Revisiting the trend of the tropical and subtropical Pacific surface latent heat flux during 1977-2006

Using the Objectively Analyzed Air‐Sea Fluxes data provided by the Woods Hole Oceanographic Institution and the trend empirical orthogonal function analysis method, we have investigated the trend of ocean surface latent heat flux (LHF) over the tropical and subtropical Pacific (100°E–70°W, 35°S–35°N) during the period 1977–2006. The present study suggests that the ocean surface LHF presents a large‐scale upward trend pattern, and the identified positive surface LHF trend is closely associated with both the sea surface temperature (SST) warming and the surface wind speed strengthening. The SST increasing is the primary direct/local cause of the surface LHF trend, while the large‐scale surface wind speed strengthening, ascribed to its contribution to the observed SST trend pattern, is an important indirect/nonlocal factor of the surface LHF trend. The present work also suggests that the coherent upward trends in surface LHF, surface wind speed, and SST should be in essence closely linked to the global warming forcing. To some extent, these results unify the two seemingly contradictory conclusions proposed previously by other researchers and attempt to help obtain a new insight into the causes of the positive basin‐scale surface LHF trend. Key Points SST warming is the primary direct/local cause of the surface LHF trend Surface wind speed strengthening is an important indirect/nonlocal factor Coherent upward trends should be closely linked to global warming