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Arctic Stratus Cloud Properties and Their Effect on the Surface radiation Budget: Selected Cases From FIRE ACE |
Meteorology Department, University of Utah,
Meteorology Department, University of Utah,
NASA Langley Research Center,
NASA Langley Research Center
xdong@met.utah.edu
To provide the Arctic stratus cloud properties and their effect on the surface radiation balance during the spring transition season, three cloudy and two clear-sky days are presented from May 1998, during the First ISCCP Regional Experiment (FIRE) Arctic Cloud Experiment (ACE). Radiative transfer models are used in conjunction with surface- and satellite-based measurements to retrieve the layer-averaged microphysical and shortwave radiative properties. At least some of the surface-retrieved cloud properties agree well with the in situ and satellite retrievals during each case. However, there are discrepancies in one or more quantities due to the effects of ice crystals in otherwise liquid clouds, mismatches between the aircraft and surface in a highly variable cloud field, and vertical structure in the clouds that is not totally sampled by the aircraft measurements. Satellite data are critical for understanding some of the observed discrepancies. The satellite-derived particle sizes agree well with the coincident surface retrievals and with the aircraft data when they coincide. Optical depths derived from visible-channel data over snow backgrounds were overestimated in three cases suggesting that methods currently used in satellite cloud climatologies are deriving optical depths that are too large. Use of a near-infrared channel with a solar infrared channel appears to simultaneously derive optical depth and particle size appears to alleviate this overestimation problem. Further study of the optical depth problem is needed. The surface-based radiometer data reveal that the Arctic stratus clouds produce a net warming of 20 Wm-2 in the surface layer during the transition season suggesting that these clouds may accelerate the spring time melting of the ice pack. This surface warming contrasts with the net cooling at the TOA during the same period. An analysis of the complete FIRE ACE datasets will be valuable for understanding the role of clouds during the entire melting and refreezing process that occurs annually in the Arctic.
