The maximum effect of open leads within sea ice on the near-surface atmospheric temperature is estimated using a 1D atmospheric model coupled with a thermodynamic snow/sea ice model. The study is restricted to clear-sky conditions during polar night. The model is initialized with a typical wintertime atmospheric temperature profile. Results are analyzed at different integration times corresponding to different fetches over the fractured sea ice as a function of wind speed and sea ice concentration A. The results demonstrate that for A > 90% small changes in the sea ice fraction have a strong effect on the near-surface temperature. A change by 1% causes a temperature signal of up to 3.5 K. A threshold value of about 4 m s-1 for the 10-m wind speed divides the air-ice interaction process into a weak-wind and strong-wind regime. Copyright 2008 by the American Geophysical Union.