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Daily to Decadal Modulation of Jet Variability

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  • 1 Department of Physics, University of Oxford, Oxford, United Kingdom
  • | 2 Department of Atmospheric Science, Colorado State University, Fort Collins, Colorado
  • | 3 University of Reading, Reading, United Kingdom
  • | 4 Imperial College, London, United Kingdom
  • | 5 Woods Hole Oceanographic Institution, Woods Hole, Massachusetts
  • | 6 National Centre for Atmospheric Science, Department of Meteorology, University of Reading, Reading, United Kingdom
  • | 7 Geophysical Institute, University of Bergen, Bergen, Norway
  • | 8 Bjerknes Centre for Climate Research, Bergen, Norway
  • | 9 Department of Geosciences, Federal University of Santa Catarina, Santa Catarina, Brazil
  • | 10 Met Office, Exeter, United Kingdom
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Abstract

The variance of a jet’s position in latitude is found to be related to its average speed: when a jet becomes stronger, its variability in latitude decreases. This relationship is shown to hold for observed midlatitude jets around the world and also across a hierarchy of numerical models. North Atlantic jet variability is shown to be modulated on decadal time scales, with decades of a strong, steady jet being interspersed with decades of a weak, variable jet. These modulations are also related to variations in the basinwide occurrence of high-impact blocking events. A picture emerges of complex multidecadal jet variability in which recent decades do not appear unusual. An underlying barotropic mechanism is proposed to explain this behavior, related to the change in refractive properties of a jet as it strengthens, and the subsequent effect on the distribution of Rossby wave breaking.

© 2018 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Tim Woollings, tim.woollings@physics.ox.ac.uk

Abstract

The variance of a jet’s position in latitude is found to be related to its average speed: when a jet becomes stronger, its variability in latitude decreases. This relationship is shown to hold for observed midlatitude jets around the world and also across a hierarchy of numerical models. North Atlantic jet variability is shown to be modulated on decadal time scales, with decades of a strong, steady jet being interspersed with decades of a weak, variable jet. These modulations are also related to variations in the basinwide occurrence of high-impact blocking events. A picture emerges of complex multidecadal jet variability in which recent decades do not appear unusual. An underlying barotropic mechanism is proposed to explain this behavior, related to the change in refractive properties of a jet as it strengthens, and the subsequent effect on the distribution of Rossby wave breaking.

© 2018 American Meteorological Society. For information regarding reuse of this content and general copyright information, consult the AMS Copyright Policy (www.ametsoc.org/PUBSReuseLicenses).

Corresponding author: Tim Woollings, tim.woollings@physics.ox.ac.uk
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