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Characteristics and atmospheric footprint of springtime freezing leads at SHEBA |
University of Colorado
pinto@monsoon.colorado.edu
The first month of the FIRE.ACE overflights of SHEBA, which took place in April and May, corresponded with a period of increased lead activity. Leads varying n width from 15-500 m were observed during a 2 week period beginning 27 Apr 98. Rapid ice production was observed to occur within the leads at air temperatures of about -25 C with frazil ice production being the dominant mechanism in the widest leads. In one case a 400 m wide lead, with the orientation/wind direction resulting in minimum fetch, was completely covered with new ice in less than 6 hours. While open water was exposed plumes of steam were observed above and downwind of this lead reaching heights of 10-20 m immediately downwind.
This study documents the surface energy budget and atmospheric footprint this lead which was observed upwind of several in situ observing platforms including an NCAR flux-PAM station and the NOAA/ETL 20 m tower. Aircraft measurements of skin temperature and with the video are used to characterize the horizontal variability across the lead. The components of the surface energy budget are used to force a ice growth model. Observations of ice growth and horizontal variability in ice thickness and temperature are used to evaluate the parameterized processes in the model. The model is used to determine the area-average heat moisture fluxes into the atmosphere which is correlated with the atmospheric footprint observed with the downwind instrumentation.
