Description of the ECMWF forecast model in 1987

The forecast model in 1987 used a spectral formulation in the horizontal, with triangular truncation at total wavenumber 106, a vertical coordinate with 19-level resolution which was terrain-following at low levels. The comprehensive physical parametrisation schemes included shallow and deep (Kuo) convection, a radiation scheme which allowed interaction with model generated clouds and the diurnal radiative cycle.

Domain	Global
Initial data time	12Z
Dependent variables	,D,T,q,In(Ps)
Vertical coordinate	Hybrid, Pk+1/2=Ak+1/2+Bk+1/2 Ps, details as above
Vertical representation	Finite-difference, energy and angular-moment conserving
Horizontal representation	Spectral, with triangular truncation at wavenumber 106
Horizontal grid	160 x 320 points on a quasi-regular (1.125°) Gaussian grid
Time integration	Leapfrog, semi-implicit (t=15 min), time filter (=0.1)
Horizontal diffusion	Linear, fourth-order (K=1x1015m4s-1)
Orography	Grid-scale average from high resolution data set, enhanced by one standard deviation of sub-grid scale orography, spectrally-fitted
Vertical boundary conditions	Kinematic
Physical parameterisation	(i) Boundary eddy fluxes dependent on local roughness length and stability (Monin-Obukov).
	(ii) Free-atmosphere turbulent fluxes dependent on mixing length and Richardson number
	(iii) Gravity wavedrag scheme. Stresses due to orographically-forced gravity waves.
	(iv) Kuo convection scheme. Shallow convection parameterised by an eddy mixing scheme.
	(v) Interaction between radiation and model-generated clouds. Albedo dependent on model snow cover.
	(vi) Large-scale condensation when grid-square saturated. Evaporation of precipitation
	(vii) Computed land temperature with diurnal cycle (3 layers in soil).
	(viii) Computed soil moisture and snow cover.
	(ix) Fixed, analysed sea-surface temperature.
Statistical correction of forecasts	None