Evaluation of Simulated Deep Convective Upscale Growth over Argentina

Abstract:

Mesoscale convective systems (MCSs) significantly affect radiative transfer and regional hydrology, while redistributing heat, moisture, and momentum, and reshaping multi-scale circulations. Accurate prediction of MCSs depends on accurate representation of deep convective upscale growth, which is the collection of processes that produce MCSs from isolated deep convection, as a function of environmental conditions. In this study, we perform a regional convection-permitting simulation over Argentina covering the primary experimental period of the RELAMPAGO-CACTI field campaign from October 2018 to April 2019 and evaluate how well the simulation reproduces observed upscale growth. 363 observed and 343 simulated MCSs are identified and tracked in observations and the simulation using 30-minute top-of-atmosphere infrared brightness temperature and surface rainfall.

Simulated MCS number, lifetime, diurnal cycle, and cloud shield metrics including growth rate are similar to those retrieved by satellite. However, the simulation produces smaller raining areas, a greater proportion of heavy rain rates, and faster propagation than retrieved by satellite, potentially from a combination of model and retrieval biases. MCSs are categorized separately by maximum areal extent, maximum depth, upscale growth time length, and upscale growth rate. Model-observation rainfall differences are greatest for large, deep, sustained, and fast growing MCSs. Each MCS is then matched with environmental conditions at its initiation time, including large-scale pressure, geopotential height, moisture and wind fields, low level vertical wind shear, and lifted parcel parameters such as the most unstable parcel starting level, convective available potential energy (CAPE), and convective inhibition energy (CIN). Analyses show that CAPE and low-level northerly moisture transport are critical factors in determining maximum system size, depth, and initial growth rate (Figure 1), while CIN and low level shear are less important. Other factors that differentiate MCS upscale growth characteristics are currently being analyzed along with ground-based radar and in-situ assets from the RELAMPAGO-CACTI field campaign over the Sierras de Córdoba range in central Argentina.