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北亚秋冬季节转换的热力学特征

Thermodynamic Characteristics of Winter Onset in Northern Asia

  • 摘要: 本文利用1958~2020年日本气象厅逐日再分析资料(JRA-55),对北亚地区(50°~75°N,80°~140°E)在入冬前后的热力收支特征以及影响入冬时间早晚的外强迫因子进行了研究。结果表明,在气候平均上,北亚于第62候入冬;在此之前,北亚地区的降温经历了从剧烈到缓慢的变化过程。在此过程中,非绝热冷却起主要作用,它部分地被暖平流所抵消。线性斜压模式的数值结果表明,欧亚大陆中高纬的非绝热冷却有利于北亚地区形成西风和偏南风,从而造成较强的局地暖平流,进而抵消部分非绝热冷却作用。在年际变率上,赤道中东太平洋和北大西洋的海温异常均可通过欧亚大陆上的波列异常进而影响北亚入冬早晚,它们可分别提前1个月和5个月出现显著信号,具有一定的预测意义。在对冬季气温的影响上,在北亚入冬偏早(晚)年,12月东亚部分地区以及我国南部地区气温偏高(低)。

     

    Abstract: Using daily reanalysis data obtained from the Japan Meteorological Agency (JRA55) spanning from 1958 to 2020, this study examines the thermal budget characteristics before and after winter onset in Northern Asia (50°–75°N, 80°–140°E) as well as the external forces affecting the timing of winter onset. The results show that climatological winter onset in Northern Asia occurs in the 62nd pentad. Before the onset, the region experiences a transition from drastic cooling to a more gradual temperature decline. Diabatic cooling plays a major role during this phase and is partially offset by warm advection. Further analysis based on the linear baroclinic model reveals that diabatic cooling across the middle and high latitudes of the Eurasian continent is conducive to the formation of westerly and southerly winds in Northern Asia. This results in strong local warm advection, which, in turn, partially offsets the effect of diabatic cooling. On an interannual time scale, anomalies in sea surface temperatures in the eastern Equatorial–central Pacific regions and the North Atlantic region affect winter onset in Northern Asia. These anomalies trigger anomalous wave trains across the Eurasian continent, presenting significant signals 1–5 months prior to winter onset, offering potential predictive value. Moreover, the study reveals that some parts of East Asia and southern China experience higher temperatures in December during years when winter onset occurs earlier and lower temperatures during those with a later onset.

     

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