Synoptic analysis of 2001-2005 significant snowfall events on Mt. Kilimanjaro

Ice cores recovered from Mt. Kilimanjaro provide evidence of significant climate changes in the East African region over the past 10,000 years. However, the atmospheric processes that lead to snowfall on Kilimanjaro are poorly understood. Earlier studies have suggested that East African climate is dominated by the seasonal shift of the tropical precipitation bands, yet the key factors causing interannual precipitation variability remain unclear, particularly for the long rains season (March-May). To advance the understanding of modern East African climate, this study used data from a new station on top of Mt. Kilimanjaro and put them into a regional atmospheric circulation context. First, the in situ data were compared to global analysis products for testing their representation of the East African region. Overall, these data showed similar activity during corresponding days of snowfall on Kilimanjaro, indicating that snowfall events are likely related to regional precipitation. Second, the use of various global (re-) analysis products allowed the examination of commonalities between individual precipitation events on Kilimanjaro, and helped to identify the key precipitation-causing processes. Results showed distinct seasonality in precipitation, propagating from west to east during the long rains and east to west during the short rains (October-December). In addition, high magnitude snowfall events occurred under the conditions of low wind speed and high humidity. Therefore, high magnitude events may be a result of local convection, and these events may represent certain atmospheric conditions favorable for snowfall accumulation, but their representation of overall regional rainfall totals remains uncertain.