An examination of zonal mean geopotential variability




Bruce, Leslie Mitchell

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A systematic sectoral empirical orthogonal function (EOF) analysis of Southern Hemisphere (SH) extratropical tropospheric zonal-mean geopotential height (GH) is conducted in order to determine how EOF shapes and shape ordering is affected by a decrease in the width of the sector. Previous work (Kushner and Lee 2007) using surface pressure found that the two lead EOFs exchange shape as the sector width decreases below seventy degrees. In the present work, the 500hPa GH field is found to exhibit a similar feature. By fitting a idealized kinematic model, in the form of a Gaussian error function, to daily 500 hPa GH for each sector, the kinematic features of the shape reordering observed in the lead EOFs is shown to arise from the covariance structure of the fluctuating model parameters. The correlations between model parameters which are shown to influence the EOF shapes are further shown to be strongly influenced by statistical properties of daily mass and angular momentum fluctuations.



Annular Mode, Geopotential Height, Empirical Orthogonal Functions