On Assessing Local Conditional Symmetric Instability from Atmospheric Soundings

Abstract

Abstract The standard parcel method of assessing the susceptibility of the atmosphere to moist convection using tephigrams is extended to account for the centrifugal as well as the gravitational potential energy of the displaced air parcel. This leads to a measure of the stability of the moist baroclinic atmosphere to finite slantwise reversible displacements of a two-dimensional air parcel; such a measure differs from previously derived measures of conditional symmetric instability which have considered only infinitesimal displacements in saturated atmospheres. It is demonstrated that the combined gravitational and centrifugal potential of a two-dimensional air parcel or “tube” can be assessed by displacing the tube slantwise along a surface of constant angular momentum, and that this combined potential energy can be estimated using a single atmospheric sounding. Several examples of the application of this technique are presented in the context of a case study of apparent slantwise convection. The result...