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Tropical cyclone activity in the South Pacific

Par ECOLA Dernière modification 09/10/2014 14:55

In recent years, increased computing power and improved modeling and observation capabilities have improved forecasts of hurricane tracks. However, their intensity is still not well predicted. The reason often given in addition to the effect of stochasticity is an inadequate consideration of the oceanic structure and air-sea exchange in operational forecasting. The interaction of tropical cyclones with the ocean are essential to their formation and evolution. The heat contained in the surface layers of the ocean is the source of energy for tropical cyclones. In return, extreme winds inject mechanical energy into the ocean and change its structure. As a result, there is surface cooling along cyclone tracks that provide a negative feedback on cyclone intensity. 

The study of ocean response to hurricanes and feedback (Jullien et al., 2012, 2014) has highlighted the importance of ocean and atmospheric dynamics and tends to contradict the extreme estimates previously made from simplified theoretical models. The impact of hurricanes on climate appear overestimated in studies that neglect advection and re-emergence of oceanic anomalies on the surface during winter. Negative feedback of surface cooling induced by cyclones is also overestimated in theoretical studies because of strong assumptions on the time scales involved in the process of hurricane intensification. Similarly, the oceanic structure at large and mesoscale is often overlooked (e.g., in cyclogenesis indices; Menkes et al., 2012), while it strongly modulates the coupling mechanisms. The use of mesoscale models and long-term simulations producing a large number of events has been critical to separate robust mechanisms from anecdotal effects.

Références :

  •  Jullien S., P. Marchesiello, C. E. Menkes, J. Lefèvre, N. C. Jourdain, G. Samson, and M. Lengaigne, 2014: Ocean feedback to tropical cyclones: climatology and processes. Climate Dynamics, DOI 10.1007/s00382-014-2096-6.
  • Jullien S., C. E. Menkes, P. Marchesiello,  N. C. Jourdain, M. Lengaigne, A. Koch-Larrouy, J. Lefèvre, E. M. Vincent, V. Faure, 2012: Impact of tropical cyclones on the heat budget of the South Pacific Ocean. J. Phys. Oceanogr.42, 1882–1906.
  • Menkes C., M. Lengaigne, P. Marchesiello, N.C. Jourdain, E.M. Vincent, J. Lefevre, F. Chauvin, J.-F. Royer, 2012: Comparison of tropical cyclogenesis indices on seasonal to interannual timescales. Climate Dynamics, 38,301-321.
  • Jourdain N., P. Marchesiello, C. Menkes, J. lefevre, E. Vincent, M. Lengaigne, F. Chauvin, J.-F. Royer, 2009: Mesoscale Simulation of tropical cyclones in the South Pacific: climatology and interannual variability. Journal of Climate, 24, 3-25.

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