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Development Mechanism of Heavy Rainfall over Gangneung Associated with
Typhoon RUSA
Tae-Young Lee, Nam-San Cho, Ji-Sun KangKun-Young Byun, Sang Hun Park
Laboratory for Atmospheric Modeling Research (LAMOR)Dept. of Atmospheric Sciences, Yonsei University, Seoul
5th International Conference on Mesoscale Meteorology and Typhoon, 31 Oct.-3 Nov. 2006, Boulder, Colorado
AMOP
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Typhoon Rusa’s track and rainfall
0420 UTC 1. Sep990 hPa, 18m/ s
0630 UTC 31 Aug.960 hPa, 35m/ s
0000 UTC 23 Aug.
0000 UTC 29 Aug.950hPa, 41m/ s
• RUSA resulted in a record-breaking daily rainfall amount of 870.5 mm at Gangneung on 31 August 2002
• RUSA claimed 236 deaths & properties of about 6.1 Bill. Dollar
GangNeung
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Terrain and location of stations
• Daegwallyeong - Near the mountain peak - 712.5 mm/day (31 Aug) • GangNeung - Relatively flat area near the coastline - Maximum daily precip. : 870.5 mm/day (31 Aug) (record)
Gangneung(GN)
Daegwallyeong (DGL)
Donghae(DH)
Sokcho (SC)
Height (m)
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Kang and Lee (2004) suggested that direct terrain effect alone could not explain the heavy rainfall at Gangneung
Other studies related low-level convergence to the heavy rain at Gangneung, with terrain as a possible cause for the convergence
Mechanism of the rainfall at Gangneung is still not well understood
The heavy rainfall has not been successfully simulated by models. Why?
Previous studies
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Goals and contents
• Goal - To explain the mechanism of the record-breaking heav
y rainfall at Gangneung associated with typhoon Rusa of 31 August 2002
• Contents - Observational analysis of the event - Preliminary numerical experiments - Analysis of results
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Observational analysis
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Two peaks on 31 August 2002
- The first peak at 09 LST (00 UTC) 31 August (before the
landfall of typhoon),
- The second peak (target periodtarget period): hourly rainfall over 50 mm continued for 5 hours. Peak at 23 LST (14 UTC) 31 August
Gangneung
0
10
20
30
40
50
60
70
80
90
100
08/30/12 08/30/18 08/31/00 08/31/06 08/31/12 08/31/18 09/01/00Time idx
Hour
ly p
reci
p(m
m/h
)
OBS(886.0mm/ 36hrs)
Hourly rainfall amount at Gangneung
(UTC)
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강수분석At GN, rainfall stronger than 50 mm/h
lasts 5 hours (19~23 LST)
At DGL, rainfall stronger than 30mm/h lasts 10 hours (15~24 LST)
At SC, rainfall greater than 30mm/h lasts 5 hours (22 LST 31Aug ~ 02 LST 1 Sep), as rainfall weakened at GN and DGL
Hourly rainfall amount at 4 stations in Youngdong area
GN DGL
DH
SC
0
10
20
30
40
50
60
70
80
90
100
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 1 2 3Time (KST)
Pre
cip
itati
on (
mm
)
DHDGLGNSC
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1240UTC 31 Aug
1030UTC 31 Aug 1130UTC 31 Aug
1330UTC 31 Aug 1420UTC 31 Aug
0930UTC 31 Aug
GN
DH (radar site)
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Surface chart for 12 UTC 31 Aug 2002
GN
DH
SC
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320
322
324
326
328
330
332
334
336
338
30/ 00 30/ 06 30/ 12 30/ 18 31/ 00 31/ 06 31/ 12 31/ 18 01/ 00
Time (UTC)
Thet
aE (
K)
Donghae (DH)Daegwallyeong (DGL)Gangneung (GN)Sokcho (SC)
COOL AIR
WA
RM
MO
IST
AIR
Equivalent potential temperature
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Summary of observed features
DH
DGL
GN
NWNE
E~ESECell movement
Obs. Fr: 0.7 ~ 0.8
Band of strong echo
1130UTC 31 Aug
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Possible causes for the presence of N or NW winds at Gangneung and Sokcho :
• blocking of low-level NE flow by mountain range• local cooling of low level air along the east coast → pressure increase along the mountain slope → deceleration of winds toward the mountain range → ageostrophic northerly • magnitude changes of surface friction into the land
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Preliminary Numerical Experiment
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Experimental design• Model: WRF (V2.1.2)• Integration period: 00 UTC 31 Aug – 00 UTC 1 Sep 2002• 1-way nesting
Domain1 (D1)
Domain2 (D2)
Domain3 (D3)
Domain4 (D4)
Horizontal grid spacing
30km(191X171)
10km(190X181)
3.3km(217X199)
1.1km(271X298)
Vertical layers
33 layers (model top : 50hPa)
Cumulus Betts-Miller_Janjic No cumulus
Microphysics WSM 6 microphysics
LW radiation RRTM scheme
SW radiation Dudhia scheme
PBL Mellor-Yamada-Janjic TKE scheme
Surface Thermal diffusion scheme
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Sea level pressure for 12 UTC 31 Aug 2002
CONT OBS
Simulated typhoon track and pressure distributionagree well with observation.
