Impact of upstream variability on the Loop Current dynamics in numerical simulations of the Gulf of Mexico

Abstract

The Loop Current (LC), which is the main mesoscale dynamic feature of the Gulf of Mexico (GoM), has a major impact on the circulation and its variability in the interior Gulf. The LC is a highly variable and dynamic feature. It changes shape from a short jet connecting the two openings of the GoM in an almost straight line ("retracted phase") to a long loop invading most of the eastern part of the GoM ("extended phase"). When it is in the extended phase, it can shed large anticyclonic eddies, called Loop Current Eddies, which then migrate to the western GoM. In this study, the processes controlling the LC dynamics are investigated using two multi-decadal simulations of the Gulf of Mexico HYbrid Coordinate Ocean Model differing in their open boundary conditions (BCs) and altimetry-derived gridded fields. The LC in the simulation with BCs derived from monthly climatology state variables frequently remains in its retracted phase significantly longer than observed. In contrast, the duration of the retracted phase is notably shorter in the simulation in which the BCs have realistic daily variability. By examining the flow properties through the Yucatan Channel from which the LC originates, we find that increased intensity of this current and a westward shift of the mean core is associated with the LC transitions from the retracted to the extended phase. This transition is accompanied by an increase of both cyclonicity of the flow in the west and anticyclonicity in the east of the core of this jet. Moreover, the number of anticyclonic eddies entering in the GoM through the Yucatan Channel is significantly higher when the LC extends in the GoM. Consequently, this study demonstrates the importance of realistic flow variability at the lateral boundaries for accurate simulation of the LC system in a model, and reveals characteristics of the upstream flow associated with different LC behavior that can potentially aid in forecasting the LC system.

ENSO Modulates Mean Currents and Mesoscale Eddies in the Caribbean Sea

“…That said, many other factors, such as the Orinoco River discharge (e.g., Muller-Karger et al, 1989), also affect the marine productivity in the Caribbean Sea and the relationships between ENSO and marine productivity across the whole Caribbean Sea are likely more complex. In addition, previous studies (e.g., Huang et al, 2021;Laxenaire et al, 2023;Mildner et al, 2013;Oey, 2004) suggest that the mean currents and eddies in the Caribbean Sea could affect downstream regions, like the GoM and the Florida Current. So, ENSO-related interannual variations in the Caribbean Sea could potentially be advected downstream and result in regional interannual variability.…”

“…They also transport nutrients, chlorophyll, Sargassum , larvae, and pollutants, and hence impact the marine ecosystem in the Caribbean Sea (Andrade & Barton, 2005; Chérubin & Richardson, 2007; E. M. Johns et al., 2014; Andrade‐Canto et al., 2022). In addition, some studies suggest that the eddies in the Caribbean Sea could impact the eddy‐shedding of the Loop Current in the GoM (e.g., Andrade‐Canto et al., 2020; Huang et al., 2021; Laxenaire et al., 2023; Murphy et al., 1999; Ntaganou et al., 2023; Oey, 2004; Yang et al., 2020).…”

Assessment of predictability of the Loop Current in the Gulf of Mexico from observing system experiments and observing system simulation experiments

“…Such definition of the LC front would work best for evaluating predictability of the LCE shedding event using the MHD metric, but it is less useful for our purposes. A better definition of the LC front (e.g., Laxenaire et al, 2023) can provide more consistent scores, thus reducing the spread of the scores in the individual forecasts.…”

The K-profile Parameterization augmented by Deep Neural Networks (KPP_DNN) in the General Ocean Turbulence Model (GOTM)

“…Gulf of Mexico and will train the KPP_DNNs using those simulations. The KPP_DNN2a will be implemented in the HYCOM model configured for the Gulf of Mexico (Dukhovskoy et al, 2015;Laxenaire et al, 2023).…”