Precipitation from convective boundary layers in arctic air masses

Cold air mass formed over the ice-covered polar area during the winter season often moves southward over the Norwegian Sea. The heat flux from the water produces a CBL (convective boundary layer) with increasing thickness and temperature in the downstream direction. Usually, snow showers are observed over the sea and at the coast of Norway. The object of this investigation is to examine the amount of precipitation measured at the coast in relation to the temperature and thickness of the CBL. A sample consisting of 37 cases is collected and a positive correlation is established between the precipitation measured by 5 coastal stations and the CBL thickness, while the temperature seems to be of minor importance. Some of the data indicates a two-regime precipitation pattern, divided by a threshold value in the thickness of the CBL. This is discussed in relation to microphysical precipitation processes. Peculiar differences in the records from the observing stations indicate interesting orographic shadow effects.