Tropical Cyclone Intensity Estimation UsingAdvanced Microwave Sounding Unit (AMSU)

Derrick HerndonUW-Madison CIMSS

Mark DeMariaNOAA/NESDIS/CIRA

Kurt F. Brueske, Major, USAFUnited States Air Force Academy Department of Physics

Chris VeldenUW-Madison CIMSS

John KnaffColorado Institute for Research in the Atmosphere (CIRA)

Tropical Cyclone Intensity Estimation Using NOAA-KLM SeriesAdvanced Microwave Sounding Unit (AMSU)

Warm Core Observations

• MSLP estimates derived from AMSU-A radiances - Provides measure of upper level warm anomaly magnitude - Channels 7 and 8 located at average ht of anomaly (150-250mb) - Anomaly strength directly related to intensity

929hPaHurricane Inez 1966 Hurricane Floyd 1999

• AMSU flown aboard NOAA 15, 16 and 17 as well as Aqua - 6 estimates per day (2 more with Aqua)

CIRA AMSU Tropical Cyclone Algorithm

V(r,Sample r/z tangential windcross-section from AMSUretrieval (steps 1-4)

1. Retrieve T(x,y,z) from all AMSU-A channels2. Correct T for rain and ice effects3. Hydrostatic integration for P(x,y,z) 4. Gradient wind for V(r,z)5. Statistical Prediction Independent Variables: Parameters from retrieved T, P, V Dependent Variables: Max Wind (Vmax) Min Sea-Level Pressure (MSLP) Azimuthally averaged radii of 34, 50, 64 kt winds (r34, r50, r64)6. Fit parametric wind model to r34, r50, r64 and storm speed to get asymmetric radii

2002 Real-Time Test • Algorithm developed from 1999-2001 Sample • 2002 Real-Time Runs

– Initiated at 00, 06, 12, 18 UTC– Storm positions from ATCF– Analysis restricted to storms within 700 km of AMSU data swath– Results sent to TPC via ftp

• Evaluation Samples– 1999-2001 Developmental cases (N=473)– 2002 All Atlantic/East Pacific cases (N=288)– 2002 Atlantic/East Pacific cases with recon (N=64)

• Ground “Truth” for Evaluation– NHC Best Track Vmax and MSLP– NHC Forecast/Advisory for wind radii

0

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0 20 40 60 80 100 120 140

AMSU Estimate Vmax (kt)

Obs

erve

d (k

t)

All Cases (n=288) Recon cases (n=64)

910

930

950

970

990

1010

910 930 950 970 990 1010

AMSU Estimate MSLP (hPa)

Obs

erve

d (h

Pa)

All Cases (n=288) Recon Cases (n=64)

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Predicted R64 (nmi)O

bser

ved

R64

(nm

i)

2002 ALL2002 RECON

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160

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Predicted R50 (nmi)

Obs

erve

d R

50 (n

mi)

2002 ALL2002 RECON

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0 50 100 150 200 250 300 350

Predicted R34 (nmi)

Obs

erve

d R

34 (n

mi)

2002 ALL2002 RECON

Predicted vs. “Observed” Scatter Plots for 2002 Real-Time Runs(Total and Recon-Only Samples)

Vmax MSLP

R34 R50 R64

Error Summary for CIRA Algorithm:Developmental, 2002 All and 2002 Recon

Samples

Wind Radii Mean Absolute Error (nmi)

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510

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2025

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Mea

n Ab

solu

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rror

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Vmax and MSLP Mean Absolute Error

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Vmax 199

9-200

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Vmax 200

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Vmax 200

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MSLP D

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MSLP 20

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MSLP 20

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VMAX

or M

SLP

Erro

r (kt

or h

Pa)

Vmax and MSLP Variance Explained

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Vmax 199

9-200

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Vmax 200

2 All

Vmax 200

2 Reco

n

MSLP 19

99-2001

MSLP 20

02 All

MSLP 20

02 Rec

on

R2 (%

)

Wind Radii Variance Explained

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R2 (%

)

Absolute Error Variance Explained

Vmaxand

MSLP

R34R50R64

Vmax MSLP Vmax MSLP

R34 R50 R64 R34 R50 R64

CIMSS AMSU Tropical Cyclone Algorithm

• Statistical Method Based on 1999-2001 regression against recon obs - Linear fit (R2 = 0.82)

• Independent estimates in 2002 comparable to Dvorak technique

• ATCF message provides RMW (Used as a proxy for anomaly size)

• Improved logic accounts for anomaly height, sub-sampling

• Channel 7 retrieval used to account for storms near limb

FOV 1 FOV 30

Resolution ~ 50km

2002 Results for Atlantic Basin

Compared to Dvorak (N= 60) in hPa

CIMSS DvorakMean Error 3.24 4.52Std Dev 2.29 3.40Bias -0.28 -0.90RMSE 3.95 5.62

Avg MSLP of sample 1002.4

Atlantic statistics for AMSU versus Recon (+/- 3 hrs) in hPa (N=63)

Mean Error 3.24 Std Dev 2.29 Bias -0.42 RMSE 3.96

Avg MSLP of sample 1002.6

2002 Atlantic Basin Results

AMSU81% within +/- 0.5T

NOAA/NESDIS Satellite Analysis Branch (SAB) vs.

AMSU (N=34, +/- 2hrs of aircraft reconnaissance)

SAB 78% within +/- 0.5T

AMSU vs. Recon for Hurricane Isadore

920.0

930.0

940.0

950.0

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970.0

980.0

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1000.0

1010.0

17/191

18/0028

19/0334

19/1238

19/1606

19/1849

19/2347

20/0318

20/0723

20/1545

22/0041

22/1308

22/1641

22/1957

24/0819

24/1555

24/1935

25/0113

25/0808

25/1337

25/1925

Day/Time

MSL

P (m

b)

AMSU Recon

20 Mile Eye Storm on edge of satellite Swath

(FOV 3)

Future WorkImprove Technique

• Bias correction when storm is near satellite limb

• Separate treatment of pinhole eye storms using new coefficients

• Time averaging / smoothing

• Add channel 8 retrieval

• Integrate algorithm into NHC/TPC operations

• Addition of AMSU on Aqua (2 more passes per day)

• Basin specific coefficients (need sufficient “observations”)

Confidence Indicator

• Measure Based on FOV, eye size (RMW), anomaly height

Summary

• Penetrates cloud cover

• 55 Ghz region radiances can quantify inner core thermal structure / changes.

• Temperature anomaly strength directly associated with tropical cyclone intensity

• Skill comparable to, and in some cases better than, the Dvorak estimates

• An important new addition to the forecaster “tool kit”

AMSU provides unique tropical cyclone perspective

Conclusions from 2002 Evaluation• Vmax, MSLP (CIRA):

– 2002 (independent) performance very similar to (slightly improved) over dependent sample

– Intensity underestimated for small-cored systems• Wind Radii (CIRA Method):

– 2002 recon-only errors generally similar to dependent sample– Tendency for high bias for R50 and R64– Observed R50 and R64 more asymmetric than predicted

• Addition of second AMSU channel (CIMSS): – Accounts for variability in TC temperature anomaly height

• Improvements resulting from advanced algorithm logic (CIMSS): – Based on evaluation of 3 years of estimates, continues to evolve

• Additional improvements foreseen in 2003:– Characterization and new regressions for small-cored storms

• JHT pathway in 2003:– Continue evaluation of 2002 performance– Implement algorithm upgrades and re-evaluate after 2003 season– If successful and approved, activate improved algorithms at TPC