Observations of Equatorially Trapped Waves in the Eastern Atlantic Ocean from Inverted Echo Sounders
Date of Award
1984
Degree Type
Dissertation
Degree Name
Doctor of Philosophy in Oceanography
Department
Oceanography
First Advisor
John Knauss
Abstract
Fourteen months of IES measured vertical acoustic travel time data and ambient noise measured wind speed data from 0° 4°W, a topographically smooth region in the eastern equatorial Atlantic, are used to study the properties of equatorially trapped waves on two time scales: 3 to 5 days, and seasonal. Sharp spectral peaks are found in the travel time records at periods between 71 and 130 hours, coinciding with the predicted periods of several resonant, low meridional mode (n = 1, 3, and 5), first vertical mode (m = 1) inertia-gravity waves. However, the identification of these waves is somewhat suspect because the Atlantic is too narrow to permit the 0(104 km) zonal wavelengths required for zero zonal group velocity. Estimates of the vertically propagating wave response to atmospheric forcing in the 3 to 5 day band produce results similar to the free, standing mode analysis. The inverted echo sounder appears to be responding to vertically propagating waves with vertical wavelengths comparable to the first vertical mode. The computed ray paths of these waves are such that prominent standing mode waves could be established without the strict requirement of zero zonal energy flux.
Simultaneous observations of thermocline depth, sea surface temperature (SST), and local wind speed from 0° 4°W are used to test the hypothesis that seasonal upwelling in the eastern equatorial Atlantic is caused by a remotely forced, equatorially trapped Kelvin wave. During 1980, a climatically normal year in terms of SST variability, the onset of the summer rise of the thermocline occured in April, not June-July as suggested by previous studies. The thermocline rose 30m (from 70m to 40m) in less than three weeks. Subsequently, the SST dropped slowly over the next three months. During this event, no significant change was noted in the local wind speed. Thus, it seems that local forcing could not have coused the rise of the thermocline. By taking into account the fact that the zonal Trade winds initially increase over the central Atlantic in April of each year, a revised Kelvin wave scenario is suggested to explain the different timing of these observations.
Recommended Citation
Miller, Laurence L., "Observations of Equatorially Trapped Waves in the Eastern Atlantic Ocean from Inverted Echo Sounders" (1984). Open Access Dissertations. Paper 1581.
https://digitalcommons.uri.edu/oa_diss/1581
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