View
224
Download
10
Category
Tags:
Preview:
Citation preview
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
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
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)
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
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
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)
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
1240UTC 31 Aug
1030UTC 31 Aug 1130UTC 31 Aug
1330UTC 31 Aug 1420UTC 31 Aug
0930UTC 31 Aug
GN
DH (radar site)
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
Summary of observed features
DH
DGL
GN
NWNE
E~ESECell movement
Obs. Fr: 0.7 ~ 0.8
Band of strong echo
1130UTC 31 Aug
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
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
Sea level pressure for 12 UTC 31 Aug 2002
CONT OBS
Simulated typhoon track and pressure distributionagree well with observation.
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
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
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
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
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
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)
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.
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.
Recommended