Ensemble Prediction of Monsoon Index with a Genetic Neural Network Model

After the consideration of the nonlinear nature changes of monsoon index, and the subjective determination of network structure in traditional artificial neural network prediction modeling, monthly and seasonal monsoon intensity index prediction is studied in this paper by using nonlinear genetic neural network ensemble prediction (GNNEP) modeling. It differs from traditional prediction modeling in the following aspects:(1) Input factors of the GNNEP model of monsoon index were selected from a large quantity of preceding period high correlation factors, such as monthly sea temperature fields, monthly 500-hPa air temperature fields, monthly 200-hPa geopotential height fields, etc., and they were also highly information-condensed and system dimensionality-reduced by using the empirical orthogonal function (EOF) method, which effectively condensed the useful information of predictors and therefore controlled the size of network structure of the GNNEP model.(2) In the input design of the GNNEP model, a mean generating function (MGF) series of predictand (monsoon index) was added as an input factor; the contrast analysis of results of prediction experiments by a physical variable predictor-predictand MGF GNNEP model and a physical variable predictor GNNEP model shows that the incorporation of the periodical variation of predictand (monsoon index) is very effective in improving the prediction of monsoon index. (3) Different from the traditional neural network modeling, the GNNEP modeling is able to objectively determine the network structure of the GNNNEP model, and the model constructed has a better generalization capability. In the case of identical predictors, prediction modeling samples, and independent prediction samples, the prediction accuracy of our GNNEP model combined with the system dimensionality reduction technique of predictors is clearly higher than that of the traditional stepwise regression model using the traditional treatment technique of predictors, suggesting that the GNNEP model opens up a vast range of possibilities for operational weather prediction.