WIND FIELDS OF TYPHOON SONGDA (2004) OBSERVED BY THE OKINAWA DOPPLER RADAR (COBRA)

1. 970hPa 08 07 945 Ogimi WPR site 940 06 925hPa 935 05 940 Nago COBRAradar site 945 04 935 03 998hPa 935 02 945 980 975 01 27 NICT OkinawaCenter (Onna) 31 29 28 30 Yonaguni Island JST Ishigaki Island Subtract radial-vel (Vr=0) and traveling speed components WIND FIELDS OF TYPHOON SONGDA (2004) OBSERVED BY THE OKINAWA DOPPLER RADAR (COBRA) 1 NICT Okinawa, Japan (satoh@nict.go.jp) 2 Tokyo Gakugei University, Japan 3 JAXA GPM DPR Project Team, Japan Shinsuke Satoh *1 , Hiroko Nagahama 2, Hiroshi Hanado 3, and Katsuhiro Nakagawa 1 Introduction Outline of Typhoon SONGDA Typhoon passed over the COBRA Estimation of Tangential-wind Distribution 　ｙ • A ground-based multi-parameter radar has the advantages of measuring the entire 3-dimensional structure and time evolution of a tropical cyclone, even though it has not mobility like an airborne radar. • The COBRA has a function of arbitrary setting of the radar parameters to realize both long-range and large-velocity observation using an optimum PRF setting. • In this study, the distribution of the tangential wind in the typhoon Songda (2004) is revealed by the COBRA Doppler data, and it is evaluated by comparisons with surface observation data. VdDoppler vel Tangential wind vector V Typhoon traveling vectorVm Vr Radial wind vector θ Tangential comp. Radial Comp. Moving-speed Comp. : azimuth angle from the typhoon center to a measurement point : azimuth angle from the radar to the point : azimuth direction of the typhoon traveling motion φ 　ｘ o 09/08,09JST 09/05, 09JST <Objectives of this study> To investigate the wind fields of typhoon SONGDA (T0418), which passed over the COBRA, using COBRA Doppler data, and surface observation data. Coefficient of Tangential- wind component Contribution rate of Tangential-wind comp Coefficient of Radial- wind component C-Band Okinawa Bistatic polarimetric RAdar (COBRA) 09/08,12JST 09/05, 12JST < Specifications > Frequency 5340 MHz Peak power 250 kW×2 (Klystron)10 kW×2 (TWTA)  COBRA+ Pulse width 0.5 / 1.0 / 2.0 s (Klystron)0.5 - 100 s (TWTA)  COBRA+ PRF 250-3000 Hz, PRT 1 s step staggered PRF Antenna 4.5 m  parabola Antenna gain 45 dBi (inc. radome) Beam width 0.91 deg Sidelobe level < -30 dB (AZ dir., one way) < -28 dB (EL dir., one way) Cross pol ratio > 36 dB (integ in a beam) Tx Polarization H / V / +45 / -45 / LC / RC Doppler estimation Pulse-pair / FFT Range bin num > 2000 Antenna scan 0.5-10 rpm (PPI) 0.1-3.6 rpm (RHI) Surface Meteor Data and Gradient Wind Radius of 20 km Estimated mean tangential velocities at 0230Z, 0430Z, and 1230Z Observed Doppler velocity Mean Tangential-wind and Surface-wind Double eyewall echoes Moving Speed of the Typhoon Center 1) Translate X-axis from time to distance using the typhoon motion 2) Calculate a pressure regression curve using Holland’ equation (1980) 3) Calculate the gradient wind from the pressure gradient (and centrifugal force + Coriolis force) COBRA was installed on a mountain peak (343 m in ASL + 15 m tower) in Nago city, Okinawa Island. The distribution of the gradient wind is comparable to the distribution of the maximum instantaneous wind speed except the radius of the maximum wind speed (calculated Rm=47 km, observed Rm=20 km). COBRA Observation Range and AWSs • Estimated mean tangential-winds are consistent with the gradient wind (~ maximum instantaneous wind speed at surface) • The radius of maximum tangential-wind coincides with the eyewall echo radius COBRA Observation Sequence Correction of Aliased Doppler Velocity COBRA+ (DualCycle Beam) Summary Simulation (reference) Observed Raw Data Corrected Velocity Sequence every 10 min ・PPI (14-EL angles) ・RHI (4 AZ angles) ・POS (EL=90 deg) • Typhoon SONGDA (2004) passed over the Okinawa main island, and was observed by COBRA for 18 hours. • The typhoon has an axial symmetry structure and a clear eyewall with a radius of 20 km. • A gradient wind calculated by the surface pressure gradient shows that the theoretical maximum wind speed is about 42 ms-1. • The distribution of the mean tangential wind speeds estimated from the single Doppler radar (COBRA) data is consistent with the gradient wind and instantaneous maximum wind distribution. • The radius of maximum tangential-wind coincides with the eyewall echo radius. Hopeless striped pattern Tx: +45 deg 、Rx: H/V simultanious Obs values: ZHH, ZVV, ZHV, Vel, Wid, NCP, ZDR, (LDR), HV, DP <COBRA Obs Data ~ 18 hours> 1030JST： dual-Cycle mode (TWTA pulse compres) | 1800JST： Typhoon center passed over COBRA site | 1950-2120JST: Missing for 2 hours | 2230JST~： dual-PRF mode (Klystron) | 9/6, 0430JST(1930Z)~: Missing by generator trouble COBRA (Dual-PRF) Vmax=5.6 m/s 5 m/s 40 m/s Dual-PRF(pulse by pulse) 280 km Assumed tangential wind < Data for analyses > - Ze + Doppler Vel (PPI EL= 0.9 deg) - AWS ground meteor data at COBRA site Range reso: 150 m/300 m Beam width: 0.9 deg Aliased vel corrected by usingthe continuity of Doppler vel Vmax=21.1 m/s 20 m/s 40 m/s