A primer on extreme weather and links to blocking and/or persistent circulation patterns
Olivia
Romppainen-Martius
University of Bern
Talk
(Invited)
A short introduction to the links between atmospheric blocking and surface extremes will be presented. Atmospheric blocking can be linked to several types of weather extremes. In a blocked state consisting of a blocking anticyclone and wave breaking upstream and/or downstream, we find conditions favorable for ascent and descent and for warm and cold air advection that can lead to temperature, hydrological, and compound extremes. Blocking anticyclones are typically associated with subsidence, inversion layers, a stable stratification, and clear sky conditions or low stratus clouds in their center and eastern half. At the eastern edge of the anticyclones, equatorward winds prevail. At the western edge of a blocking anticyclone, we find poleward winds and ascent.
Consequently, blocking anticyclones in the summer are typically associated with hot and dry surface weather conditions in their center and their eastern half and with active convection and warm air advection along their western flank. Blocking anticyclones in the winter are typically associated with cold temperatures in their center and very cold temperatures due to cold air advection along their eastern flank. These are very broad generalizations and deviations occur due to the blocking substructure and the local surface conditions (ocean, land, snow, soil moisture, topography).
Blocks are typically long-lived and quasi-stationary and may occur repeatedly in the same area over the same season. All factors contribute to the persistence of the surface weather and surface weather extremes associated with the blocks. The longevity of blocking is due to both dry dynamics and moist diabatic processes.
Consequently, blocking anticyclones in the summer are typically associated with hot and dry surface weather conditions in their center and their eastern half and with active convection and warm air advection along their western flank. Blocking anticyclones in the winter are typically associated with cold temperatures in their center and very cold temperatures due to cold air advection along their eastern flank. These are very broad generalizations and deviations occur due to the blocking substructure and the local surface conditions (ocean, land, snow, soil moisture, topography).
Blocks are typically long-lived and quasi-stationary and may occur repeatedly in the same area over the same season. All factors contribute to the persistence of the surface weather and surface weather extremes associated with the blocks. The longevity of blocking is due to both dry dynamics and moist diabatic processes.
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