Topic Area

Detection of Mesoscale Front and Eddy Features Using Altimetry Data:
Eddies detection in the Caribbean Sea and Gulf of Alaska Using TOPEX/POSEIDON
and Geosat Altimetry

LT Todd E. Barnhill, USN

In the first paper, Eddies are tracked using TREX/POSEIDON altimetry data.  Eddies in the Caribbean Sea are seen to have a frequency of one every 75 days with an average speed of 12 cm/s and an average amplitude deflection of 20 cm.  Eddies propagate in the same direction as the mean flow from the lesser Antilles to the Gulf of Mexico.  

In order for the altimetry data to be useful for tracking eddy features, many complex-processing algorithms must be used to remove noise from the data.  The two most significant processing that occurs is the removal of Tidal and Geoid undulations.  

Geoid processing has one significant effect, it removes the mean and semi-permanent flow from the data. This means that any feature that moves with the freq of less than 3 months is seen in the data, however features that move with a frequency of greater than 3 months are not seen.  

In the second paper, many possible theories for the origin of Caribbean Eddies are discussed.  Most of the theories expect Eddies to be formed on the western side of the Antilles.  Although some eddies do form on the eastern side of the lesser Antilles, many form on the east side and move through the Caribbean.  

In the third paper, Alaska Anticyclonic eddy events are discussed showing a significant rise in occurrence during warm ENSO events.  Track data between 45⁰N and 60⁰N are reviewed from the TOPEX/POSEIDON altimeter from 1992 to 1998 showing nearly twice as many events during an El Nino year than during a normal year.  Additionally, the strength and size of the eddies are much larger during and El Nino year than during a non-El Nino year.  When comparing the size and strength between Anticyclonic and Cyclonic events the Anticyclonic eddies are always much broader and stronger. 

In the Last paper, Alaskan Anticyclonic eddies are show to have a major impact on the fisheries.  Anticyclonic Eddies in the Gulf of Alaska are shown to be created near Queen Charlotte Island in Canada and near Sitka in Alaska. Large Anticyclonic eddies are produced more frequently during El Nino events, and smaller, weaker Anticyclonic eddies are produced in La Nina years as compared to a normal year.  Eddies transport both oceanic properties and biological organisms from the coast to the deep ocean.  

References

Carton, J.A., and Y. Chao, 1999: "Caribbean Sea eddies inferred from TOPEX/POSEIDON altimetry and a 1/6 degree Atlantic Ocean model simulation" J. Geophys. Res., Vol. 104, 7743-7752.

Nystuen, J.A., and C.A. Andrade, 1993: "Tracking mesoscale ocean features in the Caribbean Sea using Geosat altimetry." J. Geophys. Oceanogr., Vol. 98, 8389-8394.

Meyers, S.D., and S. Basu, 1999: "Eddies in the Eastern Gulf of Alaska from TOPEX/POSEIDON altimetry." J. Geophys. Res., Vol. 104, 13,333-13,343.

Crawford, W. and Whitney, F., “Tracking Eddies that Feed the Sea”, Earth Observatory Website, http://earthobservatory.nasa.gov/Study/Eddies/

Colorado Center for Astrodynamics Research, Global Near Real-Time Altimeter Data Viewer, http://www-ccar.colorado.edu/~realtime/global-real-time_ssh/

Colorado Center for Astrodynamics Research, TOPEX/Poseidon, ERS-1 & ERS-2 Global Mesoscale Historical Data Viewer, http://www-ccar.colorado.edu/~realtime/global-historical_ssh/
 

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