太行山东麓对流风暴下山演变气候特征

Climatic Characteristics of Convective Storms Moving from Taihang Mountains to North China Plain

影响北京和河北的对流风暴多半由太行山山区移来,为增加对从太行山东麓下山的对流风暴强度变化和维持时间等演变特征的了解,基于全国雷达组合反射率因子拼图,对2011—2020年10年期间暖季太行山东麓对流风暴下山演变的气候特征进行了统计分析。结果表明:下山对流风暴在石家庄北部、北京南部、保定中南部和沧州市西部存在≥45 dBz的强回波高频中心,且下山对流风暴常在石家庄北部近山平原和沧州西部显著增强;对于下山增强的对流风暴,17时前后在山区最为活跃,18时至次日02时主要影响平原地区;对流风暴来向越偏西,下山对流风暴数越多,下山增强的对流风暴比例越高,移速也越快;下山过程中,大多数对流风暴变得更强和更加具有组织性,下山初始时刻回波强度≥45 dBz的对流风暴86%能成功下山,其中水平尺度大于100 km、结构密实的强对流风暴超过90%能成功下山;下山增强的样本在下山过程中风暴的强回波面积急剧扩大,到达平原前一个时刻其面积约为初始面积的3倍,在平原地区继续发展后其平均面积可达到初始面积的4.6倍;下山增强的对流风暴大多下山用时仅为1~2 h,而影响平原的时长可持续4~8 h,影响平原时长4~8 h的对流风暴的风暴类型以线性MCS(47%)和非线性MCS(30%)为主。

A relatively large number of the convective storms which affect Beijing and Hebei can often be traced to the Taihang Mountains.This study analyzes warm-season convective storms developing in the eastern foothills of the Taihang Mountains during 2011-2020.The statistical analysis is based on the national composite radar reflectivity factor data mosaics to increase the understanding of the evolution of these convective storms,including the changing of intensity,lifespan and so on.The results show that there are four high-frequency centers with strong echoes≥45 dBz located in northern Shijiazhuang,southern Beijing,south-central Baoding and western Cangzhou.The storms often strengthen significantly in the foothills of northern Shijiazhuang and western Cangzhou.For the strengthened convective storms,they are most active in mountainous areas around 17:00 BT and mainly affect plain areas between 18:00 BT and 02:00 BT.The more westerly the path,the more cases of mountain-to-plain convective storms,the higher the percentage of convective intensification,and the greater the moving speed.During the downhill process,most convective storms become stronger and more organized.For the convective storms whose echo strength≥45 dBz at the initial moment of going downhill,more than 86%of them can successfully reach the plains,and more than 90%of them with horizontal scale exceeding 100 km and solidly connected structures can successfully reach the plains.The strong echo areas of the strengthened convective storms expand dramatically as they go downhill.Strong echo areas expand to about 2 times larger than their initial echo areas when they reach the foothill,and the average areas in the plains can reach 4.6 times as big as their initial echo areas.Most of the strengthened convective storms take only 1-2 hours to go downhill and last 4-8 hours on the plains.The storm types of the convective storms which last 4-8 hours on the plains are dominated by linear MCS(47%)and nonlinear MCS(30%).