WIND FIELDS OF TYPHOON SONGDA (2004) OBSERVED BY THE OKINAWA DOPPLER RADAR (COBRA)
Shinsuke Satoh *1 , Hiroko Nagahama 2, Hiroshi Hanado 3, and Katsuhiro Nakagawa 1
1 NICT Okinawa, Japan ([email protected])2 Tokyo Gakugei University, Japan3 JAXA GPM DPR Project Team, Japan
C-Band Okinawa Bistatic polarimetric RAdar (COBRA)
< Specifications >Frequency 5340 MHzPeak 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 PRFAntenna 4.5 m parabolaAntenna gain 45 dBi (inc. radome)Beam width 0.91 degSidelobe 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 / RCDoppler estimation Pulse-pair / FFTRange bin num > 2000Antenna scan 0.5-10 rpm (PPI)
0.1-3.6 rpm (RHI)
COBRA was installed on a mountain peak (343 m in ASL + 15 m tower) in Nago city, Okinawa Island.
COBRA Observation Range and AWSs
0
1
2
3
4
5
6
7
8
9:00 12:00 15:00 18:00 21:00 0:00 3:00
MO
TIO
N [
m/s
]
COBRA(± 30min)COBRA(± 90min)J MA Best Track
JST
0
10
20
30
40
50
60
-150 -100 -50 0 50 100 150DISTANCE from the Typhoon Center [km]
WIN
D S
PE
ED
[m
/s]
915
925
935
945
955
965
975
PR
ES
SU
RE
[h
Pa
]
0224Z 0900Z 1403Z
P=Pc + ΔP exp[-(Rm/R)^B]ΔP=62hPa, Rm=47km, B=1.1
Sea-Level Pressure Max. Instant. Wind Speed Mean Wind Speed
Gradient Wind
1) Translate X-axis from time to distance using the typhoon motion2) Calculate a pressure regression curve using Holland’ equation (1980)3) Calculate the gradient wind from the pressure gradient (and centrifugal force + Coriolis force)
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).
EL AZ PW PRF1 PRF2 Range Vmax Integ Ant. Speed Time[deg] [deg] [us] [Hz] [Hz] [km] [m/ s] [hit] [rpm] [sec]
1 +45 0.5 PPI 2.0 500.0 375.4 292.0 - 21.14 32 1.1 54.5 Vel Fold2 +45 0.9 PPI 2.0 500.0 375.4 292.0 - 21.14 32 1.1 54.5 Vel Fold3 +45 1.4 PPI 2.0 750.2 563.1 180.0 - 31.68 32 1.3 46.2 Vel Fold4 +45 2.0 PPI 2.0 750.2 563.1 170.0 - 31.68 24 1.8 33.3 Vel Fold5 +45 2.6 PPI 1.0 750.2 563.1 170.0 - 31.68 24 1.8 33.3 Vel Fold6 +45 3.4 PPI 1.0 750.2 563.1 170.0 - 31.68 24 2.3 26.1 Vel Fold7 +45 4.3 PPI 1.0 1000.0 750.2 140.0 - 42.15 24 3.1 19.4 Vel Fold8 +45 5.5 PPI 1.0 1000.0 750.2 140.0 - 42.15 16 4.5 13.3 Vel Fold9 +45 6.8 PPI 1.0 1000.0 750.2 140.0 - 42.15 16 5.0 12.0 Vel Fold
10 +45 8.5 PPI 1.0 1000.0 750.2 140.0 - 42.15 16 5.0 12.0 Vel Fold11 +45 10.5 PPI 1.0 1350.4 1013.2 75.0 - 56.94 16 6.0 10.0 Vel Fold12 +45 13.0 PPI 1.0 1350.4 1013.2 75.0 - 56.94 16 6.0 10.0 Vel Fold13 +45 16.1 PPI 1.0 1350.4 1013.2 75.0 - 56.94 16 6.0 10.0 Vel Fold14 +45 20.0 PPI 1.0 1350.4 1013.2 75.0 - 56.94 16 6.0 10.0 Vel Fold17 +45 RHI 41.2 1.0 1000.0 - 100.0 14.04 64 0.5 30.0 EL=0° →90°20 +45 RHI 160.0 1.0 1000.0 - 100.0 14.04 64 - 0.5 30.0 EL=90° →022 +45 RHI 245.5 1.0 1000.0 - 100.0 14.04 64 - 0.5 30.0 EL=0° →90°24 +45 RHI 340.0 1.0 1000.0 - 100.0 14.04 64 0.5 30.0 EL=90° →0°
No. Pol Note
PW PRF Range Vmax PW PRF Range[deg] [deg] TX [us] [Hz] [km] [m/ s] TX [us] [Hz] [km] [hit] [rpm] [sec]
1 +45 0.5 PPIBeam221 100.0 400.0 280.0 5.61 57 1.0 400.0 20.0 26 1.3 47.02 +45 0.9 PPIBeam221 100.0 400.0 280.0 5.61 57 1.0 400.0 20.0 26 1.3 47.03 +45 1.4 PPIBeam221 100.0 400.0 280.0 5.61 57 1.0 400.0 20.0 26 1.3 47.04 +45 2.0 PPIBeam221 100.0 400.0 250.0 5.61 57 1.0 400.0 20.0 18 1.8 34.05 +45 2.6 PPIBeam221 100.0 400.0 250.0 5.61 57 1.0 400.0 20.0 18 1.8 34.06 +45 3.4 PPIBeam221 100.0 400.0 250.0 5.61 57 1.0 400.0 20.0 16 2.0 30.07 +45 4.3 PPIBeam220 50.0 666.7 140.0 9.36 57 1.0 800.0 20.0 44 2.3 27.08 +45 5.5 PPIBeam220 50.0 666.7 140.0 9.36 57 1.0 800.0 20.0 36 3.0 20.09 +45 6.8 PPIBeam220 50.0 666.7 140.0 9.36 57 1.0 800.0 20.0 26 4.1 15.0
