DMI_WAM ensemble forecast, 51 hours ahead. NOTE half resolution, relarive to operational model.

As part of the EU-funded Mona Lisa 2 project, and later EU-CISE , DMI has undertaken to set up an operational ensemble wave model prediction system. This page describes the second such attempt, with updated ensemble atmospheric forcing, three nested model domains, and enhanced spectral resolution. The status of the system is: pre-operational. WAM-EPS is run scheduled and automatized, but without 24/7 surveillance.

• WAM cycle 4.5 model code
• Etopo5 and Etopo2 based depth maps
• DMI-Harmonie COMEPS/NEA ensemble model
• ECMWF global deterministic model

The WAM cycle 4.5 model code and parameterisations are identical to the DMI operational WAM. The model set-up has three nested grids, reduced in size to fit into the NWP forcing model domains. Only the two innermost grids are subject to ensemble prediction.

• Deterministic North Atlantic boundary model
  • 69W-30E, 30-78N
  • forcing: ECMWF global
  • resolution: 0.5 deg
• Nested ensemble North Sea - Baltic Sea model
  • 8.5W-30.5E, 48-66N
  • forcing: COMEPS-NEA ensembles
  • resolution: 10 km
• Nested ensemble Transition Area model
  • 7-16E, 53-60N
  • forcing: COMEPS-NEA ensembles
  • resolution: 2 km

WAM-EPS has 18 ensemble members plus one deterministic. The perturbation lies with the wind forcing exclusively. There is at present no direct pertubation of wave model initial state, of wave model physics/parameteristions, or of boundary (swell generator) model.

DMI-COMEPS has a total of 18 Harmonie-NEA ensemble members, covering the nested model domains.

The weather model ensemble forecast range is 57 hours. The COMEPS ensembles are arranged to have 3 ensemble members run every hour. In a six-hour scedule, this produces 18 ensemble members, with forecst range relative to the analysis time of latest member ranging from 57 hours (newest) to 51 hours (oldest). With the wave model ensembles run on a standard 6-hour schedule, 51 hours is then the limiting range.

Wave model domains

Ensemble weather model domain

• platform: Cray-XC
• cpus: 72 (2 nodes)
• runtime: ~2 hours
• schedule: 6 hours
• forecast range: 51 hours

The main deficiencies of the present set-up is thought to be

• low resolution,
• deterministic swell
• not enough spread in wind ensemble

• Work out validation along the lines of SO5-EPS validation
• Increase resolution to that of the deteministic model (half grid spacing). This requires new depth maps, in order to keep propagation time step on a reasonable level. Ensembles would have to run in parallel
• Use ice information from the DMI daily gridded remote sensing data
• Examine what can be done with respect to perturbation along open boundaries of the fine grid domain
• Optimize in terms of parallel computing. Higher resolution may use more nodes, as this is limited by the number of model latitude bands.
• Upgtrade to WAM Cycle 4.7 or higher

Validation stations: Today

Validation stations: Yesterday