The Vertical Tilt of the Planetary Waves and Its Time Change

Abstract

A study of the vertical tilt of the planetary waves by means of the so-called 2-level, quasi-geostrophic model is performed. As the levels of modeling research, 250 mb and 750 mb levels are selected, the vertical p-velocity being zero at 0 mb and 1000 mb levels. Assuming the zonal basic current in the baroclinic channel, the simple sinusoidal disturbances are superimposed on each level. Since the vertical tilt of disturbances is roughly proportional to the zonally averaged value of the northward transport of sensible heat, the time evolution of the zonally averaged value of the transport of sensible heat is treated theoretically and the stability criterion for the development of disturbances is obtained. In case of the large amplitude of disturbances the different stability criterion is given, compared with that obtaind from the discussion of the linearized perturbation equation.
The motion of the vertical tilt of disturbances with time is pseudo-periodic type, having a tilt to the east or west in the westerlies. When the upper trough moves faster than the lower one at the initial time, we expect the slowing down of the movement of the upper trough later and the lower trough moves relatively faster than the upper one. The pseudoperiod mentioned above is 3-15 days and it depends on the vertical shear of the zonal basic currents and also the intensity of disturbances.