EAMEX
East Asian Monsoon Experiment:
1. Summer Rainstorm Experiment
2. Winter Rainfall Experiment
Tsing-Chang Chen
Department of Geological and Atmospheric Sciences
Iowa State University
U.S.A
1
1. Pilot Studies of the
Summer Rainstorm Experiment
1) Importance of Rainstorms
2) Rainstorm Genesis Mechanism
3) Rainstorm Forecastability by NCEP GFS
4) Intraseasonal Variation
5) Interannual Variation
2
Climatology
GMS IR
A 1998 SCSMEX case
?
JMA-sfc
?
3
Rainfall cycle
PTaiwan
Taiwan rainfall
5/15-6/15
mmd-1
⋅season-1
Break
Active Revival
Rainstorm
TC
(Chen et al. 2004)
(Wang and Chen 2007)
4
Historical perspectives: a. TAMEX
(The Taiwan Area Mesoscale Experiment; Spring 1987)
TAMEX Network
Kuo and Chen (1990; BAMS)
5
MCS occurrence frequency
• prefrontal squall lines
• mesoscale convective systems
Kuo and Chen (1990; BAMS)
6
Historical perspectives: b. SCSMEX
(South China Sea Monsoon Experiment; May-June 1998)
Network
(SCSMEX formal
announcement 1997)
7
(1998 May-Jun)
(Lau et al. 2000; BAMS)
8
2) Rainstorm Genesis Mechanism
∆(V,|V|) [6/1-6/15]–[5/16-5/31]
L
200mb
200mb
H
H
H
L
L
400mb
400mb
H
H
H
H
L
L
600mb
H
H
L
850mb
H
L
L
H
H
600mb
L
L
L
850mb
H
L
L
H
9
a. Genesis mechanism
Charney-Stern baroclinic instability
African easterly waves
10
b. Diurnal variation
Genesis location/timing of rainstorm
6Z, 12Z → Afternoon/Evening
0Z, 18Z → Midnight/Morning
11
c. Structure & downscale development
MTSAT / GFS
May, 2006
12
Distribution of genesis location
Max(ζ) (MJ, 2005~2006)
25°N
20°N
15°N
13
21Z 6/12/05
V(600mb), IR
L
30°
30°N
20°
20°N
10°
10°N
110°E
18Z 6/12/05
14
d. topographic effect
Case: May, 2006
V(700mb),Rf
V(925mb),Rf
rainfall intensification
(V,-V⋅∇h)
(925mb)
15
e. Dissipation process
merged mid-latitude cyclone
dissipated
L
L
H
H
H
H
L
L
H
H
H
16
N-S cross section
merged midlatitude cyclone
dissipated
weak low-level
westerlies
17
3) Rainstorm Forecastability by GFS
Case 2 (R7; June 11-15, 2005)
Analysis
Forecast
(actual trajectory)
(actual trajectory)
18
, IR
Analysis
Case June 11-15, 2005
Forecast from 00Z 6/12/05
19
GFS forecast performance
(MJ, 2005-2006)
km (x-direction)
For the mid-tropospheric perturbation: (actual – forecasted)
240
200
Error of position
RMS of dx between real &
forecast trough locations
depicted in v(600mb)
160
120
80
1 standard deviation
40
t=0
ms-1
8
6
24
48
72
96 hr
Error of propagation speed
4
2
0
1 standard deviation
determined by trough
location at 600mb
-2
t= 0
24
48
72
Average duration
to reach Taiwan
96 hr
20
2. Pilot Studies of the
Winter Rainfall Experiment
1) Importance of Winter Rainfall
2) Impact of Cold Surge on Winter Monsoon
Rainfall
a. Tropical Southeast Asia
b. East Asia
c. Midlatitude
d. Indochina
21
Winter climatology of East/Southeast Asia
CMAP / ERA-40
1979-2002
A
B
C
22
Historic perspective
1) AMTEX [Air Mass Transformation Experiment (1975/76)]
(Lenschow 1972)
23
The air-sea heat flux
open
cell
ocean
ocean
closed
cell
(Sheu and Agee 1971)
ocean
ocean
24
The AMTEX storm
SLP
Feb 1975
L
H
L
H
L
L
H
H
L
H
H
H
L
Chen et al. (1985; MWR)
L
H
25
2) Winter Monsoon Experiment
(Greenfield and Krishnamurti 1979)
WMONEX (1978/79)
26
L
H
L
L
H
H
27
(Lau and Lau 1984)
(Lau and Chang 1987)
28
2) Impact of Cold Surge on Winter Monsoon
Rainfall
Multiple-scale process
Tropics-midlatitude interaction
(different perspective)
Regional hydrological cycle
29
Cold-surge vortex
Occurrence
frequency
Genesis
location
Trajectory
30
Rainfall contribution of
cold surge vortices
74%
31
Rainfall variability in tropical Southeast
Asia is caused by a multiple-scale
interaction among:
• ENSO
• MJO (30-60 day mode)
• Cold surge (12-24 day mode)
• Synoptic disturbance: cold-surge vortices
32
Taiwan low – no front
Example
Taiwan low – Taiwan front
Taiwan low – redevelopment of South China front
33
Impact on Taiwan
Contribution of rainfall from different types of perturbation
Rainfall rate
Rainy day
34
Interannual variation – Cold surge
( Chen et al. 2004; JCLI)
35
North Pacific Short-Wave Train during the Extreme Phase of ENSO
( Chen 2002; JCLI)
36
37
Clim
Cold
Warm
38
( Chen 2002; JCLI)
Field Experiment of EAMEX
1. Summer Rainstorm Experiment
2. Winter Rainfall Experiment
Tsing-Chang Chen
Department of Geological and Atmospheric Sciences
Iowa State University
U.S.A
39
1. Summer Rainstorm Experiment
Observation/
Initialization
Science plan
Multiple-scale
interaction
Tropical-midlatitude
interaction
9Z 5/28/06
Downstream
Amplification
Upstream
Genesis
Regional hydrological
cycle
NWP/Simulation
40
Summer Monsoon Rainstorm Experiment
0
|
▓
41
2. Winter Rainfall Experiment
Observation/
Initialization
Science Plan
V(925mb), pS
L
L
H
H
Multiple-scale
interaction
VIS
Tropics-midlatitude
interaction
Regional hydrological
cycle
NWP/Simulation
42
Winter Rainfall Experiment
0
|
▓
43
3. Time Table (with international projects)
WR Exp.
RS Exp.
2006
2007
pilot exp.
2006
2007
build-up phase
IPY (International Polar Year)
2008
IOP
post-EAMEX analysis phase
2009
2010
post-EAMEX analysis phase
2008
2009
2007
2008
2009
2010
2006
2007
2008
2009
2010
2007
2008
2009
2010
2007
2008
2009
AIPO
China-Japan
Weather Disaster
Reduction Project
AMY
IOP
2010
2006
MAHASRI
CEOP-II
2009
2008
2008
2011
44