2002 Annual

Wednesday, 16 January 2002
On the mechanisms determining the spatial variability of heavy precipitation in the Himalayas
Timothy Lang, Harvard University, Cambridge, MA; and A. P. Barros
A meteorological network has been installed along 3 ridges and in valleys within the Marsyandi River basin in the Annapurna region in central Nepal. This area is characterized by extremely high rainfall totals (up to 400 cm or more) over the course of the monsoon season (June-September). In addition, totals for individual weather events can exceed 45 cm. Perhaps more notably, the region also is characterized by strong spatial gradients in rainfall, over the duration of a season or an individual weather event, with rainfall totals changing by a factor of 4 or more over distances of only a few km. Ostensibly, the steep topography in the region is the primary cause of these rainfall differences, but the exact processes by which this occurs are not well understood. In order to examine these mechanisms in more detail, a modeling study has been undertaken, using a small-scale meteorological model that resolves the steep topography in the region. The model is initialized using sounding data collected during the Monsoon Himalayan Precipitation Experiment (MOHPREX), which took place during June 2001. Radiosondes were launched around the clock for 3 weeks from two sites, one right at the foothills of the Annapurnas and one 90 km away to the southwest.

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