Mountain-Crossing Dynamics of Mesoscale Convective Systems Over the Sierras de Córdoba: Insights from Idealized Large-Eddy Simulations

Authors

Wu, Fan — Pennsylvania State University
Lombardo, Kelly — The Pennsylvania State University

Category

ARM field campaigns – Results from recent ARM field campaigns

The Sierras de Córdoba region in Argentina is known for having some of the most intense storms. This mountain range, oriented north–south with a relatively narrow width, features steep slopes and abrupt elevation rises, creating unique meteorological dynamics that influence the mountain-crossing behavior of storms. This study investigates various storm evolutions as storms attempt to traverse the Sierras de Córdoba, emphasizing the impacts of base-state conditions, cold pool characteristics, and mountain topography.

A series of idealized numerical experiments are conducted using the Cloud Model 1 (CM1). The base-state condition for the control experiment is from a realistic sounding observed west of the mountains on 15 March 2019, during the Department of Energy (DOE)-sponsored Cloud, Aerosol, and Complex Terrain Interactions (CACTI) field project. A quasi-linear convective system (QLCS) is initiated in the upstream plains and propagates eastward toward the mountains. In the control experiment with the base-state convective available potential energy (CAPE) of 1636 J kg⁻¹, the QLCS matures before reaching the windward slope, weakens obviously while crossing the mountain, and redevelops rapidly upon descending to the downstream plain.

Sensitivity experiments explore the impact of CAPE versus cold pool characteristics on storm behavior. Storm evolution varies with different CAPE values. Weak storms with reduced CAPE (e.g., 1000–1250 J kg⁻¹) are blocked by the mountains, while moderate storms (e.g., 1750–2250 J kg⁻¹) exhibit discrete mountain crossing due to enhanced downstream redevelopment. Strong storms with higher CAPE (e.g., 2500–3000 J kg⁻¹) traverse the mountains more smoothly. The mountain-crossing process is primarily governed by the movement of cold pools, which depends on their depth and thermal deficit. Sensitivity experiments altering the evaporation ratio reveal that deeper and colder cold pools are more likely to traverse the mountain, resulting in vigorous downstream convection and prolonged storm lifecycles. However, the impact of changes in cold pool characteristics is less pronounced compared to variations in CAPE, as demonstrated through extensive simulations exploring cold pool modifications across a range of CAPE values.  Mountain height and width also play critical roles, with higher and narrower mountains more effectively blocking cold pools due to their steeper slopes. For instance, storms encountering the tallest 3-km mountain with the widest range exhibit the most intense downstream redevelopment. This is driven by the enhanced cold-pool lifting, resulting from a larger portion of the cold pool traversing the gentler windward slope and descending from the higher peak. These findings advance our understanding of storm behavior in complex terrain, providing valuable insights for predicting severe storms in mountainous regions.

Lead PI

Lombardo, Kelly — The Pennsylvania State University