This seminar is concerned with an investigation of the intrinsic dynamics of the life-cycle of fronts with a 3D inviscid adiabatic semi-geostrophic model in physical coordinates rather than geostrophic coordinates. The Sawyer-Eliassen equation is generalized to two coupled equations that govern the ageostrophic circulation in a 3D balanced flow. A formal solution of it is obtained in the form of two functionals of the geostrophic streamfunction.
The model integration demonstrates simultaneous development of realistic cold and warm fronts starting from a weak unstable wave disturbance in the presence of an initial baroclinic jet. The dynamical difference between cold and warm fronts stems from the differences in the thermal advection by the geostrophic and ageostrophic flow components in the frontal regions. The model fronts reach full intensity in a few days under representative conditions. They inexorably evolve towards a singularity that is interpreted as the demise of model fronts. The mathematical nature of frontal collapse is understandable from the perspective of semi-geostrophic potential vorticity.