Relations between Sea Surface Temperature and Air-Sea Heat Flux at Periods from 1 Day to 1 Year Observed at Ocean Buoy Stations around Japan

Abstract

Relations between sea-surface temperature (T s) and heat flux at the sea surface (F) have been investigated using data from ocean observation buoys located off Shikoku in the Sea of Japan and in the East China Sea. Wavelet transformation decomposed F and T s to wavelet coefficients (WLC) in the period-time domain. Assuming one-dimensional heat transfer by eddy diffusion in the upper ocean, the phase difference (δθ) defined as the difference between the phase of the temporal change rate of T s, and the phase of F ranges statistically from 0 to +π/4 when F changes T s, and is around −π/2 when heat convergence in the sea (Av) forces T s. The δθ values are distributed from 0 to +π/4 at one-day and one-year periods at all buoys. WLC amplitude (WLCA) of F at periods from 16 to 32 day periods, which may be caused by the atmospheric ridge-trough systems, maintains energy longer than WLCA at periods from 2 to 16 days, which may be caused by monsoonal surges. At periods from 2 to 64 days, δθ values distribute from 0 to +π/4 or around −π/2 at each event, reflecting the surroundings of each ocean, i.e., Kuroshio recirculation in the off-Shikoku area, water-temperature front in the Sea of Japan, and water exchange in the continental shelf edge in the East China Sea. We demonstrate that the wavelet analysis can characterize the correspondence between irregular signals of F and T s in various time scales and locations.