Poleward Heat Transport in a Barotropic Ocean Model

Abstract

A barotropic ocean circulation model coupled to a mixed-layer temperature equation is used to study the poleward heat transport by the horizontal wind-driven ocean currents. Through scaling analyses, two different regimes of the heat transport are found, characterized by ??∞ and ??0, respectively, where ? is the ratio between the ocean advection timescale and the restoring timescale of Newtonian cooling at the air?sea interface. In the regime ??∞, the heat transport is proportional to ??1 and to the second power both of the basin east?west width and of the magnitude of wind stress curl. In the regime ??0, the heat transport is proportional to ? and to the basin width, and insensitive to the magnitude of wind stress curl. The heat transport is a maximum for intermediate values of ?, and the numerical experiments show that a restoring timescale of 5 months maximizes the heat transport for a barotropic square basin 500 m deep and 400 km wide (North Atlantic size). The corresponding maximum heat transport is about 0.32 PW. If the basin width is doubled (North Pacific size), the maximum poleward heat transport by the modeled ocean currents is estimated to be 0.73 PW. The numerical experiments also show that the heat transport can be underestimated if the model resolution is too coarse?for example, for a horizontal resolution of 4° ? 4°, the heat transport is underestimated by about 50%.