Rainfall and surface kinematic conditions over central Amazonia during ABLE 2B

Publisher Website
Google Scholar
Abstract
Meteorological and chemical data collected during the wet season Amazon Boundary Layer Experiment near Manaus, Brazil, are used to investigate the rainfall, rainfall systems, and surface kinematics of the central Amazon basin wet season. Analysis of the Geostationary Operational Environmental Satellite (GOES‐West) imagery indicates that, based on location of initial development, there are three main types of convective systems which influence a mesoscale network near Manaus. Coastal Occurring Systems (COS) are mesoscale to synoptic scale sized systems of generally linear orientation which form along the northern coast of Brazil and propagate across the Amazon basin. The Basin Occurring Systems (BOS) form in the basin east and north of Manaus and also propagate toward the network. Locally Occurring Systems (LOS) form in and around the mesoscale network and rarely are larger than 1000 km2. Composites of hourly rainfall totals and satellite‐derived cloud cover show that rainfall and cloudiness associated with COS occurred in the network between 1400 and 1800 UT, while BOS rainfall was most common between 1000 and 1400 UT. Little rain or cloud cover was seen before 1600 UT during days influenced by LOS. Chemical analysis of the rainwater delivered by these systems also shows significant differences in the concentrations of formate, acetate, pyruvate, sulfate, and hydrogen ion. In addition, aerosol concentrations measured near Manaus indicate large influxes of aerosols (sodium, chlorine, and silicon) into central Amazonia after the passage of BOS and COS. The satellite‐based classification indicates a definite intraseasonal variation in regard to the dominant rain‐producing system. During April 11–20, BOS occurred on 8 days and produced 98% of the rainfall. Eight COS occurred during April 21 to May 3 and accounted for 89% of the rainfall. The final part of the experiment, May 4–14, was influenced solely by LOS. Harmonic analysis of surface divergence during this period exhibits a peak at 24 hours. This peak, representing the diurnal heating cycle, does not exist earlier in the experiment when BOS and COS are more frequent.