experimental uses of quikscat at tpc and future requirements jack beven hurricane specialist,...

Experimental Uses of QuikSCAT at TPC and Future Requirements

Jack Beven

Hurricane Specialist, Tropical Prediction Center

Chris Hennon

Visiting Scientist, UCAR, Tropical Prediction Center

Outline

• Operational Applications and Examples of QuikSCAT

• Applied Research– Auto center detection– Dealing with rain

• Future– WindSat– Operational Requirements and Desires

Does a circulation center exist?Is this center fix accurate?

Is 50 kt an accurateMSW measurement?

Is this a valid representationof the 34 kt. wind radii?

Isabel (45 kt from Dvorak)

How timely isthe QSCT Pass?

Operational Examples

A good center location

A bad example - QuikSCAT can fail to detect circulation centers,even in tropical storms or hurricanes

Erika (45 kt from aircraft)

Fausto (2003) – distance betweenpositions = 56 mi

When a center is found, it is frequently in the wrong place

NRCS analysis may provide a more accurate center

QuikSCAT Research at TPC

Auto Center Detection• Motivation

– For TDs and TSs, QuikSCAT solution contains a discernable fix about 35% of the time

– The ambiguity field may contain a circulation center not shown in the solution field

– In general, operational time constraints do not allow a manual ambiguity analysis

– An automated ambiguity analysis procedure will identify any possible circulations and assign a confidence level to each

• Confidence based on directional probabilities embedded in data

Draw 4 x 4 degree (or user specified size) box around chosen location

Rain Contamination

• Rain severely limits QuikSCAT usefullness for:– Wind Radii estimation (esp. 50 and 64 kt.)– Circulation center detection– Maximum wind estimation

• Can we ‘correct’ the retrieved wind speeds based on the rain rate?

Operational Rain Correction?

• Need QuikSCAT retrieved wind speed, hi-res rain rate, and ‘true’ wind speed to develop an algorithm– Accurate rain rate generally not available (no radiometer on board)– Good surface wind speed analysis for TCs difficult if not

impossible in most situations

• Can MUDH rain probability serve as a proxy for rain rate?– MUDH considers brightness temperature and normalized beam

difference – two parameters that should be correlated with rain rate

– If so, than a correction algorithm may be developed

• Two TRMM/QuikSCAT coincident passes analyzed

Fabian 2 Sep. 2003TRMM 0244 QSCAT 0159

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

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0 10 20 30 40 50 60

Rain Rate (mm/hr)

MU

DH

Pro

b.

Can WindSat Provide Usuable TC Retrievals?

Rain Not Likely Rain Likely

Fabian (2003)- Verification against QSCAT

Verification against surface wind analysis (Fabian 3 Sep. 2003 2147 UTC)

H*Wind Wind Speed

WindSat – H*Wind

WindSat Rain Rate (experimental)

Highest differencesexactly match heavy rain areas

Generally good agreementaround storm periphery

Very Large (> 10 m/s)differences over muchof the storm

Figures courtesy of Ian Adams (UCF)

Isabel (2003)

Windsat September 14

QuikScat September 15

WindSat figure courtesy of Zorana Jelenak (NESDIS)

Summary

• QuikSCAT has been useful in many cases for operational application– Center detection, location, wind radii

• Rain impacts and lack of rain information severly limits further use of QuikSCAT winds

• Preliminary TC WindSat looks not encouraging– Development continues

Requirements for Future Missions

• Wind measuring instrument and rain detection instrument on the same satellite – CMIS instrument on NPOESS will fulfill this

• Less ambiguity in the measurements• More coverage!• New techniques (physical, model function)

– Limit rain effects

– Developed specifically for tropical cyclones