Main Influencing Factors of Summer Precipitation and Prediction Method of Annual Increment in Shaanxi

Basic conditions that affect main factors of summer precipitation in Shaanxi are determined, which means that the correlation coefficient is high and the significance is verified, the physical meaning is clear, abnormalities of meteorological factors could be reflected and have lasting effect. NCEP/NCAR reanalysis data of the monthly mean 500 hPa height, sea surface temperature, ERA-40 climate index, and 74 meteorological characteristics of National Climate Center are used in the investigation. Six main climatic factors are met by the census, including the western Pacific subtropical high intensity, equatorial strata, zonal wind, lower-level equatorial airflow, atmospheric angular momentum, equatorial Pacific SST, and the equatorial 500 hPa height field. The analysis of the correlation between anomalies of inter-annual increment, the standard deviation in the six incremental factors and the summer precipitation in Shaanxi, showing that the inter-annual increment factor have obvious signal amplification effect. The standard deviation of six increment factors is 1.5 times larger than anomaly factors, and the correlation coefficient of the increment factor is about 0.1. Both predictive factors and predictive variables have long-term changes, and changes are often inconsistent, resulting in unstable factors. After incrementally transformed in meteorological elements, long-term changes of summer precipitation and main factors are effectively filtered out, and the stability of factor quality and prediction model is improved. Based on the increment and anomaly of six main factors, the summer precipitation forecasting model of Shaanxi is established. Results show that the incremental forecasting model have obvious advantages with good accuracy. The cross test of the same rate show that the increment is 70% and the anomaly is 66%. The distribution of SST in the eastern equatorial Pacific in the precious summer is closely related to summer precipitation in Shaanxi. When the annual increment of the sea area is positive, 700 hPa subtropical high is abnormally northerly or westerly in the next summer, the west periphery side of it is strong southerlies, leading to rainy circulation situation. On the contrary, 700 hPa subtropical high being abnormally easterly prone to drought circulation situation in Shaanxi.