Abstract
In Part I of this pre-winter MONEX study a synoptic analysis on the interaction between cold air surges off the East Asian continent and the synoptic-scale disturbances, especially their associated convection, in the equatorial South China Sea during December 1974 was carried out. In this paper we investigate some kinematic characteristics of the planetary-scale circulation changes during the same period in the midlatitudes and tropics in relation to the cold surge and the synoptic-scale disturbances.
The main findings suggest a picture of coherent variations of several planetary-scale circulation features which may he described by the following sequence of events:
1) The East Asia local Hadley circulation strengthens as the cooling due to cold air advection over northern China increases prior to a cold surge on the South China coast. This is accompanied by an intensified jet stream maximum centered over Japan, which is apparently a result of the upstream acceleration by the upper level poleward flow.
2) The jet stream maximum over Afghanistan–Pakistan varies inversely with the eastern jet maximum and appears to be related to a West Asia meridional circulation which becomes thermally indirect prior to the surge.
3) Immediately after a cold surge the convection associated with preexisting synoptic-scale disturbances in the equatorial South China Sea intensifies which causes the East Asia local Hadley circulation to reach its maximum intensity and also strengthens two east–west (Walker) cells along the equator.
4) Shortly (≲1 day) after the surge the increased large-scale ascending motion over the equatorial South China Sea due to the continued strong convective activity associated with the synoptic disturbances contributes mainly to a further increase in the intensity of the two Walker cells.
The foregoing events suggest that the winter monsoon cold surge is basically a phenomenon controlled by the northern midlatitudes and its influences penetrate significantly equatorward into the tropics. The feedback into the Northern Hemisphere extratropics appears to be relatively unimportant.
