Factors Controlling Convective Storm Mode and Heavy Rainfall Production Near the Sierras De Córdoba, Argentina

Satellite observations have revealed that some of the world’s most intense convective storms occur across subtropical South America. This convection has been linked to large mesoscale convective systems (MCSs) that appear to back-build along a region of higher terrain called the Sierras de Córdoba, Argentina. The satellite data fail to reveal high temporal evolution of these storms, however, and thus, how convective modes and transition between modes relates to the extreme intensity and heavy rainfall production. This research is particularly interested in how isolated convection, initiated across the Sierras de Córdoba, transitions to larger MCSs to the east, and how such “upscale convective growth” relates to heavy rainfall production across regions such as the La Plata River basin. Nearly 90% of the annual rainfall that accumulates across this region of South America owes to these intense MCSs (e.g., Rasmussen et al. 2016).

As part of a new observing network in Argentina, a C-band, dual-polarization radar was installed in Córdoba, Argentina in 2015, now allowing for the characterization of convective storm properties in the region surrounding the Sierras de Córdoba. Radar reflectivity and radial velocity were used to characterize features of convection over a 3˚ x 3˚ domain (-30 to -33˚S and -62.5 to -66˚W) centered on the Córdoba radar site (31.44˚S, 64.19˚W). Additionally, radar-derived precipitation estimates were constructed to reveal relative storm intensities by convective mode.

A total of 85 convective-storm cases were identified between July 2015 – April 2016; the analysis of data from the austral warm season of 2016 – 2017 is ongoing. Cases were grouped by convective mode (i.e., discrete vs. multicell), initiation location/time, time between initiation and upscale convective growth (if any), among others. Preliminary results indicate that 10 (12%) of the cases were characterized as discrete-supercell, 20 (24%) as discrete-non-supercell, 25 (29%) as multicell-organized (e.g., MCS), and 30 (35%) as multicell-unorganized. Radar attributes, such as reflectivity hook echoes, are common features documented with convection. Environmental characteristics associated with the convective modes and pathways of upscale convective growth were also analyzed using ERA-Interim reanalysis composites (owing to the lack of high spatiotemporal surface and upper-air data). Rainfall contribution and local intensities were also examined for each storm type.

These analyses have been undertaken in preparation for the RELAMPAGO (Remote sensing of Electrification, Lighting, And Mesoscale/microscale Processes with Adaptive Ground Observations intensive observing period (1 November – 15 December 2018; more information available at https://publish.illinois.edu/relampago/) in west central Argentina.