Characterization of Storm Properties During the TroCCiBras Experiment

The field experiment TroCCiBras (Tropical Convection and Cirrus Brazil) was conducted during the period of 22 January to 11 March 2004 in the central area of the State of São Paulo, with the objective to study the contribution of lightning generated NOx (LNOX) from tropical convective storms to the already existing background NOx in the upper troposphere and lower stratosphere (UTLS). This was done in collaboration with scientists from two projects funded by the European Community, viz., TROCCINOX (Tropical Convection, Cirrus and Nitrogen Oxides Experiment) and HIBISCUS (a project on “Impact of tropical convection on the upper troposphere and lower stratosphere”). By combining and coordinating the available resources, it was possible to gather data, which not only characterize the storms, but also the atmosphere in which they occur. A variety of sensors, including two S-band Doppler weather radars, an elastic backscattering Lidar for aerosol profiling, up to 6 daily radiosonde ascents, two aircraft equipped for meteorological and chemical measurements, as well as a Lightning Detection Network, were deployed. Thus, a unique database for the State of São Paulo could be built up.

The characteristics of rainstorms monitored by the Bauru S-band Doppler radar are being evaluated to determine the large-scale organization of the storms, their frequency of occurrence and spatial distribution, as well as their history of size and intensity. For this study, a specialized software package, TITAN (Thunderstorm Identification, Tracking, Analysis and Nowcasting), which was developed at NCAR (National Center for Atmospheric Research) and made available as part of the on-going collaboration between the Meteorological Research Institute (IPMet) and NCAR, is being utilized. By processing the radar data, collected during the TroCCiBras Experiment, a statistical analysis of the storm properties can be determined with TITAN, and the results will characterize the convective activity during this period. The radar data considered for the analysis are volume scans recorded every 7.5 or 15 minutes within the 240 km range of the Bauru S-band Doppler radar. For the storm identification it was set a threshold of 35 dBZ and a volume threshold of 50 km³, as a first approach. Preliminary results show, that during the period of the TroCCiBras experiment, a large percentage of the storms were small, with a mean volume of less than 600 km³ and duration of less than 3 hours, indicating the predominantly isolated convective activity during the period considered. Other properties of the observed storms, such as, VIL (Vertically Integrated Liquid water content), echo tops, velocity and direction of storm displacement, will be discussed further in this paper.