A comparison between CERES OLR and OLR calculated from

AIRS temperature & humidity for clear-sky regions

J. Lee, A. E. Dessler, P. YangDepartment of Atmospheric Sciences

Texas A&M University

280260240220200Temperature (K)

1000 1000

800 800

600 600

400 400

200 200Pr

essu

re (

hPa)

2 4 60.1

2 4 61

2 4 610

Water vapor (g/kg)

Temperature Water vapor

2

280260240220200Temperature (K)

1000 1000

800 800

600 600

400 400

200 200Pr

essu

re (

hPa)

2 4 60.1

2 4 61

2 4 610

Water vapor (g/kg)

Temperature Water vapor

Calculate OLR

3

280260240220200Temperature (K)

1000 1000

800 800

600 600

400 400

200 200Pr

essu

re (

hPa)

2 4 60.1

2 4 61

2 4 610

Water vapor (g/kg)

Temperature Water vapor

Calculate OLR

4

Compare to CERES measurements

Methodology• Use CERES Aqua SSF edition 2a data• Consider those CERES measurements

where > 96% of the collocated MODIS cloud-mask measurements are clear

• Combine with AIRS measurements within ~20 km of the CERES measurement

• Calculate TOA flux from CERES surface skin temperature and AIRS profiles of q, T, and O3

• Nighttime, ocean, March and September 2005 5

Model Chou et al., 2001: A Thermal Infrared Radiation Parameterization for

Atmospheric Studies. NASA Tech. Memo. 104606, vol. 19, 1-55. The infrared spectrum (0~3000 cm-1) is divided into 9 bands and a

subband, in total 10 bands Using the Air Force Geophysical Laboratory HITRAN data base (1996

version) The parameterization includes the absorption due to major gaseous

absorption (water vapor, CO2, O3) and most of the minor trace gases (N2O, CH4, CFC’s) as well as clouds and aerosols.

The gaseous transmission function is computed either using the k-distribution method or the table look-up method.

Accuracy: within 1% of the high spectral-resolution line-by-line calculation In this calculation, band 9 (1900~3000 cm-1) is excluded to match with

CERES TOA flux band (50~2000 cm-1). The flux at 30 km between 1900 and 2000 cm-1 is 0.9 Wm-2 using tropical atmosphere.

Vertical atmospheric profiles from AIRS are used, including temperature, water vapor, and ozone profile

Atmosphere is divided into 100 layers from surface to 100 km and the AIRS profiles are interpolated at each level.

Sept. 2005, 30°N-30°S

Avg. difference4.7 W/m^2

Standard deviation2.3 W/m^2

CERES=0.96 calc + 8

7

330

320

310

300

290

280

270

260

CERE

S O

LR

330320310300290280270260Calculated OLR

8

300250200150OLR (W/m^2)

10

8

6

4

2

0

Frac

tion

of T

NTC

188 K

194 K

191 K

Dessler et al. (2006), Tropopause-level thin cirrus coverage revealed by ICESat/Geoscience Laser Altimeter System, J. Geophys. Res., 111, D08203, DOI:

10.1029/2005JD006586.

data

at t

ropo

paus

e-le

vel

Sept. 2005, 30°N-30°S

Avg. difference4.7 W/m^2

Standard deviation2.3 W/m^2

CERES=0.96 calc + 8

9

330

320

310

300

290

280

270

260

CERE

S O

LR

330320310300290280270260Calculated OLR

worse

better

10

300

298

296

294

292

290

288

286

OLR

(W

/m^2

)

304302300298296SST (K)

ERBE RS+model ceres modelj

ERBE analysisby Collins and InamdarJ. Clim., 1995

March 2005

-20

-10

0

10

20

360270180900

300

290

280

270

Clear-sky OLR

model - meas.

11

-20

-10

0

10

20

360270180900

7

6

6 6 6

6 6

6

5 5

5

5

5

5 5

5

5 4

4

4 4

4

4

4

4

4

4 3

Sept. 2005

Clear-sky OLR

model - meas.

-20

-10

0

10

20

360270180900

300

290

280

270

260

12

-20

-10

0

10

20

360270180900

7

6

6 6

6 6

6

5

5

5

5

5 5

5

5 5

4

4

4

4

4

4

4

4

3

Sept. 2005

Oct. 2003

Dessler, A.E., S.P. Palm, and J.D. Spinhirne (2006), Tropical cloud-top height distributions revealed by the Ice, Cloud, and Land Elevation Satellite (ICESat)/Geoscience Laser Altimeter System (GLAS), J. Geophys. Res., 111, D12215, DOI: 10.1029/2005JD006705.

