The atmosphere heat budget over the tropical oceans

The earth's energy budget gets its source from solar radiation. About one-third of them are reflected back to space. The rest are absorbed by atmosphere (~16%), clouds (~3%), and surface (~51%). The net radiation flux (NRF) at top-of-atmosphere (TOA) is estimated as the incoming solar radiation reduced by the emitted longwave radiation. The surface NRF is the combination of shortwave and longwave NRF absorbed by the ocean. Atmospheric NRFs are calculated from the differences of TOA and surface NRF values. These fluxes are general negative, indicating the net cooling effect of atmospheric radiation. The nature adjusts the imbalance of atmospheric radiation mainly through the release of latent heat by precipitation and sensible heat transfer due to the air-sea temperature difference.

This study uses data collected from the TRMM satellite over tropical oceans (30S to 30N) for 199801-199808 to examine the latitudinal and diurnal variations of the atmosphere heat budget. The TOA and surface NRFs are provided by the Clouds and the Earth's radiant Energy System (CERES) project. The retrieval bias are 2W/m^2 and 3W/m^2 for TOA LW and SW, and 8W/m^2 and 15W/^2 for surface net LW and SW based on monthly means. The latent heat and sensible fluxes are estimated using satellite estimated meteorology parameters and bulk algorithms. The pixel level bias (rms) errors for latent heat flux are about 1.53 (54.30) W/m^2 and 0.27 (50.0)W/m^2 when compared to ship direct covariance and inertial-dissipation methods. They are -9.74 (37.08) W/m^2 when compared to ship bulk results. For sensible heat flux, the bias (rms) are -1.77 (9.34), -3.66 (9.20), and -1.90 (8.23) W/m^2 for direct covariance, inertial-dissipation, and bulk results, respectively.

Based on the latitudinal means over the tropical oceans, the TOA and surface NRFs range from 0 to 70 W/m^2 and from 150 to 200 W/m^2, respectively. This results a negative atmosphere NRF ranging from -100 to -150 W/m^2. Latent and sensible heat fluxes contribute 70 to 170 W/m^2 and 3 to 8 W/m^2 over the tropical oceans, respectively. Therefore, there is merely a variation of -50 to 30 W/m^2 for atmosphere heat budget over the tropical latitudes. Due to heavy rainfall, atmosphere heat budget is negative between 10S and 10N. The biggest atmosphere heat loss and ocean heat gain are at the equator.

Based on hourly means, both TOA and surface NRFs can reach 700W/m^2 at the noon time but they are negative values during 7PM to 7AM because of the weakness or absence of shortwave radiation flux. Atmosphere NRF budget are mostly negative except between 10AM and 2PM. It can lose more than 200 W/m^2 between 6PM and 6AM. With the heat released by condensation (120-150W/m^2), the atmosphere heat budget becomes 150 to -100W/m^2 during day and night time hours. The atmosphere heat gain during the day and heat loss during the night almost cancel each other out. From the TRMM data, it is obvious that latent heat plays an important role in regulating the atmosphere heat budget. It compensates the heat loss of atmosphere NRF.