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Climatic Impacts of Intermittent Tropical Cyclone-Induced Alterations in Sea Surface Temperature
Manucharyan, G.E., Brierley, C.M. and Fedorov, A.V. 2011. Climate impacts of intermittent upper ocean mixing induced by tropical cyclones. Journal of Geophysical Research 116: 10.1029/2011JC007295.

The studies of Dare and McBride (2011) and Park et al. (2011) have demonstrated that tropical cyclones (TCs) can significantly cool the surface waters in their wakes for periods of several days to weeks; and Manucharyan et al. write that "TC-induced ocean mixing can have global climate impacts as well, including changes in poleward heat transport, ocean circulation, and thermal structure." They note, however, that "in several previous modeling studies devoted to this problem, the TC mixing was treated as a permanent (constant in time) source of additional vertical diffusion in the upper ocean," and, therefore, they go on to explore what they call the "highly intermittent character of the mixing" and what it portends for global climate, using a global ocean-atmosphere coupled model and a simple heat transfer model of the upper ocean.

What was done
The three Yale University researchers mimicked the effects of tropical cyclones using several representative cases of time-dependent mixing that yield the same annual mean values of vertical diffusivity, conforming with the studies of Jansen and Ferrari (2009) and Fedorov et al. (2010), wherein spatially uniform (but varying in time) mixing is imposed on zonal bands in the upper ocean.

What was learned
Manucharyan et al. report that they observed "a weak surface cooling at the location of the mixing (~0.3°C), a strong warming of the equatorial cold tongue (~2°C), and a moderate warming in middle to high latitudes (0.5°C-1°C)," together with "a deepening of the tropical thermocline with subsurface temperature anomalies extending to 500 m [depth]." And they say that "additional mixing leads to an enhanced oceanic heat transport from the regions of increased mixing toward high latitudes and the equatorial region."

What it means
"Ultimately," in the words of the researchers, "simulations with TC-resolving climate models will be necessary to fully understand the role of tropical cyclones in climate," for they note, in this regard, that "the current generation of GCMs are only slowly approaching this limit and are still unable to reproduce many characteristics of the observed hurricanes, especially of the strongest storms critical for the ocean mixing (e.g., Gualdi et al., 2008; Scoccimarro et al., 2011)."

Dare, R.A. and McBride, J.L. 2011. Sea surface temperature response to tropical cyclones. Monthly Weather Review 139: 3798-3808.

Fedorov, A., Brierley, C. and Emanuel, K. 2010. Tropical cyclones and permanent El Niņo in the early Pliocene epoch. Nature 463: 1066-1070.

Gualdi, S., Scoccimarro, E. and Navarra, A. 2008. Changes in tropical cyclone activity due to global warming: Results from a high-resolution coupled general circulation model. Journal of Climate 21: 5204-5228.

Jansen, M. and Ferrari, R. 2009. Impact of the latitudinal distribution of tropical cyclones on ocean heat transport. Geophysical Research Letters 36: 10.1029/2008GL036796.

Park, J.J., Kwon, Y.-O. and Price, J.F. 2011. Argo array observation of ocean heat content changes induced by tropical cyclones in the north Pacific. Journal of Geophysical Research 116: 10.1029/2011JC007165.

Soccimarro, E., Gualdi, S., Bellucci, A., Sanna, A., Fogli, P.G., Manzini, E., Vichi, M., Oddo, P. and Navarra, A. 2011. Effects of tropical cyclones on ocean heat transport in a high resolution coupled general circulation model. Journal of Climate 24: 4368-4384.

Reviewed 4 April 2012