**PMIP Documentation for BMRC**

**Bureau of Meteorology Research Centre:
Model BMRC (R21 L9) Version 3.2 1993**

Australia; Phone: +61-3-9669-4000; Fax: +61-3-9669-4660; e-mail: bma@bom.gov.au

WWW URL: http://www.bom.gov.au/bmrc/clchhp.htm

Number of days in each month: 31 28 31 30 31 30 31 31 30 31 30 31

The model configuration for the PMIP experiment is described by :

McAvaney B.J., and Colman R.A., 1993: The BMRC Model : AMIP Configuration. BMRC Research Report No 38.

Colman R.A., and McAvaney B.J., 1995: JGR 100, 3155-3172.

McAvaney B.J., and G.D. Hess, 1996: The Revised Surface Fluxes Parametrisation in BMRC: Formulation. BMRC Research Report No 56.

secondary reference(s):

Key documentation of the BMRC model is provided by Bourke (1988) , Hart et al. (1988 , 1990 ),

Colman and McAvaney (1991) , McAvaney et al. (1991) , and Rikus (1991) .

Colman R.A., and McAvaney B.J., 1995: JGR 100, 3155-3172.

dim_longitude*dim_latitude: 64*56

For a surface pressure of 1000 hPa, 3 levels are below 800 hPa and 3
are above 200 hPa.

Stability dependent vertical diffusion after Louis (1979) is only applied
for sigma levels > 0.5 in stable layers, but it operates in all unstable
layers with no separate removal of dry superadiabats, and with a minimum
wind speed difference of 1 m/s assumed between model levels.

Longwave radiation follows the simplified exchange method of Fels and
Schwarzkopf (1975) and Schwarzkopf and Fels (1991) , with slight modifications.
(The parent code is compared against benchmark computations by Fels et
al. 1991 .) Longwave calculations follow the broad-band emissivity approximation
in 8 spectral intervals (with wavenumber boundaries at 0, 1.6 x 10^{4},
5.6 x 10^{4}, 8.0 x 10^{4}, 9.0 x 10^{4}, 9.9 x
10^{4}, 1.07 x 10^{5}, 1.20 x 10^{5}, and 2.20
x 10^{5} m^{-1}). Another 14 bands are accounted for in
the cooling-to-space corrections. Included in the calculations are Fels
and Schwarzkopf (1981) transmission coefficients for carbon dioxide, the
water vapour continuum of Roberts et al. (1976) , and the effects of water-carbon
dioxide overlap and of a Voigt line-shape correction. , and the effects
of water-carbon dioxide overlap and of a Voigt line-shape correction.

The treatment of cloud-radiative interactions is as described by Rikus
(1991) and McAvaney et al. (1991) . Shortwave cloud reflectivity/absorptivity
is prescribed for ultraviolet-visible and near-infrared spectral bands
and depends only on the height class of the cloud (see Cloud Formation).
In the longwave, all clouds are assumed to behave as black bodies (emissivity
of 1). For purposes of the radiation calculations, all clouds are assumed
to be randomly overlapped in the vertical.

Simulation of shallow convection is parameterized in terms of the model's
vertical diffusion scheme, following the method of Tiedtke (1983 , 1988
). Shallow convection is triggered when the lower layers are conditionally
unstable and have a relative humidity greater than 75%.

For 6 fix: SSTs and sea-ice prescribed at their present day value, as
in the control run.

The roughness length over oceans is determined from the surface wind
stress, following Charnock (1955) , with a coefficient of 0.0185 assigned
after Wu (1982) ; the ocean roughness is constrained to a minimum value
of 1.5 x 10^{-5} m. Roughness lengths are prescribed uniform values
over sea ice (0.001 m) and land surfaces (0.168 m), but the presence of
snow cover changes the roughness to a new (fixed) value (0.001m).

Over oceans, the surface albedo depends on solar zenith angle, following Payne (1972). Seasonal climatological surface albedos of Hummel and Reck (1979) are prescribed over land. The surface albedos of sea ice and snow-covered land follow the temperature-ramp formulation of Petzold (1977) , with different values of albedo limits and a lower temperature range for sea ice and snow, as described by Colman and McAvaney (1992)

Longwave emissivity is set to unity for all surfaces (i.e., black body
emission is assumed).

The surface turbulent eddy fluxes of momentum, heat, and moisture follow Monin-Obukhov similarity theory, and are formulated in terms of bulk formulae with stability-dependent drag/transfer coefficients determined as in Louis (1979) . The momentum flux is given by the product of the air density, a neutral drag coefficient, wind speed and wind vector at the lowest prognostic level (sigma = 0.991), and a transfer function that depends on roughness length (see Surface Characteristics) and stability (bulk Richardson number). Surface wind speed is constrained to a minimum of 1 m/s. The flux of sensible heat is given by a product of a neutral exchange coefficient, the wind speed at the lowest prognostic level, the difference in temperatures between the ground and the first prognostic atmospheric level, and a modified form of the transfer function for unstable conditions (cf. Louis 1979) .

The flux of surface moisture is given by a product of the same transfer
coefficient and stability function as for sensible heat, an evapotranspiration
efficiency beta, and the difference between the specific humidity at the
first prognostic level and the saturation specific humidity at the surface
temperature and pressure. For calm conditions over the oceans, evaporation
also is enhanced following the approximation of Miller et al. (1992) for
the transfer coefficient. Over oceans, sea ice, and snow, beta is prescribed
to be unity; over land, beta is a function of the ratio of soil moisture
to a constant field capacity (see Land Surface Processes).

Prognostic soil moisture is represented by a single-layer "bucket" model with uniform field capacity of 0.15 m after Manabe and Holloway (1975). . Both precipitation and snowmelt contribute to soil moisture. The evapotranspiration efficiency beta (see Surface Fluxes) is a function of the ratio of soil moisture to the field capacity. Runoff occurs implicitly if this ratio exceeds unity.

Last update November 9, 1998. For further information, contact: Céline Bonfils (pmipweb@lsce.ipsl.fr )