Extended Abstract (304K)7A.4
Influence of an oceanic warm anomaly on the intensity of tropical cyclone Dora (2007) in the South West Indian Ocean
Guillaume Samson, Meteo-France/LACy, Sainte Clotilde, France; and D. Barbary, H. Giordani, G. Caniaux, and F. Roux
The South West Indian Ocean (SWIO) shows remarkably interesting oceanic features with different spatial and temporal scales which can affect tropical cyclones (TCs) evolution in this basin.
A noticeable feature of the SWIO is the absence of a western boundary current due to the presence of Madagascar and the formation of eddies in the Mozambique Channel and south of Madagascar. Associated with high oceanic heat contents (OHC), these anticyclonic eddies are suspected to be an important potential source of energy for TCs crossing the Mozambique Channel or passing near of Madagascar. Indeed, the interaction between warm mesoscale structures and TCs can lead to strong and rapid intensity changes as it has been already shown in the Gulf of Mexico and in the Northwest Pacific.
But large scale oceanic patterns can modify the OHC as well. An illustration is given by the Seychelles-Chagos thermocline ridge located in the North-East of Madagascar. This feature created by the thermocline doming is typically associated with a shallow oceanic mixed layer and low OHC and displays a strong interannual to intraseasonal variability. As a consequence, this thermal structure is highly sensitive to atmospheric forcings and is also suspected to influence the TCs intensity in this region.
Considering these particularities, this study aims at determining whether the OHC spatial variations observed in the SWIO can significantly influence the intensification rate of TCs. To adress this question, several experiments are conducted by using Meso-NH, a high-resolution atmospheric cloud model coupled with an ocean mixed layer model (1D-Ocean). This coupled model indicates good skills to simulate heavy rainfall events and severe air-sea interactions under high winds. We show that Meso-NH-1D-Ocean is able to simulate realistic ocean responses to TCs (with a cold wake located on the left-hand side of the TC track in the Southern Hemisphere) and a realistic TC life-cycle. Preliminary results suggest that both oceanic mesoscale and large scale structures in the SWIO play an important role in the TC intensity by modifying the surface heat fluxes. The influence of the along-track OHC gradients is also studied in details.
Session 7A, Ocean-atmosphere interactions and influences on tropical and extratropical storms: Part 2
Tuesday, 13 January 2009, 3:30 PM-5:00 PM, Room 128A
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