Features of the polar air outbreak and the energy balance in the transformed air-mass observed over the Japan Sea

Abstract

Features of the polar-air outbreak and the energy balance in the transformed air-mass over the Japan Sea, during a period of strong polar-air outbreak in 1977, are studied by using upper observation data on a research vessel (Keifu-maru) and two coastal stations (Akita and Wajima). The analysis is made over an area of 3.8 × (100 km)2 using vertically dense (25-hPa interval) data interpolated from data at standard pressure levels and significant levels. The mixed layer capped by the stable layer is formed in the transformed air-mass. The large apparent heat and moisture sources are evaluated within the mixed layer. The apparent heat and moisture sources decrease abruptly at the top of the mixed layer. The large kinetic energy dissipation due to the sharing stress in the lower layer almost offsets the large generation of the kinetic energy due to the work down by the pressure gradient force. The present analysis indicates that the use of vertically dense data is important to resolve the multilayer structure of the transformed air-mass, and to obtain accurate vertical distribution of apparent energy sources, in the transformed airmass. The results of the present analysis are consistent, in general, with numerical simulations on the air-mass transformation over the Japan Sea. However, the apparent heat and moisture sources in the lower portion of the boundary layer in this study are considerably small as compared with results of the simulation studies. This discrepancy will be due to the use of data at the land stations on the outflow side of the budget analysis area. © 2006, Meteorological Society of Japan.