Detection of Asian dust in California orographic precipitation

Abstract

[1] Aerosols impact the microphysical properties of clouds by serving as cloud condensation nuclei (CCN) and ice nuclei (IN). By modifying cloud properties, aerosols have the potential to alter the location and intensity of precipitation, but determining the magnitude and reproducibility of aerosol-induced changes to precipitation remains a significant challenge to experimentalists and modelers. During the CalWater Early Start campaign (22 February to 11 March 2009), a uniquely comprehensive set of atmospheric chemistry, precipitation, and meteorological measurements were made during two extratropical cyclones. These two storms showed enhanced integrated water vapor concentrations and horizontal water vapor transports due to atmospheric river conditions and, together, produced 23% of the annual precipitation and 38% of the maximum snowpack at California's Central Sierra Snow Lab (CSSL). Precipitation measurements of insoluble residues showed very different chemistry occurring during the two storms with the first one showing mostly organic species from biomass burning, whereas the second storm showed a transition from biomass burning organics to the dominance of Asian dust. As shown herein, the dust was transported across the Pacific during the second storm and became incorporated into the colder high-altitude precipitating orographic clouds over the Sierra Nevada. The second storm produced 1.4 times as much precipitation and increased the snowpack by 1.6 times at CSSL relative to the first storm. As described in previous measurement and modeling studies, dust can effectively serve as ice nuclei, leading to increased riming rates and enhanced precipitation efficiency, which ultimately can contribute to differences in precipitation. Future modeling studies will help deconvolute the meteorological, microphysical, and aerosol factors leading to these differences and will use CalWater's meteorological and aerosol observations to constrain the model-based interpretations. The ultimate goal of such combined efforts is to use the results to improve aerosol-cloud impacts on precipitation in regional climate models.

Relating aerosol absorption due to soot, organic carbon, and dust to emission sources determined from in-situ chemical measurements

“…During the CalWater flights, dust particles were detected mainly at higher altitudes in layers, while during CARES flights were focused at much lower altitudes. Long range transported dust crossing the Pacific has been detected during the winter in northern California and it is thought to have an impact on the precipitation in California (Ault et al, 2011;Creamean et al, 2013).…”

Categorisation of northern California rainfall for periods with and without a radar brightband using stable isotopes and a novel automated precipitation collector

“…1 and Table 1 for locations and elevations): Bodega Bay (BBY), CZD, Alta (ATA) and Shasta Dam (STD). The deployments supported the National Oceanic and Atmospheric Administration's (NOAA) Hydrometeorological Testbed programme (Ralph et al, , 2013bWhite, 2012) and the California Energy Commission's CalWater Project (www.esrl.noaa.gov/psd/calwater; Ault et al, 2011). Details of the instrumentation are described below.…”

Satellite perspective of aerosol intercontinental transport: From qualitative tracking to quantitative characterization

“…For comparison, a recent model simulation estimates that the decrease of US anthropogenic aerosols over 1990-2010 yields a decrease of 0.8 W m −2 for all-sky direct radiative forcing at TOA (Leibensperger et al, 2012). Besides the aerosol direct radiative effects, the imported aerosols could have other significant impacts, such as changing atmospheric stability by absorbing solar radiation (Yu et al, 2002;Ramanathan and Carmichael, 2008), altering cloud and precipitation processes through acting as ice nuclei (Sassen, 2002;Ault et al, 2011), and accelerating the melting of snow in the Sierra Nevada by deposition on snow (Hadley et al, 2010). It is possible that a change in meteorological conditions resulting from these processes could further influence surface PM concentrations and air quality.…”