An Observational and Numerical Studies on flooding Events Associated with the Southwesterly Flow After the Passage of Typhoon Mindulle Pay-Liam Lin,and Wen-Da Hsu Department of Atmospheric Science, National Central University

1. Introduction 2. Synoptic Analysis 3. Model Setup 4. Simulation Results 5. Conclusion Outline

˙Landfall from Hualiam at 22:40LST ˙Heavy Rainfall and Flood during July 2 to July 4 。 1-1 Case Description 1.Introduction

The daily rainfall accumulation July 1 July 2 July 3

July 4 July 5 The daily rainfall accumulation

Total accumulative rainfall during typhoon Mindulle passage over Taiwan

1-2 Scientific Issues 1.A rainfall minimum is normally observed in Taiwan between the end of the Mei-Yu season and the early July. 3. Flooding is unusual in most of Taiwan during the monsoon break period. However, flash floods occurred in central and southern Taiwan on 2-4 July 2004 during the climatological minimum rainfall period (16 June to 15 July). 4. The WRF model was used to investigate heavy rainfall event, The objective is to test the performance of the WRF model and to evaluate it’s capability as a severe weather research tool in a subtropical area. 2. Most of the total rainfall accumulation was not high due to the presence of the western Pacific subtropical high (WPSH) over Taiwan.

2-1 Synoptic weather analysis q(shading) ） SLP （ contour ） 0630_00 UTC （ 2 ） Synoptic Analysis 0702_00 UTC IR3 WP 0701_00 UTC0703_00 UTC 0702_00 UTC

850 hPa ， ws （ contoures ） ws>20ms （ red shading ） 0702_12 UTC 975 hPa Div. 0702_12 UTC 975 hPa div(qv)0702_12 UTC

q(shadding ） SLP （ contoure ） 0704_00 UTC 500hpa vorticity 0703_12 UTC

850 hPa ws （ contour ）， ws >20ms （ red shading ） 0703_12 UTC 975 hPa div(V) 0703_12 UTC 975 hPa div(qv) 0703_12 UTC

2002 RAMMASUN 2003 Soudelor Case: the sixth track of typhoon 2-2 cases comparison

2002 Rammasun q （ contour ）， SLP （ contour ） 0616_00 UTC 0618_00 UTC 2003 Soudeler q （ shading ）， SLP(contour ） 0703_00 UTC 0703_12 UTC

2002 Rammasun 925hpa div(qV) 0617_00 UTC0618_00 UTC hpa Div 0703_00 UTC0703_12 UTC

2002 Rammasun 500 hPa vorticity 0618_00 UTC0619_00 UTC 2003 Soudelor 500 hPa vorticity 0704_00 UTC0705_00 UTC

Characteristics of typhoon Mindulle 1 ） The moisture is very plentiful in the SCS before landfall of Mindulle 。（ great than 20g/kg ） 2 ） Mindulle coincided with the monsoon trough during landfall in Taiwan ， the strong southwesterly extended from the southeastern side region of typhoon to the southern part of Taiwan (ws > 20 m/s) 3 ） As Mindulle left Taiwan ， the convergence of the outer circulation of Mindulle with the environmental southwesterly in the southwestern part of Taiwan Strait trigger the initiation of MCS, then MCS moved into Taiwan and lead to the precipitation moved from coaster to upslope area 4 ） After leaving Taiwan, Mindulle coincide with the upper layer trough,then the upper trough deepen and lead to the increase of positive vorticity above Taiwan. It provide favorable condition to the development of low level disturbance 5 ） The strong Southwesterly continue to transport the warm moisture air to Taiwan area to support the development of MCS. How develop of the Southwesterly ？ What affect the initiation and development of MCS ？ Are there any difference between two precipitation episodes?

（ 3 ） Model Setup I.C. NCEP/AVN 1° × 1° Vertical: 32 levels EXP 1EXP 2 Starting time 1800 UTC,July UTC,July 3 Simulation time72 hours36 hours Domains Domain 1 ： 45km ， 140×105 Domain 2 ： 15km ， 142×124 Domain 3 ： 5km ， 127×127 Domain 1 ： 45km ， 140×105 Domain 2 ： 15km ， 151×151 Domain 3 ： 5km ， 163×160 Physical Parameterization mp_physics （雲微物理參數化） WSM 5-class scheme ra_lw_physics （長波輻射參數化） Rrtm scheme ra_sw_physics （短波輻射參數化） Dudhia scheme sf_sfclay_physics （地面層參數化） Monin-Obukhov sf_surface_physics （地表參數化） Thermal diffusion scheme bl_plb_physics （邊界層參數化） YSU scheme cu_physics （積雲參數化） Grell-Devenyi ensemble scheme

