East Asia and Western Pacific METEOROLOGY AND CLIMATE

arc around the Plateau is seen between mid and lower latitudes of
the eastern Asian continent, with NW (NE) winds north (south) of
30°N,which is obviously in close relation to the flow-steering role
of the orography. The 36~h integration indicates that NE winds in
the southern part of the Sea keeps on intensifying and extending
westward to the northern Indian, with the maximum wind center of 8
m/s displaced southward to the central South-China Sea. At the 48 h
the surge has moved further southward, with the NE wind of 6 m/s
reaching equatorial latitudes and a reduced wind region of 8 m/s
travelling westward to the Bay of Bengal. The 60~h result indicates
that the maximum NE wind has dropped to 6 m/s, implying that the
surge is beginning to weaken.
It can be seen in Fig.3a that, north of 5°N, after the starting
of integration,the V - isopleths are getting N - S directed and become
closer together,suggest ing that the northerly wind strengthens
rapidly in the first 12 hr, whereas for 5 N and south of it the reinforcement
is initiated at the 12th hr. At the 72-h integration
no northerly wind is seen at 25°N, indicating the cutoff of cold
air supply, thus suggesting that the surge moves into the decaying
stage. A salient feature displayed in Fig.Bb is that temperature
drop south of 25°N occurs after the integration of 12 hr.lt follows
that the enforced northerly wind due to the surge is always ahead
of temperature drop caused by it, which may be explained by the
character of cold surges as gravity waves *^.
In the 120°E cross section at the 24-h integration (Fig.4a) the
local Hadley cell intensifies to a considerable degree, with the
ascending leg around the equator and in the Southern Hemisphere
and descending leg equatorward of 20°N. In the 48-h cross section
(Fig»4b) the surge-caused near-surface northerly flow extends to
equatorial latitudes and the ascending leg of the cell ahead of the
surge retreats to 5°S and south of it* Fig.4c gives the difference
in vertical speed (fl^gr- w pA^* which shows enhanced legs of the cell.
Hence, in the southward travel of the surge, the Hadley cell retreats
and intensifies.