ESRL/PSD Seminar Series

Radar-based analysis of current and future precipitation in the Swiss Alps

James V. Rudolph
University of Colorado, Dept. of Atmospheric and Oceanic Sciences, Boulder, Colorado


Eleven years (2000-2010) of ground-based operational weather radar data are used to analyze three-dimensional precipitation distribution in the Swiss Alps. Daily synoptic scale weather patterns associated with high resolution (2 x 2 km2) radar-estimated precipitation show an advective synoptic scale pattern with southerly flow results in the highest median and 90th quantile values for total daily precipitation while a convective synoptic scale pattern results in elevated frequency of extreme rainfall rate events. Radar-estimated precipitation observations are coupled with geopotential height fields from Community Climate System Model Version 3.0 (CCSM3) and indicate that changes in synoptic pattern frequencies will result in an approximately 10-15% decrease in decadal precipitation over the course of the 21st century for seven Swiss river basins. Radar is also used for analysis of precipitation systemsą vertical structure on the southern side of the Alps. Storms occurring in summer are more convective than winter season storms as indicated by more frequent observation of reflectivity at higher altitudes during summer. Seasonal classification of individual storms by vertical structure reveals a transition between winter and summer-type storms during spring and fall that follows changes in average daily surface temperature. Although summer and winter-type storms result in a similar amount of total precipitation, summer-type storms have shorter duration, and therefore, greater intensity. The dependence of storm type on temperature has implications for intensification of the hydrologic cycle due to climate change. Warmer winter, spring, or fall surface temperatures may affect average precipitation intensity by increasing the number of days per year that experience more intense convective precipitation while decreasing the probability of less intense stratiform precipitation..

Thursday, March 22

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