On the Vertical Angular Momentum of the Loop Current

Abstract The concept of angular momentum is employed to examine the northward intrusion of an idealized Loop Current (LC) for the first time. The analysis reveals that the LC intrudes in dynamical equilibrium as forces and torques along the vertical are in balance. The Coriolis forces associated with the northward and southward flows of the LC has a net eastward force. The eastward force pushes water against the Florida Escarpment, piling water along it and creating a sea level difference across the LC. The Florida Escarpment topography, in turn, pushes the LC westward, keeping it nearly stationary, and the sea level change balances the net Coriolis force of the fluid particles. Because forces acting on the idealized LC are in balance, the LC’s angular momentum per unit mass is constant and equals dA L / dt (= k ), where A L is the surface area of the LC. The constancy of the angular momentum explains why dA / dt is indeed constant during the intrusion. The need to conserved angular momentum results in a meridional movement of mass or the LC intrusion. Angular momentum considerations allow predicting the northward intrusion distance ( b ) of the LC into the Gulf of Mexico as , where k = 225 km 2 day −1 and T (days) is the shedding period. On the basis of these results, a forecasting algorithm for the LC is proposed and tested using observations of the retreat latitude of the LC.