East Asia and Western Pacific METEOROLOGY AND CLIMATE

72
(iii) The mid-latitude westerlies over Indo-China at the
700 and 500 hPa levels extended as far south as
12°N. The subtropical ridge axis also progressed
southward to a position between 15°N and 10°N.
(iv) Tropical depressions/tropical storms/typhoon
occurred more frequently over the West and central
Pacific during the suppressed period than the
period of enhanced convective activity. They were
present for 12 out of 14 days of the suppressed
period.
(v) There was a 500 hPa north-south oriented westerly
wave trough moving eastward from India across Indo-
China to the South China Sea.
(vi) As a result of the conditions stated in (ii), (iii)
(iv) and (v) 3 there were no broad easterlies from
the West Pacific to the South China Sea at the 700
and 500 hPa levels during most of the days of
suppressed convective activity over Malaysia.
Figures 3a and b are those for the 7th December 1986,
when there was a cold outbreak over China but there was no heavy
rain in Malaysia. There were one typhoon (KIM) and one tropical
depression over the West Pacific on the 7th December. Both of them
were located in the region north of latitude 10°N.
4.0 SPECIFIC HUMIDITY AND WATER VAPOUR FLUX
Figures 4a, b and c and 5a, b and c are the latitude -
time cross-sections along 115°E for the upper winds, specific
humidity and water vapour flux for the 850, and 500 hPa levels
respectively for the above-stated period. In the figures, the
subtropical ridges are represented by bold lines whereas the
near-equatorial troughs, by dashed lines. The bold arrows below
the date axes separate the period of enhanced convective activity
before the 2nd December 1986 from the following period of
suppressed convective activity. The letters M and D in the