OCEAN PHYSICS AND MODELLING GROUP - TRITON WAVE FORECAST SYSTEM

THE AEGEAN AND IONIAN SEAS WAVE FORECAST SYSTEM

The core of the Aegean and Ionian Seas wave forecast system is based on the WAM model code (WAMDI group, 1988; Komen et al., 1994). WAM is one of the best tested wave models in the world. It has been distributed among over 40 research groups for forecasting on global and regional scales. WAM (CYCLE 4) is a third generation wave model, which computes spectra of random short-crested wind-generated waves.

The WAM code used in the Aegean and Ionian Seas forecast system was modified in order to get reliable wave forecasts especially in coastal areas (dissipation by depth induced wave breaking, etc.).

In certain high resolution applications of the forecasting system, the SWAN model code (Booij et al., 1999) is used instead of WAM. SWAN model (acronym for Simulating WAves Nearshore) is a third generation wave model very similar to WAM model focusing on obtaining realistic wave parameters estimates in coastal areas, lakes and estuaries.

WAM model forecasts are intercompared with WAVEWATCH-III model predictions within the Mediterranean & Black Sea area. For this reason WAVEWATCH-III is also run operationally by our group. WAVEWATCH-III (Tolman, 1991) has been developed at the Ocean Modelling Branch of the Environmental Modelling Center of the National Centers for Environmental Prediction (NCEP, USA)

The TRITON wave forecast system runs daily (1 cycle) using atmospheric data (wind speed and direction etc.) from the SKIRON weather forecast system (Kallos, 1997) which runs twice daily and provides 72-hours forecast ahead. The wave forecast system issues 66-hour forecasts of significant wave height and direction.

The wave forecast system setup consists of 14 one-way nested overlapping grids covering the areas of 1) Global Ocean 2) Mediterranean and Black Sea 3) Eastern Mediterranean 4) Aegean and Ionian Seas 5) North Aegean Sea 6) South Aegean Sea 7) Ionian Sea 8) Central Aegean Sea (Cyclades region) 9) Cretan Sea 10) Saronikos Gulf 11) Saronikos Coast 12) Eastern Attica Coast 13) Thermaikos and 14) Adriatic Sea

Coarse resolution models

The Mediterranean and Black Sea wave model covers the geographical area 6W-42E and 30N-47N with a spatial resolution of 1/5 x 1/5 deg. It is a standalone model since it has no open boundaries (Gibraltar is closed). This is justified in the sense that normally no significant swell from the Atlantic ocean is expected to propagate into the Mediterranean basin through the Gibraltar Straits. In the future the model will be nested with the global wave forecast system.

The Aegean and Ionian Seas wave model is nested to the Mediterranean and Black Sea wave model (i.e. wave spectra at its open boundaries are provided by the Mediterranean and Black Sea wave model run). It covers the geographical area 19E–30E and 33N-43N with a spatial resolution of 1/10 x 1/10 deg. The Aegean and Ionian Seas wave model run provides boundary conditions to the North, Central, South Aegean Sea and Ionian Sea wave models.

Intermediate resolution models

The North Aegean Sea wave model covers the geographical area 22.5E-27E and 38N-41N with a spatial resolution of 1/30 x 1/30 deg. It provides boundary conditions to the Thermaikos Bay wave model.

The Central Aegean Sea (Cyclades area) wave model covers the geographical area 23E-26.5E and 36N-38.5N with a spatial resolution of 1/30 x 1/30 deg. It provides boundary conditions to the Saronikos Gulf wave model.

The South Aegean Sea wave model covers the geographical area 21E-29E and 34N-38.5N with a spatial resolution of 1/30 x 1/30 deg. It provides boundary conditions to the Cretan Sea wave model.

Fine resolution models

The Saronikos Gulf wave model covers the geographical area 23E-24.2E and 37.4N-38.2N with a spatial resolution of 1/60 x 1/60 deg. It provides boundary conditions to the Saronikos coastal area wave model.

The Cretan Sea wave model covers the geographical area 23.2E-26.5E and 34.6N-36N with a spatial resolution of 1/60 x 1/60 deg. This wave model is based on the SWAN code.

The Ionian wave model covers the geographical area 19.5E-21.75E and 36.8N-40.5N with a spatial resolution of 1/60 x 1/60. This wave model is based on the SWAN code.

Very fine resolution models

The Thermaikos Bay wave model covers the geographical area 22.5E-23.5E and 39.4N-40.8N with a spatial resolution of 1/90 x 1/90 deg (approx. 960m x 1200m).

The Saronikos coastal area wave model covers the geographical area 23.6E-24E and 37.7N-38N with a spatial resolution of 1/180 x 1/180 deg (approx. 485m x 616m).

WAVEWATCH-III applications

Mediterranean and Black Sea wave model

Eastern Mediterranean wave model

The Eastern Mediterranean wave model covers the geographical area 18.7E-36.2E and 30N-42.3N with a spatial resolution of 1/10 x 1/10.

THE GLOBAL WAVE FORECAST SYSTEM

The global wave forecast system is based on the WAM model code. It has a spatial resolution of 1 x 1 deg.

The forecasting system runs daily (1 cycle) using NCEP global 3-hour atmospheric data (wind speed and direction) with a spatial resolution of 1.25 x 1 deg. The wave forecast system issues 120-hour forecasts ahead of significant wave height and direction.

References

Booij, N., R.C.Ris and L.H. Holthuijsen, 1999: A third-generation wave model for coastal regions, Part I: Model description and validation. J. Geophys. Research, 104, C4, 7649-7666.

Kallos, G., 1997: The Regional weather forecasting system SKIRON. Proceedings of the Symposium on Regional Weather Prediction on Parallel Computer Environments, 15-17 October 1997, Athens, Greece. Pp 9.

Komen, G.J, L.Cavaleri, M.Donelan, K.Hasselmann, S.Hasselmann, P.A.E.M.Janssen, 1994: Dynamics and Modelling of Ocean Waves. Cambridge University Press, 532 pp.

Tolman, H.L., 1991: A third-generation model for wind waves on slowly varying, unsteady and inhomogeneous depths and currents. J. Phys. Oceanogr., 21, 782-797.

WAMDI group, 1988: The WAM model – a third generation ocean wave prediction model. J. Phys. Oceanogr., 18, 1775-1810.