The Traditional View of Air-sea Interaction
Ocean plays a key role in Earth's climate, transporting huge amounts of heat away from the equator in its poleward currents. Climate researchers know now much about how sea surface temperatures in the tropics impact the atmosphere and climate. Also, there are many media coverage on how El Niño, La Niña, or the Indian Ocean Dipole influence Japan's climate.
In the midlatitudes, large-scale measurements over the ocean show that wind speeds are generally higher over cooler waters than over warmer waters, and the typical view among scientists has been that the midlatitude ocean responds passively to the atmosphere. The same way that blowing over coffee to cool it down, while it has no effect back on its breath, high winds were thought to cool the midlatitude ocean surface without any feedback on the winds.

Discovery of the Kuroshio's Effect on Local Winds
We had a hunch that this view was not the full picture. To see whether the midlatitude ocean may influence the atmosphere, we analyzed satellite observations of temperature fronts-sharp horizontal temperature gradients-on the ocean surface. These fronts occur where currents transporting tropical warm water poleward meet currents from polar regions transporting cool water equatorward. Examples are such fronts where the warm Kuroshio and the cold Oyashio currents meet in the Northwestern Pacific, where the Gulf Stream meets cold water from the Arctic, and where the Brazil current off Argentina meets cold water from Antarctica.
Studying the Kuroshio-Oyashio front, we found something surprising: Wind speeds are higher over the warm Kuroshio and lower over the adjacent cool waters. Figure 1 shows Tropical Rain Measuring Mission (TRMM) satellite observations of the distributions of sea surface temperatures and wind speeds along the southern coast of Japan and eastward during 1998 and 2001. In 2001, the Kuroshio took an offshore path, and temperatures off Tokai region (black arrow in Fig. 1) and east of Japan (white arrows in Fig. 1) were about 3ºC lower than in the immediate vicinity. Over these cool waters, winds were about 1 m/s lower than over the warmer areas. Similarly, when the Kuroshio meanders around 34ºN, 146ºE in 1998, and cool water extends southward, wind speeds over the cool area are lower by 1 to 2 m/s. Analyzing satellite data over the Gulf Stream and off the coast of Argentina, we found the same relationship: stronger winds over warm and weaker winds over cool water.
These observational results, showing a different relation between wind speed and ocean surface temperature to what was previously assumed, strongly suggest the ocean does in fact make feed back to the atmosphere. This does not mean that the traditional relationship is wrong, but rather that in these midlatitude regions, a two-way relationship between the atmosphere and ocean exists.