INTRODUCTION

The forecasting of surface wave conditions has been a major feature of the services offered by the Meteorological Office since the development of the North Sea oil industry in the 1970s. Originally, forecasters made use of surface wing speed, direction and fetch as the forcing functions. The increase in demand for sea-state forecasts, linked with a growing confidence in numerically modeled surface wind fields, provided the impetus for the development of a numerical wave model. Such a model, for use in deep water areas was brought into operational use in 1976, followed by a shallow-water version in 1977. Various improvements have since been made to those models, leading to the present status of the models which are briefly described later in this paper.

In the decade since the introduction of the models the range of services based on their products has grown rapidly. Some idea of the scope of present services is present later, illustrating that the great majority of work is done in the "operational" mode, i.e. the forecast products are used in real time. A growing amount of interest is, however, now being shown in applications for the archive of "hind-cast" data, accumulated since January 1978. This archive contains the best simulation of the actual sea state that is possible with the present models, being generated by numerical wind fields that are mainly influenced by recent observations (see below). At the time of writing, nearly 8 years of this archive have been accumulated, forming a mass of data which almost rivals in length the data from a single-wave measurement location in European waters. The archive is now of such a length that climatological statistics can be inferred, albeit with reasonably wide confidence limits. As more data are routinely added the usefulness of this data source can only improve.

This presentation is completed by a brief discussion about the accuracy of the hindcast data (both the resultant wave fields and the generating wind fields), and a speculative look at some climatological applications which will be statistically of use in few years time.

The Wave Model

The wave model at present run on an operational basis in the Meteorological Office is the result of an evolving series of such models, in use since 1976. The model(in three versions covering different geographical areas) is driven by wind fields extracted from the operational numerical weather prediction (NWP) models. All models are run twice daily throughout the year. The three versions of the wave model in operational use cover different areas on different scales, and are run for different forecast periods (see Table 1). The only difference in formulation between these three models is the inclusion of extra shallow-water processes in the continental shelf model.

The wind input for the wave models is taken either from a global NWP model (resolution 1 ½ ° x 1 7/8°) or a limited are fine mesh NWP model.

TABLE 1 Physical specifications of operational wave models in the Meteorological Office (available in full paper)

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