Cloud Optical Properties Over Antarctica From Shortwave Spectral and Broadband Measurements During AWARE
Authors
Dan Lubin — Scripps Institution of Oceanography
Maria Paola Cadeddu — Argonne National Laboratory
Andrew M. Vogelmann — Brookhaven National Laboratory
Virendra Prakash Ghate — Argonne National Laboratory
kris scarci — Scripps Institution of Oceanography
Ryan C Scott — NASA - Langley Research Center
Category
ARM field campaigns – Results from recent ARM field campaigns
Description
A shortwave spectroradiometer was deployed on the West Antarctic Ice Sheet (WAIS) as part of the US Department of Energy Atmospheric Radiation Measurement (ARM) program ARM West Antarctic Radiation Experiment (AWARE). This instrument recorded one-minute averages of downwelling hemispheric spectral irradiance covering the wavelength range 350-2200 nanometers. Using simultaneous micropulse lidar (MPL) data to identify the thermodynamic phase of stratiform clouds, a radiative transfer algorithm is used to retrieve optical depth and effective droplet (or particle) size for single-phase liquid water and ice water clouds. The AWARE campaign on the WAIS first sampled typical climatological conditions between 7 December 2015 and 9 January 2016, and then a much warmer air mass with more moisture associated with a surface melt event between 10-17 January 2016. Before the melt event most liquid cloud effective droplet radii were consistent with pristine polar maritime clouds (mode radius 13.5 microns) but showed a second local maximum in the distribution (at 8 microns) consistent with colder, moisture-limited conditions. Most ice clouds sampled occurred before the melt event (mode optical depth 4 and effective particle size 19 microns). During the melt event liquid water cloud optical depth nearly doubled (mode value increasing from 8 to 14). AWARE therefore sampled on the WAIS two cases relevant to climate model simulations: typical current climatological conditions, followed by warmer meteorology possibly consistent with future increasing surface melt scenarios.
Shortwave spectroradiometer measurements were not available for the AWARE AMF-2 deployment at McMurdo Station during summer 2015-16, but a new technique was successfully applied combining SKYRAD and MFRSR shortwave measurements. A k-means clustering technique was used to identify four prevailing meteorological regimes. With cloud optical depth retrieved from MFRSR data, the SKYRAD broadband measurements show statistically significant differences between these four clusters that are consistent with the meteorological drivers of microphysical contrasts.
