On the Fields of Wind and Temperature over Japan and Adjacent Waters during Winter of 1950–1951

Abstract

First, a mean cross section along the meridian 140° E during three months (Dec. 1950–Feb. 1951) is discussed. The main characteristics are:
 
 An extremely strong subtropical jet (75 m sec-1) situated at 33° N near 190 mb;
 A semi-stationary sloping surface which divides almost barotropic warm tropical air in the south from more or less baroclinic temperate air situated in the north;
 A slight indication of a polar-front jet situated near 230 mb at 41° N; the weak intensity of this jet depends upon the strong variability in position of the polar front.
 Much warmer temperature in the upper troposphere to the south, and much colder temperature in the lower troposphere north of the subtropical jet, as compared with mean conditions at 76° E and 80° W.
 
 The computed mean winds at 140° E are combined with the mean isotachs given by Yeh over China, at the 12-km level. Using the acceleration determined from the isotach pattern, the mean angle of cross-contour flow at 200 mb is determined to be about 8° (between longitudes 110° and 140° E), with a mean cross-contour component of 8 in sec–1 toward lower heights, in the center of the mean jet stream.
 Second, daily meridional cross sections through Japan are presented for the period 8 to 15 December 1950. These show an extremely strong individual jet stream in which the observed maximum wind speed reached a velocity of more than 110 m sec–1, with near-zero absolute vorticity to the south. An associated nearly-isothermal layer underneath is much deeper (up to 4 and even 6 km) than in other parts of the globe. It is suggested that this unusual depth results from a combination of a stable layer associated with the semi-stationary subtropical jet, and the polar front, when the latter moves southward in east Asia. The behavior of the tropopause in the intermediate atmosphere south of the polar front during this series suggests subsidence of the tropopause and its transformation into the lower boundary of a deep stable layer which is transformed into some kind of front separating the real tropical air from a more temperate air moving in from the regions north of the Himalayas.