The slope of isentropes constituting a frontal zone

This paper investigates the use of the slope of isentropes as an objective indicator of the presence of frontal zones in the atmosphere. It derives an equation for the change in time relative to the front of the slope of isentropes and applies this equation to a specific case. It discusses the advantages and disadvantages of this approach and compares it with the traditional approach based 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 traditional definition, especially cold fronts which lean forward toward the warm air. Three new frontogenetic terms appear in the equation governing the time rate of change of frontal intensity. In the particular case studied here, these frontogenetic terms cannot be neglected, although they play only a secondary rôle.