Observed Air–Sea Net Longwave Radiation and New Parameterization in the Western Tropical Pacific Using TPOS Buoy Observations

Accurate estimation of net radiation is crucial for understanding the sea surface energy budget and improving climate models. Existing formulas for net longwave (NLW) radiation at the air–sea interface still show large uncertainties in the tropics. Using high-resolution observations from the Tropical Pacific Observing System (TPOS 2020) buoys in the western Pacific warm pool, this study develops new parameterizations for downward longwave (DLW) radiation, upward longwave (ULW) radiation, and net longwave radiation. A new parameterization of the DLW radiation is developed following an existing bulk parameterization. The root-mean-square error of the ULW radiation estimate is reduced by 65% by performing an initial simple linear fit to the sea surface emissivity at buoy 1. The accuracy of the NLW radiation estimates is improved by using the new bulk formulas derived from direct longwave radiation observations with reasonable correlation coefficients of 0.83 and 0.58. The two new formulations correspond to the northern margin of the warm pool (10°–20°N) and the equatorial core (10°S–5°N), where buoy observations capture distinct radiative regimes validated against ERA5 and CERES data. These parameterizations provide an improved empirical representation of air–sea longwave radiation exchange in the western Pacific warm pool and strengthen the observational basis for evaluating surface fluxes in tropical climate analyses.
Significance Statement

Accurate estimation of net radiation is the basis of all studies on the sea surface energy budget. However, existing parameterization schemes for net longwave radiation at the air–sea interface exhibit significant uncertainties. In this study, new parameterizations based on direct observations supported by the Tropical Pacific Observing System (TPOS 2020) in the western tropical Pacific are proposed. Valuable dual-direction radiation observations are used to evaluate multiple reanalyses and satellite products, which helps improve climate models and predictions. Accurately quantifying the energy exchange between the atmosphere and the ocean is crucial for enhancing our knowledge of the tropical Pacific climate system.