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06 UTC
12 UTC
GN
DGL
DH
SC
GN
DGL
DH
SC
06 UTC
12 UTC
SLP and surface winds.
obs. (left) and model (right)
SC
GN
DH
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06 UTC 09 UTC
12 UTC 15 UTC
Sim. Rainfall
GN
DGL
DH
SC
GN
DGL
DH
SC
GN
DGL
DH
SC
GN
DGL
DH
SC
GN
C
DH
SC
Terrain
1130UTC 31 Aug
Radar
GN
DH
DGL
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Hourly rainfall amount1-hr accumulated precipitation (Gangneung)
Time (UTC)
6 7 8 9 10 11 12 13 14 15 16 17 18
Pre
cipi
tatio
n (m
m)
0
10
20
30
40
50
60
70
80
90
100
OBS CONT
1-hr accumulated precipitation (Daegwallyeong)
Time (UTC)
6 7 8 9 10 11 12 13 14 15 16 17 18
Pre
cipi
tatio
n (m
m)
0
10
20
30
40
50
60
70
80
90
100
OBS CONT
GN DGL
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Simulated and observed surface-air temperature at Gangneung
31/
Gangneung
15
16
17
18
19
20
21
22
23
24
25
00 03 06 09 12 15 18
Time (UTC)
Tem
pera
ture
(°C
)
OBS
CONT
GDAS
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Froude Number
Time Observation Simulation
06 UTC 31 0.69 1.52
12 UTC 31 0.77 3.13
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Simulations with other models, initial and boundary conditions
Numerical models• Weather Research and Forecasting (WRF) model V2.1.2• PSU/NCAR Mesoscale Model (MM5) V3.7• CSU Regional Atmospheric Modeling System (RAMS) V4.4
Initial and boundary conditions from:• NCEP GDAS• KMA GDAPS
Integration periods:• 24hr (00 UTC 31 Aug – 00 UTC 1 Sep 2002)• 36hr (12 UTC 30 Aug – 00 UTC 1 Sep 2002)
All simulations failed to reproduce observations at and to the north of Gangneung
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Possible causes for failure
• Errors in the initial conditions over the East Sea and coastal area
• Errors in boundary conditions (e.g., SST, surface roughness)
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Summary (1)
• Heavy rainfall of 31 August 2002 at Gangneung (GN) is being examined using observation and numerical experiments.
• A band of strong rainfall develops along the mountain range as easterly associated with the typhoon Rusa blows toward the range.
• The band development is limited to GN and to its south during the heavy rainfall period at GN.
• Low-level N or NW winds prevail at GN and to its north as strong easterlies are found at higher levels.
• The presence of N - NW winds at low level to the north of GN appears to be a key factor for the heavy rainfall at GN.
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Summary (2)
• Models have successfully reproduced the propagation of typhoon Rusa across the Korean peninsula, but not the heavy rain at Gangneung.
• N or NW winds at Gangneung and to its north are not simulated.
• Froude number of simulated flows toward the mountain range are significantly higher than the observation due to higher low-level temperature.
• Simulations using other models and initial conditions failed to reproduce observation at GN and in the area to its north.
• The cause of failure is being examined.
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Thanks !