A few additional data sets are used for particular purposes. These have been extensively described in the literature and are briefly summarized here.
C.1. Directly measured subsurface velocity
Directly measured velocities are shown in Fig. 6 at 110°W and 125°W, from the sections constructed by Johnson et al. (2002). These data were taken from an ADCP (Acoustic Doppler Current Profiler) mounted on the ship servicing the TAO moorings along those longitudes. Twelve sections were made along 110°W and 14 along 125°W, within 8°S–8°N, during 1991–2001. Data processing is described in Johnson et al. (2002); an objective mapping along isopycnals produced a mean, annual cycle, and ENSO variability estimate. Here, just the mean zonal velocity along two sections is shown (Fig. 6, top two panels) to supplement the geostrophic velocity estimates from XBT data. These data are available from http://www.pmel.noaa.gov/~gjohnson/.
The TAO mooring at 0°W, 110°W has been instrumented with current meters of various types since the early 1980s. Until 1997, the surface mooring included Vector Averaging Current Meters (VACMs), typically mounted at eight depths from 10 to 250 m. Since 1991, velocities have been measured using Acoustic Doppler Current Profilers (ADCPs), which provide much finer vertical resolution (typically 8 m; McPhaden et al., 1991). At first the ADCPs were mounted on the surface mooring to look downward; since 1995 they have been mounted on subsurface platforms (300 m) looking upward, which alleviates damage from fishing operations around the surface mooring. Velocity (as well as temperature, winds and some other meteorological quantities) data from these moorings are available from http://www.pmel.noaa.gov/tao/disdel/.
C.2. Reynolds SST
A gridded sea surface temperature (SST) product based on satellite AVHRR sampling ground-truthed with in situ data is produced by the National Centers for Environmental Prediction on a weekly, 1° × 1° grid for the period October 1981 through the present. Reynolds and Smith (1994) describe the data processing and quality control procedures. This data set is commonly known as the "Reynolds SST", and we use that nomenclature here. It is available from http://www.cdc.noaa.gov/cdc/data.noaa.oisst.v2.html.
C.3. Topex altimetric sea level anomalies
The TOPEX/POSEIDON altimeter has measured sea surface height (SSH) nearly continuously since October 1992. A follow-on mission, Jason-1, was launched in December 2001, following the same track as Topex, and the data used here consist of Topex through 2001, then continuing with Jason-1 through November 2004. The Topex/Jason orbit repeats a diamond formed by the overlapping patterns of ascending and descending tracks every 9.9 days; in the tropics the diamond spans about 2.8° latitude and 7.8° longitude. Fu et al. (1994) describe the technical characteristics and measurement accuracy of the instrument. These data are available either along the satellite tracks or as a 1° × 1° gridded product from NASA through http://podaac.jpl.nasa.gov/ost/.
C.4. Drifter surface currents
Surface currents estimated from drifters are used as a check on the geostrophic currents derived from XBT data. Surface Velocity Program (Niiler et al., 1995) drifter data were obtained from the Atlantic Oceanographic and Meteorological Laboratory as 6-hourly kriged positions and velocities (Hansen and Poulain, 1996), for the period 1979–2000. 1045 drifter tracks were found in the study region, however the distribution is not ideal since the drifter population falls off sharply closer than about 1000 km to the Central American coast. The region west of Cabo Corrientes and south of Baja California is especially poorly sampled. Nevertheless, the 6-hourly velocities were mapped to a 1° × 1° by monthly climatological grid by the same method and with the same scales as was done for the XBT temperatures described in Appendix A. In Fig. 4, any gridpoints with either fewer than 10 total samples or 4 climatological months represented was left blank. The drifter data are available from NOAA at http://www.aoml.noaa.gov/databases.html.
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