Clinogenesis and Frontogenesis in Jet-Stream Waves. Part I: Analytical Relations to Wave Structure

Abstract

The circulations that alter the baroclinic structure along wave-shaped currents are investigated for gradient and nongradient flow. In the case of deformations which result in an increase of baroclinity and vertical shear (and, with a jet stream, lateral shear), the process is called ?clinogenesis,? in distinction to frontogenesis (FG) in which static stability is also increased. In gradient flow, convergence and confluence are related to curvature variations and are also wind-speed dependent. Hence, in a wave on the jet stream, lateral shears result in solenoidally-indirect tilting on the cyclonic flank, in the midtropospheric airstream from a ridge to a trough. This and the other clinogenetic processes of confluence and canting (turning of wind with height) are related to the structure and dimensions of a jet-stream wave. These features are numerically simulated in Part II, where additional consequences of ageostrophic flow upon FG are examined. Clinogenesis is also discussed in more general terms of streamwise variations of both curvature and wind speed, which are associated with distinctive transverse circulations and whose net effect depends upon the degree of gradient wind control. Static stability generation, as the additional quality of FG, is related to transverse ageostrophic flow as well as to divergence. Thus FG appears to be favored by suitable combinations of both curvature and speed variations along the current.