qThe air approaching the lake has temperature near -5°C~-25°C,
while the unfrozen
lake has a temperature near 0°C~4°C.
qSurface friction is smaller over lake than over land è Air moves faster over lake than over land è divergence of air is produce on the
upwind side of the lake and convergence is produced on the downwind side of the lake è descending (clear sky) in the upwind side and ascending in
the downwind side.
qDue to the divergence, descending occurs on the upwind side and
produce clear sky.