MEAN ANNUAL VARIATION OF TRANSPORT OF MAJOR CURRENTS IN THE TROPICAL PACIFIC-OCEAN

Expendable bathythermograph (XBT) data and the climatological temperat ure/salinity relationship were used to calculate the mean annual cycle of dynamic height and geostrophic transport of major currents relativ e to 400 db along live shipping tracks covering a large part of the tr opical Pacific Ocean. The data were selected in bands centered on the most frequently repeated XBT tracklines for the period 1967-1988. Long -term bimonthly mean temperature was calculated in 1 degrees latitude bins along the tracks. The transport function (Vertically integrated d ynamic height) was then calculated using the mean temperature/salinity relationship. The mean annual cycle of transport of the North Equator ial Current (NEC), the North Equatorial Countercurrent (NECC) and the South Equatorial Current (SEC) (south of 2.5 degrees S) were determine d between the ridges and troughs of the transport function. The stocha stic errors in bimonthly mean transports were 1-2 Sverdrups on the mos t sampled tracks. Mean transports of the NEC and NECC increase regular ly with longitude from east to west. The NECC has a large annual cycle with a transport-maximum during northern fall and winter. Seasonal va riations of the NEC are small. Seasonal Variations of the SEC are slig htly larger, and they have considerably different phase from track to track. The variation of thermal structure associated with the currents is described. The results of this study are compared in detail to the results of earlier studies of the transports. The differences between the studies are larger than the expected stochastic errors in the mea n transports due to differences in the definition of boundaries of the currents and to differences in the procedure for calculating the mean annual variation. The results of all the studies are summarised to fa cilitate future comparisons to ocean general circulation models and ot her applications. Copyright (C) 1996 Elsevier Science Ltd.