Study on the diversity in the structure of the Meiyu front and the distribution of rainfall and cloud

1. 中国上空梅雨锋面扰动的形成过程因其初始出现位置的不同而不同。即青藏高原东麓形成的中尺度α-扰动导致长江流域上空强降水，而寒冷的东北风通过温度梯度的增大激活了华南上空的梅雨锋。尽管中国连续南移和静止强雨区的高度异常分布都表现出类似EU型的遥相关，但正、负异常的位置不同。前一种情况下，东海高度负异常导致副热带高压东南向后退，冷气团从日本海进入长江流域。本例梅雨锋北部气团偏冷，锋面系统显示垂直较高结构。在后一种情况下，华南上空的高度场没有减弱，副热带高压脊仍在那里。由于东北冷风仅局限于日本海北部，除了低层外，梅雨锋周围没有出现温度负异常。白羽锋在日本附近的产雨云（对流/层状云）的结构会随锋面区特征而变化。在这种情况下，白球锋对应于欧亚极锋区。，来自层状云的降雨占上风。与此相反，白锋下对流降雨盛行，白锋面以北有冷空气团，从中国延伸而来。研究了白雨季节日降雨量对总降雨量的贡献，阐明了日本降雨强度统计特征的地理和年际差异。

1. The formation process of the Meiyu frontal disturbance over China is different corresponding to its initial appearance location. That is, the meso-α-scale disturbance that formed in the eastern foot of the Tibetan Plateau causes heavy rainfall zone over the Yangtze River basin, while the cold northeasterly wind activates the Meiyu front over South China through the increase in temperature gradient.2. Though the distributions of height anomaly for the cases of both continuous southward migrating and stationary heavy rainfall zone over China indicate EU pattern-like teleconnection, the location of positive and negative anomaly is different between respective case. As for the former case, negative height anomaly locates in the East China Sea, which causes the southeastward retreat of the Subtropical High and the incursion of cold airmass into the Yangtze River basin from the Japan Sea. Airmass to the north of the Meiyu front of this case is rather cold and the frontal system indicates vertically higher structure. Concerning the latter case, height field over Southern China dose not decrease and the Subtropical ridge remains there. Since the cold northeasterly is restricted to the northern Japan Sea, negative temperature anomaly around the Meiyu front is not observed except in the lower layer.3. The structure of rain-producing cloud (convective/stratiform cloud) in the Baiu front around Japan could vary according to the characteristics of the frontal zone. In case the Baiu front corresponds to the Eurasian Polar frontal zone., rainfall from the stratifrom clouds preveils. On the contrary, convective rainfall prevails under the Baiu front that prolonged from China with cold airmass to the north of the front4. Contribution of daily rainfall amount to total rainfall amount during the Baiu season is investigated to clarify the geographical and year-to-year difference in the statistical feature of rainfall intensity over Japan.