Mesoscale organization of the continental tropical convection

The focus of this study is the mesoscale organization of convective storms over the SW Amazon. The data were colleted during the WETAM/LBA Project held in January and February of 1999. The convective storm organization was classified by visual inspection of radar reflectivity fields from the NCAR S-Pol and visible images from satellite. Based on the analysis of 24 events two primary modes of organization were identified. A day was classified as an event if the convection was initiated inside the radar range (150km ray) and the sounding was considered representative of the prestorm environment. The first mode is “line storms” which typically evolved from shallow morning showers associated with horizontal convective rolls (cloud streets). The second mode is “arc storms”, which were typically associated with the leading edges of cold pools generated by previous convective storms. Three hourly sounding data showed the importance of low level wind in modulating the storm organization. The “line storms” were associated with a low level jet exceeding 10 m/s whereas “arc storms” were associated with very low wind speeds.