Radiosonde Analysis of Environments Supporting Deep Convection Initiation During RELAMPAGO-CACTI

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 (hourly launches from 6-7 sites with horizontal spacing of ~15-45 km) to examine environments supporting deep moist convection in the complex terrain of central Argentina. In this presentation, we make use of this radiosonde data set to assess atmospheric profiles most representative of the near-cloud environment (in time and space) to identify environmental ingredients governing storm formation.

To determine the most appropriate profiles to examine per near-cloud environment, we perform a spatial and temporal autocorrelation analysis across neighboring launches, revealing considerable environmental heterogeneity in the target region. Neighboring boundary layer thermodynamic and kinematic profiles are statistically uncorrelated on scales of 1–2 hr and 30 km. Based on this analysis, 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, during which 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.

Such sounding analysis results will be elaborated upon in the context of other measurements of the 3D mesoscale triggering mechanisms and used as motivation for companion work performing idealized cloud-scale LES that will probe physical mechanisms related to the environmental factors governing deep convective growth.