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Keywords:

  • atmosphere;
  • probability density function;
  • extreme event;
  • Eady waves;
  • baroclinic systems

Abstract

The present study analyses meridional atmospheric heat transport, due to transient eddies, in the European Centre for Medium-Range Weather Forecasts ERA-Interim reanalysis. Daily, 0.7° latitude and longitude resolution data at the 850 mb pressure level are used. Probability density functions (PDFs) of meridional transient-eddy heat transport display a near-zero most likely value and a very large skewness, which highlights the dominant role played by extreme events. When considering zonal sections, in both the Northern and Southern Hemispheres, events in the top five percentiles typically contribute to over half of the net poleward transport. As a result of this sensitivity to extremes, a large fraction of the heat transport by transient eddies, at a given location and season, is realised through randomly spaced bursts (a few per season), rather than through a continuum of events.

The predominance of extreme events can be explained by the favourable phase relationship between meridional velocity and moist static energy temporal anomalies. This and the spatiotemporal characteristics of the events are compatible with Eady-type growing systems. Copyright © 2012 Royal Meteorological Society