Large-scale eddies in the upper troposphere and stratosphere diagnosed with quasi-conservative coordinates

Abstract

[1] A new diagnostic for the amplitudes of large-scale eddies in the upper troposphere and stratosphere is introduced. It is based on the instantaneous azonality (area displacement) of the contours of a potential vorticity-like tracer on the isentropic surface, easily calculable from the surface integral of the Coriolis parameter within the contour, or the planetary circulation. Unlike the traditional Eulerian definition, the diagnostic does not involve zonal averaging and provides an absolute measure of eddy amplitude. Seasonal climatology as well as interannual variability of this amplitude diagnostic are examined with the United Kingdom Meteorological Office Stratospheric Analysis data for 1992–2005. In the potential temperature-equivalent latitude plane, the eddy amplitudes are generally large (small) at the flanks (axes) of the jets. This paints a very different picture from the traditional Eulerian zonal-mean diagnostics in which eddy amplitudes are often maximal along the jets.