One of the most important causes for snowfall over the Japanese Islands in winter is associated with the transformation of continental polar air-masses during passage over the Japan Sea. The cP air-masses are rapidly modified over the relatively warm water owing to the addition of sensible and latent heat. The theory of air-mass transformation due to eddy diffusions is re-examined by taking account of the phase change of water vapor and the variable exchange coefficient dependent on the static stability. Numerical experiments are made to test the model.
It is shown that the present simple model can describe the average weather condition over the Japan Sea in winter, if the variation of exchange coefficients in the model is taken into consideration.