Updraft and Downdraft Core Kinematics of Mesoscale Convective Systems through Observations and Idealized Simulations

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Description

Mesoscale Convective Systems (MCSs) regulate the global energy cycle through their extensive cloud coverage and the exchange of latent heat, and are associated with a large proportion of extreme precipitation events. The dynamic and thermodynamic processes within MCSs are complex, exhibiting a variety of convective and stratiform cloud characteristics in tropical and continental regions. It is challenging to represent MCSs in global climate models (GCMs), since they incorporate processes that interact across a large range of scales. The convection-permitting models (CPMs) with horizontal grid-spacing < 4 km improve many bulk MCS properties (e.g., propagation, size), but still have large uncertainties representing convective processes (e.g., updraft, downdraft core intensity, size) since they operate in the gray-zone of turbulent motion where convection is not fully resolved. This motivates exploring potential new high-resolution observations of convective properties to better constrain CPM/GCM depictions of MCSs. This study contrasts updraft and downdraft core kinematic properties from extended ground-based radar wind profiler (RWP) measurements collected within mature MCSs over tropical and mid-latitude continents. Multi-instrument datasets from the DOE Atmospheric Radiation Measurement (ARM) Southern Great Plains (SGP) site in Oklahoma, U.S. (16 events) and the ARM Mobile Facility deployment to Manaus, Brazil (GoAmazon2014/5, 46 events) are investigated. Oklahoma MCSs are observed having more intense and larger convective up- and downdraft cores than Amazon MCSs, leading to larger mass flux. Updraft/downdraft intensity is found to be positively correlated with core size, and increases with altitude. Most variability in core properties is observed within the deeper (higher cloud top) parts of the MCSs. To highlight the potential usefulness of these unique observations, we present a model-observational inter-comparison of convective core properties, as simulated with 5 idealized (WRF) MCS events for environments consistent with SGP conditions. These simulations are performed across a wide range of model grid-spacings (Δx = 4 km – 250 m) to explore the ability of CPMs to capture these convective core processes, and at what scales these properties of MCSs converge. The higher resolution simulations (< 1 km) better capture the convective updraft core size-intensity/mass flux relationships, but underestimate convective downdraft intensity and probability.