Andrew Burton Bureau of Meteorology , Perth, Australia

Andrew BurtonBureau of Meteorology, Perth, Australia

Use of Scatterometer Winds in TC Forecasting

Tropical Cyclone Warning Centre Perth

Application of Scatterometer to Tropical Cyclone Forecasting

• Formation• Size (radius of gales)• Wind distribution• Not for absolute intensity (winds saturate at >60 90? knots)

Where to Get Scatterometer Data

• NRL Monterey http://www.nrlmry.navy.mil/tc_pages/tc_home.html

• NOAA/NESDIS QuikSCAT http://manati.wwb.noaa.gov/quikscat

Storms page – includes ambiguities: http://manati.wwb.noaa.gov/cgi-bin/

qscat_storm.pl Alternative NOAA site, with SSMI wind speeds:

http://polar.wwb.noaa.gov/winds/globdata.html• FNMOC

http://152.80.49.210/PUBLIC/SCAT or http://www.fnmoc.navy.mil/PUBLIC/SCAT• Remote Sensing Systems

http://www.ssmi.com

NRL Monterey http://www.nrlmry.navy.mil/tc_pages/tc_home.html

NOAA/NESDIS QuikSCAT http://manati.wwb.noaa.gov/quikscat

FNMOChttp://152.80.49.210/PUBLIC/SCAT/

Near Real-Time Ambiguity Removal

FNMOC Ambiguity Removal over SSMI

Remote Sensing Systemshttp://www.ssmi.com

Scatterometer Coverage

QuikSCAT: SeaWinds Measurements

From Dr. M. Freilich, Oregon State University

V-pol H-pol

SeaWinds: Swath Geometry

From Dr. M. Freilich, Oregon State University

Red = V-polBlue = H-polEdge

View (2 solns) V-pol only

Subtrack View (4 solns,but small angle var)

Ideal View(4 solns, 90

deg var)

Forward Look

Backward Look

Scatterometry: 2-Look Solutions

From Dr. M. Freilich, Oregon State University

1 2 3 4

Solution: wind ~10m/s at ?? degFrom Dr. M. Freilich, Oregon State University

Scatterometry: 4-Look Solution(s)

From Dr. M. Freilich, Oregon State University

1 2

3 4

Most-likely solution: 10m/s at 40deg

From Dr. M. Freilich, Oregon State University

Ambiguities: The Chicken-Scratch Diagram

Location, Intensity, Wind Distribution

Source: Tropical storms discussion group

25 Jan 1800Z 26 Jan 0517Z 26 Jan 1800Z

27 Jan 1712Z 28 Jan 0427Z

XX

X

X

O O

O

O

O

20S170W170W

170W170W

160W 160W

Small system (X) analysed for 3 days --no help from NWP model

• Edge of swath (~ 7 wind vector cells)

• Rain effects

• Sensitivity to errors in NWP• Practical wind regime 3-45? m/s

(problems with both very light and very strong winds)

• Resolution (25km) – impact in tight gradients

• Ambiguity Removal Process and rain flag process can affect final solution

Interpretation Challenges

Edge Problems

Along the whole edge… or small portion…

FNMOC DISPLAY

•Position using the curvature outside ‘rain block’ region.

•Look for good north-south winds.

Rain Effects – “tear drop”

Streamlines

X

Look for non-rain flagged winds

Beware of winds perpendicular to the swath, even when they are not flagged

TC Chris 03/02/02 0914Z

Isotachs

X

Look for min speed near centreTC Chris 04/02/02 1002Z

Errors in NWP

Wrong Model

Position?

TC Guillaume

19/02/02 1341Z

Where is TC HUDAH?No circulation!

?

Max Winds 95 knots

Try to fix in trough equator-ward of the strongest winds

?

? cc

Max Wind 55 KTS

(Light winds?) -----low skill

AVN 19/12Z tau 2420/2356Z

10S10S

20S

20S

In this case, poor model initialization combined with a lower skill nadir position, picks proper wind speed, but NO circulation center

TC Paul

Model initialization errors

Comparing Different Solutions

FNMOC-NOGAPSFNMOC-NRT

NRCS imageryNormalised Radar Cross Section

14 S

10 S

18 S

92 E 88 E 84 E 92 E 88 E 84 E

Scatterometer winds give wrong estimate for centre

Comparison between Quikscat solution from NESDIS 30/11/2001 at 0023Z and fair LLCC seen in SSMI near 14.4S 89.1E 30/11/2001 at 0218Z

Microwave Imagery vs Quikscat

Analysis Methods - Summary

• Ignore the bad - streamline the good

• Tear-drop – curved end

• TC’s – equatorward side of max wind

• Compare different solutions

• Isotach method – ignore direction

Conclusions

• Provides coverage over data sparse areas

• Wind speeds generally good – useful for areas of gales etc

• Use the data if it makes sense

• Be aware of low skill areas and different ambiguity removal processes (compare!)

• Do not use in isolation