SUMMARYA set of empirical orthogonal functions is produced which enable the large-scale features of the 500 mb topography over the Northern Hemisphere to be represented with near optimal efficiency. The more important functions are described. Some of the properties of the coefficients of these functions which best represent the 500 mb charts for each day of the years 1965 to 1967 are summarized. The question of the number of functions required to obtain the most satisfactory representation of the 500 mb fields is discussed.

JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact support@jstor.org.

No abstract

In recent years, there have been notable advances in the science of forecasting the weather by solving the thermohydrodynamic equations governing atmospheric flow by using numerical methods. The development of an operational numerical weather-forecasting system requires a high level of expertise in areas such as fluid dynamics, atmospheric physics, numerical methods, supercomputers, space-based remote sensing, and radar. By incorporating the better forecasts into planning and decision making, improved levels of efficiency have been achieved within weather-sensitive areas of both industrial and service sectors of the economy. The Meteorological Office has developed a computer-based weather-forecasting system for civil aviation that permits the provision of weather forecasts for any aircraft anywhere in the world. Information provided by airlines has indicated that they are saving an additional £50M per year through reduced aviation fuel consumption directly related to the improved forecasts. Current research indicates that further substantial improvements to weather forecasting will be achieved within the coming decade, enabling meteorology to be integrated even more closely into air traffic control and airline operations.