Investigating Loop Current Deep Dynamics and Separation Events from a Coupled Ocean-Atmosphere Regional Model and In-situ Observations

Abstract

A 9-year nature run (free run) and two assimilative runs of R-CESM are used to reveal the mechanisms of Loop Current (LC) deep dynamics. The numerical outputs are compared to the in-situ observations. Our results indicate the R-CESM has the capability to capture the major features of Loop Current Eddies (LCEs) shedding events in both upper and lower layers, the thermal structure is biased (warmer upper layer, cooler lower layer) as most previous modeling studies. The assimilation of sea surface height (SSH) improves the simulation of upper-layer Loop Current System (LCS) dynamics, and the assimilation of sea surface temperature (SST) revises the bias induced by the assimilation of SSH. The Self-organizing Map (SOM) analysis of SSH and stream function at 27.5 kg/m^3 potential density layer under the LCS indicates the different stages of the LCEs shedding events in the upper and lower layers. The circulation features under the LCS display the precursor patterns of the LCEs shedding events identified by the SOM. The Principal Component Analysis (PCA) is applied to combine different variables from different locations as one metric via weighted parameters from the critical regions of the precursor patterns at the bottom of the LCS. The leading variables are the 8-16 days scale-averaged variance of kinetic energy as de-rived from wavelet transform. These 8-16 days variations, identified as the Mixed Rossby-Gravity (MRG) waves in this dissertation, are stimulated by the interaction between the penetrating LC and sharp topography. There are three critical regions for the propagating wave trains: the Mississippi Fan, the Yucatan Shelf, and the Florida Escapement. The wave trains determine five different scenarios: the East Yucatan Shelf Scenario (EYSS), the West Yucatan Shelf Scenario (WYSS), the West Florida Escarpment Scenario (WFES), the Mississippi Fan Scenario (MFS), and the Quiescent Scenario (QS). A west necking-down region associated with the LCEs separations is found below the LCS around 88.5 ◦W. The wave train scenarios passing through the west necking-down region from the Mississippi Fan and Yucatan Shelf are used to indicate the LCEs separations. The description of the lower-layer structure can improve the understanding of the LCS dynamics.