HURRICANES

The heavy winds associated with tropical cyclones generate strong upper ocean mixing. Recent studies suggest that this enhanced mixing significantly contributes to the ocean poleward heat transport, mainly due to a strengthening

of the subtropical cells. However, the currently published literature makes the assumption that all heat pumped below the mixed layer by tropical cyclones is finally released in higher latitudes. In our research we questioned this assumption by addressing some overlooked characteristics of tropical cyclone induced ocean mixing.

The first regards the observation that tropical cyclones rarely occur polewards of about 10º. A general circulation model is used to show that if mixing is enhanced solely in the subtropical bands, where tropical cyclones are observed most of the heat taken up in the subtropics is transported into the equatorial strip, effectively reducing the poleward heat transport out of the deep tropics.

We are now investigating other aspects of the problem. Stay tuned.

Figure 1. (a) Total northward OHT in four model runs

described. The control run has a constant background vertical diffusivity. In the “no gap” run the vertical diffusivity is enhanced equatorward of 30º in the upper 170m. In the “5.6º gap” run, the eddy diffusivity is increased in the 31ºS-5.6ºS and 5.6ºN-31ºN bands in the upper 170m. In the “11º gap” run, the eddy diffusivity is increased in the 31ºS-11ºS and 11ºN-31ºN bands in the upper 170m. (b) The OHT in the three model runs with increased upper ocean mixing minus the OHT in the control run. Positive values correspond to increased (reduced) poleward heat transport in the northern (southern) hemisphere while the signs are opposite for the southern hemisphere.

References

Jansen, M., R. Ferrari,  and T. Mooring, 2010: The effect of the seasonal cycle on heat anomalies generated in the wake of tropical cyclones, Geophys. Res. Lett., Vol. 37, L03602.

Jansen, M., and R. Ferrari, 2009: The latitudinal distribution of tropical cyclones and ocean heat transport, Geophys. Res. Lett., Vol. 36, L06604.

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