Wave Disturbances over the China Continent and the Eastern China Sea in February 1968

Abstract

Wave disturbances appeared in the China continent and the Eastern China Sea in February 1968 are studied by the spectral method and the dynamical computations of the vertical velocityand the diabatic heating. Two types of disturbances are obtained. The one is the wave with 4-to 5-day period and the other is the wave with 1.5-to 2-day period.
The disturbances with 4-to 5-day period exist in the regions to the south of 32*N where the southern jet currents flow. These disturbances propagate from west to east with the wavelength about 4, 000-5, 000km and their amplitude becomes large in the Eastern China Sea. The vartical structure of the disturbance is similar to that of a baroclinic unstable wave. Some disturbances of these waves develop suddenly as going over the Eastern China Sea. The diaba tic heating and the coupling between the lower tropospheric disturbances and the troughs in the upper troposphere may play an important role in the extreme development of the disturbances.
Short-period disturbances with 1.5- to 2-day period exist in the lower troposphere below 600mb in the southern part of the Eastern China Sea especially during the period from 1 to 10 February. These disturbances have the wavelength about 2, 000km and their vertical structure is also similar to that of the baroclinic wave, i.e., the trough axes tilts slightly westward with height, warm air covers the region on and the east of the trough and upward motion occurs to the east of the trough. These medium-scale disturbances can be seen in the synoptic patterns. The Richardson number of the mean field is order of unity and these medium-scale disturbances are the baroclinic waves developing in the atmosphere of low Richardson number as suggested theoretically by Gambo (1970, a, b) and Tokioka (1970).