A Visualization of the Global Dynamic Tropopause
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A 20–yr loop of the global tropopause, defined in terms of potential vorticity (PV), is constructed using the NCEP–NCAR reanalysis dataset. This method of visualizing observed upper–tropospheric dynamics is useful for studying a wide range of phenomena. Examples are given of the structure of jet streams and planetary–scale tropopause folds, the propagation of a high–amplitude Rossby wave packet partway around a hemisphere, several subtropical wave breaking events, the similarities between exceptional cases of rapid cyclogenesis, favorable regions for cross–equatorial propagation of Rossby waves, the annual cycle of the tropical tropopause, the structure of the Tibetan anticyclone and equatorial easterly jet associated with the Asian monsoon, the meridional structure of the upper branch of the Hadley cell, the interaction of a hurricane and midlatitude trough to form the "perfect storm," and the upper–tropospheric PV changes associated with El Niño and La Niña. Plumes of anticyclonic potential vorticity are frequently seen to be pulled from the subtropical reservoir and roll up into large anticyclones. These previously undescribed plumes may be particularly relevant to jet streak dynamics and stratosphere–troposphere exchange.