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SUMMARY:Balance model for equatorial long waves - Ian Chan (University of 
 Toronto)
DTSTART:20131017T120000Z
DTEND:20131017T130000Z
UID:TALK48319@talks.cam.ac.uk
CONTACT:9780
DESCRIPTION:When a dynamical system admits both fast and slow timescale dy
 namics\, a\nsimplified model can be constructed by systematically filterin
 g out the\nfast dynamics. In the context of atmospheric dynamics\, these m
 odels are\ncalled balance models\, with the quasi-geostrophic (QG) model b
 eing the\nmost notable example. Although the QG model is immensely useful 
 for the\nmidlatitudes\, it is not applicable to the tropics as a singulari
 ty\ndevelops. Previous attempts at deriving equatorial balance models have
 \nbeen unsuccessful as they filter out Kelvin waves\, which play a dominan
 t\nrole in equatorial dynamics. In this talk I will demonstrate how a\nmod
 ified asymptotic approach can be used to systematically derive\nequatorial
  balance models in the planetary scale regime\, which capture\nslow Rossby
  and Kelvin wave modes while filtering out fast gravity wave\nmotions. The
  expansion is based on the smallness of the ratio of\nmeridional to zonal 
 scales\, which can also be interpreted as a\nseparation in timescale. Both
  the adiabatic and the diabatic (forced)\ncase are considered. An interest
 ing result is that even though the\nleading order balance dynamics fails i
 n the isotropic regime\, the\nbalance relations remain accurate\; this sug
 gests that the balance\nrelations can potentially be useful in application
 s such as data\nassimilation.
LOCATION:MR5\, Centre for Mathematical Sciences
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