Numerical simulations of initiation and evolution of convection over the Sierras de Córdoba mountains, Argentina

The Sierras de Córdoba (SDC) mountain range in Argentina is a hotspot of deep moist convection initiation (CI). Radar climatology indicates that 44% of daytime CI events that occur near the SDC in spring and summer seasons and that are not associated with the passage of a cold front or an outflow boundary involve a northerly LLJ, and these events tend to preferentially occur over the southeast quadrant of the main ridge of the SDC. To investigate the physical mechanisms acting to cause CI, idealized convection-permitting numerical simulations with a horizontal grid spacing of 1 km were conducted using CM1v19.3. The sounding used for initializing the model featured a strong northerly LLJ, with synoptic conditions resembling those in a previously postulated conceptual model of CI over the region, making it a canonical case study. Differential heating of the mountain caused by solar insolation in conjunction with the low-level northerly flow sets up a convergence line on the eastern slopes of the SDC. The southern portion of this line experiences significant reduction in convective inhibition, and CI occurs over the SDC southeast quadrant. The simulated storm soon acquires supercellular characteristics, as observed. Additional simulations with varying LLJ strength also show CI over the southeast quadrant. A simulation without background flow generated convergence over the ridgeline, with widespread CI across the entire ridgeline. A simulation with mid- and upper-tropospheric westerlies removed indicates that CI is minimally influenced by gravity waves. We conclude that the low-level jet is sufficient to focus convection initiation over the southeast quadrant of the ridge. Analysis of radar data from RELAMPAGO hints towards a potential relationship between LLJ strength and the motion of supercells originating over the SDC: supercells tend to move northeastward in weaker LLJ environments and more eastward in the presence of a stronger LLJ. In order to examine this potential linkage, we analyze the evolution of convection in simulations with varying LLJ strength by tracking the updrafts and recording various characteristics of the storm as well as the thermodynamic and kinematic properties of the storm inflow. We find that in weaker LLJ simulations, storms tend to move more parallel to the north-south oriented main ridge of the SDC and become cold-pool-dominated, while in stronger LLJ simulations, storms tend to move eastward. The storms in weaker LLJ environments have wider and stronger updrafts, larger rain areas, and bigger and more intense cold pools. These storms, in general, experience larger SBCAPE values and lower SBCIN values. They deviate more strongly from the mean winds and show little agreement with Bunkers-predicted motion. On analyzing the patterns of low-level convergence ahead of the gust front and dynamic vertical perturbation pressure gradient forcing functions, we find that the larger and more intense cold pools produced by these storms play a major in their propagation. This is significant from a forecasting perspective as storms in weaker LLJ environments are more likely to grow upscale into mesoscale convective systems which pose different hazards from supercells.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Atmospheric Sciences

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2022

Author dc:creator

• Singh, Itinderjot

Contributors dc:contributor

• Nesbitt, Stephen
• Trapp, Robert J
• Hence, Deanna
• Schumacher, Russ

• numerical modeling
• convection

Statement dc:rights

• Copyright 2022 Itinderjot Singh

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/115656

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F115656