# 15 meter current seasonal cycle in the tropical Pacific

Gilles Reverdin
This gridded data set is constructed as described by
Reverdin et al. (1994) from current data during the period 1987 to April 1992.
We merged the drifts of more than 1000 surface buoys with currents from
current-meter morings at 5 sites (4 along the equator at
165E, 170W, 140W and 110W and one at 6N, 140W). The drifters were
initially drogued by a sea anchor of various designs centered at 15
meters. The proportion of drifters with drogue present is large
near the equator (more than 80%), but diminish to roughly 50% near
20N and 20S. We did not correct for drogue loss, and the systematic error
we make on the 15m currents can therefore exceed 5 cm/s near 20N and 20S.

The analysis of an average seasonal cycle is presented with 12 fields
of u (zonal velocity) and v (meridional velocity)
for each mid-month date on a 5x1 degrees latitude*longitude grid.

Longitude ranges from 122.5E to 82.5W (32 grid points)
Latitude ranges from 19.5N to 19.5S (40 grid points)
Time ranges from mid-January to mid-December

No analysis is made on land, but values are reported for grid boxes
partially over land.
Because the analysis is an optimal fit on a set of specified functions
applied locally and which involve a substantial zonal smoothing,
the currents near the continents should not be expected to be represented
properly. We should also warn that the conditions sampled by the current
measurements may not be representative of the long-term conditions. This
seems in particular to be the case near the date-line along the equator.

The data are here.

## Reference

Reverdin, G., C. Frankignoul, E. Kestenare and M. McPhaden, 1994:
Seasonal variability in the surface currents of the equatorial Pacific.
Journal of Geophysical Research, in Press.

Gilles Reverdin reve@ldeo.columbia.edu