The Global Environmental Multiscale (GEM) Model is the operational model at the Canadian Meteorological Center (CMC) and is described by Côté et al.(1998). The temporal discretization is a two-time-level Crank–Nicholson iterative semi-Lagrangian method with an advecting wind interpolated in time. Recently, the vertical staggering (Charney-Phillips grid) was introduced and is described by Girard et al. (2010). The terrain-following vertical coordinate [ln p = A(zeta) + B(zeta) ln(ps/pref); zeta = ln(pref) + ln (eta)] is adopted, where ps=Surface pressure and pref=10**5. GEM Lat-Lon is based on the global latitude–longitude grid system with a uniform Arakawa C grid.
In GEM, the dynamics and physics are time split. All prognostic variables are updated by the dynamics and then the physics. The time step is the same for dynamics and physics.
GEM Lat-Lon uses the latitude-longitude grid. Implicit 2D diffusion damps the winds [u,v,d(zeta)/dt,dz/dt]. A 6th order selective diffusion (Qaddouri and Lee, 2008) is adopted with a 2 Delta-x removal ratio of 4% per timestep and is applied after the physics. In the case with Simplified/Full physics, the temporal scheme is decentered along the trajectory with a off-centering parameter epsilon=.1. In the case of Idealized cyclones, a vertical sponge layer based on 2nd order implicit 2D diffusion is applied on the winds [u,v,d(zeta)/dt,dz/dt] and temperature, with vertical modulation on 3 top levels and damping coefficient C = .380000*10**6 m**2/s.
||# of horizontal
|Grid spacing at
the equator (km)
time step (s)
time step (s)
|List of all dissipation coefficients
(with physical units)
|1x1||180x360=64800||111||1800||1800|| see text
||55||900||900|| see text
|.25x.25||720x1440=1036800||28||900||900|| see text
Horizontal: Lat-Lon Grid (Left); Vertical Staggering: Charney-Phillips (Right)
GEM-latlon will be featured as a remotely-participating model.
Additional contributions: Bernard Dugas (NetCDF), Ayrton Zadra and Paul Vaillancourt (Physics)
DCMIP-2012: News Report on DCMIP
Check out the NCAR CISL News report http://www2.cisl.... More »
cjablono @ 09/20/2012 10:56 a.m.
DCMIP-2012: Photo Gallery
Check out the photos of the Saturday hike on the ... More »
cjablono @ 08/04/2012 5:12 p.m.
DCMIP-2012: Welcome & Ice Breaker Reception
Monday (7/30/2012) 4:30-6:30pm, NCAR Mesa Lab Tree Plaza More »
murphysj @ 07/27/2012 12:16 p.m.
DCMIP-2012: Pre-Workshop Informal Get-Together
Sunday (7/29/2012) at the Baker Street Pub & Grill near ... More »
murphysj @ 07/27/2012 12:13 p.m.