An Ensemble Study of Wet Season Convection in Southwest Amazonia: Kinematics and Implications for Diabatic Heating

Abstract

Dual-Doppler radar data from the Tropical Rainfall Measuring Mission Large Scale Biosphere?Atmosphere Experiment in Amazonia (TRMM-LBA) field campaign are used to determine characteristic kinematic and reflectivity vertical structures associated with precipitation features observed during the wet season in the southwest region of Amazonia. Case studies of precipitating systems during TRMM-LBA as well as overarching satellite studies have shown large differences in convective intensity associated with changes that develop in low-level easterly flow [east regime (ER)] and westerly flow [west regime (WR)]. This study attempts to examine the vertical kinematic and heating structure of convection across the spectrum of precipitation features that occurred in each regime. Results show that convection in the ER is characterized by more intense updrafts and larger radar reflectivities above the melting level, in agreement with results from lightning detection networks. These regime differences are consistent with contrasts in composite thermal buoyancy between the regimes: above the boundary layer, the environment in the ER is characterized by a greater virtual temperature excess for near-surface rising parcels. Both regimes showed a peak in intensity during the late afternoon hours, as evidenced by radar reflectivity and kinematic characteristics, consistent with previous studies of rainfall and lightning in the Rondônia (TRMM-LBA) region. After sunset, however, convective intensity in the WR decreases much more abruptly compared to the ER. In the stratiform?weak convective region, the ER showed both reflectivity and kinematic characteristics of classic stratiform structure after sunset through the early morning hours, consistent with the life cycle of mesoscale conjective systems (MCSs). Apparent heating (Q1) profiles were constructed for each regime assuming the vertical advection of dry static energy was the dominant forcing term. The resulting profiles show a peak centered near 8 km in the convective regions of both regimes, although the ER has a broader maximum compared to the WR. The breadth of the ER diabatic heating peak is consistent with the more dominant role of ice processes in ER convection.