10 +45 8.5 PPIBeam220 50.0 666.7 140.0 9.36 57 1.0 800.0 20.0 26 4.1 15.011 +45 10.5 PPIBeam220 50.0 666.7 100.0 9.36 57 1.0 800.0 20.0 26 4.1 15.012 +45 13.0 PPIBeam220 50.0 666.7 100.0 9.36 57 1.0 800.0 20.0 26 4.1 15.013 +45 16.1 PPIBeam220 50.0 666.7 100.0 9.36 57 1.0 800.0 20.0 26 4.1 15.014 +45 20.0 PPIBeam220 50.0 666.7 100.0 9.36 57 1.0 800.0 20.0 26 4.1 15.017 +45 RHI 41.2Beam57 1.0 1000.0 100.0 14.04 57 1.0 1000.0 20.0 64 0.5 30.0 El=0→ 9020 +45 RHI 160.0Beam57 1.0 1000.0 100.0 14.04 57 1.0 1000.0 20.0 64 - 0.5 30.0 El=90→ 022 +45 RHI 245.5Beam57 1.0 1000.0 100.0 14.04 57 1.0 1000.0 20.0 64 - 0.5 30.0 El=0→ 9024 +45 RHI 340.0Beam57 1.0 1000.0 100.0 14.04 57 1.0 1000.0 20.0 64 0.5 30.0 El=90→ 0
No. Pol2nd Beam (Short Pulse)
PulseNo.
PulseNo.
NoteEL AZ Integ Ant.Spd Time1st Beam (Long Pulse)
COBRA+ (DualCycle Beam)
COBRA (Dual-PRF)
coscossin mr VVVTangential 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
cos
sin
sinsincoscos
cossinsincos
mmr
mmrd
VVVV
VVVVV
o
θ
Tangential wind vector V
Vd Doppler vel
Typhoon traveling vector Vm
ｘ
ｙ
φ
Vr Radial wind vector
Coefficient of Tangential- wind component
Coefficient of Radial- wind component
Contribution rate of Tangential-wind comp
0
10
20
30
40
50
60
-150 -100 -50 0 50 100 150DISTANCE from the Typhoon Center [km]
WIN
D S
PE
ED
[m
/s]
915
925
935
945
955
965
975
PR
ES
SU
RE
[h
Pa
]
0224Z 0900Z 1403Z
P=Pc + ΔP exp[-(Rm/R)^B]ΔP=62hPa, Rm=47km, B=1.1
Gradient Wind
0230Z-Doppler
0430Z-Doppler Sea-Level Pressure Max. Instant. Wind Speed Mean Wind Speed
1230Z-Doppler
- 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
• 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.
Summary
09/08,09JST09/05, 09JST
09/08,12JST09/05, 12JST
998hPa
2728293031
0102
0304
05
06
07
980975945935
935945
935940
940
945
08 970hPa
925hPa
<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.
Assumed tangential wind
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20
30
40
50
60
70
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
[km]台風中心からの距離
[m
/s]
接線
速度
Observed Raw Data Simulation (reference)
Dual-PRF(pulse by pulse)
Aliased vel corrected by usingthe continuity of Doppler vel
20 m/s
Vmax=5.6 m/s
40 m/s
40 m/s
Vmax=21.1 m/s
5 m/s
Corrected Velocity
Hopeless striped pattern
0
10
20
30
40
50
0 25 50 75 100 125 150 175DISTANCE from the Typhoon Center [km]
TAN
GE
NTI
AL
VE
L [m
/s]
0230Z0330Z0430Z1230Z
Observed Doppler velocity Subtract radial-vel (Vr=0) and traveling speed components
Introduction
Double eyewall echoes
Radius of 20 km
Estimated mean tangential velocities at 0230Z, 0430Z, and 1230Z
Mean Tangential-wind and Surface-wind
Estimation of Tangential-wind Distribution
Correction of Aliased Doppler Velocity
Moving Speed of the Typhoon Center
Typhoon passed over the COBRA
COBRA Observation Sequence
Surface Meteor Data and Gradient Wind
Outline of Typhoon SONGDA
• 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.
<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
Sequence every 10 min ・ PPI (14-EL angles)・ RHI (4 AZ angles)・ POS (EL=90 deg)
Tx: +45 deg 、 Rx: H/V simultaniousObs values: ZHH, ZVV, ZHV, Vel, Wid, NCP, ZDR, (LDR), HV, DP
280 km
Ishigaki Island
Yonaguni Island
Nago COBRAradar site
Ogimi WPR site
NICT OkinawaCenter (Onna)
< Data for analyses >- Ze + Doppler Vel (PPI EL= 0.9 deg)- AWS ground meteor data at COBRA site
Range reso: 150 m/300 mBeam width: 0.9 deg
