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2002 LAPCOD Meeting
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Mean and variability of the flow from quasi-Lagrangian floats
Claudia Schmid, Elizabeth Johns, Robert L. Molinari, Silvia L. Garzoli
NOAA/AOML
Claudia.Schmid@noaa.gov(Abstract received 10/15/2002 for session C)
ABSTRACT
Quasi-Lagrangian trajectories from profiling floats deployed in the tropical Atlantic are used to derive the mean flow and the variability at intermediate depth (800-1100m) for January to June and for July to December. The mean fields as well as individual trajectories reveal reversals of the flow on the equator. Indications for such reversals were also found in Lagrangian trajectories obtained during earlier experiments and they are confirmed in comparisons of Eulerian observations collected at different times of the year. Signs for reversals are also found at off-equatorial latitudes (e.g. 6°S, 6°N). Differences between the equatorial band (roughly 3°S to 3°N) and the region outside of this band are present in the vertical and zonal extent of unidirectional zonal flow. There are also signs for differences in the temporal variability of the flow. To date the best coverage with data from profiling floats in the tropical Atlantic is found around 6°S. Therefore the latitude band 5°-7°S is chosen for an analysis of the temporal variability of the flow outside of the equatorial band. It is found that the zonal velocity reverses on an annual time scale, and that the time of reversal depends on the longitude. In addition shorter-periodic variability is observed. In some cases westward propagating signals can be identified in a longitude-time diagram. Their propagation can be associated with an apparent westward phase velocity on the order of 6cm/s. Similar characteristics are found in a numerical model with time-varying climatological winds. It is possible to derive a longitude-time diagram of the velocity that is strikingly similar to that from the model with a superposition of only two planetary waves.
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2002 LAPCOD Meeting, Key Largo, Florida, December 12-16, 2000