Distribution characteristics and the possible mechanism of mesoscale disturbance in the subtropical upper-level jet stream over East Asia
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摘要: 东亚副热带高空急流强度变化和天气气候密切相关，本文利用WRF模式输出的高时空分辨率模拟资料研究了东亚副热带高空急流区的中尺度扰动特征，并结合动力学理论，揭示了急流区中尺度扰动产生的可能机制.研究表明，急流轴南侧更容易出现水平尺度为几十公里的高频扰动，这些扰动的时空分布具有波动特征.对高空急流区中出现中尺度扰动区域的拉格朗日Rossby数、Richardson数以及绝对涡度的计算发现，高空急流轴南侧中尺度扰动出现的物理机制与非地转平衡流的不稳定发展有关，并且高空急流强度的大尺度整体变化与急流区中尺度扰动变化的累积效应有关.因此，开展高空急流强度变化规律研究不能忽视其内部中尺度动力过程的作用.Abstract: The intensity variation of the subtropical upper-level jet stream over East Asia is closely related to weather and climate in this region. In this paper, the characteristics of mesoscale disturbances in this jet stream are investigated by using the high temporal and spatial resolution output of the mesoscale model WRF. The possible mechanism for the disturbances formation is explained in terms of numerical simulations and dynamic analysis. The results indicate that high frequency disturbances, with a horizontal scale of about tens of kilometers, occur in the south side of the jet axis more frequently with fluctuation in temporal and spatial distribution. The calculations of the Lagrangian Rossby number, Richardson number and absolute vorticity show that in the areas where mesoscale disturbances are present, the formation mechanism of the mesoscale disturbances in the south side of the jet axis is related to the instability and development of ageostrophic balance flow. Besides, the large-scale intensification of the jet is related to the accumulation of mesoscale disturbances in the jet stream. Therefore, the mesoscale dynamic processes should be taken into consideration in research on large-scale intensity variation of the upper-level jet stream.
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