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SUMMARY:Effects of large-scale energy dissipation in geostrophic turbulenc
 e - Scott\, R (St Andrews)
DTSTART:20081209T103000Z
DTEND:20081209T110000Z
UID:TALK15604@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:We compare the distinct effects of frictional damping and radi
 ative\, or thermal\, damping on the equilibration of two-dimensional geost
 rophic turbulence. The spatial distribution of energy in both physical and
  spectral space is examined with particular attention to the distribution 
 of coherent vortices\, which are found to be ubiquitous with either form o
 f large-scale energy dissipation. Consideration of the stochastically forc
 ed vorticity equation suggests that in the case of frictional damping\, ma
 ximum vorticity values depend on the damping coefficient $r$ through $qext
  im r^{-1/2}$\, while in the case of thermal damping $qext$ is approximate
 ly independent of damping coefficient. These are well-supported by numeric
 al experiments.\n\nThe difference between frictional and thermal damping b
 ecomes striking in simulations of forced shallow water turbulence on the s
 phere. While shallow-water models have been successful in reproducing the 
 formation of robust\, and fully turbulent\, latitudinal jets similar to th
 ose observed on the giant planets\, they have to date consistently failed 
 to reproduce prograde (superrotating) equatorial winds. Here it is demonst
 rated that shallow water models not only can give rise to superrotating wi
 nds\, but do so very robustly\, provided that the physical process of larg
 e-scale energy dissipation by radiative relaxation (thermal damping) is ta
 ken into account. With appropriate choice of thermal damping rate\, equato
 rial superrotation can be achieved at apparently any deformation radius. 
LOCATION:Seminar Room 1\, Newton Institute
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