1970—2019年陇东地区强对流天气的 气候特征分析

Climatic Characteristics of Severe Convective Weather in Eastern Gansu During 1970-2019

利用1970—2019年庆阳市8个国家观测站的常规观测资料、联防记录、SRTMDEMUTM 90 m分辨率数字高程和归一化植被指数(NDVI)数据,对雷暴、冰雹和雷暴大风3种强对流天气的气候特征进行对比分析。结果表明:庆阳市不同类型强对流天气的空间分布差异明显,雷暴东南部多,中、西部少。冰雹西北、东南部多中部少;雷暴大风则是中部多,东、西部少。不同强对流天气受下垫面的影响不同,冰雹的空间分布主要与海拔高度有关,两者呈显著的正相关关系,而雷暴大风则与NDVI呈显著的反相关关系。近50年3类强对流天气的范围和日数的年际变化整体呈减少趋势,尤其是21世纪以来减少趋势显著,并先后发生了显著的减少突变。雷暴大风的突变较早,发生在20世纪80年代中期,而雷暴和冰雹的突变较迟,发生于90年代中期前后;月变化基本呈“单峰型”特征,其中雷暴大风的平均日数出现最早为5月,但其平均站数峰值出现在7月;冰雹平均日数和站次的峰值均出现在6月,雷暴大风的峰值出现在7月;日变化呈“午后”型特征,14—19时最频发;白天时段的对流频率是夜间的2倍以上,夜间的对流主要集中在20—22时。

Using conventional observation data from 8 national observation stations in Qingyang city from 1970 to 2019,joint defense record,SRTMDEMUTM 90 m resolution DEM data and annual 1 km normalized vegetation index(NDVI)data,the climatic characteristics of severe convective weather including thunderstorm,hail and gale wind were analyzed.The results indicates that:The spatial distribution characteristics of different severe convective weather are significantly different.There are more thunderstorms in the southwest,fewer in the middle and west;more hails in the northwest,southeast and fewer in the middle,while more thunderstorm gales in the middle,whereas fewer in the east and west.The influence of the underlying surface is disparate in different severe convective weathers.Altitude is the most significant factors on spatial distribution of hail and there is a remarkable positive correlation between them.The distribution of thunderstorm gales is mainly affected by forest vegetation coverage and has a remarkable negative correlation with NDVI.The interannual variation of range and days of the three kinds of severe convective weather shows a decreasing trend in the past 50 years,especially after the beginning of the 21st century,when the significant reduction mutation occurred.The abrupt change of thunderstorm gales occurred earlier in the mid-1980s,while that of thunderstorm and hail occurred later in the mid-1990s.The monthly distribution presents a unimodal type,and the peak of average days and stations among three kinds of severe convective weather shows different.The average days of thunderstorm gales peaked in May,but stations peaked in July.The average days and stations of hail peaked in June,while thunderstorm peaked in July.The daily change is characterized by“after-noon”,with the convective current being the most concentrated from 2pm to 7pm.The frequency of convection in daytime is more than twice that at night,and the convection at night is mainly concentrated from 8pm to 10pm.