Clinogenesis and Frontogenesis in Jet-Stream Waves. Part II: Channel Model Numerical Experiments

Abstract

Frontogenesis (FG) is examined in a ?channel model? based on a primitive-equation isentropic formulation by Eliassen and Raustein. Meridional temperature gradients, static stability and a tropopause are specified to give a jet stream with realistic shears. An imposed weak cyclone-anticyclone couplet initiates ?self-development,? of surface vortices and an upper-level wave, which is fastest with weaker static stability or with a more concentrated jet stream. All processes are evaluated that lead to the formation, in the vicinity of the wave trough, of a frontal layer in which intensity increases as the wave amplitude grows. Midtropospheric FG is associated with solenoidally indirect tilting and confluence, modified by advections connected with canting (turning of wind with height), which are all features related to the structure of a gradient wind wave in Part I. The additional role of transverse ageostrophic flow in generating static stability is demonstrated, along with the total deformation field in a transverse plane.