Validation of Atmospheric Infrared Sounder (AIRS) Data Using GPS Dropsondes in Tropical

Cyclone Environments

Eddy HildebrandHRD Research Report

10 July 2009

Atmospheric Infrared Sounder - AIRS• Aboard Aqua satellite launched in May 2002• 2378 spectral channels• Expected performance ability (Tobin et al. 2006):

– Temperature – 1K RMS differences in 1km layers– RH – 20% in 2km layers

• Vertical profiles ~50km horizontal resolution with 28 vertical levels (Wu et al. 2006)

• Compare this data with NOAA/HRD dropsonde data from each TC

Courtesy: www.nasa.gov

Tracking the SAL

• IR and microwave satellites – e.g. GOES, Meteosat

• Twice-daily weather balloons – sparse coverage

• Aircraft measurements in and around TCs

• All 3 storms (Irene, Debby, Helene) combined – 50 sondes, 123 AIRS profiles

• Greatest differences around 850 hPa – lots of variability in moisture here

• All Non-SAL profiles – 5 sondes, 16 AIRS profiles (not a whole lot of non-SAL sondes to begin with, plus some did not have any AIRS matches)

• AIRS does OK (within 10-15% of sonde RH) except around 600mb.

• All SAL sondes – 35 sondes, 84 AIRS profiles• AIRS shows a greater decrease in moisture with height near the SAL base• AIRS also carries dry mid-level air further down than what the sondes show• Slight AIRS moist bias in mid-levels

Drop 2 from Helene 16 Sep 2006

•SAL base ~850-900 hPa

•Dry all the way to 200 hPa

Sonde vs. AIRS MR (Drop #2)SAL

200

300

400

500

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700

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900

1000

0 2 4 6 8 10 12 14 16 18

MR (g/kg)

Pre

ss

ure

(h

Pa

)

Sonde MR

AIRS MR #316

AIRS MR #317

AIRS MR #361

AIRS MR #362

Sonde vs. AIRS V5 MR (Drop #20)SAL

200

300

400

500

600

700

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900

1000

0 2 4 6 8 10 12 14 16 18 20 22

MR (g/kg)

Pre

ss

ure

(h

Pa

)

Sonde MR

AIRS MR #1227

AIRS MR #1228

Irene 7 Aug 2005 – Drop 20

Future Work

• More accurate to compare one AIRS match or an average of AIRS matches to a given dropsonde?

• Does AIRS performance vary with different layers of the troposphere?• Calculate TPW for each AIRS granule

– Compare with TPW calculated from dropsonde profiles– Compare with other TPW measurements (AMSR-E)

• Expand to the entire N.H. tropical Atlantic– PDF of AIRS mixing ratio 2002-present– PDF of dropsonde mixing ratio 2002-present– Is AIRS better/worse in each quadrant of a TC?– Life cycle of TC?