Satellite- and ground-based radar observations have shown that the northern half of Argentina, South America, is a region susceptible to rapid upscale growth of deep moist convection into larger organized mesoscale convective systems (MCSs). In particular, the complex terrain of the Sierras de Córdoba is hypothesized to be vital to this upscale-growth process. A canonical orographic supercell-to-MCS transition case study was analyzed to determine the influence that complex terrain had on processes governing upscale convective growth. High-resolution numerical modeling experiments were conducted in which the terrain height of the Sierras de Córdoba was systematically modified by raising or lowering the elevation of terrain above 1000 m. The alteration of the terrain lead to both direct and indirect effects on storm morphology. A direct effect included terrain blocking of cold pools, whereas indirect effects included terrain-induced variations in pertinent storm environmental parameters (e.g., vertical wind shear, convective available potential energy). When the terrain was raised, low-level and deep-layer vertical wind shear increased, mixed-layer convective available potential energy decreased, deep moist convection initiated earlier, and cold pools were blocked and generally became stronger and deeper. The reverse occurred when the terrain was lowered, resulting in a weaker supercell that did not grow upscale into an MCS. The control simulation supercell displayed the deepest cold pool and correspondingly fastest transition from supercell to MCS, potentially revealing that the unique terrain configuration of the Sierras de Córdoba was supportive of the observed rapid upscale convective growth of this orographic supercell.
- NSF-PAR ID:
- 10171957
- Date Published:
- Journal Name:
- Journal of the atmospheric sciences
- Volume:
- 77
- ISSN:
- 1520-0469
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract -
Abstract During the early morning hours of 5 November 2018, a mature mesoscale convective system (MCS) propagated discretely over the second-most populous province of Argentina, Córdoba Province, during the Remote Sensing of Electrification, Lightning, and Mesoscale/Microscale Processes with Adaptive Ground Observations–Cloud, Aerosol, and Complex Terrain Interactions (RELAMPAGO–CACTI) joint field campaigns. Storm behavior was modified by the Sierras de Córdoba, a north–south-oriented regional mountain chain located in the western side of the province. Here, we present observational evidence of the discrete propagation event and the impact of the mountains on the associated physical processes. As the mature MCS moved northeastward and approached the windward side of the mountains, isolated convective cells developed downstream in the mountain lee, 20–50 km ahead of the main convective line. Cells were initiated by an undular bore, which formed as the MCS cold pool moved over the mountain ridge and perturbed the leeside nocturnal, low-level stable layer. The field of isolated cells organized into a new MCS, which continued to move northeastward, while the parent storm decayed as it traversed the mountains. Only the southern portion of the storm propagated discretely, due to variability in mountain height along the chain. In the north, taller mountain peaks prevented the MCS cold pool from moving over the terrain and perturbing the stable layer. Consequently, no bore was generated, and no discrete propagation occurred in this region. To the south, the MCS cold pool was able to traverse the lower-relief mountains, and the discrete propagation was successful.more » « less
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Abstract Global satellite studies show a maximum in deep convection and lightning downstream of the Andes in subtropical South America. The Remote sensing of Electrification, Lightning, And Mesoscale/microscale Processes with Adaptive Ground Observations (RELAMPAGO) field campaign was designed to investigate the physical processes that contribute to the rapid development of deep convection and mesoscale convective systems (MCSs) in Argentina. A lightning mapping array (LMA) was deployed to Argentina as part of RELAMPAGO to collect lightning observations from extreme storms in the region. This study combines lightning data from the LMA and the Geostationary Lightning Mapper onboard
GOES‐16 with 1‐km gridded radar data to examine the electrical characteristics of a variety of convective storms throughout their life cycle observed during RELAMPAGO. Results from the full campaign show 48% of flashes are associated with deep convection that occurs along the eastern edge of the Sierras de Córdoba (SDC) overnight. These flashes are 65 km2smaller on average compared to stratiform flashes, which occur most frequently 50–100 km east of the SDC in the early morning hours, consistent with the upscale growth of MCSs off the terrain. Analysis of the 13–14 December MCS shows that sharp increases in flash rates correspond to deep and wide convective cores that have high graupel and hail mass, 35‐dBZ volume, and ice water path. This work validates previous satellite studies of lightning in the region, but also provides higher spatial and temporal resolution information across the convective life cycle that has not been available in previous studies. -
null (Ed.)Abstract The Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field campaign was designed to improve understanding of orographic cloud life cycles in relation to surrounding atmospheric thermodynamic, flow, and aerosol conditions. The deployment to the Sierras de Córdoba range in north-central Argentina was chosen because of very frequent cumulus congestus, deep convection initiation, and mesoscale convective organization uniquely observable from a fixed site. The C-band Scanning Atmospheric Radiation Measurement (ARM) Precipitation Radar was deployed for the first time with over 50 ARM Mobile Facility atmospheric state, surface, aerosol, radiation, cloud, and precipitation instruments between October 2018 and April 2019. An intensive observing period (IOP) coincident with the RELAMPAGO field campaign was held between 1 November and 15 December during which 22 flights were performed by the ARM Gulfstream-1 aircraft. A multitude of atmospheric processes and cloud conditions were observed over the 7-month campaign, including: numerous orographic cumulus and stratocumulus events; new particle formation and growth producing high aerosol concentrations; drizzle formation in fog and shallow liquid clouds; very low aerosol conditions following wet deposition in heavy rainfall; initiation of ice in congestus clouds across a range of temperatures; extreme deep convection reaching 21-km altitudes; and organization of intense, hail-containing supercells and mesoscale convective systems. These comprehensive datasets include many of the first ever collected in this region and provide new opportunities to study orographic cloud evolution and interactions with meteorological conditions, aerosols, surface conditions, and radiation in mountainous terrain.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1175/JAS-D-19-0190.1
