11th Conference on Atmospheric Radiation and the 11th Conference on Cloud Physics

Friday, 7 June 2002
New results from NASA/GEWEX Surface Radiation Budget Project: Evaluating El Nino effects at Different Scales
Paul W. Stackhouse Jr., NASA/LARC, Hampton, VA; and S. K. Gupta, S. J. Cox, J. C. Mikovitz, and M. Chiacchio
Poster PDF (132.4 kB)
This paper compares and contrasts two El Nino events to evaluate the effect that these events had on the Surface Radiation budget of the Tropical Pacific. The two events analyzed are the late 1986-1987 El Nino and the brief 1992 El Nino. These are compared to the tropical Pacific radiative budgets in the non El Nino years of 1986, 1993 and the La Nina year of 1988. The data used are from Release 2 of NASA's World Climate Research Programme (WCRP) Global Energy and Water Cycle Experiment (GEWEX) Surface Radiation Budget (SRB) Project data set. The new data set will eventually span the years July 1983 - October 1995. The analysis here is made by applying the SRB algorithms to International Satellite Cloud Climatology Project (ISSCP) DX cloud data and the fluxes are computed at 1 degree resolution. This data set is being archived at the NASA Langley Research Center Atmospheric Science Data Center and is being released for validation studies to users who request it.

The first part of the presentation is a comparison of the fluxes to surface measurements of solar and thermal infrared fluxes during the 1993 Tropical Ocean Global Atmosphere Coupled Ocean Atmosphere Response Experiment (TOGA-COARE) time period. Surface observations from both land based and ship platforms are used in the analysis. The fluxes are also compared to the data set of Chou et al., (2000, JGR) and Rossow and Zhang (COARE-98, Jan. 1999, WCRP-107).

The second part of the presentation gives the comparison and contrast of these two El Nino events on the SRB of the tropical Pacific Ocean region. In a simplified sense, an El Nino involves warming of the sea surface temperature (SST) in the eastern Pacific that corresponds to a geographic shift of the convective regions toward the east. The changing SSTs and cloud distributions cause the perturbations in the solar and infrared surface radiative fluxes. To the first order, the solar fluxes respond to the changes in the cloud distributions while the thermal infrared fluxes respond to perturbations in the SST and moisture contents. We present results relating changes in the SST, moisture contents, and cloud distributions to the surface radiative response. For instance, we found monthly averaged solar flux in March decreased 30 W m**-2 from 1986 (non El Nino) to 1992 (El Nino) in the Eastern Pacific compared to an increase of merely 10 W m**-2 in the Western Pacific during that time period. Despite these solar flux differences the monthly averaged cloud fraction differences between the two regions showed an absolute increase of 15% in the Eastern Pacific and a 15% decrease in the Western Pacific. This is indicative of the nonlinear response of the solar radiation field to the cloud properties in addition to the the cloud fraction. Thus, the contributions of other cloud property changes are studied. The talk concludes with an assessment of the perturbation of two El Nino events to the tropical western pacific to the yearly surface radiation budget.

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