East Asia and Western Pacific METEOROLOGY AND CLIMATE

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In all three experiments, a deep trough over the Yun-Gui area is simulated. However,
their intensities are quite different. In CON, the trough is similar to that observed. In
SOE, the trough is much deeper than observed but in SME it is much weaker.
Figs. 9 a-c show the 12 hour simulated 500mb wind, temperature and height fields
for the above three experiments. The trough over Yun-Gui area in the SOE experiment
is deeper than that in CON but in SME this trough is weaker.
3.4 The vertical profile of vorticity field :
The vertical cross-section along 27.6°N for the observation and model simulations
are shown in Figs. 10 to 12 (The cyclogenesis in this study is around 105°E±3.75°E).
Fig. 10 is the evolution of the observed vorticity field. From this figure we can get:
(A) At 12 GMT Feb. 19, there exists a weak positive vorticity area at lower level around
105°E.
(B) At 00 GMT Feb. 20, the positive vorticity area at 105°E has intensified and extended
to the upper level. The maximum center is at around 600mb.
(C) For the next 12 hour, the vorticity at all levels around 105°E is much stronger
than that at 00 GMT, and the maximum center has ascended to 450mb and is moving
towards the east.
(D) At 00 GMT Feb. 21, this vorticity is much weaker than 12 hour before and the
maximum center has descended to 750mb.
Fig. 11 is from simulation AA. In general, the predicted vorticity field around
105°E is about the same as that observed. However, its intensity is weaker.
Fig. 12 is from simulations A, B and C. We can find the following features when
compared with the observations at 12 GMT Feb. 20:
(A) From simulation A, we find the predicted vorticity profile to be very close that
observed. The maximum vorticity is around 108.75°E which is the same as observed.
However, the maximum center is at around 650mb instead of 600mb.
(B) From simulation B we find the vorticity field around 108.75°E has become more
extensive and stronger than that in simulation A. This is apparently due to a charge
a the orography.