Surface Energy Balance Measurements around Ocean Weather Station-T during OMLET/WCRP

Abstract

Sea surface energy balance was analysed at the ocean weather station-T (OWS-T; 29°N, 135°E), south of Japan, based on direct measurements on board. The intensive observation periods were set up during OMLET (Ocean Mixed Layer Experiment) as two cruises of the R/V Hakuhomaru, University of Tokyo around OWS-T in Apr/May 1988 and Jan/Feb 1991. The first period corresponds to the decaying stage of the ocean mixed layer and the second one is the stage of the development. Radiation measurements and turbulent flux measurements by the eddy correlation method were carried out during the cruises as well as the upper air soundings and the ocean measurements. A part of the results from OMLET'88 was already reported by Tsukamoto et al. (1990).
The eddy correlation flux measurement is the most accurate one. However it is not always applicable for the sea-surface flux evaluations for a long term. The bulk aerodynamic formulas are usually accepted for practical purposes. The bulk transfer coefficient should be determined based on the eddy correlation flux measurements. However previous energy budget studies are based on universal bulk models and no confirmation was made of those results. In the present study, the bulk transfer coefficients were determined based on the eddy fluxes as a function of wind speed as in situ values. The bulk coefficients were applied to the continuous surface meteorological data for the evaluation of long-term fluxes.
The net heat fluxes into the water were evaluated as +54Wm^-2 (downward) in Apr/May and -192Wm^-2 (upward) in Jan/Feb. The local time changes of the ocean mixed layer heat content were calculated with JMA buoy data as 356Wm^-2 and -297Wm^-2, respectively. The difference of these values can be regarded as due to horizontal or vertical heat transfer.