A comparison between CERES OLR and OLR calculated from AIRS temperature & humidity for clear-sky regions J. Lee, A. E. Dessler, P. Yang Department of Atmospheric Sciences Texas A&M University
Water vapor (g/kg) 4 6 0.1 4 6 1 4 6 10 2 2 2 200 200 400 400 Pressure (hPa) 600 600 800 800 Temperature Water vapor 1000 1000 200 220 240 260 280 2 Temperature (K)
Calculate OLR Water vapor (g/kg) 4 6 0.1 4 6 1 4 6 10 2 2 2 200 200 400 400 Pressure (hPa) 600 600 800 800 Temperature Water vapor 1000 1000 200 220 240 260 280 3 Temperature (K)
Compare to CERES measurements Calculate OLR Water vapor (g/kg) 4 6 0.1 4 6 1 4 6 10 2 2 2 200 200 400 400 Pressure (hPa) 600 600 800 800 Temperature Water vapor 1000 1000 200 220 240 260 280 4 Temperature (K)
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 O 3 • 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, CO 2 , O 3 ) and most of the minor trace gases (N 2 O, CH 4 , 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.
330 CERES=0.96 calc + 8 320 310 Avg. difference CERES OLR 300 4.7 W/m^2 290 Standard deviation 280 2.3 W/m^2 270 260 260 270 280 290 300 310 320 330 Calculated OLR Sept. 2005, 30°N-30°S 7
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 tropopause-level 10 Fraction of TNTC 8 6 188 K 4 191 K 2 194 K 0 150 200 250 300 OLR (W/m^2) 8
worse 330 CERES=0.96 calc + 8 320 better 310 Avg. difference CERES OLR 300 4.7 W/m^2 290 Standard deviation 280 2.3 W/m^2 270 260 260 270 280 290 300 310 320 330 Calculated OLR Sept. 2005, 30°N-30°S 9
300 ERBE analysis by Collins and Inamdar 298 J. Clim., 1995 296 OLR (W/m^2) 294 292 290 ERBE 288 RS+model ceres 286 modelj 296 298 300 302 304 SST (K) 10
20 300 10 290 Clear-sky OLR 0 280 -10 270 -20 0 90 180 270 360 March 2005 6 6 6 20 7 6 6 5 10 4 5 6 4 5 4 model - meas. 0 3 4 4 4 5 4 -10 4 4 5 5 5 5 6 -20 4 5 0 90 180 270 360 11
20 300 10 290 Clear-sky OLR 0 280 -10 270 260 -20 0 90 180 270 360 Sept. 2005 4 4 5 20 4 5 4 10 5 4 4 5 model - meas. 3 0 6 5 5 5 4 -10 6 6 4 6 -20 6 5 6 5 7 0 90 180 270 360 12
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. Oct. 2003 4 4 5 20 4 5 4 10 5 4 4 5 3 0 6 Sept. 2005 5 5 5 4 -10 6 6 4 6 -20 6 5 6 5 7 0 90 180 270 360 13
300 ERBE analysis by Collins and Inamdar 298 J. Clim., 1995 296 OLR (W/m^2) 294 292 290 288 ceres modelj 286 296 298 300 302 SST (K) data from 9/05 14
300 298 296 OLR (W/m^2) 294 292 290 288 ceres modelj 286 296 298 300 302 SST (K) data from 9/05 15
Compare to 299 to 303 K 303 K OLR Surface T 2.0 289.3 W/m^2 Lower Trop T 2.8 299 K OLR 297.7 W/m^2 Upper Trop T 0.6 ∆ OLR Lower Trop q -7.9 -8.4 W/m^2 Upper Trop q -6.3 Lower Trop = 1000-500 hPa, Upper Trop = 500-100 hPa data from 9/05 16
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. 17
Variations of T with SST 200 230 240 250 400 260 Pressure (hPa) 270 600 280 800 290 1000 296 298 300 302 Surface Temperature (K) data from 9/05 18
Variations of q with SST 200 0.1 0.2 400 Pressure (hPa) 0.5 1 600 2 4 6 800 8 10 12 14 1000 296 298 300 302 Surface Temperature (K) data from 9/05 19
300 298 296 OLR (W/m^2) 294 292 290 288 ceres modelj 286 296 298 300 302 SST (K) data from 9/05 20
Compare to 295 to 299 K 299 K to: 295 K 303 K 299 K OLR 297.7 W/m^2 Surface T 8.3 2.0 295 K OLR Lower Trop T 9.7 2.8 285.3 W/m^2 Upper Trop T 4.8 0.6 ∆ OLR 12.4 W/m^2 Lower Trop q -7.6 -7.9 Upper Trop q -3.2 -6.3 Lower Trop = 1000-500 hPa, Upper Trop = 500-100 hPa data from 9/05 21
Variations of q with SST 200 0.1 0.2 400 Pressure (hPa) 0.5 1 600 2 4 6 800 8 10 12 14 1000 296 298 300 302 Surface Temperature (K) data from 9/05 22
T’s effect on OLR 0.05 200 0.1 0.15 0.2 0.25 0.3 0.35 400 600 0.4 0.45 0.5 800 0.55 0.5 0.45 0.4 0.35 0.3 0.25 0.2 0.15 0.1 1000 294 296 298 300 302 304 Surface Temperature (K) 23
q’s effect on OLR 0.05 200 0.1 0.15 0.2 400 0.2 600 0.6 0.55 800 0.5 0.45 0.4 0.35 0.2 0.3 0.15 0.25 1000 294 296 298 300 302 304 Surface Temperature (K) 24
250 346 hPa Dessler and Minschwaner 200 (2007), An analysis of the % per (g/kg) 150 regulation of tropical 100 tropospheric water vapor, 50 J. Geophys. Res ., in press. 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 H2O (g/kg) 25
Dessler and Minschwaner (2007), An analysis of the regulation of tropical tropospheric water vapor, J. Geophys. Res ., in press. Distance from detrainment (km) 26
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 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 27
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