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Abstract
It has been hypothesized in the peer reviewed literature, albeit somewhat controversially, that the amount of surface rainfall and snowpack in the California Sierra Nevada has decreased by 10 to 20 percent over the past few decades due to increased air pollution. One theme of the California Energy Commission sponsored CalWater experiment is to collect coordinated meteorological and aerosol measurements to better isolate the impact of pollution (aerosols) on the precipitation processes from the naturally occurring meteorological processes. Scientists from NOAA Earth System Research Laboratory (ESRL) and the Universities of California at San Diego (UCSD) and at Davis (UCD) installed an Aerosol – Meteorological (Aerosol – Met) observatory about half-way up the slope of the California Sierra Nevada in the American River basin in February/March 2009 as an "early start" component of the full CalWater experiment scheduled for the November 2009 - March 2010 winter season. Initial analyzes of Aqua Aerosol Optical Depth at 550 nm and air parcel back trajectories suggest that the chemical composition of a snow event in the Central Sierra Nevada can be traced back to Asian dust that was transported across the Pacific. At the same time, an Atmospheric River event was supplying moisture from the Tropics into California. While more in-depth analysis and comparisons will be conducted before the conference, it appears that moisture from the Tropics and Asian aerosols were influencing the snowfall in the Central Sierra Nevada.