification of the synoptic fields due to these processes. Simulations show adequate performance compared to regional and local scale meteorological observations as well as satellite derived cloud cover. Analysis of flow patterns show the blocking caused by the mountain changes over the course of the year, dependent on the slope as well as cross section of the mountain normal to the prevailing wind. Local scale precipitation shows the elevation of maximum precipitation of around ~800 m higher then previously reported, while following existing function fits with elevation. The blockage caused by the topography interacting with wind patterns causes a mean 0-1000m wind of < 3.5 ms-1 greater then 25% during months in the dry seasons, whereas the number of points with low wind speeds is much smaller (<10%) during months in the wet seasons. There is a distinct signal in the thermal circulation between each season, with differences in the cloud patterns and formation present, leading to higher cloud bases during certain seasons. Local processes contribute >60% of the precipitation from elevations ranging from 2000 m to 4000 m, and contribute 20% of the precipitation at the peak.