Journal of Oceanography, Vol. 63 (No. 5), pp. 721-744, 2007Review
Yoshimi Kawai1* and Akiyoshi Wada2
1Institute of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka 237-0061, Japan
2Meteorological Research Institute, Japan Meteorological Agency, Nagamine, Tsukuba 305-0052, Japan
(Received 6 November 2006; in revised form 2 April 2007; accepted 14 April 2007)
Abstract: The importance of the diurnal variability of sea surface temperature (SST) on air-sea interaction is now being increasingly recognized. This review synthesizes knowledge of the diurnal SST variation, mainly paying attention to its impact on the atmosphere or the ocean. Diurnal SST warming becomes evident when the surface wind is weak and insolation is strong. Recent observations using satellite data and advanced instruments have revealed that a large diurnal SST rise occurs over wide areas in a specific season, and in an extreme case the diurnal amplitude of SST exceeds 5 K. The large diurnal SST rise can lead to an increase in net surface heat flux from the ocean of 50-60 Wm-2 in the daytime. The temporal mean of the increase exceeds 10 Wm-2, which will be non-negligible for the atmosphere. A few numerical experiments have indicated that the diurnal SST variation can modify atmospheric properties over the Pacific warm pool or a coastal sea, but the processes underlying the modification have not yet been investigated in detail. Furthermore, it has been shown that the diurnal change of ocean mixing process near the surface must be considered correctly in order to reproduce SST variations on an intraseasonal scale in a numerical model. The variation of mixed-layer properties on the daily scale is nonlinearly related to the intraseasonal variability. The mixed-layer deepening/shoaling process on the daily scale will also be related to biological and material circulation processes.