The slope of isentropes constituting a frontal zone

Abstract

This paper investigates the use of the slope of isentropes as an objective indicator of the presenceof frontal zones in the atmosphere. It derives an equation for the change in time relative to thefront of the slope of isentropes and applies this equation to a specific case. It discusses theadvantages and disadvantages of this approach and compares it with the traditional approachbased on the horizontal temperature gradient. It appears that the use of the slope of isentropesto identify fronts brings out some features of frontal systems more clearly than the traditionaldefinition, especially cold fronts which lean forward toward the warm air. Three new frontogeneticterms appear in the equation governing the time rate of change of frontal intensity. In theparticular case studied here, these frontogenetic terms cannot be neglected, although they playonly a secondary rôle.