Description of the Mesoscale Eta Model

(Workstation Version 0.2 March 2000 Release, NCEP)

Grid: Semi-staggered Arakawa E-grid

Horizontal Resolution: 32 km

Vertical levels: 38

Model Domain: 60 – 100 E & 0 – 40 N (Variable)

Model Time step (Dt): 90 seconds

Topography: Silhouette step topography

Model Dynamics: (Black, 1994; Weather & Forecasting)

· Fundamental prognostic variables – T, u, v, q, Ps, TKE, cloud water/ice

· Inertial gravity wave adjustment – forward-backward scheme (Dt=90s)

· Vertical advection

§ Euler-backward scheme

§ centred in space

§ piecewise linear for q

· Horizontal advection

§ modified Euler-backward scheme

§ Janjic advection in space

§ Conservative, (nearly) shape-preserving scheme for H₂O

§ Upstream advection near boundaries

Model Physics: (Janjic, 1994; Mon. Wea. Rev.)

· Betts-Miller-Janjic convection

· Mellor-Yamada level 2.5 turbulent exchange

· GFDL Radiation

· Explicit cloud water/ice prediction

· 4 layer soil scheme with vegetation

· D² horizontal diffusion

Initial and Lateral boundary conditions: One way interaction

· NCMRWF global analysis and 6 hourly global model forecasts

Time-dependent Surface Fields:

· SST, Snowdepth,

Surface analysis from NCMRWF global model