Factors on the Development of Deep Convection in the Southern Region far from the Baiu Front over Eastern China during the GAME/HUBEX IOP '98
Taro Shinoda (1), Hiroshi Uyeda (1)
(1) HyARC, Nagoya University
A meridional convergence of water vapor flux within the Baiu
frontal region causes the heavy precipitation. This convergence
is brought about by a strong northward horizontal transport of
water vapor. It is important to clarify the transport process
and the source of water vapor in the southern region far from
the Baiu front. This region is covered by the Pacific subtropical
high and there is no large-scale convergence. Meanwhile, diurnal
variation of convective activity was observed over this region
during the GAME/HUBEX IOP. We use a numerical simulation to
investigate the factors concerning the development process of
deep convection in the southern region far from the Baiu front
over eastern China during the summer monsoon season.
This study employs a two-dimensional compressible cloud
resolving model developed by Yoshizaki and Ogura (1988) with
some modifications. We simulate a convective cloud system
observed by Doppler radar on July 14, 1998. A convective mixing
layer develops as a result of the supply of sensible heat flux
from the surface, and initial shallow convective clouds are
generated in the early afternoon. After the generation of
these clouds, some of them develop into deep convective clouds.
The simulated characteristics of deep convection correspond
to the observed ones.
From simulating results, when paddy fields mainly occupy
as the surface boundary, a large amount of latent heat flux
is given off to the lower atmosphere, and deep convective
clouds are generated in the afternoon. On the other hand,
when farmlands mainly occupy as the surface boundary, the
sensible heat flux is greater than the latent heat flux, and
deep convective clouds do not develop. Therefore, a large
amount of latent heat flux from paddy fields affects the
development of deep convection.
From simulating results, when the environment in the middle
troposhere is humid (RH > 80%), shallow convective clouds can
develop into deep convective clouds because they do not lose
its positive buoyancy by evaporation cooling.
On the other hand, when the environment in the middle
troposhere is relatively dry, shallow convective clouds
cannot develop into a deep convective cloud because they do
not maintain its positive buoyancy. However, these shallow
convective clouds moisten the environment in the middle
troposhere by evaporation when they disappear.
These moist air masses in the middle troposhere moves into
the Baiu frontal region by the monsoon southerly and we can
see these moist air masses by the propagation of convective
cloud regions that generate in the afternoon over the China
continent.
We study the factors in the development of deep convection
in the southern region far from the Baiu front over eastern
China during the summer monsoon season. A large amount of
latent heat flux from paddy fields and the moist environment
in the middle troposhere are suitable conditions for
developing deep convective clouds over this region.
This moist environment in the middle troposhere is formed
by shallow convective clouds that transport water vapor
from the convective mixing layer to the middle troposhere.
This moist air mass extended from the lower to middle
troposhere eventually merges into the Baiu frontal region
and supplies water vapor to it.
Submittal Information
Name :
Date :
Taro Shinoda
30-May-01-02:28:26
Organization :
Theme :
Hydrospheric Atmospheric Research Center, Nagoya University
