Understanding the Life Cycle of Deep Convective Storms Traversing Mountains Using CACTI Observations

Organized deep convective storms, specifically mesoscale convective systems,

mesoscale convective system (MCS)

A collection of thunderstorms that act as a system. An MCS can spread across an entire state and may appear as a solid line, a broken line, or a cluster of cells that can last more than 12 hours.

Source: NOAA Source

are responsible for numerous hazards, including flash floods, frequent lightning, high winds, hail, and tornadoes. As mesoscale convective systems move over mountainous landscapes, storm behavior, and thus the threat of these hazards, changes rapidly. Anticipating storm response to the underlying mountains remains a challenge, resulting in dangerous and unanticipated conditions for residents. In a future climate, the projected increase in the frequency of such extreme precipitation events will exacerbate the problem. This work will uncover the physical processes supporting observed storm behaviors over mountains in the present day and future climate.  

As mesoscale convective systems move over mountains, they experience variations in the slope of the land surface, and in environmental conditions as they move both horizontally and vertically through the troposphere following the sloping surfaces. Exposure to such heterogeneities induces a variety of storm responses, including changes in mesoscale convective system intensity (i.e., strengthening, weakening), localized regions of convective initiation displaced away from the main storm which may or may not extend the lifetime of the mature storm, and upscale growth transitions from isolated cloud populations to new organized deep convective storms. Our knowledge of the physical processes driving these different evolutions has been derived from a limited number of idealized numerical modeling studies and observational studies that rely on spatially and temporally infrequent observations. Consequently, there remain large gaps in our fundamental understanding, which hinder advancements in predictability. Further, climate models are unable to replicate these observed evolutions, in part due to their inability to represent topography

topography

The land's physical attributes within a specific area or region, comprising both natural formations like mountains, valleys, and rivers, alongside human-made additions such as roads and buildings.

Source: Source

and deep convection

convection

The rising of warm air and the sinking of cool air. Convection can cause local breezes, winds, and thunderstorms.

Source: NASA earth observatory Source

at spatial scales necessary to reproduce the most important storm-scale physical processes.

This work will leverage fine-spatiotemporal-scale observations from the Department of Energy sponsored Cloud, Aerosol,

aerosols

Small particles or droplets, such as wildfire smoke, volcanic gases, or salty sea spray, that float in the air. They are emitted by both natural events and human activities.

Source: NASA Global Climate Change Source

and Complex Terrain Interactions (CACTI) field project, which took place in Argentina, complemented with idealized numerical modeling experiments to address these deficiencies in our knowledge. Cases of mature mesoscale convective systems traversing the Argentine Sierras de Córdoba and of storms initiating over the mountain chain will provide insight into the range of possible evolutions, environment variables that may be used as predictors for these behaviors, and the dominant storm-scale physical processes supporting each evolution type. Numerical experiments will quantify the sensitivity of storm evolution to the base-state environment, characteristics of the storm outflow (important for the maintenance of mesoscale convective systems), and complexities in mountain shape. This research will also determine the climate model grid spacings necessary to accurately reproduce the resulting precipitation patterns and regional hydrological cycle in mountainous areas.