Three-dimensional computations of equivalent potential vorticity

Abstract

Moore and Lambert showed how a quantity called equivalent potential vorticity (EPV) can provide quantitative values to assess conditional symmetric instability (CSI), also known as slantwise instability. Expanding the EPV equation into three dimensions, the equation becomes a function of the geostrophic wind shear, the horizontal equivalent potential temperature gradient, the absolute geostrophic vorticity, and the vertical equivalent potential temperature gradient, all of which are easily computed from gridded data. The equation reduces further by recognizing that the geostrophic wind shear is a function of the horizontal equivalent potential temperature gradient in a saturated environment. This reduced equation shows that horizontal temperature gradients will always act to promote slantwise convection.