Studies on rainfall variability during the TRMM-Brazil and WET AMC/LBA campaigns of Austral Summer 1999

Rainfall characteristics, such as the diurnal cycle and the daily variations associated with significant weather events, have been studied based on the December 1998-February 1999 TRMM-Brazil and WET AMC/LBA campaingns field data. High resolution rainfall data as well as satellite information have been used to determine the diurnal cycle of rainfall on the sites, and to identify the weather systems responsible for extreme rainfall during the period of observations for two cases study: January 6 and February 15 1998, which were days with extremely large rainfall events.

The rainfall network was part of a 30 NASA TRMM and 10 LBA tipping buckets, that were part of the TRMM-LBA (or TRMM-Brazil) campaign planned by NASA and was parallel to the Brazilian Atmospheric Mesoscale Campaign (WET AMC/LBA), being both integral part of the Large Scale Biosphere Atmosphere experiment ion Amazonia (LBA). They were ordered on 4 clusters.

Preliminary results indicate that on the region, rainfall accumulated during the period of observation was lesser than that during the same period during the El Nino year 1982-83 and La Nina year 1988-89. In addition, the daily variability is characterized by several dates with precipitation larger than 20 mm that occurred more frequently on the networks located on the southeast side, and during the first half of January 1999. On the diurnal cycle of rainfall, maximum of rainfall occurred between 15 and 20 LST, while there are indications of a second peak at night 00 and 04 LST, possibly related to weather events like squall lines and thunderstorms, and then tend to move from northeast to southwest. However, this did vary during the 1999 campaing. January 1999 did show rarely those night rainfall events, as they were more frequent during February, but the afternoon rainfall events were more frequent and intense on January.