Effects of Low-Level and Deep-Layer Shear on Squall Line Intensity
Abstract
Squall lines are a subset of mesoscale convective systems that are characterized by a long quasi-linear region of convection. Squall lines cause a wide range of weather-related impacts on society, warranting considerable research efforts to better understand their dynamics. Despite their societal impacts, there are many unknowns surrounding how vertical wind shear and entrainment affect the intensity of squall line updrafts. This paper investigated these unanswered questions using sophisticated numerical simulations from a cloud model. Low-level shear, deep-layer shear, and relative humidity are varied among a set of simulations. Increasing low-level shear, deep-layer shear, or relative humidity resulted in greater updraft velocities with larger vertical mass flux and wider updraft areas. These wide updraft areas insulate the updraft core from entrainment driven dilution and make updrafts more buoyant than in environments with weaker shear. However, these increases in buoyancy were canceled by the downward effects from the buoyancy pressure accelerations. Upward dynamic pressure accelerations increased with shear, especially at low levels, which ultimately resulted in a positive correlation between vertical accelerations, vertical velocities, and low-level and deep-layer shear. It is therefore concluded that the primary way in which shear influences squall line intensity is to enhance mechanically generated dynamic lifting along the cold pool edge and within updrafts.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jun 01, 2019
- Accession Number
- AD1080478
Entities
People
- Nicolaas A. Verhoeven
Organizations
- Naval Postgraduate School