Contribution of tropical cyclones to meridional heat transport by the oceans

Tropical cyclones mix warm surface waters with cooler water within the thermocline, leaving pronounced, cold wakes that over a period of weeks are restored to normal conditions by mixing and surface fluxes. This restoration is associated with net, vertically integrated heating of ocean columns, which in statistical equilibrium must be balanced by oceanic heat transport out of the regions affected by the storms. Observed tropical cyclone tracks together with coupled ocean-atmosphere hurricane models are used to estimate the net ocean heating induced by global tropical cyclone activity during one calendar year (1996). This estimate, amounting to (1.4 ± 0.7) × l0¹⁵ W, represents a substantial fraction of the observed peak poleward heat flux by the oceans, suggesting that tropical cyclones may play an important role in driving the thermohaline circulation and thereby in regulating climate. In particular, the strong sensitivity of tropical cyclone intensity to tropical ocean temperatures in turn implies that the net poleward heat flux by the ocean is sensitive to tropical temperature, reducing tropical climate sensitivity and increasing climate sensitivity at higher latitudes.