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SUMMARY:Second and third order structure functions calculated from QuikSCA
 T measured near-surface winds over the Pacific Ocean - Greg King (Universi
 ty of Warwick\, UK and Instituto Gulbenkian de Ciencia\, Portugal)
DTSTART:20080205T100000Z
DTEND:20080205T110000Z
UID:TALK10463@talks.cam.ac.uk
CONTACT:Anje Neutel
DESCRIPTION:Spectral analysis of observed large-scale horizontal velocity 
 fields  \nin the atmosphere show a power law dependence of kinetic energy 
 on  \nspatial wavenumber _k_.  A recent analysis of near-surface winds ove
 r  \nthe tropical western Pacific [Wikle\, Milliff and Large (1999)]  \nin
 dicates a _k_^ -5/3^ power law over the entire mesoscale range  \n(10-1000
  km).  Both upscale quasi-2D and downscale 3D turbulence  \ncascades can h
 ave _k_^ -5/3^ energy spectra\, but since the _k_^ -5/3^ power law was fou
 nd in the tropics where rotation and stratification  \neffects are too wea
 k to suppress three dimensional motions\, the  \ntemptation is to assume t
 hat the near-surface mesoscale energy cascade  \nmust be 3D-downscale. On 
 the other hand\, it is possible that the  \nstrong and sweeping horizontal
  winds arising from the large-scale  \nsubsidence into the marine boundary
  layer in the tropics could give  \nrise to a dimensionality constraint re
 sulting in a quasi-2D upscale  \ncascade.\nTo investigate this issue we ha
 ve calculated second- and third-order  \nvelocity structure functions from
  QuikSCAT measured near-surface winds  \nover the Pacific Ocean (40N to 40
 S\, and 150E to 110W)\, covering the  \nperiod January 2000 to December 20
 04.  Latitude variations\, regional  \nvariations (east vs west Pacific)\,
  as well as variability in time have  \nbeen investigated.  Calculations o
 f the third-order structure function  \nyield results consistent with a do
 wn-scale energy transfer in the  \ntropical western Pacific and the possib
 ility of an up-scale energy  \ntransfer in the tropical eastern Pacific.  
 In addition\, the third- \norder structure function shows an interesting s
 patial oscillation  \narising from events along the ITCZ in early autumn.\
 n\nThis work was carried out in collaboration with R M Kerr and K C Pien.\
 n
LOCATION:British Antarctic Survey\, Room 330B
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