The Low Frequency Oscillation and Circulation Characteristics of Cold Rainy Weather in Guangdong

In order to predict cold rainy weather on medium-term and extended range during February—March in Guangdong, the relationship between annual prospect of cold rainy weather during 1953—2011 in Guangdong and that in Guangzhou, and the relationship between low-frequency oscillation of Guangzhou daily temperature and cold rainy weather are analyzed from December to next April with wavelet transform and correlation analysis. The result shows that the similar ratio between the annual prospect of Guangzhou cold rainy weather and that of Guangdong is 94.9%(56/59). In mild year of cold rainy weather, Guangzhou daily temperature exhibits quasi-periodic oscillations of 8.0—18.3 days, 10.1—28.4 days and 30—89.6 days for middle and severe year, respectively.The long cold rainy weather during February—March has mainly close relationship with the intraseasonal oscillation with period more than 18 days, especially with the oscillation intensity more than 45 days. The weather concept model of long cold rainy weather with intraseasonal oscillation of 30—64 days is set up based on composite analysis of typical cases.They reflect the evolution characteristics of atmospheric circulation of warmer—cooling—starting—maintenance—ending period of long cold rainy weather. During warmer—cooling—starting period, the blocking high in Ural Maintain and west of Baikal Lake at 500 hPa geopotential height field is maintained, the South China is controlled by straight and fluctuant westerly from weak ridge at warmer period and obvious negative anomalies of height field, the Mongolian High gradually enhances and moves southward in ground, and the South China is controlled by enormous cold pressure ridge from weak trough.The stronger cold air moves southwards and weak cold air continuously supplements. All of the above lead to strong temperature drop and the start of cold rainy weather. When the blocking high in Ural Mountain—west of Baikal Lake is weakened, an obvious ridge maintains, the South China is still controlled by straight and fluctuant westerly, the weak cold air is continuously supplement, the cold rainy weather maintained. When Ural Mountain—north of Baikal Lake controls by weak trough, the South China is controlled by weak ridges at 500 hPa and surface which moving eastwards, the cold rainy weather ends. So the blocking high in Ural Mountain—west of Baikal Lake can be regarded as 500 hPa precursor of cold rainy weather in Guangdong. When this precursor stably maintains, the straight and fluctuation westerly influences the South China, Mongolian High gradually intensifies and move southwards at surface, the long cold rainy weather in Guangdong can be predicted.