Daily Variations Characteristics of Rainfall in Flood Season in Yining City

The formation of precipitation variation is often closely linked with all sorts of daily variation of atmospheric phenomena,is one of the most main oscillation phenomenon in the earth's atmosphere. Based on the hourly automatic rainfall data in Yining station from 2007 to 2011,the diurnal variation characteristics of rainfall was analyzed in main flood season( 5- 8 month). The results showed that the rainfall was mainly concentrated at 22: 00 to 09: 00 next day of Beijing time,with the maximum rainfall value appearing at 02: 00 next day,and it took second place at 18: 00 to 19: 00 next day with the minimum value appearing at 13: 00 next day. The high value of rainfall frequency occurred at 23: 00 to 11: 00 next day,it was not easy to generate at16: 00. The highest rainfall intensity generally appeared at 18: 00 and the higher intensity was at 19: 00,which was consistent with the accumulated precipitation. The minimum rainfall intensity generally occurred at 13:00,corresponding to the low value of accumulated precipitation. The correlation of rainfall intensity and accumulated precipitation was higher than the rainfall frequency and accumulated precipitation. According to the different levels,defined by the hourly rainfall of ≥ 0. 1 mm or ≥ 1 mm or ≥ 3 mm,respectively,rainfall easily occurred at night or morning than afternoon,the rainfall( hourly rainfall ≥ 0. 1 mm) was more frequent than other levels. Precipitation mainly occurred in night,and the 1- 3 hour rainfall duration made the greatest contribution to the total rainfall. The total and low cloud cover both showed a significant positive correlation with rainfall. The above result is helpful to understand rainfall characteristics in yining city thoroughly.