Role of Midwater Mixed Waves in the Loop Current Separation Events From a Coupled Ocean-Atmosphere Regional Model and In Situ Observations

Abstract

A previously uninvestigated necking-down region in the Gulf of Mexico, associated with the Loop Current eddy (LCE) separations is defined by the 8–16 days variance below the Loop Current system (LCS) around 88.5°W, using an Ocean-Atmosphere Coupled Regional-Community Earth System Model (R-CESM) 9-year nature run, which reveals the mechanisms of Loop Current (LC) deep dynamics. Scaled wavelet analysis of flow fields in five regions at the 27.5 kg/m³ potential density layer under the LCS shows that the 8–16 days variance is reproduced by the R-CESM model dynamics, aligning with in situ observations. This weather band deep variance, identified as the mixed waves located between the mixed Rossby-gravity waves and Rossby waves in the ocean wave dispersion relationship, is stimulated by the interaction between the penetrating LC and steep topography. Then, these waves are released from the constraints of the topography and become free wave trains. There are three critical regions for the propagating wave trains: the Mississippi Fan, the Yucatan Shelf, and the Florida Escapement. The various wave trains define five distinct scenarios: East Yucatan Shelf (EYSS), West Yucatan Shelf (WYSS), west Florida escarpment (WFES), Mississippi Fan (MFS), and quiescent (QS) scenarios. The scenarios passing through the west necking-down region can be used to indicate the LCE separations. After the separations, the retracted LC may encounter interference from either the EYSS or the WFES, preventing the reattachments. These 8–16-day waves offer insights into describing the LC shedding events from the lower layer of the LCS, enhancing the understanding of LCS dynamics.