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SUMMARY:Computational modes: What are they and how bad are they for a weat
 her/climate model dynamical core? - Thuburn\, J (University of Exeter)
DTSTART:20121204T133000Z
DTEND:20121204T143000Z
UID:TALK41827@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:In this presentation we will take a broad definition of `compu
 tational mode'\, namely any gross mis-representation of linear wavelike be
 haviour of the continuous system by the discrete system. Computational mod
 es are potentially problematic for a dynamical core because they are likel
 y to be excited by nonlinear processes\, physical parameterizations\, or d
 ata assimilation. Some well-known and less well-known examples of computat
 ional modes will be reviewed\, including isolated computational modes and 
 entire branches of computational modes. Spatial computational modes will b
 e related to grid staggering and to degrees of freedom of prognostic varia
 bles. The triangular and hexagonal C-grid cases will be examined in detail
 . It will be argued that the extra branch of Rossby modes that occurs for 
 the hexagonal C-grid is\, in fact\, well behaved in the presence of a back
 ground flow provided an adequate advection scheme is used. The relation of
  computational modes to `parasitic' mo des and to trapped modes on non-uni
 form grids will be discussed. \n
LOCATION:Seminar Room 2\, Newton Institute Gatehouse
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