Genesis and effects of long waves in the equatorial Pacific

Abstract

Data from 20 satellite‐tracked drifting buoys deployed in the eastern equatorial Pacific Ocean during the summer of 1979 were used to investigate the nature, effects, and energetics of currents associated with cusp‐shaped long waves observed in satellite IR imagery of the sea surface during all except El Nino years. It is shown that the long waves are associated with a vigorous pattern of mesoscale eddies lying primarily between the equator and 7°N. The spatial structure of the eddy kinetic energy closely resembles the eigenfunctions obtained from Philander's (1978) investigation of barotropic instability of that part of the South Equatorial Current lying north of the equator. Computation of the energy exchange between the eddies and the mean field suggests an e folding time of about two weeks for the eddies and a braking effect on the mean flow comparable to a change of surface wind stress of a few tenths of a dyne per square centimeter. The eddies also effect an equatorward transport of heat that amounts to about two thirds of the poleward heat transport of the divergent Ekman transport in the near‐surface waters.

On the surface circulation in the western Coral Sea and residence times in the Great Barrier Reef

“…[13] Surface velocity drifter observations in the tropical Pacific started in 1978 [Hansen and Paul, 1984] with the objective of mapping the surface currents from local to regional scales with accuracy that is only possible with this type of instrument [Griffa et al, 2007]. In the last 4 years, the number of drifter observations has increased sufficiently to obtain a statistically robust representation of the WCS basin surface circulation.…”

Inter-ocean fluxes south of Africa in an eddy-permitting model

“…It is not possible with the current design to determine the eddy momentum flux divergence of the TIW and it is difficult to determine their eddy heat flux divergence, both of which are of major importance for the equatorial circulation (Hansen and Paul (1984) and Bryden and Brady (1989)). It takes, however, only minor additions to PIRATA to correct for this.…”

“…Their period is between 20 and 40 days and their wavelength is of the order of 1000km (Legeckis (1977) and Weisberg and Weingartner (1988)). Hansen and Paul (1984) and Bryden and Brady (1989) show that the equatorward heat flux of the TIW exceeds the atmospheric heat flux at the equator. Thus, the position and strength of the equatorial cold tongue is sensitive to the structure of the TIW.…”

High frequency fluctuations in the heat content of an ocean general circulation model

“…They also show that the zonal temperature advection due to the TIWs is as important as the meridional one. On the other hand, the study of Hansen and Paul (1984) in a similar region concluded that the zonal eddy heat flux is small. They used datasets which had been averaged over several days so this may explain why their analysis came to this conclusion.…”