Evaluating Interannual Variability and Trends of Surface Heat Flux Over the Tropical Indian Ocean Across Diverse Products

Abstract Accurate quantification of net surface heat flux (NHF) over the tropical Indian Ocean (TIO) is essential for understanding regional air‐sea interactions, yet substantial uncertainties remain among existing flux products. Here we evaluate 14 NHF products using in situ buoy observations as an observational constraint and a multi‐product ensemble mean as a baseline for assessing interannual variability and trends. Comparisons with the buoys indicate that several products reproduce the amplitude of local NHF reasonably well, whereas others show large departures. Relative to the MME, a number of products, including NCEP‐2 and GODAS, overestimate interannual NHF variability by more than 40%, whereas MERRA‐2, TropFlux, J‐OFURO3 and SODA3.4.2 provide more reliable estimates. A basin‐wide declining trend in NHF, indicating reduced ocean heat gain, is evident across most products during 1988–2018, with the strongest decreases observed near the equator. This reduction is primarily driven by enhanced ocean evaporation, accounting for 50%–80% of the total decline. However, substantial inter‐product discrepancies exist in both the spatial structure and magnitude of the trend. A subset of products shows spatially coherent negative trends, with the J‐OFURO3 and JRA‐3Q exhibiting the strongest declines. In contrast, NCEP‐1, NCEP‐2 and GODAS display contrasting and heterogeneous spatial patterns, while ORAS5 and TropFlux show weak basin‐averaged trends. These pronounced inter‐product discrepancies in both interannual variability and long‐term trends emphasize limitations in current NHF products and highlight the need for improved observational coverage and enhanced parameterization to reduce uncertainties in air‐sea flux representations over the TIO.