References

ACP

Atmospheric Chemistry and Physics

ACP

1680-7324

Copernicus GmbH

Göttingen, Germany

10.5194/acp-7-2617-2007

Radiation budget estimates over Africa and surrounding oceans: inter-annual comparisons

Ben Rehouma

¹ Viollier

¹ Desbois

Laboratoire de Météorologie Dynamique, Institut Pierre Simon Laplace, Ecole Polytechnique, 91128 Palaiseau Cedex, France

21 05 2007

7 10 2617 2629

This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

This article is available from http://www.atmos-chem-phys.net/7/2617/2007/acp-7-2617-2007.html

The full text article is available as a PDF file from http://www.atmos-chem-phys.net/7/2617/2007/acp-7-2617-2007.pdf

Three independent datasets of Radiation Budget at the top of the atmosphere (TOA) spanning two decades are compared: the Scanner Narrow Field of View data (from ERBE, ScaRaB, and CERES instruments, 1985–2005), the ERBS Nonscanner Wide Field of View data (1985–1998) and the simulated broadband fluxes from the International Satellite Cloud Climatology Project (ISCCP-FD, 1983–2004). The analysis concerns the shortwave (SW) reflected flux, the longwave (LW) emitted flux and the net flux at the Top Of the Atmosphere (TOA) over Africa and the surrounding oceans (45° S–45° N/60° W–60° E), a region particularly impacted by climate variability. For each month, local anomalies are computed with reference to the average over this large region, and their differences between the 2002–2005 and 1985–1989 periods are analysed. These anomalies are, for a large part, independent on the general observed trends (about 2.5 W m−2 per decade), which may be affected by possible calibration drifts. Although the regional flux anomalies can be related to calibration through the scene identification and the choice of the anisotropy correction, this effect is limited if the calibration drifts remains reasonable. Large inter-annual variations are observed locally. Over a part of the South East Atlantic (35°–10° S/10° W–10° E), including the marine low cloud area off Angola, there is a decrease of the yearly means of net flux estimated to 2.2, 3 and 6 W m−2 respectively for the Scanner, Nonscanner and ISCPP-FD data. Over a narrow strip of the Sahel Zone, the net flux increases by about 5 W m−2. We believe that these observations are real. They could be due to the impact of calibration drift but only if the drifts were significant (>4%) and correlated between the datasets, which is highly improbable.

References 1

Allan, R. P., Slingo, A., and Ringer, M. A.: Influence of Dynamics on the Changes in Tropical Cloud Radiative Forcing during the 1998 El Niño, J. Climate, 15, 1979–1986, 2002.

Allan, R. P. and Slingo, A.: Can current climate model forcings explain the spatial and temporal signatures of decadal OLR variations?, Geophys. Res. Lett., 29(7), 1141, doi:10.1029/2001GL014620, 2002.

Barkstrom, B. R.: The Earth Radiation Budget Experiment (ERBE), B. Am. Meteorol. Soc., 65, 1170–1185, 1984.

Barkstrom, B. R., Harrison, E. F., Smith, G. L., Green, R. N., Kibler, J., Cess, R., and the ERBE Science Team: Earth Radiation Budget Experiment (ERBE) Archival of April 1985 Results, B. Am. Meteorol. Soc., 70, 1254-1262, 1989.

Bony, S. and Dufresne, J.: Marine boundary layer clouds at the heart of tropical cloud feedback uncertainties in climate models, Geophys. Res. Lett., 32, L20806, doi:10.1029/2005GL023851, 2005.

Campbell, G. G.: View angle dependence of cloudiness and the trend in ISCCP cloudiness, 13th AMS Conference On Satellite Meteorology And Oceanography, Norfolk, VA, 9/20/2004–9/23/2004, 2004.

Cess, R. D., Zhang, M., Wielicki, B. A., Young, D. F., Zhou, X., and Nikitenko, Y.: The Influence of the 1998 El Niño upon Cloud-Radiative Forcing over the Pacific Warm Pool, J. Climate, 14, 2129–2137, 2001.

Eklundh, L. and Olsson, L.: Vegetation index trends for the African Sahel 1982–1999, Geophys. Res. Lett., 30(8), 1430, doi:10.1029/2002GL016772, 2003.

Green, R. N. and Smith, G. L.: Shortwave Shape Factor Inversion of Earth Radiation Budget Observations, J. Atmos. Sci., 48, 390–402, 1991.

Haeffelin, M., Wielicki, B. A., Duvel, J. P., Priestley, K., and Viollier, M.: Intercalibration of CERES and ScaRaB Earth radiation budget datasets using temporally and spatially collocated radiance measurements, Geophys. Res. Lett., 28(1), 167–170, 2001.

Harries, J. E., Russell, J. E., Hanafin, J. A., et al.: The Geostationary Earth Radiation Budget Project, Bull. Am. Meteor. Soc., 86(7), 945–960, doi:10.1175/BAMS-86-7-945, 2005.

Hatzidimitriou, D., Vardavas, I., Pavlakis, K. G., Hatzianastassiou, N., Matsoukas, C., and Drakakis, E.: On the decadal increase in the tropical mean outgoing longwave radiation for the period 1984–2000, Atmos. Chem. Phys., 4, 1419–1425, 2004.

