1 theoretical research works in institute of heavy rain 2 evolution and propagation of mcss over...
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1 Theoretical research works in Institute 1 Theoretical research works in Institute of Heavy Rainof Heavy Rain
2 Evolution and propagation of MCSs over 2 Evolution and propagation of MCSs over Meiyu frontsMeiyu fronts
and inertia-gravitational wave-CISKand inertia-gravitational wave-CISK
Hu Bowei(胡伯威)Wang Xiaofang(王晓芳)Cui Chunguang(崔春光 )
(Institute of heavy rain,China Meteorological Administration,Wuhan 430074,China)
1 The theoretical research works in Institute of Hea1 The theoretical research works in Institute of Heavy Rainvy Rain
1 The meso-scale dynamically balance mechanisms of the heavy rain systems over the Mid-and-Lower reaches of Yangtze river.
2 The chance of the temporary meeting between two of the meso-scale conditions or among further more conditions in space and time is particularly important to whether or not the rain storm events can occur and what time what location the events occur.
3 The influence of the complicated “meso-scale” terrain in the Mid-and-Lower Reaches of Yangtze River on the heavy rain occurrence and its mechanism.
4 What/s the role of the so called “low-level moisture front” in the initiation and evolution of the heavy rain weather systems over the equivalent-barotropic-characterized Meiyu front.
5 The effects of the meso-scale inertia-gravitational waves on the initiation and propagation of severe convective rain storm.
2004071601 ( UTC ) 2004071604 ( UTC)
2 Evolution and propagation of MCSs over Meiyu fronts2 Evolution and propagation of MCSs over Meiyu frontsand inertia-gravitational wave-CISKand inertia-gravitational wave-CISK
1998072323 ( Beijing Time )1998072108 ( Beijing Time ) Such MCSs usually appear the “up and down—stream development” phenomena and hence a “cloud clusters wave
train” along the Meiyu fronts. This often cause the locally outburst heavy rain, which the forecasters can not track before.
2.1 2.1 “Low-level moisture fron“Low-level moisture front”t”
CISK is not only related to the atmospheric humidity condition and the convective instability energy but also related to their horizontally non-homogeneous distribution. So the effect of “Low-level moisture front”, which is adhering to the Meiyu front, is the important factor that must be considered.
2.2 The basic equations and the parameterized 2.2 The basic equations and the parameterized eexpression of the cumulus heatingxpression of the cumulus heating
0
020
wz
w
y
v
x
u
c
RQwC
z
uv
zxu
t
fuy
vx
ut
fvxz
uw
y
uvu
xu
t
p
0
lnp
pz
dt
dzw 22
0 pC
(1)
fvxy
uvu
xu
t
fuy
vx
ut
0
wz
w
y
v
x
u
(2)
(3)
(4)(5)
020
wCzx
ut
Here the terms containing ( ) are omitted, and ( ) is in direct proportion to the weighted vertically integration of moisture in the lower troposphere. The equations system is reduce to:
z
u
2.3 W2.3 W——equation:equation:
(7)
022
222
02
22
2
wyy
w
ywC
z
w
z
wF
xu
t
y
uffF 2
( 6)
Wherein
tnymxiz
eezH
Ww
2sin
2sin,z
g ezH
yxww
Taking (7)
(8)
2.4 Frequency equation:2.4 Frequency equation:
wherein
2
1
22222
12
122
2222
2
2
MNKFMnMNKFum cc
2
1
22222
12
122
2222
2
2
MNKFMnMNKFi cc
20
2 CENc
yEM
21 2
2
2y
EM
1
2
2
4
1
HE
222 nmK
In the common situation the convective stability of second kind is determined by the value of ( ), but around the “moisture front”,
the stability is also influenced by the -ward second order
derivative of the humidity field M2 ( ),
The contribution of M2 is maximal where its negative val
ue takes the maximum ,and this place is just near the south border of the “moisture frontal zone”.
So here the largest increase rate occurs.
222cNKF
2
2
2y
EM
2.5 The energy dispersion a2.5 The energy dispersion and the up and down-stream dnd the up and down-stream d
evelopmentevelopment
The wave speed:
The envelop velocity:
)0(,2
)0(,)(8
2
1
2
2
222222
1
22221
222222
3
23
2
3
423
22
21
2
2
1
22222
2
1
22
222
22222
221
2
22222
MKNKFMKNFbM
MKNKFMKKNKFMb
MKNKF
u
KMNKFMKNKF
KMbMKNKFuC
cc
ccc
c
c
c
dK
dCKCC
dK
dCKCC eag
dK
dC
dK
dC e
2
52
2222
322
22221
2
2
12
2222
32
2
8
2
KMNKF
KKMNKFMb
KMNKF
KMF
dK
dC
c
c
c
e
The condition permitting the “up and down-stream development” to occur:
In stable range: 1.6*10 m2·s-2 <M< 0.87*103m2·s-2
In instable range: 0.87*103 m2·s-2<M<1.31*103 m2·s-2
Theoretically, the possibility of the occurrence of “up and down-stream development” along Meiyu front is hopeful.
The situation which is most favorable to the occurrence of the up and down-stream development is that the disturbances take place near the south border of the “low-level moisture front” and propagate along the frontal zone. And the most favorable condition of stability is nearly neutral.
2.6 The effect of horizontal-wind shear2.6 The effect of horizontal-wind shear
In the “dry” stratified atmosphere without cumulus heating, practically in any case the effect of horizontal wind sear can not make the inertia-gravitational waves become instable. And only in the nearly “CISK” situation the strong horizontal wind shear has a positive contribution to the instability of the wave disturbances. And such additional instability is mainly attributing to the meridional second order derivative of the velocity of basic flow. So the most favorable location is around the low-level jet stream on the south of the Meiyu front.