On the Modification of Air-mass over the Japan Sea when the Outburst of Cold Air Predominates

Abstract

Japan Sea is generally considered to be one of the places where the most rapid airmass transformation takes place in winter season.As it is surrounded by the dense network of radiosonde and surface observation stations, quantitative investigation about the modification of airmass is possible.Selecting the period of a typical continuous outburst of cold air from 20 Dec.'54 to 3 Jan.'55 during which the air-sea temperature difference exceeded 10°C, we computed the integrated netflux divergence of enthalpy and water vapor and the vertical transport of them at the standard levels in the lower half of the troposphere, and further estimated the amount of heating and cooling due to radiation and condensation.Then, based upon the balance requirement, the amount of heat or water vapor supplied from the sea to the atmosphere was obtained.According to the results of above computations, it is concluded that the amount of supplied heat is as much as 1000ly/day in such a typical unstable situation, and is 2.3 times as large as that of supplied latent heat in spite of the fact that mean Bowen's ratio expected from mixing length theory was nearly equal, to unity.Finally, for several periods when no remarkable cyclone passed over the Japan Sea, the amount of evaporation computed by the scheme above-mentioned are compared with the results obtained by use of climatological evaporation equation after Jacobs.