NMOC Quarterly Summary January-March 2002

Summary of System Performance
Wave Forecasting Verifications

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The following diagrams show the verification of the significant wave height forecasts from the operational sea state models at wave recording sites around the Australian coast for the period January-March 2002.

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The first series of graphs shows the mean bias (average error) and RMS error of the global (1° resolution), Australian region (1° resolution) and the SE mesoscale region (0.25° resolution) wave models at Cape Sorell and Brisbane averaged over the three months. Also included for comparison are the verifications of the UK wave model (blue diamonds). At Cape Sorell the major contribution to the error is the negative bias whereas at Brisbane there is very little bias evident over this period although the UK model exhibits a slight positive bias. At sites exposed to the mid-lattitude westerlies (such as Cape Sorell) the local models perform slightly worse than the UK model whereas the performance of all models is similar on the east coast.

The following charts show the performance of the 12 hour and 24 hour forecasts of the operational models (glbass = Global Model, regass = Australian region model, mesass = SE mesoscale model) and the UK wave model (UK_glo) together with wave height observations on a daily basis at all of the above sites.

At Brisbane there is generally good agreement in the phase of the forecasts. The peaks on March 14 and March 23 were underforecast while the general underlying swell for the month was overforecast.

At Cape Sorell the waves were underforecast by all the models although the phase of the predictions was quite good. The major event of the period on February 21, which was caused by a very intense depression south of Tasmania with strong westerly winds, was reasonably well forecast by all models. The other events of the month caused by the passage of fronts in the westerly wind stream, were forecast by the models but the amplitudes were underestimated to various degrees.

Although there were no major wave events at Rottnest Island during the period, all models performed reasonably well except for the amplitude of the event of 14 February.

The final graph shows the number of observations per month and the verification of the 24 hour forecast from the Australian Region Wave Model since the beginning of 1999.

Running monthly statistics and time series plots of model performance at all the verifying sites are available on the Bureau's internal web site.