Variabilidade interdiurna da convecção na América do Sul: a propagação meridional da convecção / Day-to-day convective variability over south America: the meridional propagation of convection.

AUTOR(ES)
DATA DE PUBLICAÇÃO

2003

RESUMO

A climatology for the meridional propagation of convection (MPC) over South America (SA) for the 1983-93 years is built by using cloud and atmospheric circulation composites. Results reveal three important types of MPC over SA. Type 1 focuses the frequent penetrations of cold fronts that organize tropical convection and move with it towards equator. Type 1 is more frequent during austral spring and contributes to at least 37% of the total day-to-day convective variability over SA during that season. The advance of a low level transient cyclone from southeast to northeast SA which is maintained by the convergence of moisture fluxes from the Amazon and cold air from the midlatitudes constitutes the main atmospheric circulation pattern during the type 1 events. Type 2 is characterized by an organization of tropical convection due to cold fronts over the subtropics and is associated with intensification and apparent propagation of convection from the tropics towards the subtropics. Type 2, which is associated with the South Atlantic Convergence Zone (SACZ) formation, is more frequent in austral summer and contributes to more than 16% of the total day-to-day convective variability during that season. The type 2 circulation pattern is similar to the type 1, except by the low level quasi-stationary transient cyclone over southeast SA that intensifies and favors the SACZ formation during the majority of the type 2 events. The cold fronts that have only weak interaction with tropical convection and remain quasistationary with convection in the subtropics (with respect to the meridional direction) are classified as type 3. Type 3 is more frequent in austral winter and contributes to at least 50% of the total day-to-day convective variability during that season. The existence of a low level quasi-stationary transient anticyclone (cyclone) over central (southeast and south) SA and a subtropical jet is the main circulation pattern observed for type 3. An intense upper level cyclonic vortex over northeast SA is present, apparently also contributing for the blocking of cold fronts over the subtropics that are frequently observed during the type 3 events. An austral wet season climatology of the cloud and rain properties of the convective systems formed during the occurrences of the MPC types was done by using collocated images from different types of sensors for the 1998-2000 years. Results show that the three MPC types modulate strongly the convective cloudiness and the rainfall regimes over SA and exhibit significant structural differences between their convective systems. A two cases study for the MPC (one for type 1 and other for type 2) revealed that the atmospheric circulation patterns during the type 1 case are basically equivalent to the ones described in its climatology, except by the occurrence of an upper level cyclonic vortex over northeast SA and a subtropical jet that seem to inhibit the northward advance of the low level though associated to the cold front during the event. For the type 2 case, the circulation patterns exhibited consistence with respect to its climatology and permitted to comprove the development of a type B cyclogenesis over SA during the event.

ASSUNTO(S)

climatology modos de propagação nuvens convection propagation modes radiômetros de microondas convecção precipitation climatologia precipitação meteorologia clouds meteorology microwave radiometers

ACESSO AO ARTIGO

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