Controls on Initiation and Evolution of Deep Convection in the Complex Terrain of Central Argentina

Abstract:

The Sierras de Córdoba in central Argentina is a north-south oriented ridgeline that rises 2000 m above surrounding plains and serves as a hot spot for convective cloud development. Between October 2018 and April 2019, the RELAMPAGO and CACTI field campaigns deployed a large array of instrumentation in this region for the study of deep convective life cycle sensitivity to a variety of interactive, multi-scale environmental controls. Taking advantage of the large number of variable convective cells observed, we developed a database of spatially and temporally tracked cells using C-band radar observations. A range of properties are saved for each cell including whether they merge or split with other cells. Cells were also identified in routine radar hemispheric range-height indicator scans that provide high-resolution vertical slices through cells. Cell properties within these vertical slices are saved and linked with the cell tracks that they correspond to in the database.

Cell tracks show that the topography in the region imposes a strong control on deep convective initiation (CI). Convective cells prefer to initiate just east of the highest terrain, particularly in a concave portion of the topography. In early afternoon, CI peaks over a high plateau, but it shifts south to the highest terrain by late afternoon (see attached figure with terrain height contoured every 500 m). A nocturnal CI maximum is found on the western slopes of the mountains in contrast with the afternoon peak on the eastern slopes. Some cells over the mountains quickly grow to depths that are comparable to the deepest cells found on the plains to the east. The plains to the east also experience a nocturnal peak in CI with cells that reach the largest sizes in the region associated with mesoscale organization. We further present analyses on conditions that influence CI timing and location, and cell growth and organization, including roles of topographic thermal and forced upward motion in the context of boundary layer coupling, inversion layers, free tropospheric humidity, vertical wind shear, and larger-scale circulations. Meteorological, aerosol, and adjacent convective cloud influences on cell microphysical and macrophysical properties as a function of life cycle stage are also explored.