北半球季节转换中的大气波动特征

Characteristics of Atmospheric Waves during Seasonal Transitions in the Northern Hemisphere

摘要: 本文利用1948~2019年NCEP/NCAR再分析资料，根据高原西风急流季节性移动的特征，逐年确定了北半球季节转换的日期，通过谐波分析、相关分析、合成分析方法研究了大气波动在季节转换中的特征，并分析了季节转换日期的早晚与海温的关系。结果表明：(1) 冬夏与夏冬季节转换的平均日期分别为32候和59候，冬夏与夏冬的季节转换日期都存在显著的年际与年代际周期；(2) 季节转换在西风带主要表现为行星波数的调整和位相的移动；(3) 中高纬2波与海陆热力差异有关且受全球变暖影响，3波与4波分别对欧洲东部槽和欧洲西海岸槽的贡献显著，而1波可反映极涡的偏转程度；(4) 3月SST呈现El Niño型和PDO暖位相分布时，冬夏转换偏晚；9月SST呈现La Niña型分布时，夏冬季节转换偏晚，因此前期SST对季节转换日期的异常有较好的指示意义，可作为前期信号。

Abstract: Based on the NCEP/NCAR reanalysis data from 1948 to 2019, the dates of seasonal transitions in the Northern Hemisphere were determined. The characteristics of atmospheric waves in seasonal transitions were analyzed by harmonic analysis, correlation analysis, and composite analysis methods. Thus the relationship between the dates of seasonal transitions and SST was also analyzed. The results show that: 1) For climatology, the date of winter-summer seasonal transition is the 32nd pentad, while date of summer-winter seasonal transition is the 59th pentad. Interannual and decadal periods of these two seasonal transitions are both significant; 2) Seasonal transitions in westerlies are shown as the changes of planetary wavenumbers and the moving of planetary waves phase; 3) Wave 2 at middle-high latitudes is related to the sea-land thermal difference and is influenced by the global warming. Wave 3 and wave 4 have no table impacts on the intensity of East European trough and West Coast European trough respectively. Wave1 reflects the deflection of polar vortex; 4) El Niño and warm PDO phase in March can delay the dates of winter-summer transitions. Otherwise La Niña in September can delay the dates of summer-winter transitions. SST has a good indication of the abnormal seasonal transition dates, it can be used as an early signal of the dates of seasonal transitions.