| Summary: | 博士 === 國立中央大學 === 大氣物理研究所 === 85 === Due to the lower latitude of location and smaller scale when
generated, the development of cyclones over the East China Sea
can not be explained simply by baroclinic instability. The
cyclogenesis and development of cyclones over the East China Sea
may have many complicate dynamical and thermal dynamical
mechanisms. The mechanisms include the terrain effect induced by
mountains on the west side of the East China Sea, the large
gradient of sea surface temperature in cold seasons and
continual supply of water vapor over ocean. So, it is
interesting to find the main mechanism of cyclogenesis over the
East China Sea. The understanding of East China Sea cyclogenesis
will also help us to realize the weather of Taiwan area in
winter and spring. This study wants to find the main mechanism
of cyclogenesis and development of cyclones over the East China
Sea by using the global analysis data and model simulations.
The result shows that the development of cyclones includes two
stages. Cyclones will occur over the East China Sea as the
result of the interactions of baroclinity of low-level
atmosphere, disturbances of low-level atmosphere and latent heat
release. Latent heat release is the most important mechanism at
this stage. Baroclinic instability will become the most
important mechanism at the stage when cyclones move out the East
China Sea and toward high latitude. Latent heat release is the
key factor in the lifetime of East China Sea cyclones. Cyclone
intensity will decrease or even vanish when the simulations
remove the effect of latent heat release. Latent heat release
will also help to amplify the cyclones even at the stage when
the baroclinic instability is the most important mechanism.
Latent heat release can increase the size of cyclones from meso-
scale when occurred over the East China Sea to synoptic scale
when well developed. There will be more interactions between
cyclones and environmental atmosphere when cyclones have larger
scale. So, latent heat release can increase the probabilities
that cyclones will continue to develop with synoptic forcing
when cyclones move out the East China Sea. Latent heat release
plays an important role that chaining the two development stages
of cyclones. It help cyclones to transfer from the stage with
thermal instability over the East China Sea to the stage with
baroclinic instability at higher latitude.
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