A review of global products of air-sea turbulent heat flux: accuracy, mean, variability, and trend

Air-sea turbulent heat flux is vital to the exchange of global water and energy between the atmosphere and the Earth's surface and is essential for understanding Earth-climate mutual feedback. In this paper, we comprehensively review the accuracy and spatiotemporal patterns of 15 global products of air-sea turbulent heat flux from 1988 to 2020. Compared to observations at 139 buoys, all the products overestimate monthly latent heat flux (LHF) and most products overestimate sensible heat flux (SHF), with higher correlation coefficients found for LHF than for SHF. Compared to the reanalysis-based and in situ-based products, the remote sensing-based, machine learning-based, and hybrid-based monthly LHF products are generally more consistent with the buoy observations. The annual mean LHF and SHF values vary greatly between 75 and 115 W/m2 and between 0 and 25 W/m2, respectively. Different products have similar spatial patterns of annual means and interannual variabilities of LHF and SHF in most ocean areas but they have very different magnitudes. Most products show consistent annual trends in LHF and consistent but overall weaker annual trends in SHF, except for in the areas around and beyond 45°S, where larger discrepancies in annual SHF trends are observed. Analogous unimodal shapes of monthly SHF frequency curves from the 15 products are shown in all oceans, but for the monthly LHF frequency curves, both unimodal and bimodal shapes are shown. Seasonal LHF and SHF values are higher (lower) in December–January-February than in June–July-August in the Northern (Southern) Hemisphere. The interseasonal variations in LHF and SHF are more pronounced in the Northern Hemisphere than in the Southern Hemisphere. This review could benefit the algorithm development and improvement of air-sea turbulent heat flux products, provide insightful scientific guidance for selecting flux products for different applications, and characterize the advances in the global datasets of air-sea turbulent heat flux.