Application Method of Monthly Dynamics Extended-range Forecast Based on EOF Iteration Scheme

Based on EOF iteration scheme model with dynamic extended range forecast products, experiment of precipitation prediction is done for 121 station of Hebei Province from June to August in 2005—2007. It is necessary to use 500 hPa correlation area in the EOF iteration scheme model in order to improve the prediction accuracy. Experiment in different correlation areas indicates that the model performs best when the critical correlation coefficient is 0.45, correlation area is of 90 grids. The average sign coincidence rate between predicted precipitation and observed precipitation is 0.54.When critical correlation coefficient is 0.45, grid number is 90 and iteration error is 0.05, let truncation order of eigenvector equal 1, 2, …, 11 and do experiment separately. The first two eigenvectors account for about 50% of total variance explained. When truncation order equal 1 and 2, average sign coincidence rate are 0.60 and 0.58. When truncation order is greater than 2, average sign coincidence rate decreases as truncation order increases slightly until stability in 0.54—0.52.When critical correlation coefficient is 0.45, grid number is 90 and truncation order of eigenvector is 4, let iteration number equal 0, 1, …, 19 do the prediction experiment separately.The experiment shows that iteration error decreases as iteration number increases, but the decrease rate is very different. As accuracy reaches 0.05, the fastest experiment requires only one times of iterative operator and the slowest one requires 15 times. The predicted result affected by iteration error is slight. To acquire good result, many times of iteration is unnecessary, usually no more than three times. When truncating the first eigenvector without iteration, the average sign coincidence rate of monthly precipitation prediction can reach 0.63 and operational scores PS can reach 0.74.