An Interfacial Wave Treatment of Tropopause Dynamics

The tropopause is the sharp transition, roughly at an altitude of 10 km, between the two lowest layers of the atmosphere - the troposphere and the stratosphere. Vertical disturbances of this internal atmospheric interface propagate as waves in an eastward direction following the midlatitude jetstream.

For a strongly-stratified, rotating atmosphere, a next-order perturbation theory is shown to be necessary for capturing the enhanced downward displacement evident from tropopause observations. A travelling wave solution for a tropopause disturbance clearly demonstrates an asymmetric bias towards low pressure and cyclonic flow. This bias is consistent with the association of tropopause disturbances as precursors to midlatitude cyclonic storm systems.

(in collaboration with Greg Hakim, University of Washington)

The figures below compare the vertical cross-sections of potential temperature comparing the tropopause wave solutions for the leading-order quasigeostrophic theory (top panels) and the QG+1 next-order theory (bottom panels). In both figures, the heaviest gray line represents the tropopause interface which separates the stratosphere above from the troposphere below. The colors show levels of potential temperature as it increases with altitude (density decreases). The thin lines indicate level curves at uniform intervals of potential temperature which emphasize the stronger stratification that is characteristic of the stratosphere.

A vertical cross-section of the solution in the meridional direction, the colder, poleward direction is towards the left. The undisturbed tropopause has a tilt downward towards the pole. Note that the next-order wave solution clearly captures the enhanced downward penetration of the tropopause that is associated with a cyclonic disturbance.

A vertical cross-section of the solution in the zonal direction. It is a travelling wave drifting to the left, slower relative to the stronger eastward flow of the jetstream. The thick white lines indicate contours of vertical motion (dashed are downward).