Investigation of the linkages between insoluble precipitation residues and cloud properties at Yosemite National Park during U.S. West Coast storms

Ice formation in orographic mixed-phase clouds can enhance precipitation, and depends not only on cloud depth and temperature, but also on the type of aerosols that serve as ice nuclei (IN). The resulting precipitation from these clouds serves as a viable source of water, especially for mountainous regions such as the California Sierra Nevada. Thus, a better understanding of the sources of IN that impact these particular clouds is important for assessing water availability in California. We present a multi-site, multi-year (2011 and 2012) analysis of single, insoluble residue particles in precipitation samples that potentially served as IN and influenced ice formation in the clouds above Yosemite National Park, USA. Dust and biological particles typically represented the dominant fraction of the total residues (64% on average) and were ultimately removed via precipitation. Cloud glaciation was determined using GOES satellite observations and was not only dependent on high cloud tops (> 6.2 km MSL) and low temperatures (< -26°C), but also on the composition of the dust and biological residues. The greatest prevalence of ice-phase clouds occurred in conjunction with biologically-rich residues and mineral dust particularly rich in calcium, followed by iron and aluminosilicates. Dust and biological particles are known to serve as efficient IN, and thus we hypothesize that these precipitation residue types induced ice formation in the clouds above the site. The goal of this study is to use precipitation chemistry data to gain a better understanding of the potential sources of IN in the south-central Sierra Nevada, where aerosol-cloud-precipitation interactions are under-studied and where mixed-phase orographic clouds are a key element to precipitation and thus water supply in California.