Upper Ocean Heat and Salt Balances in Response to a Westerly Wind Burst in the Western Equatorial Pacific during TOGA COARE

Ming Feng{1}, Peter Hacker, and Roger Lukas

School of Ocean and Earth Science and Technology
University of Hawaii
{1} Also at:
Institute of Oceanography
Chinese Academy of Sciences
Qingdao, P. R. China 266071

Abstract

Two volume control methods are used to analyze the upper ocean heat and salt balances in response to a Westerly Wind Burst event in the western equatorial Pacific warm pool during the Tropical Ocean Global Atmosphere Coupled Ocean-Atmosphere Response Experiment. One method uses a fixed thickness surface layer, and the other uses an isopycnal depth as the lower boundary.

Horizontal advection terms in the budget calculations are estimated using the R/V Wecoma repeat hydrographic survey data within a 133 km x 133 km region (Figure 1).

During a 19-day time period, which covers the December 1992 Westerly Wind Burst and a low wind recovery period in early January 1993 (Figure 2), the upper ocean heat budget is balanced within 10 w/m2 of the surface air-sea flux observations in both methods (Figure 3). The standard error in the estimation of heat advection is 11 w/m2. The salt budget yields a rainrate estimate of 15 mm/day with an error bar of 4 mm/day during the same time period (Figure 3). This estimate is within 20% of the optical rain gauge measurements on the R/V Wecoma and R/V Moana Wave.

During this time period, the advection terms are important in both the heat and salt balances (Figure 4). Meridional advection dominates over zonal and vertical advection, acting to decrease temperature and increase salinity in the surface layer.

From the isopycnal boundary method, the diapycnal turbulent flux, estimated from microstructure measurements on the R/V Moana Wave, transports a mean heat flux of 17 w/m2 into the thermocline. Diapycnal advection (use diapycnal velocity also calculated from the microstructure data (Figure 5)) is almost equally important, so that the total heat flux into the thermocline is estimated to be more than 30 w/m2 during the study time period. Both the diapycnal turbulent flux and diapycnal advection terms are also important in the salt budget.

Reference:

Feng, M., P. Hacker, and R. Lukas, Upper Ocean Heat and Salt Balances in Response to a Westerly Wind Burst in the Western Equatorial Pacific during TOGA COARE. J. Geophys. Res., accepted. 1997.

Last modified: October 27, 1997