Seasonal and spatial variations of air-sea heat exchange in the seas around the Korean Peninsula: Based on the observations and reanalysis products from 2011 to 2016

Abstract

It is important to better understand air–sea heat exchange for weather and climate systems prediction. In the seas around the Korean Peninsula (KP), the annual cycles of most oceanic and atmospheric variables have long been well recognized, whereas those of the air–sea heat exchange are still not completely clear primarily due to a lack of in-situ observations applied to estimate surface heat flux. This is particularly true over the region affected by the Tsushima Warm Current (TWC), where cold and dry air and a northwesterly wind over the warm sea surface enhance heat exchange during the winter monsoons (when the ocean loses heat), which may often be over or underestimated through atmospheric reanalysis model products. Herein, we present estimates of the mean annual cycles of air–sea heat fluxes from in-situ observations at two locations (I-ORS and ESROB) and from two atmospheric reanalysis products (CFSv2 and MERRA-2) during the period of 2011–2016. The results show that the net heat loss of the ocean (net heat flux (NHF) of −68 Wm-2, positive downward) at ESROB near the east coast of Korea is 146 Wm-2 larger than that (+78 Wm-2, net heat gain) at I-ORS located ~250 km southwest of KP, except in June when the incoming shortwave radiation flux decreases significantly (by 208 Wm-2) only at the I-ORS, a response associated with the meiyu-baiu rain band. Greater sensible and latent heat losses (SHF and LHF) of 32 and 47 Wm-2 during both winter and spring, respectively, and less LHF of 22 Wm-2 during fall, were observed at ESROB than at I-ORS. The CFSv2 yields −24, −84, −41, and −180 Wm-2 (−43, −110, −56, and −120 Wm-2) in terms of the average NHF, winter SHF, and spring and fall LHFs at I-ORS (ESROB), whereas MERRA-2 yields −28, −56, −26, and −161 Wm-2 (−108, −134, −71, and −155 Wm-2), which is indicative of significant biases in the air–sea temperature difference and the wind speed. Spatial distributions of SHF and LHF of both reanalysis products, which are consistent each other and with the observations despite their biases, indicate the significant impact of TWC and the associated currents through the sea surface temperature and saturation-specific humidity on the annual air–sea heat exchange cycles within the region.