Groisman and Genikhovich (1996) developed a method to obtain direct estimates of surface turbulent heat fluxes. We now apply it to the territory of the former USSR, using the 3- / 6-hourly data of 257 stations for the past several decades to assess the sensitivity of sensible heat flux to cloud and snow cover. This property was quantified for bare soil landscapes over the entire country. During the day, the presence of clouds is associated with low values of sensible heat flux from the surface to the atmosphere. At night (and during the day in winter in high latitudes), the sign of the effect is different, but because the direction of sensible heat flux is also different (from the atmosphere to the surface), the presence of clouds again reduces the turbulent heat exchange between the bare soil and the atmosphere. The estimates of "overall cloud effect" on summer sensible heat flux are compared with similar estimates from four general circulation models (GCMs) to assess the abilities of these GCMs to reproduce the response of this flux to cloud cover change.
Snow on the ground is associated with temperature depression. When the
effect of this depression is excluded, the presence of snow on the ground
generally is associated with less water vapor in the lower troposphere
under clear sky conditions while the evaporation rate and sensible heat
flux are higher than average.