北京地区闪电活动与气溶胶浓度的关系研究

基于2015—2017年北京闪电定位网(BLNET)总闪资料与35个自动空气质量监测站PM2.5数据,分析了北京地区(39.5°N—41.0°N,115.0°E—117.5°E)夏季(6—8月)闪电活动与PM2.5的时空分布特征,同时针对117次雷暴天气,探讨了气溶胶浓度变化对闪电活动的可能影响.结果表明:PM2.5浓度及总闪密度均呈现自西北向东南升高的空间分布特征.闪电峰值在污染背景下出现的时间(19∶00LT)晚于清洁背景下(15∶00LT)约4h,且总闪百分比(～20%)可达清洁背景下(～9%)的两倍.对雷暴前1～4h的PM2.5浓度与时间窗(12∶00—22∶00LT)内总闪数目的中位数进行相关分析,发现PM2.5浓度低于130μg·m-3时,PM2.5与总闪数存在明显正相关,此时气溶胶可能通过影响云微物理过程进而影响雷暴的对流发展,增强闪电活动;PM2.5大于150μg·m-3时,总闪数随PM2.5浓度的增加呈减少趋势,可能的原因是高气溶胶浓度下地面太阳辐射显著下降,对流活动受到抑制,导致闪电活动减少.当PM2.5浓度在130～150μg·m-3时,两者关系不明显.

Analysis of potential effects of aerosol on lightning activity in Beijing metropolitan region

Based on the lightning data from Beijing Lightning Network (BLNET) and PM_2.5 data from 35 automatic air-monitoring stations, spatiotemporal distributions of total lightning activities and aerosols have been analyzed in Beijing (39.5°N—41.0°N, 115.0°E—117.5°E). The response of lightning activities to aerosols is further investigated for a total of 117 thunderstorm days. The results indicated both spatial distributions of lightning density and pollutant demonstrated a gradual increase from northwest to southeast of Beijing metropolitan region. The peak lightning activity under relatively polluted condition occurred at 19:00 LT (Local Time), 4 hours later than that (15:00LT) under relatively clean condition, higher aerosol concentration enhanced the percentage of total flashes by a factor of ~2. Correlation analysis of PM_2.5 prior to the occurrence of thunderstorms to lightning density showed a significant positive correlation when PM_2.5 lower than 130 μg·m^-3. This is likely because aerosols enhanced lightning activities by affecting the convective activities through microphysical processes. On the contrary, as PM_2.5 exceeded 150 μg·m^-3, total flashes showed a negative relationship to PM_2.5. This might be attributed to lower solar radiation reaching the surface as a result of increasing aerosol loading. When PM_2.5 ranged from 130 and 150 μg·m^-3, the correlation between aerosols and lightning was very weak, which might be caused by the balance of microphysical and radiative effects of aerosols.