Long waves in the equatorial Atlantic Ocean during 1983

Abstract

Long waves appeared at a zonally oriented sea surface temperature (SST) front in the eastern equatorial Atlantic during June and July of 1983. The low frequency, westward moving long waves (1000 km, 24 days) are monitored in the NOAA 7 satellite infrared images as meridional displacements of the front. The long waves observed in the Atlantic are similar to the waves previously seen in the eastern equatorial Pacific with several exceptions. The Atlantic long waves have a shorter duration (nearly three wave cycles at 15°W), and the wave amplitude is limited eastward of longitude 10°W. The Atlantic equatorial front appears to have a minimum north‐south displacement between longitudes 5°W and 10°W, while westward of 10°W the displacements exceed 400 km. Several buoys were launched south of the equator at longitude 4°W by the Programme Français Océan‐Climat en Atlantique Equatorial group on June 21, 1983. For the first 3 weeks, three of the buoys moved westward parallel to the equatorial SST front and measured relatively constant temperatures at 2 m. During mid‐July, changes were observed in the buoy temperatures, the buoy trajectories, and the long‐wave pattern. A comparison of the buoy temperatures at a depth of 2 m and atmospherically corrected satellite estimates of SST show a residual dependence of the satellite data on the zenith angle, even when the angle is limited to 45°. In general, the satellite SST measurements reproduce the trends observed in the buoy measurements, but small bias differences occur between buoys and between day and nighttime SST comparisons. Equatorial cross sections by ship and satellite over a 7‐day interval in June 1983 also show that SST trends are comparable in both sets of data.