Relationship between mesoscale properties of convection and large-scale regimes during TRMM-LBA in Rondonia, Brazil

e regimes. Time series of reflectivity areal coverage provided by the NASA TOGA radar, partitioned into convective and stratiform raining area, is used to identify distinct rainfall regimes during the 55-day TRMM LBA experiment in Rondonia, Brazil (January – February 1999). A time series analysis of convective and stratiform precipitation areal coverage identifies two distinct rainfall regimes. For periods where convection moved to the west, deep convective precipitation dominated, while eastward-moving systems contained a much higher fraction of stratiform rainfall. These regimes were similar to break vs. monsoon convection at Darwin, Australia. The eastward moving systems in Rondonia had many characteristics of oceanic convection.

A preliminary analysis of soundings at two LBA sites illustrates the different wind and moisture regimes in which these mesoscale convective systems (MCS) developed, as shown by mean vertical profiles constructed for each regime. Multi-day periods of low-level northwesterly flow featured MCS that were monsoon-like in character, containing a large fraction of lighter and more widespread (stratiform) rainfall relative to convective rain, with little lightning activity. This contrasts with a northeasterly flow or "break" regime in which convective systems generated more vigorous and organized convection, as evinced by larger convective raining fractions and the frequent occurrence of lighting.

These regimes are related to synoptic-scale flow features from the NASA Data Assimilation Office (DAO) analysis. The goal is to understand the origin of the convective regimes observed by radar and sounding data in Rondonia. The relationship between mesoscale properties of convection in both regimes and the large scale flow is examined through a trajectory analysis of the source air. The propagation of the convective phase of the intraseasonal oscillation from the Pacific region into Amazonia is investigated to establish a possible linkage to regimes of convection in Rondonia. We also study the interaction between extratropical baroclinic waves and the transition of convecti