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Lubin, D, Vogelmann AM.  2011.  The influence of mixed-phase clouds on surface shortwave irradiance during the Arctic spring. Journal of Geophysical Research-Atmospheres. 116   10.1029/2011jd015761   AbstractWebsite

The influence of mixed-phase stratiform clouds on the surface shortwave irradiance is examined using unique spectral shortwave irradiance measurements made during the Indirect and Semi-Direct Aerosol Campaign (ISDAC), supported by the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program. An Analytical Spectral Devices (ASD, Inc.) spectroradiometer measured downwelling spectral irradiance from 350 to 2200 nm in one-minute averages throughout April-May 2008 from the ARM Climate Research Facility's North Slope of Alaska (NSA) site at Barrow. This study examines spectral irradiance measurements made under single-layer, overcast cloud decks having geometric thickness <3000 m. Cloud optical depth is retrieved from irradiance in the interval 1022-1033 nm. The contrasting surface radiative influences of mixed-phase clouds and liquid-water clouds are discerned using irradiances in the 1.6-mu m window. Compared with liquid-water clouds, mixed-phase clouds during the Arctic spring cause a greater reduction of shortwave irradiance at the surface. At fixed conservative-scattering optical depth (constant optical depth for wavelengths lambda < 1100 nm), the presence of ice water in cloud reduces the near-IR surface irradiance by an additional several watts-per-meter-squared. This additional reduction, or supplemental ice absorption, is typically similar to 5 W m(-2) near solar noon over Barrow, and decreases with increasing solar zenith angle. However, for some cloud decks this additional absorption can be as large as 8-10 W m(-2).

Lubin, D, Vogelmann AM.  2010.  Observational quantification of a total aerosol indirect effect in the Arctic. Tellus Series B-Chemical and Physical Meteorology. 62:181-189.   10.1111/j.1600-0889.2010.00460.x   AbstractWebsite

We use 6 yr of multisensor radiometric data (1998-2003) from the U.S. Department of Energy Atmospheric Radiation Measurement (ARM) program to provide an observational quantification of the short-wave aerosol first indirect effect in the Arctic. Combined with the previously determined long-wave indirect effect, the total (short-wave and long-wave) first indirect effect in the high Arctic is found to yield a transition from surface warming of +3 W m(-2) during March to a cooling of -11 W m(-2) during May, therefore altering the seasonal cycle of energy input to the Arctic Earth atmosphere system. These data also reveal evidence of a first indirect effect that affects optically thinner clouds during summer. which may represent an additional negative climate feedback that responds to a warming Arctic Ocean with retreating sea ice.