EARTH SYSTEM PHYSICS SEMINAR THURSDAY

[Pandora Malchose]

EARTH SYSTEM PHYSICS SEMINAR

Thursday, 13 May  2010
Oppenheimer room, LB Second Floor, 11:00 am

Peter Hjort LAURITZEN
National Center for Atmospheric Research
Boulder, Colorado
USA

A GEOMETRICALLY FLEXIBLE CONSERVATIVE SEMI-LAGRANGIAN SCHEME FOR 
MULTI-TRACER TRANSPORT

Isotropic spherical grids considered for next generation weather and 
climate models challenge
the advection operator in new ways compared to the traditional regular 
latitude-longitude grids.
These newer grids are primarily non-orthogonal which might question the 
accuracy of
dimensionally split schemes implemented on such grids. Also, zonally 
symmetric flows, that on
a lat-lon grid are always parallel or orthogonal to grid lines, are at 
best locally parallel to grid
lines on the non-traditional grids. For balanced flows the lack of zonal 
alignment might
spuriously perturb balances that lat-lon based models are able to 
maintain (Lauritzen et al.
2010a).  To minimize the level of spurious `grid-imprinting' and to 
resolve highly
deformational flow structures, fully two-dimensional schemes may be an 
attractive choice.
 
In this talk a new conservative semi-Lagrangian multi-tracer scheme is 
introduced (Lauritzen et
al. 2010b) which can be cast in either Lagrangian and flux-form 
(Lauritzen et al. 2010c, Harris
and Lauritzen, 2010). Initially the scheme has been implemented on the 
cubed-sphere, however,
it can be generalized to other unstructured grids reusing much of the 
same technology. The
scheme is largely based on the computation of geometric quantities that 
can be reused for each
additional tracer. In the context of testing the scheme a set of (or 
suite of) new deformational
flow problems on the sphere has been developed (Nair and Lauritzen, 
2010). These flow fields
are divergent or non-divergent and, contrary to the popular solid-body 
advection test case,
employ non-trivial trajectories.


Everyone is most welcome.