Convective Mode Transitions in the Lee of Mesoscale Terrain As Observed during RELAMPAGO-CACTI (Invited Presentation)

The highly synergistic Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) and Clouds, Aerosols, and Complex Terrain Interactions (CACTI) field campaigns provided novel new observations in unprecedented detail of repeated convection initiation and upscale growth in and near the Sierras de Córdoba Mountains in central Argentina., RELAMPAGO-CACTI took place from 15 October 2018 through 30 April 2019, and, from 1 November to 16 December 2018, a dense network of ground-based mobile platforms supplemented the stationary assets to target specific storms in finer-scale detail. Throughout the warm season, this region provides a natural laboratory for understanding convective and hydrometeorological processes influenced by orography due to the high frequency of convection initiation and wide variety of convective modes and life cycles that occur over a relatively small area. During RELAMPAGO-CACTI, more than 40 well-observed deep convective events were observed during the project’s extended observing period, while 19 intensive observing periods allowed for detailed aircraft, surface-based in situ, and multi-Doppler radar observations during a variety of storm events.

In this presentation, the multitude of observations from the RELAMPAGO-CACTI field campaign will be highlighted to elucidate processes that control the observed rapid evolution of convective mode from convection initiation, to discrete cells, some of which were supercellular, and ultimately into mesoscale convective systems. Results indicate the environment east of the Sierras de Córdoba support storm modes that produce strong convective updrafts, and produce hazards including large hail and flash flooding in close proximity to the complex terrain. Case studies documenting the process pathways controlling the evolution of environmental vertical wind shear and conditional instability proximate to the terrain and in the vicinity of surface boundaries, as observed by radiosondes, mobile and fixed mesonets, and radar and lidar remote sensing, will be presented as an illustration of the impacts on storm environments caused by mechanical flow around the terrain, diurnal slope flows, mountain waves, and previous or distant convection. These spatially-and temporally-evolving environments are examined relative to the timing and location of convection during their characteristic diurnally phase-locked life cycle. Idealized and real-data model simulations are used to elucidate the roles of the terrain in modulating storm environments. It is found that the unique configuration of complex terrain modifies the background flows, such as the South American Low Level Jet, to produce spatially asymmetric, inhomogeneous, and rapidly evolving storm environments that provide for unique prediction challenges in the region.