青藏高原冬季积雪与华南前汛期降水年际变率的联系

Connections between winter snow depth over the Tibetan Plateau and the interannual variation of precipitation during the first rainy season in South China

利用1979—2018年青藏高原(简称高原,下同)卫星积雪数据集、华南地区261站逐日降水及ERA5再分析资料,探讨了高原冬季积雪与华南前汛期降水的联系。结果表明:1)高原西部积雪与华南前汛期降水的正相关关系最为稳定,其主要影响前汛期的锋面降水,对夏季风降水的影响较小;2)华南前汛期在高原西部积雪偏多年比偏少年偏早20 d,使得前汛期降雨日数偏多,持续时间偏长,总降水量偏多,而降水强度受积雪的影响较小;3)高原积雪偏多年,积雪的冷却作用形成了低层异常反气旋环流,而东亚沿岸为“+-+”的位势高度异常,中纬度“西高东低”的环流配置有利于中高纬冷空气南侵,使得华南上空温度偏低,同时偏强偏南的西太平洋副热带高压加强了低纬地区偏南气流和水汽输送。3—4月锋面在华南北部南北摆动,4月初偏北干冷空气南侵和偏南暖湿气流的持续北推使得锋面加强,触发了前汛期的较早建立;积雪偏少年冷空气和偏南暖湿气流均较弱,华南北部锋面在4月初中断,4月中下旬华南北部锋面在偏北弱冷空气和偏南暖湿气流的共同作用下重新建立,从而华南前汛期开始偏晚。

Based on satellite-derived snow depth(SD)over the Tibetan Plateau(TP),daily rainfall data from 261 meteorological stations in South China(SC),and the ERA-5 reanalysis dataset during 1979—2018,the relationships between TP winter snow depth and precipitation during the first rainy season(FRS)in SC are investigated in this study.The results show that:1)The connections between SD over the western TP and precipitation during the FRS in SC are the most robust,and TP SD mainly affects frontal precipitation during the FSR,whereas it shows less impact on summer monsoonal rainfall.2)The onset date of the FRS in above-normal TP snow years is about 20 days earlier than that in below-normal snow years,leading to more rainy days,a longer FRS,and more rainfall during the FRS.However,rainfall intensity during the FRS shows little difference between different types of TP snow years.3)The TP is colder in an above-normal snow year,and the cooling effect stimulates abnormal anticyclonic circulation over the TP.However,tripole anomaly patterns of the 500 hPa geopotential height occur in the East Asian coastal region.The circulation configurations facilitate cold air invading SC in middle-high latitude regions,making SC colder.The enhanced northwest Pacific subtropical high intensifies the low-level southerly flow and water vapor supplement.The front swings northward-southward in northern SC during March and April.The FRS is established once the dry,cold,northerly flow and the warm,wet,southerly flow invade the SC in early April.In below-normal TP snow years,both the cold northerly and warm southerly flow are weak and inactive,and the front over northern SC is interrupted in early April.When the northerly and southerly flow invades the SC in mid-to-late April,the front is reverted and the FRS in the SC occurs later.