The Loop Current frontal eddies: Observations, generation mechanisms, and their movements

The Loop Current frontal eddies (LCFEs) are cyclonic eddies moving downstream along the outside edge of the Loop Current (LC) in the eastern Gulf of Mexico. A detailed description of the kinematics of the LCFEs is given using TOPEX/POSEIDON and ERS-2 sea surface height (SSH) data from January 1998 through July 2001. Satellite sea surface temperature (SST) imagery is also used to confirm the existence of the LCFEs detected in the SSH images. Warm water filaments from the LC are frequently seen to wrap around the LCFEs and sometimes the warm filaments can penetrate onto the Western Florida Shelf due to their interaction with the LCFEs. The outputs from an Atlantic Ocean numerical model are analyzed to identify the generation mechanisms of the LCFEs. The suggested LCFE generation due to the impingement of a Caribbean anticyclone on the Yucatan Current is studied in detail in a reduced-gravity numerical model. Horizontal shear instability of the LC also generates cyclonic frontal eddies but, with a translation speed too high and eddy size too small to account for the LCFEs found in the SSH images and in the outputs of the models. The fully-developed cyclonic eddy translation speed and the morphology of the LC front are found to depend on the eddy size, eddy potential vorticity, and the potential vorticity of the cyclonic shear side of the LC in a reduced-gravity contour dynamics model.