PNNL

Abstract

The Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations (RELAMPAGO) and Cloud, Aerosol, and Complex Terrain Interactions (CACTI) projects deployed a high-spatiotemporal-resolution radiosonde network to examine environments supporting deep convection in the complex terrain of central Argentina. This study aims to characterize: 1) mesoscale heterogeneity of the environment surrounding convection initiation events, and 2) atmospheric profiles most representative of the near-cloud environment (in time and space) to identify physical processes affecting storm initiation and growth. Spatial and temporal autocorrelation analysis reveals considerable environmental heterogeneity, with boundary layer thermodynamic and kinematic fields becoming statistically uncorrelated on scales of 1–2 hr and 30 km. We examine a variety of environmental parameters derived from soundings collected within close proximity (30 km and 30 min in space and time) of 43 events over 9 days wherein the atmosphere either: 1) supported the initiation of sustained precipitating convection, 2) yielded only weak and short-lived precipitating convection, or 3) produced no precipitating convection despite numerical forecasts of precipitating convection from convection-allowing models (i.e., Null events). There are large statistical differences between the Null event environments and those supporting any convective precipitation. Null event profiles contained larger convective available potential energy, but had low free tropospheric relative humidity, higher freezing levels, evidence of elevated subsidence, and limited horizontal convergence near the terrain at low levels, which likely suppressed deep convective growth.