Numerical Forecasting with the Barotropic Model

The experiments with numerical forecasting using the barotropic model have been continued and a number of 24, 48 and 72 hour forecasts are presented. The initial data for these forecasts covered an area of about 9,000 by 12,000 km. The results indicate that the boundary influences have been reduced to be unimportant in the centre of the area in the 24-hour forecasts but they may still cause errors in the 72-hour forecasts. In view of the approximations made very good 72-hour forecasts have been obtained in some cases. The most successful one gave a correlation of 0.87 and a relative error of the forecast height changes of 0.58. Most of these extended forecasts should be of definite value in forecasting the weather. Large errors are, however, still obtained in some cases. The neglection of baroclinic process is one of the reasons for these errors but it is quite obvious that the largest errors are of a different nature. Experiments are at present conducted to find the sources of these errors. One line of this research is a general re-analysis of the assumptions made in deriving the barotropic model which is presented in the latter part of this paper. A number of improvements are suggested for further tests.