Cold and transition season cloud condensation nuclei measurements in western Colorado

Abstract

Abstract.Recent studies have shown that orographic precipitation and the water resources that depend on it in the Colorado Rocky Mountains are sensitive to the variability of the region's aerosols, whether emitted locally or from distant sources. However, observations of cloud droplet nucleating aerosols in western Colorado, climatologically upwind of the Colorado Rocky Mountains, have been limited to a few studies at a single, northern site. To address this knowledge gap, atmospheric aerosols were sampled at a ground site in southwestern Colorado and in low-level north to south transects of the Colorado Western Slope as part of the Inhibition of Snowfall by Pollution Aerosols (ISPA-III) field campaign. Total particle and cloud condensation nuclei (CCN) number concentrations were measured for a 24-day period in Mesa Verde National Park, in September and October 2009. Regression analysis showed a positive relationship between mid-troposphere atmospheric pressure to the west of the site and the total particle count at the ground site, but no similar statistically significant relationship was found for the observed CCN. These data were supplemented with particle and CCN number concentration, as well as particle size distribution measurements collected aboard the King Air platform during December 2009. A CCN closure attempt was performed and suggested that the sampled aerosol may have had a low hygroscopicity that changed little with the largescale wind direction. Together, the sampled aerosols from these field programs were characteristic of a rural continental environment with CCN number concentrations that varied slowly in time, and little in space along the Western Slope.

Microphysical controls on the isotopic composition of wintertime orographic precipitation

“…The results have potential implications for research and field campaigns looking to study the influence of different atmospheric regimes on orographic precipitation, such as Isotopic Fractionation in Snow (IFRACS; a 2014 campaign led by Doug Lowenthal, Gannet Haller and colleagues at the Desert Research Institute: https://www.eol.ucar.edu/field_projects/ifracs), ISPA‐III [ Ward and Cotton , ], and StormVEx [ Mace et al , ]. As liquid processes are most responsive to CDNC, locations where precipitation primarily forms through accretion of cloud liquid and/or riming are likely to experience decreased accumulation, a shift in the location of, and a decrease in the .…”