The surface and TOA heat budgets over tropical oceans observed by TRMM satellite

During the first half of 1998, the Earth's climate transited from El Nino to near normal status. The Tropical Rainfall Measuring Mission (TRMM) satellite clearly observed the transition. The TRMM data for January, April, and July, 1998 have been used to estimate top-of-atmosphere (TOA) and surface heat budgets over tropical oceans. The major components of the heat budgets are the radiative fluxes at both the TOA and the surface and latent and sensible heat fluxes at the surface.

We used the Clouds and the Earth's Radiant Energy System (CERES) on TRMM for the TOA longwave (LW) and shortwave (SW) broadband radiative fluxes. At the sea surface, a combination of the TOA CERES LW and SW broadband radiances, the cloud and aerosol properties retrieved from the TRMM Visible and Infrared Scanner (VIRS), and ECMWF data is used to estimate LW and SW fluxes. The net radiative heating within the atmosphere and at the surface are evaluated from these results.

Sea surface latent and sensible heat fluxes are calculated from stability-dependent bulk formulae. Since the TRMM Microwave Imager (TMI) has measurements at about 10, 19, 21, 37 and 85 GHz, most input values required by the bulk formulae (e.g., near sea surface wind speed, sea surface temperature and water vapor mixing ratio) are retrieved from the TMI observations. The only major parameter that can not be remotely sensed by satellite at present is the air-sea temperature gradient which is obtained from ECMWF data.

Considering the tropical area mean during the El Nino and the transition period, the SW and LW radiative fluxes at the sea surface are largely balanced by the latent and sensible heat fluxes. The net differences among these energetic components are probably caused by the oceanic storage and horizontal transport of heat and/or by the errors in our analysis at the surface.