（ 5 ） Simulation Results 4-1 Validation Exp. 1 initiation ： 16 hours from starting time ， 702_10UTC dissipation ： 27 hours ， 0702_21UTC

4-1 Validation -- EXP. 2 initiation ： simulated 12 hours ， 0703_18UTC dissipation ： simulated 20 hours ， 0704_02UTC

850hpa Streamline 0702_15 UTC 4-2 Episode 1 Heavy Rainfall 0702_11UTC~0702_15 UTC u difference 0702_11UTC~0702_15 UTC v difference

Horizontal Momentum EQ ： Advection Vertical Advection PGF Coriolis force Viscous force Ageostrophic acceleration

U ageostrophic acceleration V ageostrophic acceleration U horizontal advection V horizontal advection

850 hPa Vg 0702_10UTC0702_12 UTC0702_14 UTC 850 hPa AVg 0702_14 UTC

850 hPa 非地轉風分量 0702_14UTC 0702_11UTC~0702_15 UTC u difference 0702_11UTC~0702_15 UTC v difference 850 hPa Height 0702_11 UTC 0702_13 UTC0702_15 UTC

0702_15 UTC 300 hPa H （ contour ）， Ws >30m/s （ shading ） W >2m/s （ red contour ） 0702_15 UTC 850 hPa H （ contour ）， ws>30m/s （ shading ） W >2m/s （ red contour ） 850 hPa div （ dash contour ） 0702_15 UTC 300 hPa div （ blue solid contour ） 0702_15 UTC ˙The southerly and southwesterly from SCS confluence with the typhoon outer circulation leads to the development of the strong southwesterly flow ˙As Mindulle left Taiwan, the northwesterly associated with typhoon circulation converge with environmental southwesterly in the southwestern part of Taiwan Strait. The increasing PGF associated with the 850 hpa mesolow enhance the southwesterly, and continuously to transport warm moisture to help the development of MCS. ˙The low level confluent entrance area at 850 hpa coincide with the 300 hpa upper level divergent outflow area and the upper jet stream located at the downstream area of the low level jet provide a favorable condition for the development of MCS. This situation is consistent with the papers of Chen(1998;2000) summary

0703_16 UTC~0703_20 UTC u difference0703_16 UTC~0703_20 UTC v difference 4-3 Heavy rainfall : episode 2

850hpa div. 0703_18UTC 850hpa streamline ， W>2m/s(red shading) 0703_18UTC ˙After typhoon Mindulle passage, the southwesterly flow still prevail and transport moisture in the vicinity of Taiwan. ˙The low level convergence mainly located in the windward side of CMR.The warm moisture air lifted by the terrain lead to the development of local convection. summary ：

4-3 Sensitivity Test No Terrain ：

Decrease the SCS moisture ： 東經 110˚ ～ 120 ˚ 北緯 15 ˚ ～ 21 ˚

（ 6 ） Summary-1 ˙Observational analysis shows that abundant moisture already exist in the south china sea before Mindulle invade Taiwan. ˙During Mindulle invade Taiwan, typhoon is just located inside the monsoon trough, southerly and southwesterly flow confluent with typhoon circulation in the south and eastern side of Taiwan and generated a strong wind zone and help to transport warm moisture to the vicinity of Taiwan. ˙As Mindulle left Taiwan, the northwesterly associated with typhoon circulation converge with environmental southwesterly in the southwestern part of Taiwan Strait. The increasing PGF associated with the 850 hpa mesolow enhance the southwesterly, and continuously to transport warm moisture to help the initiation and development of MCS, then MCS moved into Taiwan and lead to the precipitation moved from coast to upslope area. ˙

（ 6 ） Summary-2 ˙After leave from Taiwan, Mindulle coincide with the upper trough,then the upper trough deepen and lead to the increase of vorticity above Taiwan. It provide favorable condition to the development of low level disturbance. The low level convergence mainly located in the windward side of CMR.The warm moisture air lifted by the terrain lead to the development of local convection. ˙Sensitivity test shows that the terrain effects is the main mechanism for the intesity and distribution of rainfall, while moisture quantity in SCS and Taiwan Strait will affect the intensity of the convective system. ˙