13

-20

-10

0

10

20

360270180900

7

6

6 6

6 6

6

5

5

5

5

5 5

5

5 5

4

4

4

4

4

4

4

4

3

14

300

298

296

294

292

290

288

286

OLR

(W

/m^2

)

302300298296SST (K)

ceres modelj

ERBE analysisby Collins and InamdarJ. Clim., 1995

data from 9/05

15

300

298

296

294

292

290

288

286

OLR

(W

/m^2

)

302300298296SST (K)

ceres modelj

data from 9/05

16

Surface T 2.0

Lower Trop T 2.8

Upper Trop T 0.6

Lower Trop q -7.9

Upper Trop q -6.3

Compare to 299 to 303 K303 K OLR289.3 W/m^2

299 K OLR297.7 W/m^2

∆OLR-8.4 W/m^2

Lower Trop = 1000-500 hPa, Upper Trop = 500-100 hPa

data from 9/05

17

Correlation between the tropical averaged (20 N–20 S) daily temperature at 925 hPa and the tropical averaged daily temperature at other levels of the troposphere. AIRS data are represented by the black solid line, radiosonde by the black dashed line, and GCMs by the gray lines. 95% confidence intervals at 850 hPa, 500 hPa, and 200 hPa are plotted.

Wu, Dessler, and North (2006), Analysis of the correlations between atmospheric boundary-layer and free-tropospheric temperatures in the Tropics, Geophys. Res. Lett., 33, L20707, DOI: 10.1029/2006GL026708.

Variations of T with SST

18data from 9/05

1000

800

600

400

200

Pres

sure

(hP

a)

302300298296Surface Temperature (K)

290

280

270

260 250

240 230

Variations of q with SST

19

1000

800

600

400

200

Pres

sure

(hP

a)

302300298296Surface Temperature (K)

14 12 10 8 6

4 2

1 0.5

0.2 0.1

data from 9/05

20

300

298

296

294

292

290

288

286

OLR

(W

/m^2

)

302300298296SST (K)

ceres modelj

data from 9/05

21

Lower Trop = 1000-500 hPa, Upper Trop = 500-100 hPa

Compare to 295 to 299 K299 K OLR297.7 W/m^2

295 K OLR285.3 W/m^2

∆OLR12.4 W/m^2

299 K to: 295 K 303 K

Surface T 8.3 2.0

Lower Trop T 9.7 2.8

Upper Trop T 4.8 0.6

Lower Trop q -7.6 -7.9

Upper Trop q -3.2 -6.3

data from 9/05

Variations of q with SST

22

1000

800

600

400

200

Pres

sure

(hP

a)

302300298296Surface Temperature (K)

14 12 10 8 6

4 2

1 0.5

0.2 0.1

data from 9/05

T’s effect on OLR

23

1000

800

600

400

200

304302300298296294Surface Temperature (K)

0.55

0.5

0.5

0.45

0.45

0.4

0.4

0.35

0.35

0.3

0.3

0.25

0.25

0.2

0.2

0.15

0.15

0.1

0.1

0.05

q’s effect on OLR

24

1000

800

600

400

200

304302300298296294Surface Temperature (K)

0.6 0.55

0.5 0.45 0.4 0.35 0.3 0.25

0.2

0.2

0.2

0.15

0.15

0.1 0.05

25

250

200

150

100

50

0

% p

er (g

/kg)

1.41.21.00.80.60.40.20.0H2O (g/kg)

346 hPa

Dessler and Minschwaner (2007), An analysis of the regulation of tropical tropospheric water vapor, J. Geophys. Res., in press.

26

Distance from detrainment (km)

Dessler and Minschwaner (2007), An analysis of the regulation of tropical tropospheric water vapor, J. Geophys. Res., in press.

Conclusions• OLR calculated using AIRS measurements

agrees with CERES measurements within ~5 W/m^2– Agreement best in the deep tropics and worst in

the subtropics• We are also studying the mechanisms that

regulate clear-sky OLR• T and q are the most important factors

– T dominates below 298 K, q dominates above

27

This work was supported by a NASA EOS/IDS grant and by a NASA Aqua, Terra, ACRIM data analysis grant, both to Texas A&M