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SUMMARY:A new approach to implement sigma coordinate in a numerical model 
 - Li\, Y (Chinese Academy of Sciences)
DTSTART:20120824T100000Z
DTEND:20120824T103000Z
UID:TALK39384@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:This study shows a new way to implement terrain-following σ-c
 oordinate in a numerical model\, which does not lead to the well-known pre
 ssure gradient force (PGF) problem. First\, the causes of the PGF problem 
 are analyzed with existing methods that are categorized into two different
  types based on the causes. Then\, the new method that bypasses the PGF pr
 oblem all together is proposed. By comparing these three methods and analy
 zing the expression of the scalar gradient in a curvilinear coordinate sys
 tem\, this study finds out that only when using the covariant scalar equat
 ions of σ-coordinate will the PGF computational form have one term in eac
 h momentum component equation\, thereby avoiding the PGF problem completel
 y. \n\nA convenient way of implementing the covariant scalar equations of 
 σ-coordinate in a numerical atmospheric model is illustrated\, which is t
 o set corresponding parameters in the scalar equations of the Cartesian co
 ordinate. Finally\, two idealized experiments manifest that the PGF calcul
 ated with the new method is more accurate than using the classic one. Spec
 ifically\, the relative error of PGF in the new method is reduced by order
 s of magnitude compared with the result obtained by the classic method\; a
 nd the pattern of PGF in the new method is more consistent with the analyt
 ical PGF pattern than using the classic method. This new method can be use
 d for oceanic models as well\, and needs to be tested in both the atmosphe
 ric and oceanic models. \n\n\n
LOCATION:Seminar Room 1\, Newton Institute
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