Modeling the intrusion of the Loop Current into the Gulf of Mexico

Abstract

The Loop Current (LC) intrusion into the Gulf of Mexico is analyzed using steady, 2-D nonlinear shallow water equations expressed in Cartesian and natural coordinates. The model suggests that the LC moves with constant relative vorticity along isopleths of the Bernoulli function B such that its surface area (A) has a steady dA/dt and frontal velocity. The intrusion is envisioned as an initial transport imbalance that creates volume storage within the Gulf. Because of the advection of relative vorticity, the intruding inflow splits into a northward flow on the west and a southward flow on the east. The storage creates a sea level difference across the LC that induces a northward force due to Coriolis. This force reinforces the northward flow but opposes the southward flow, helping store water inside the Gulf. This sea level difference is in addition to the one in the B field. The storage implies loss of kinetic energy, which creates a speed shear across the LC and gives rise to the small speed of the LC front. The relative vorticity equation in natural coordinates reveals three aspects of the LC: (1) a velocity difference across the LC, (2) a parabolic shape of the sea surface; and (3) a negative curvature of the LC meaning the velocity changes direction anticyclonically along the B-contours.