Net air–sea surface heat flux during 1984–2004 over the North Pacific and North Atlantic oceans (10°N–50°N): annual mean climatology and trend

Using the Objectively Analyzed air–sea Fluxes dataset (and also the National Oceanography Centre Southampton Flux Dataset v2.0), we examined both the annual mean climatology and trend of net air–sea surface heat flux ( Q net ) for 1984–2004 over the North Pacific and North Atlantic oceans (10°N–50°N). The annual mean Q net climatology shows that oceans obtain the positive Q net over much of the North Pacific and North Atlantic oceans. Exceptions are the regions of western boundary currents (WBCs) including the Kuroshio and its extension off Japan and the Gulf Stream off the USA and its extension, where oceans release lots of heat into the atmosphere, mainly ascribed to the large surface turbulent heat loss. The statistically significant negative Q net trends occurred in the WBCs, while the statistically significant positive Q net trends appeared in the central basins of Northern Subtropical Oceans (CNSOs) including the central basin of Northern Subtropical Pacific and the central basin of Northern Subtropical Atlantic. These indentified Q net trends, which are independent of both El Niño-Southern Oscillation (ENSO) and ENSO Modoki but closely related to global warming forcing, are predominately due to the statistically significant surface latent heat (LH) trends. Over the WBCs, the positive LH trends are mainly induced by the sea surface temperature increasing, indicating the ocean forcing upon overlying atmosphere. In contrast, over the CNSOs, the negative LH trends are mainly caused by the near-surface air specific humidity increasing, indicative of an oceanic response to overlying atmospheric forcing.