Area and Seasonal Subdivisions

Map 1 - The Worldwide Database Area Subdivision.  

Map 1 shows a map of the area subdivision used in the 104 area world-wide database. The area and seasonal subdivision was worked out [32] [33] by reference to three main criteria. These were:

  1. The availability of data.
  2. The likely patterns of demand for data.
  3. The need for climatological consistency.

Considering first data availability, the objective was to achieve a maximum extent of global coverage of all regions with adequate data density, and to ensure that the sea areas each contained an acceptable number of observations. Information about data availability in the form of global charts showing the observation count for each one degree square of sea area was used.

Regarding demand, consideration was given to the main types of application anticipated for the world-wide database. Potential users in the fields of naval architecture, and offshore and coastal engineering were canvassed. As a result, particular attention was devoted to designing an area subdivision suitable for use in assessment of shipping and long-haul towing routes, and to achieving good coverage of continental shelf areas where offshore and coastal engineering activity is generally concentrated.

It was unfortunately not possible to meet all these requirements due to conflict between demand and practical constraint. For long-haul towing routes, for example, it may often be desirable for the areas to be vertically stratified with large spans in the north/south direction. It was decided however that this requirement could not be met, because of unacceptable conflict with the overriding requirement for climatological consistency within individual areas.

In continental shelf regions, it was also unfortunately not possible to accommodate requests made for subdivision into smaller areas, due to the need for balance between adequate resolution and an excessive number of areas. Areas such as the North Sea, where finer subdivision was requested, are quite well endowed with instrumental data. The world-wide database is not intended to be a source of highly localized site-specific data. Such information should be obtained by use of the NMIMET wave data service, or from the relevant meteorological or oceanographic agencies.

The third main criterion was climatological consistency. Consistency of conditions throughout any given area is clearly a requirement if the corresponding data are to be regarded as representative of the whole area. Such consistency is particularly important when considering the choice of seasonal breakdowns.

The need for seasonal subdivisions in each area to be matched to local climatology was strongly emphasized by potential users. A study was therefore undertaken, involving analysis of the monthly statistics for each individual area, as a basis for choosing corresponding seasonal breakdowns matched to the local climatology.