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Keywords:

  • stratosphere;
  • Planetary wave;
  • Blocking;
  • sudden warming

Abstract

[1] Case studies are used to elucidate the relationship between stratospheric planetary wave reflection and blocking formation in the troposphere. The enhanced upward propagation of a planetary-scale wave packet from the Eurasian sector, involving a Euro-Atlantic blocking, leads to a stratospheric sudden warming (SSW). Following the weakening of the stratospheric westerly jet due to polar warming, the stratospheric planetary wave packet then propagates downward over the American sector, inducing a ridge over the North Pacific as well as a trough over eastern Canada in the upper troposphere. The ridge promotes the formation of a Pacific blocking. This result explains why Pacific blockings tend to form after SSW, and why they are associated with suppressed upward propagation of planetary waves.