Open-water leads in sea ice dominate the exchange of heat between the ocean
and atmosphere in ice-covered regions, and so must be included in climate
models. A parameterization of leads used in one such model is compared to
observations and the results of a detailed Arctic sea-ice model. Such
comparisons, however, are hampered by the errors in observed lead fraction,
but the parameterization appears to compare better in winter than in summer.
Simulations with an atmospheric general circulation model (AGCM), using
prescribed sea-surface temperatures and ice extent, are used to illustrate
the effect of parameterized lead fraction on atmospheric climate, and so
provide some insight into the importance of improved lead-fraction
parameterizations and observations. The effect of leads in the AGCM is
largest in Northern Hemisphere winter, with zonal mean surface-air
temperatures over ice increasing by up to 5 K when lead fraction is
increased from 1% to near 5%. The effect of leads on sensible heat loss in
winter is more important than the effect on radiative heat gain in summer.
No significant effect on sea-level pressure, and hence on atmospheric
circulation, is found, however. Indirect effects, due to feedbacks between
the atmosphere and ice thickness and extent, were not included in these
simulations, but could amplify the response.
Influence of Sea Ice Thickness on the Atmosphere in the Winter Arctic Region in an Atmospheric General Circulation Model