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SUMMARY:Probing the temporal power-law characteristics of the global atmos
 pheric circulation - Dmitry Vyushin\, Department of Physics\, University o
 f Toronto
DTSTART:20081027T103000Z
DTEND:20081027T113000Z
UID:TALK13829@talks.cam.ac.uk
CONTACT:Christian Franzke
DESCRIPTION:Climate variability on timescales longer than a year is often\
 ncharacterized by temporal scaling ("power law") behaviour for which\nspec
 tral power builds up at low frequencies in contrast to red-noise\nbehaviou
 r for which spectral power saturates at low frequencies. We\nestimate temp
 oral power-law exponents ("Hurst exponents") for the global\natmospheric c
 irculation of pre-industrial control and 20th century\nsimulations for the
  troposphere and stratosphere. We consider 17 most\nestablished climate mo
 dels from the CMIP3 archive. We show that\ncurrent-generation climate mode
 ls generally simulate the spatial\ndistribution of the Hurst exponents wel
 l. We also use simulations of an\natmospheric GCM with different climate f
 orcings to explain the Hurst\nexponent distribution and to account for dis
 crepancies in scaling\nbehaviour between different observational products.
  Our analysis\ndemonstrates that at the surface regions of large power law
  exponents\ncoincide with the regions of strong decadal variability\, name
 ly northern\nNorth Atlantic\, northern and tropical Pacific\, and the Sout
 hern Ocean.\nIn the free atmosphere these regions are confined to the trop
 ical and\nsubtropical troposphere and stratosphere. The spectral steepness
  in the\nformer is explained by its strong coupling to the surface and in 
 the\nlater by its sensitivity to the volcanic aerosols. We conclude that\n
 characterization of temporal power-law behaviour provides a valuable\ntool
  for cross-validating low-frequency variability in various datasets\,\nfor
  elucidating the physical mechanisms underlying this variability\, and\nfo
 r statistical testing of trends and periodicities in climate time\nseries.
LOCATION:British Antarctic Survey\, Room 187
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