Structural characteristics of mesoscale convective systems over southeast Brazil related to cold frontal and non-frontal incursions

Abstract

International Satellite Cloud Climatology Project (ISCCP DX) and microwave sensor data collected by the Tropical Rainfall Measuring Mission (TRMM) are used to identify and describe structural characteristics of mesoscale convective systems (MCSs) over southeast Brazil in a three-year period. A seasonal climatology for MCS events related to cold frontal and non-frontal incursions over the continental and oceanic areas is built by applying Hovmöller diagrams and a cloud tracking method to DX data. Results show that the frontal and non-frontal events strongly modulate convective cloudiness over continental and oceanic southeast Brazil, producing MCSs with significant fractions of deep convective clouds and rain in their mature phase. The continental MCSs related to cold frontal incursions (LF MCSs) appear as MCSs with more uniform fractions of deep convective clouds and consequently with larger rain fractions over southeast Brazil compared to continental MCSs related to non-frontal incursions (LNF MCSs). The oceanic MCSs related to non-frontal incursions (ONF MCSs) contain larger deep convective cloud fractions and rain compared with the oceanic MCSs related to cold frontal incursions (OF MCSs). This results in larger convective rain fractions and larger convective rainfall rates over oceanic southeast Brazil. The continental MCSs (related to cold frontal incursions) have larger fractions of deep convective clouds and stronger vertical development of clouds compared to the oceanic MCSs (related to cold frontal incursions), which results in larger fractions of rain and larger mean convective rainfall rates over continental southeast Brazil. This implies that the cold frontal incursions over continental southeast Brazil organise convective cloudiness and precipitation over larger areas and more strongly than over oceanic southeast Brazil, most likely due to the stronger surface and atmospheric heating over continental areas (land-sea heating contrasts)