Paolo Davini, Chiara Cagnazzo, Silvio Gualdi, and Antonio Navarra

American Meteorological Society

Published date April 5, 2012

Bidimensional Diagnostics, Variability, and Trends of Northern Hemisphere Blocking

  • Analyzes Northern Hemisphere winter blocking through the introduction of a set of new bidimensional diagnostics based on geopotential height that provide information about the occurrence, the duration, the intensity, and the wave breaking associated with the blocking
  • Performs analysis with different reanalysis datasets in order to evaluate the sensitivity of the index and the diagnostics adopted
  • Defines a new category of blocking placed at low latitudes that is similar to midlatitude blocking in terms of the introduced diagnostics but is unable to divert or block the flow
  • Finds that over the Euro-Atlantic sector it is possible to phenomenologically distinguish between high-latitude blocking occurring over Greenland, north of the jet stream and dominated by cyclonic wave breaking, and the traditional midlatitude blocking localized over Europe and driven by anticyclonic wave breaking
  • Finds these latter events are uniformly present in a band ranging from the Azores up to Scandinavia
  • Finds a similar distinction cannot be pointed out over the Pacific basin where the blocking activity is dominated by high-latitude blocking occurring over eastern Siberia
  • Analyzes the variability and the trend, considering the large impact that blocking may have on the Northern Hemisphere
  • Results show a significant increase of Atlantic low-latitude blocking frequency and an eastward displacement of the strongest blocking events over both the Atlantic and Pacific Oceans