Kandel R., Viollier, M., Raberanto, P., Duvel, J. Ph., Pakhomov, L. A., Golovko, V. A., Trishchenko, A. P., Mueller, J., Raschke, E., Stuhlmann, R., and the International ScaRaB Scientific Working Group (ISSWG).: The ScaRaB Earth Radiation Budget Dataset, B. Am. Meteorol. Soc., 79, 765–783, 1998.

Kandel, R. and Viollier M.: Planetary Radiation Budgets, Space Sci. Rev., 120, 1–26, 2005.

Loeb, N. G., Kato, S., Loukachine, K., and Manalo-Smith, N.: Angular Distribution Models for Top-of-Atmosphere Radiative Flux Estimation from the Clouds and the Earth's Radiant Energy System Instrument on the Terra Satellite. Part I: Methodology, J. Atmos. Ocean. Techn., 22, 338–351, doi:.10.1175/JTECH1712.1, 2005.

Matthews, G., Priestley, K. J., Spence, P., Cooper, D., and Walikainen, D.: Compensation for spectral darkening of short wave optics occurring on the Cloud's and the Earth's Radiant Energy System, in Earth Observing Systems, Proceedings of SPIE, 5882, doi:10.1117/12.618972, 2005.

Minnis, P., Harrison, E. F., Stowe, L. L., Gibson, G. G., Denn, F. M., Doelling, D. R., and Smith Jr., W. L.: Radiative Climate Forcing by the Mt. Pinatubo Eruption, Science, 259, 1411–1415, 1993.

Pinker, R. T., Zhang, B., and Dutton, E. G.: Do Satellites Detect Trends in Surface Solar Radiation?, Science, 308, 850–854, 2005.

Rigollier C., Lefèvre M., and Wald L.: The method Heliosat-2 for deriving shortwave solar radiation data from satellite images, Solar Energy, 77(2), 159–169, 2004.

Ringer, M. A.: Interannual variability of the Earth's radiation budget: Some regional studies, Int. J. Clim., 17, 929–951, 1997.

Ringer, R. and Shine, K. P.: Sensitivity of the Earth's radiation budget to interannual variations in cloud amount, Clim. Dynam., 13, 213–-222, 1997.

Robertson, F. R. and Lu, H.: How Well Are Recent Climate Variability Signals Resolved By Satellite Radiative Flux Estimates?, 13th AMS Conference On Satellite Meteorology And Oceanography, Norfolk, VA, 9/20/2004–9/23, 2004.

Rossow, W. B. and Schiffer, R. A.: ISCCP cloud data products, B. Am. Meteorol. Soc., 72, 2–20, 1991.

Rossow, W. B. and Schiffer, R. A.: Advances in Understanding Clouds from ISCCP, B. Am. Meteorol. Soc., 80, 2261–2288, 1999.

Smith, G. L., Szewczyk, Z. P., Rutan, D. A., and Lee III, R. B.: Comparison of measurements from satellite radiation budget instruments, J. Geophys. Res., 111, D04101, doi:10.1029/2005JD006307, 2006.

Weatherhead, E. C., Reinsel, G. C., Tiao, G. C., Meng, X.-L., Choi, D., Cheang, W.-K., Keller, T., DeLuisi, J., Wuebbles, D. J., Kerr, J. B., Miller, A. J., Oltmans, S. J., Frederick, J. E.: Factors affecting the detection of trends: Statistical considerations and applications to environmental data, J. Geophys. Res., 103(D14), 17 149–17 162, 1998

Wielicki, B. A., Barkstrom, B. R., Harrison, E. F., Lee III, R. B., Smith, G. L., and Cooper, J. E.: Clouds and the Earth's Radiant Energy System (CERES): An Earth Observing System Experiment, B. Am. Meteorol. Soc., 77, 853–868, 1996.

Wielicki, B. A., Wong T., Allan R. P, et al.: Evidence for Large Decadal Variability in the Tropical Mean Radiative Energy Budget, Science, 295, 841–844, 2002.

Wild, M., Gilgen, H., Roesch, A., et al.: From Dimming to Brightening: Decadal Changes in Solar Radiation at Earth�s Surface, Science, 308, 847–850, 2005.

Wong, T., Wielicki, B. A., Lee III, R. B., Smith, G. L., and Bush, K. A.: Re-examination of the Observed Decadal Variability of Earth Radiation Budget using Altitude-corrected ERBE/ERBS Nonscanner WFOV data, J. Climate, 19, 4028–4040, 2006.

Young, D. F., Minnis, P., Doelling, D. R., Gibson, G. G., and Wong, T.: Temporal interpolation methods for the Clouds and the Earth's Radiant Energy System (CERES) experiment, J. Clim. Appl. Meteorol., 37, 572–590, 1998.

Zhang, Y., Rossow, W. B., Lacis, A. A., Oinas, V., and Mishchenko, M. I.: Calculation of radiative fluxes from the surface to top of atmosphere based on ISCCP and other global data sets: Refinements of the radiative transfer model and the input data, J. Geophys. Res., 109, D19105, doi:10.1029/2003JD004457, 2004.