Affiliation:
1. Universidad Nacional Autónoma de México, Mexico City, Mexico
2. NOAA/OAR/National Severe Storms Laboratory, Norman, Oklahoma
Abstract
Abstract
The environmental factors that drive the dissipation of linear severe-wind-producing mesoscale convective systems (MCSs) are investigated. Layer-lifting indices are emphasized, which measure convective instability in forward-propagating MCSs by considering that deep convective latent heating depends on 1) the potential latent heating within the atmospheric column, measured by the integrated CAPE (ICAPE), and 2) the dilution of buoyancy due to midtropospheric inflow, measured by the inflow fraction (IF) of convectively unstable air to total system-relative inflow. These elements are integrated to define the layer-lifting CAPE (CAPEll), which depends on environmental thermodynamics, kinematics, and the MCS’s movement vector. Radar reflectivity plots are used to subjectively identify and classify MCSs in terms of their stage (mature or dissipating) and degree of organization (highly or weakly organized). Nonparametric statistical inferences are performed on several metrics computed at maturity and dissipation from RUC/RAP analysis data, aiming to identify the most skillful indices for diagnosing three different aspects of MCS dissipation: 1) the transition from maturity to dissipation, 2) the stage of an MCS, and 3) the disorganization that characterizes the dissipating stage. In terms of MCS dissipation CAPEll is the best diagnostic. A close approximation to CAPEll is accomplished by estimating an MCS’s movement with Corfidi vectors, providing a potentially useful index in operational settings. ICAPE is the most skillful thermodynamic metric, while IF is the best kinematic discriminator of MCS stage and stage transition, suggesting the fundamental importance of layer-lifting convective instability for MCS maintenance. Layer-lifting indices are not particularly skillful at distinguishing the degree of MCS organization at maturity, which is best diagnosed by deep vertical wind shear.
Funder
Dirección General de Asuntos del Personal Académico, Universidad Nacional Autónoma de México
Publisher
American Meteorological Society
Cited by
8 articles.
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