Internal Variability of the Troposphere-Stratosphere Coupled System Simulated in a Simple Global Circulation Model.

Details Internal Variability of the Troposphere-Stratosphere Coupled System Simulated in a Simple Global Circulation Model. Internal Variability of the Troposphere-Stratosphere Coupled System Simulated in a Simple Global Circulation Model.

Nov 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001jats...58.3184t&link_type=abstract

Journal of Atmospheric Sciences, vol. 58, Issue 21, pp.3184-3203

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21

Scientific paper

Internal variability of a troposphere-stratosphere coupled system is investigated in a series of numerical experiments with a simple global circulation model under a perpetual winter condition. In order to examine the relative importance of forced planetary waves in the interaction with the zonal mean zonal flow and baroclinic disturbances, amplitude of a sinusoidal surface topography of zonal wavenumber 1 or 2 is swept as an experimental parameter; 1000-day integrations are performed for 110 combinations of the external parameters.Intraseasonal variability of the extratropical winter stratosphere in the parameter sweep experiment of the zonal wavenumber-1 topography is classified into four regimes, dependent on the topographic amplitude: (I) a nearly radiative equilibrium state; (II) small undulations of the polar vortex; (III) intermittent breakdowns of the polar vortex, or occurrence of stratospheric sudden warming events; and (IV) a usually weak and warm state of the polar vortex. The behavior of planetary waves in the stratosphere is characterized by linear propagation in regime I, and by quasi-linear, or weakly nonlinear, wave-mean flow interaction in regime II. In regimes III and IV, on the other hand, it is in a highly nonlinear state, reflecting the occurrence of sudden warming events and the usually distorted polar vortex, respectively. The Northern Hemisphere winter stratosphere corresponds to regime III in the intraseasonal variations, while the southern counterpart is close to regime II.A lag-correlation analysis shows that the dynamical linkage between the stratosphere and the troposphere is also dependent on the regimes. The vertical linkage is primarily the upward control in regime I; planetary waves are generated by nonlinear interaction of baroclinic disturbances in the troposphere and propagate into the stratosphere. In regime II, stratospheric variations are largely confined in the stratosphere, although planetary waves are generated in the troposphere. The linkage in regime III, on the other hand, is inevitably two-way. Planetary wave variability has upward influence from the troposphere to the stratosphere as well as the zonal mean zonal wind shows preconditioning in the troposphere before stratospheric sudden warming events. Downward propagation of signals to the upper troposphere are also seen in the zonal mean temperature in high latitudes; it is higher than normal at the final stage of the sequence of sudden warming events. The linkage is also two-way in regime IV.

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