A Study of Tracer Transports by Planetary Scale Waves in the Mit Stratospheric General Circulation Model

Abstract

The quasi-geostrophic global stratospheric model at MIT developed by is used to study the zonal and time-averaged transport of potential temperature and ozone by the planetary zonal wavenumbers 1-6. Several types of covariances between the winds, geopotential, and the tracers are calculated in order to evaluate the directions and strength of the fluxes and the winds causing the fluxes. The eddy covariances show that, in the lower stratosphere, ozone and potential temperature b6th move polewards and downwards in longitudes of low geopotential, in agreement with observations. In the upper stratosphere and lower mesosphereozone and potential temperature are negatively correlated. In the midlatitudes of this region the eddy flux of potential temperature horizontally diverges; with downwards eddy fluxes occuring in low latitudes and upwards fluxes occurring in high latitudes. The meridional eddy flux of ozone is found to be only 1-3% efficient since the meridional wind and ozone waves are nearly 900 out of phase. Another contributing factor to the inefficiency of the eddy transport is the tendency for the transient eddy flux to nearly cancel the standing eddy flux in the lowest layers of the stratosphere. The total flux of ozone is further diminished in some regions of the atmosphere by the opposition of the eddy fluxes to the mean circulation flux. In the final chapters, some of the calculated covariances are applied in an attempt to calculate the eddy diffusivities. Because of the unsuita-bility of the mathematical form of the equation used to define the eddy diffusivity, Kyy, and the uncertainties in the averaged covariances; Kyy could not be estimated in a straightforward manner with any accuracy. The eddy diffusivity Kyy is then assumed to be the product of the meridional EKE and the timescale typical of the mixing processes taking place. The timescale was calculated two ways. One used the LaGrangian integral timescale of Taylor's dispersion theorem. The other was an attempt to find the timescale typical of the advective processes by using a mean length scale and the mean zonal wind. Both results showed reasonable agreement of the timescale with previously observed timescales in the atmosphere.

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Cite this paper

@inproceedings{Moore2010ASO, title={A Study of Tracer Transports by Planetary Scale Waves in the Mit Stratospheric General Circulation Model}, author={Gary Edward Moore}, year={2010} }