【作者】 罗建英；

【导师】 周军；

【作者基本信息】 南京气象学院 ， 气象学， 2003， 硕士

【摘要】 包括急流暴雨在内的梅雨降水存在显著的日变化。过去曾从低空急流日变化等一些梅雨系统的内部联系寻求解释。本文通过实例分析、气候比较和数值模拟认为：梅雨降水日变化的根本原因是东亚低层大气温度场日变化的区域性差异，造成这种差异的基本原因又包括两个方面，一是东亚特殊的地形构造，二是梅雨期内特殊的云区分布。由于梅雨云带的存在，梅雨锋低压槽内温度日变化很微弱；由于梅雨系统四围高大地形的存在，梅雨锋低压槽南北两侧温度日变化非常明显，使南海副高和中纬度变性高压在夜间增强，梅雨锋低压槽也在夜间变深、变窄，改变了早、晚时刻梅雨系统的相对强度和降水功能，导致降水日变化。低空急流等系统的日变化是梅雨天气系统内，低层气压场形势出现日变化后发生的众多中间变化过程之一。气候分析表明低层温度场日变化的区域性差异是东亚梅雨季节经常存在的一种气候现象。利用非静力中尺度数值模式MM5V3.5成功地模拟了“98．7”持续性暴雨过程中气压场形势的变化和降水现象以及低空急流的日变化现象。模拟结果表明，当模式中考虑了南岭山脉地形时，低空急流在05时达到最强盛状态，在14时达到最弱状态。而当模式中仅仅去掉南岭和武夷山山脉地形后，低层大气温度场日变化的区域性差异明显变弱，梅雨低压带南侧原南岭山脉所在地的温度日较差明显减小，使得梅雨低压槽与华南地区之间的南北向水平温度梯度和水平气压梯度的日较差显著变小，导致华南低空急流日变化的显著减弱。说明南岭山脉的存在对华南低空急流的日变化具有非常明显的推动作用。更多还原

【Abstract】 Meiyu frontal rainfall including jet-related rainstorms experiences pronounced daily variation (DV). Scientists tried to seek explanations from the DV of low-level jet as a member of the Meiyu precipitating system. Based on case study and climate analysis, this work arrives at the central cause of DV of the Meiyu rainfall, which lies in the regional difference in DV of the lower-level temperature field of east Asia, and the cause relates essentially to 1) distinct topography in this region and 2) a particular cloud pattern during the wet season. Because of the existence of Meiyu precipitating cloud band the temperature DV is faint inside the Meiyu trough and on account of large-scale prominent terrain available, significant temperature DV occurs on both sides of the trough, leading to the reinforcement of the subtropical high and middle latitude transformed high, and the deepening and narrowing of the trough in the night with the result that the relative intensity and precipitating function of the Meiyu frontal rainfall system are changed at day and night, resulting in precipitation DV. And the DV of lower-level systems, e.g., jet stream, is among the intermediate changes happening after the DV is displayed in the Meiyu pressure field. Regional difference in lower-level temperature DV is a climatic phenomenon that often emerges in this wet season of east Asia.The effect of Nanling ridge on the DV of LLJ is conducted in terms of MM5V3.5. Results indicate that LLJ becomes strongest at 5a.rn.and weakest at 14p.m. by the influence of the Nanling ridge. Regional difference in lower-level temperature DV and pressure DV are greatly weakened and DV of LLJ is distinctly faint without the Nanling ridge. This result show that Nanling ridge acts as a critical role in the establishment of DV of the lower-level temperature and pressure,which give rise to the DV of LLJ in South China.更多还原