A general extremum tracking routine has been applied to a number of fields in ECMWF reanalysed data for the DJF season. In each case, maps are produced for average system speed and strength, feature density, track density, genesis and lysis regions, tendency and growth rate. When applied to mean sea-level pressure minima the diagnostics are those for the standard storm-track and highlight the North Pacific and North Atlantic regions and also the Mediterranean. The diagnostics are qualitatively similar if the seasonal average field or the instantaneous low planetary waves are removed from the mean sea-level pressure before the tracking routine is applied. This procedure has also been performed for pressure maxima. The same planetary wave removal technique has allowed the tracking diagnostics to be applied to both positive and negative extrema in height, meridional wind, vorticity and temperature at 850mb and 250mb, omega at 500mb, 330K PV and PV=2 potential temperature.
The diagnostics highlight the differences between the Atlantic and Pacific storm-tracks. The large range of perspectives on each given by the various fields is being assembled into a coherent picture.
The diagnostic procedure is also being applied separately to winters of opposite sign in the North Atlantic Oscillation and in the PNA. Early results suggest that a clear picture of storm-track variation with these low-frequency modes of behaviour is emerging.
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