Possible mechanisms yielding an explosive coastal cyclogenesis over South America: Experiments using a limited area model
The LAHM/GFDL-CIMA model, has been used to simulate an explosive cyclogenesis which produced a strong southeast gale over the Río de la Plata (a phenomenon locally known as 'sudestada'). The main purpose of this work is to analyse the physical processes related to this development, after h...
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1998
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| Acceso en línea: | https://bibliotecadigital.exactas.uba.ar/collection/paper/document/paper_00049743_v47_n4_p309_Seluchi http://hdl.handle.net/20.500.12110/paper_00049743_v47_n4_p309_Seluchi |
| Aporte de: |
| Sumario: | The LAHM/GFDL-CIMA model, has been used to simulate an explosive cyclogenesis which produced a strong southeast gale over the Río de la Plata (a phenomenon locally known as 'sudestada'). The main purpose of this work is to analyse the physical processes related to this development, after having verified the model's ability to reproduce the situation. Through different experiments, the model's potential to represent the event is demonstrated, while two other experiments have been designed in order to analyse the impact of topography and of condensation/evaporation processes during the cyclogenesis. Latent heat release resulting from precipitation processes is proposed as the main mechanism acting to intensify the system. The major air mass instability over the southeastern South American region was triggered by the entrance of a rather weak upper-level trough, and later reinforced by diabatic processes. By running the experiment without topography it was shown that, though the Andes did not cause the cyclonic development, they may have had a significant role during the early stages of the system's evolution. The processes undergone by this system might be summarised as follows: as the cyclonic disturbance approaches the Andes, it is blocked at lower levels, but continues propagating in the middle and upper troposphere, becoming more vertical and barotropic. As a consequence, increased westerly winds lead to a reduction in static stability leeward of the Andes which contributes to the strengthening of a thermal-orographic low pressure system and favours a sustained warm and moist advection over the region. Finally, once the depression traverses the mountains and recovers its tilt, classical baroclinic development starts, dramatically strengthened by latent heat release. |
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