ATMOSPHERIC CIRCULATION ANOMALIES ASSOCIATED WITH 1996 1997 SUMMER PRECIPITATION EVENTS ON SAJAMA ICE CAP, BOLIVIA/

The analysis of atmospheric circulation anomalies related to snowfall events on Sajama volcano (Bolivian Andes) provides important informati on for the calibration of an ice core, recently recovered from the sum mit. Seventeen precipitation episodes were recorded on Sajama volcano during the 1996/1997 summer season (November 1996 to March 1997) by sn ow depth sensors and additional measurements of an automatic weather s tation located on the summit. The analysis of atmospheric circulation patterns during these events is based on zonal and meridional wind, ai r temperature, relative humidity, geopotential height and horizontal d ivergence at three pressure levels (400, 500, and 700 hPa levels), atm ospheric thickness (700 hPa-400 hPa), and precipitable water (vertical ly integrated), all extracted from the National Centers for Environmen tal Prediction (NCEP) data set. Highly convective situations prevailed through most of December and January, with strong vertical motion ove r the Bolivian Altiplano. In February and March, increased moisture ad vection from the east occurred in midtropospheric levels. These result s are confirmed by isobaric 5-day back trajectories and transit time a nalysis at the 400 hPa level. The extremely southern position of the u pper air high-pressure system (''Bolivian High'') in February and Marc h is the main reason for the unusually high precipitation amounts on t he Altiplano in 1996/1997. Highly variable patterns of atmospheric cir culation can lead to snowfall on Sajama during the summer months.