BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Talks.cam//talks.cam.ac.uk//
X-WR-CALNAME:Talks.cam
BEGIN:VEVENT
SUMMARY:The hyper-CASL algorithm: an accurate\, efficient new approach to 
 modelling complex atmospheric and oceanic flows - Dritschel\, DG (St Andre
 ws)
DTSTART:20081210T120000Z
DTEND:20081210T123000Z
UID:TALK15632@talks.cam.ac.uk
CONTACT:Mustapha Amrani
DESCRIPTION:We describe a powerful new approach to the simulation of layer
 wise-2D geophysical flows. Our approach combines the CASL algorithm\, a hy
 brid contour-dynamics method ideally suited for the Lagrangian advection o
 f potential vorticity (PV) contours across an Eulerian fixed grid\, with a
  standard vortex-in-cell method. The latter is here used to compensate for
  errors arising from contour regularisation or `surgery' appearing at the 
 level of the grid. In this way\, (essential) dissipation occurs only at su
 b-grid scales\, and there is no direct impact of surgery on the computed v
 elocity field\, which is obtained on the grid by standard spectral or (com
 pact) finite-difference methods. This is particularly important for long-t
 erm simulations\, where error accumulation needs to be minimised.\n\nThis 
 new approach\, coined the `hyper-CASL algorithm'\, also allows for general
  non-conservative effects\, by design. For instance\, one may take account
  of radiative (thermal) effects which attract a given flow to some thermal
  equilibrium distribution\, or one can account for `Ekman pumping' which c
 onverts wind stress at the ocean's surface into a vorticity source or sink
  there. In fact\, very general forms of forcing or damping can be accounte
 d for (e.g. stochastic\, moisture\, small-scale convection\, etc.).\n\nHyp
 er-CASL is not limited to PV\, but can be applied to other tracers such as
  chemical species in the atmosphere\, including moisture. In particular\, 
 modelling water vapour by contours and subgrid-scale convection by Lagrang
 ian particles may be a timely opportunity to improve the forecasting of pr
 ecipitation.\n\nHyper-CASL is illustrated here in long-term simulations of
  quasi-geostrophic and shallow-water turbulence. These simulations reveal 
 unprecedented detail\, in particular vortices spanning a very wide range o
 f scales and significantly affecting flow statistics. 
LOCATION:Seminar Room 1\, Newton Institute
END:VEVENT
END:VCALENDAR