Atmospheric Response to the Quasi-Resonant Growth of Forced Planetary Waves

Abstract

The forcing of the second-order zonally-averaged wind and temperature fields due to the quasiresonant growth of planetary waves in a two-layer model is considered.Dissipation in the form of linear drag and Newtonian cooling is allowed for. Calculations are made in a mid-latitude * -plane channel bounded by two vertical walls . The linear or first order solution is constrained so as to not transport momentum meridionally.Three neutral modes in the adiabatic two layer model are brought to resonance separately by adjusting the basic zonal flow configuration.For a dissipation time scale of 2 days, the quasi-resonant enhancement of the response is negligible. A time scale of 4 days is used.For resonance involving the two layer equivalent of the Rossby wave, the strong westerly zonal flow configuration causes most of the second order effects to be confined to the lowest few scale heights, where a slow easterly acceleration of the zonal flow occurs.A second resonance associated with weak westerlies surmounted by moderate westerlies leads to a very rapid high level easterly acceleration lasting about two weeks. A final resonant wind configuration with easterlies above westerlies is associated with very rapid temperature rises near the pole.Calculations suggest that the quasi-resonant enhancement of the planetary wave-zone flow interaction resulting from certain basic flow configurations might be the explanation of the stratospheric warming.It is hypothesized that the timing of warmings is determined by how well tuned the zonal flow structure is in the sense that appreciable secondorder effects will result in response to small influxes of planetary-wave energy from below. Furthermore, it is suggested that the subsequent evolution of a warming into a full scale warming depends on the ability of the zonal flow configuration to evolve through a series of tuned or resonant states.

How Well do we Understand the Dynamics of Stratospheric Warmings?

“…According to this idea, planetary waves forced by topography or stationary thermal forcing can grow anomalously if the basic state evolves into a configuration such that a free mode of the whole atmosphere exists and is nearly stationary. This possibility has been discussed by a number of authors, most extensively by Tung and Lindzer (1979a, b); see also Clark (1974) and Simmons (1974).…”

Sudden Stratospheric Warmings

“…The top down perspective has often been framed in the context of resonant growth of wave disturbances (e.g., Clark, 1974; Tung & Lindzen, 1979b). In a particularly insightful incarnation of this mechanism, the wave‐mean flow interaction causes the vortex to tune itself toward its resonant excitation point (Matthewman & Esler, 2011; Plumb, 1981; Scott, 2016).…”

Sudden Stratospheric Warmings and Anomalous Upward Wave Activity Flux

“…The importance of these wave-mean flow feedbacks has long been recognized (e.g. Clark 1974;Geisler 1974;Holton and Mass 1976;Plumb 1981). Note that this is a nonlinear effect that comes about due to the coupling between two quasi-linear fields -the mean flow and the waves.…”