Precipitation Characteristics of Landfall Typhoons in the Taiwan Area Ben Jong-Dao Jou Department of Atmospheric Sciences National Taiwan University Taipei, Taiwan 2nd International Precipitation Working Group (IPWG) October 2004, Monterey, California
Typhoon Nock-Ten Mei-yu Asian Continent Pacific Ocean Taiwan
Torrential rains with high rain rates have produced devastating hazards to the society.
QPESUMS: Quantitative Precipitation Estimation and Segregation Using Multiple Sensors NSSL CWB WRA
Purpose of this study From radar point of view, to illustrate the structure changes of precipitation of landfall typhoons in the Taiwan area • The azimuth-mean reflectivity pattern • The asymmetrical structure of precipitation • The effect of terrain on precipitation structure change • Rainfall intensity vs Rainfall strength
History of Typhoon NARI September 2001 05-12z, F-tropical depression 06-00z, I-tropical storm Looped over Okinawa area 09-12z, I-typhoon 10-00z, D-tropical storm 11-00z, I-typhoon 12-00z, D-tropical storm 14-00z, started to move SW 15-00z, I-typhoon 16-13z, landed at Taipei/I-Lan D-tropical storm 18-14z, left Tainan 20-03z, landed Quandong 21-03z, D-tropical depression Typhoon NARI Sept. 16, 2001
IV I C B A III II TC rainfall distribution Inner core (A<100km); 1st outer ring (B 100~200km); 2nd outer ring (C, 200~300km)
Space and time distribution of mean reflectivity at 4 km height of Typhoon Nari (0116) derived from data observed by RCWF Doppler radar in the northern Taiwan. The period of data used is from 0000 0UTC to 1800UTC, September 16 2001. Time “-” means hours before landfall and “+” means hours after landfall. The reflectivity data is 6 minutes in interval.
Time variation of rainfall distribution of typhoon Nari (0116) 8% per hour A 2% per hour landfall Ratio B 300 km radius average rain rate increased from 2.51 mm/h to 3.74 mm/h, about 50% increase.Rainfall enhancement inside the inner core of the storm was greatly manifested during the landfall period. Pronounced structure changes were identified. C
Area occupied by reflectivity larger than 40 dBZ within 60 km around the TC eye Typhoon Herb (9608)
S S 25 22 29 24 62 S M M S M 54 57 15 22 27 36 26 19 31 24 22 16 35 27 63 M Asymmetrical structure of rainfall of Typhoon Nari (0116)0000, 0600, 1200, 1800UTC, September 16, 2001 Moving speed 2.75m/s Vertical shear 1.05m/s TYPE3 M-S=180 45°
IV IV I III I II M IV II III I Motion front Motion right Motion rear Inner core quadrant-mean rain rates of Nari (0116) landfall Asymmetrical precipitation structure was enhanced and closely related to the manifestation of flow interaction with terrain, windward side rain rates intensified and leeside decayed during landfall period. Extremely high rain rates were found over fourth quadrant after landfall.
2001/9/16/1735UTC First quadrant 2001/9/15/0000UTC Fourth quadrant Convective precipitation Km dBZ
TRMM-TMI 2001/9/15 0028UTC (U) 2001/9/16 1735UTC (R)
First quadrant Fourth quadrant
Summary • The precipitation structure of Nari before and after landfall is examined using the reflectivity and brightness temperature data collected by RCWF and TRMM TMI and PR. Pronounced precipitation structure changes were identified. • The contraction of the eye and the intensification of precipitation in the inner core were observed and this phenomenon can be traced back to 4-5 hours before the storm made landfall. The final hour enhancement of precipitation (about 50% increases) before landfall suggests the strengthening low level convergence induced by the differential friction may play an important role. • The asymmetrical distribution of precipitation of the storm in the open ocean was changed significantly during landfalling period. The change of the asymmetry can be crudely attributed to the effect of land surface and topography. • From TRMM observations, the detection of very low brightness temperature by 85GHz TMI and significant intensification of radar reflectivity by PR all suggest the existence of severe convective activity and the possibly cause for extreme high rain rate.
Ring-averaged rainfall rates (ring A=0-100, B=100-200, C=200-300km) Herb (1996/7/31, 0600/1200UTC) Kai-tak (2000/7/9, 0600/1200UTC) Toraji (2001/7/29, 0600/1200UTC) Nari (2001/9/16, 0600/1200UTC) Lekima (2001/9/25-26, 1800/0000UTC)
Climatological-statistical rainfall prediction model for TC near Taiwan Chang (CP), Yeh, Chen (1993) MWR: rain rates v.s. storm center, based on 1971-1990, 82 TCs, every 3h, 1446 cases, 22 surface stations rainfall data.
dBZ 50 40 Herb 30 Nari 20 Toraji 10 300 60 120 180 240 Km Storm center Rainfall intensity vs Rainfall strength降雨強度 vs 降雨壯度