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 large-scale 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.
Highlights
Variations in the concentration of cloud condensation nuclei (CCN) in the atmosphere have been shown to impact the microstructure of clouds (Andreae and Rosenfeld, 2008), leading to changes in cloud radiative properties (e.g. Twomey, 1977; Kaufman et al, 2002) and precipitation efficiency (e.g. Warner, 1968; Givati and Rosenfeld, 2004; Saleeby et al, 2009)
An increase in CCN number concentration results in a higher cloud droplet number concentration (CDNC) and smaller droplets compared to a cloud with similar liquid water content (LWC) but relatively fewer CCN, potentially causing numerous microphysical and dynamical feedbacks (Ramanathan et al, 2001)
passive cavity aerosol spectrometer probe (PCASP) aerosol size distribution bins and condensation particle counter (CPC) particle number were averaged over 20 s time periods (20 observations), beginning ten seconds before the CCN instrument chamber opened and ending ten seconds after it was opened
Summary
Variations in the concentration of cloud condensation nuclei (CCN) in the atmosphere have been shown to impact the microstructure of clouds (Andreae and Rosenfeld, 2008), leading to changes in cloud radiative properties (e.g. Twomey, 1977; Kaufman et al, 2002) and precipitation efficiency (e.g. Warner, 1968; Givati and Rosenfeld, 2004; Saleeby et al, 2009). Since a majority of atmospheric particles originate from or are influenced by anthropogenic activities (Andreae, 2007) the CCN population is an essential element in our understanding of the human impacts on clouds, which modulate regional and global climate (Charlson et al, 2001; Ghan and Schwartz, 2007). Despite numerous studies on this topic, there is considerable uncertainty regarding the effect of anthropogenic aerosols on global precipitation. The magnitude and even the sign of the feedbacks of aerosols on clouds and precipitation depend on the cloud regime being affected and in many cases are not well known (Stevens and Feingold, 2009), making studies of CCN variability important on local and regional scales
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
