hirlam

Model equations and discretization

The HARMONIE model is a non-hydrostatic spectral model, of which the dynamical core (developed by ALADIN) is based on a two-time level semi-implicit Semi-Lagrangian discretisation of the fully elastic equations, using a hybrid coordinate in the vertical. Optionally, for larger domains and coarser resolutions the hydrostatic version of this semi-Lagrangian scheme can be used. An Eulerian dynamics core is available, but has been little used in recent years.

A description of the model equations are presented here by P. Bénard. In practice normally a rotated lat-lon grid projection is adopted by HARMONIE for the output grid. A fourth-order implicit horizontal diffusion.

Physical parametrizations

A variety of sub-gridscale physical processes are taken into account by parametrization schemes. Basically, the parametrizations adopted in HARMONIE are the same as those of the AROME model, developed by the meso-NH community. Extensive scientific documentation is available from the Meso-NH scientific documentation on the upper air physics and on the surface module SURFEX.
The following table gives a short overview on the schemes used operationally and on additional options implemented so far:

There is no separate parametrization for gravity wave drag.

Optionally two other upper air physics packages can be used:

• the ALARO convection and microphysics package (Gerard 2007, Catry et al 2008, ALARO information on RCLACE website).

• the HIRLAM upper air physics: Savijärvi radiation scheme, Kain-Fritsch convection (Calvo 2007) and Rasch-Kristjansson condensation (Ivarsson 2007) schemes, prognostic moist TKE (Tijm and Lenderink 2003), and a mean and subgrid-scale orography parametrization (Rontu et al 2002).

Surface and soil processes:

• The externalized surface scheme SURFEX is used for the soil description. It assumes a tile approach, distinguishing 7 surface types. Surface physiographies are prescribed using the 1km resolution ECOCLIMAP database. SURFEX contains several modules:
  • Soil: a three-layer force-restore ISBA scheme (Noilhan and Planton, 1989).
  • Sea surface fluxes (ECUME empirical formulae)
  • Urban areas: the Town Energy Budget (TEB) urban canyon model (Masson 2000)
  • Lakes: the Flake model (Mironov 2008, Kourzeneva 2008)
  • A 1D high resolution column model CANOPY to describe the boundary layer with the canopy (Masson 2008)
  • Snow : Several parametrizations for snow are available in SURFEX. In HARMONIE, the HIRLAM snow and forest parametrization by Gollvik (Gollvik 2002, Gollvik 2004) is to be used.

Data assimilation

The default upper air data assimilation scheme in HARMONIE is the 3DVAR scheme developed in ALADIN . Background error statistics are be calculated using the NMC method. An analytical balance condition is applied.
The observation data types which are assimilated by default presently are conventional observations (TEMP, SYNOP, AIREP, PILOT, SATOB, SHIP, DRIBU) and AMSU-A / ATOVS radiances over sea. Additionally, it is possible to assimilate AMSU-A over land and sea ice, AMSU-B, geostationary and MODIS atmospheric motion vectors, SEVIRI cloud-cleared radiances, GPS zenith total delay, wind profilers, radar radial winds and profiles and Seawinds scatterometer data.
Variational bias correction is applied by default to all satellite data. Observation screening involves logical and representivity checks, background quality checks, black-or whitelisting, multi-level and station level checks, redundancy checks and moving platform checks. Thinning is used to reduce the amount of observations.

Optionally, 3D-VAR with FGAT can be applied for upper air data assimilation. A 4D-VAR scheme is under construction.

Analysis of surface variables is done within the spatial interpolation tool CANARI, applying optimum interpolation for the assimilation of screen level parameters T2m and RH2m, and sea surface temperature. This is to be extended with snow depth. Assimilation of other soil variables (soil moisture, leaf area index, etc) will be done in a <simplified extended Kalman filter> which is presently under development.

Initial and boundary conditions

To reduce noise and spinup, analyses are initialized out by incremental digital filter initialisation (DFI), (Lynch et al. 1997). In HARMONIE, initial and boundary conditions are normally taken from a larger scale HIRLAM or ALADIN model.Lateral boundaries are overspecified, all variables being externally prescribed by the nesting model. Normally a relaxation zone of 10 grid points is adopted. Boundary relaxation is performed after the horizontal diffusion. At the upper boundary a condition of zero vertical velocity is imposed.

The HARMONIE system

To allow the model to be used for routine operational numerical weather forecasting, the model analysis and forecast code has been embedded in a system of scripts, executables, support libraries, documentation and tools. This overall HARMONIE system must be applicable in all HIRLAM institutes for both operational and research applications. As such, portability of the code and tools included is an important issue.
There is a standard version of HARMONIE, which is referred to as the Reference System. This Reference system (which consists of code, scripts, libraries and tools) is maintained on the HIRLAM server and at ECMWF.
More information on the status of the Mesoscale model in HIRLAM is given in the corresponding item in the system wiki.

To install HARMONIE on a local computer, a copy of the Reference system should be obtained. Instructions on how to do this are given in the HIRLAM system wiki (only accessible for registered users).