中国华南地区6月降水变化特征及大气环流条件分析

CHARACTERISTICS OF PRECIPITATION IN SOUTH CHINA IN JUNE AND ATMOSPHERIC CIRCULATION ANALYSES

文章分析了华南6月降水的时间演变特征,指出华南6月降水有很明显2年、4年、9年和30年左右的周期。并对引起降水异常的大气环流条件进行了研究。华南6月降水与华南沿海低空西南气流有显著正相关。西南气流偏强时,有利于华南气旋性气流辐合加强。加强的索马里跨赤道气流引起西南季风加强。而西太平洋副热带高压的强度和东西位置决定了其北侧华南沿海低空西南气流的强度。华南6月降水与西太平洋副热带高压强度有显著正相关。同时,华南6月降水与西太平洋副热带高压西北侧西风槽强度也有显著正相关。这说明当西太平洋副热带高压偏强和偏西时,华南沿海低空西南气流偏强,华南沿海低空西南气流与西太平洋副热带高压西北侧西风槽带来的冷空气汇合,造成华南低空辐合增加,有利于华南降水。高空急流中存在稳定的长波波列。当华南降水增加(减少)时,在青藏高原西北侧为反气旋(气旋)异常环流,高原东部到我国东部为气旋(反气旋)异常环流,华南高空辐散增加(减少)。

The precipitation of June over South China has significant periods of 2-year,4-year,9-year and 30-year. The circulation anomalies greatly influence the precipitation in June in South China. The precipitation of June over South China has a remarkable positive correlation with the low-level southwesterly flow over coastal areas of South China, indicating that the stronger southwesterly flow over coastal areas of South China is favorable for the flow cyclonic convergence over South China. The intensity and longitudinal position of the subtropical high in the Western Pacific （SHWP） decide the southwesterly flow in its north side. When the SHWP is stronger and extends westward,the southwesterly flow over coastal areas of South China becomes stronger. So the rainfall of June in South China increases. If the cross equator flow around 120°E is stronger, the SHWP is weaker. So the stronger cross equator flow around 120°E is unfavorable for the rainfall of June in South China. The Somali cross equator flow can influence the precipitation of June over the South China through the southwesterly flow. When the Somali cross equator flow is stronger, the rainfall increases. In addition, the precipitation of June over South China is significantly related to the trough in the northwest side of the SHWP. The warm and wet air by southwesterly flow converges with the cold air by the trough over South China continuously, which is favorable for the occurrence of continuous rain. There is a wave train along the jet stream over high level. When the precipitation of June over South China increases, an anticyclonic anomalous circulation locates over the northwest side of the Tibetan Plateau and a cyclonic anomalous circulation situates from the East Tibetan Plateau to East China, high-level divergence over South China increases.