East Asia and Western Pacific METEOROLOGY AND CLIMATE

Diagnosis using the balanced o> equation (36,74) showed that the
vertical motion in the mid latitude were primarily due to vertical
differential of the vorticity advection and Lapiacian of the
temperature advection. The upward motion to the south of the Mei-Yu
trough was primarily contributed by the convective latent heating. To
the south of Japan and the vicinity of Taiwan, upward motion was
contributed by vertical differental of the vorticity advection,
Lapiacian of the temperature advection and convective latent heating.
On the other hand, the boundary layer frictional effect and convective
latent heating were primarily responsible for the upward motion over
southern China and northern Vietnam. Chen and Chang (27) studied the
structure and dynamics over different sections of the Msi-Yu front.
The results indicated that the structure of the eastern and central
sections resembles a typical midlatitude baroclinic front with strong
vertical tilt toward an upper level cold core and a strong horizontal
temperature gradient, \\faereas the western section resembles a
semi tropical disturbance with an equivalent barotropic warm core
structure, a weak horizontal temperature gradient, and a rather strong
horizontal wind shear in the lower troposphere. The vorticity budget
showed that generation of cyclonic vorticity by horizontal convergence
was counteracted by cumulus damping in the eastern section and by
boundary layer friction in the mountainous western section.
Analysis of moisture structure and rainfall for the sane case by
Chen (7) showed that low level southwesterlies, especially the low
level jet, tend to creat potential instability on the warm side of
the Mei-Yu front. Continued large-scale ascent then led to the release
of potential instability through organized mesoscale convective
systems. The convection produced radar echoes and cells of heavy
rainfalls. The moisture budget (12) showed that convergence of
horizontal moisture fluxes together with the divergence of vertical
fluxes in the lower troposphere below 700 mb were responsible for the
maintenance of the IVfei-Yu cloud band. It was found that the subgrid
convective process predominates over the large-scale process in
providing moisture in the cumulonimbus area, with the ratio of the two
terms being 1.5, 8.5, 5, and 5 at 850, 700, 500, and 400 mb,
respectively.
A composite study was carried out by Chen (14,15) using 8 cases
of Nfei-Yu frontal systems which affected the Taiwan area in 1975 and
1977. Results showed that the cloud band and convective area coincided
with the area of upward motion indicating that the large scale
circulation controlled the cloud development. In the later stage of
the Ivfei-Yu season, the Tibetan thermal low intensified and the
migratory high behind the Mbi-Yu trough weakened. Also, the
southerlies to the south of the Mei-Yu trough intensified and the
frontal system retrograded northward. Meanwhile, the convective
activities and rainfall amount over Taiwan area increased. Chen
(19,22) analyzed the composite structure and dynamics over
different sections of the Mei-Yu front using these 8 cases. Results
were consistent to those obtained in the individual case study by Chen
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