In this study, the ground potential rise(GPR) phenomenon caused by a lightning current injected into a field-shaped artificial grounding grid, as well as the potential difference between two different nodes at the edg...In this study, the ground potential rise(GPR) phenomenon caused by a lightning current injected into a field-shaped artificial grounding grid, as well as the potential difference between two different nodes at the edge of the grounding grid, was observed and analyzed under artificially triggered lightning conditions. Based on circuit theory and measured current data, a π-equivalent circuit was established to simulate the transient response of the grounding grid.Nineteen return strokes from three artificially triggered lightning events were analyzed. The peak currents of the 19 return strokes range from -6.7 to -25.1 kA, and the mean value was -14.3 kA. The GPR decreased rapidly and formed a subpeak after reaching the initial peak, with the mean value of the initial peak being -148.65 kV and the mean value of the subpeak being -92.87 kV. The GPR induced by the triggered lightning currents exhibited a subpeak phenomenon. Simulation results indicate that the subpeak phenomenon is related to localized corrosion of the vertical grounding electrode. The potential difference at the grounding grid edge exhibited a multi-pulse waveform with alternating polarity, dominated by positive pulses. The peak values of both the positive and negative polarity pulses gradually decreased, with the first positive pulse displaying a significantly higher intensity than that of subsequent pulses.展开更多
随着城市人口密度的不断增长和城市化进程的加快,城市生态系统已成为影响全球气候变化的热点区域。但是,城市草地作为城市生态系统的重要组成部分,其对土壤—大气CO_(2)和CH_(4)交换过程的影响尚不明确。为此,本文依托北京城市绿地生态...随着城市人口密度的不断增长和城市化进程的加快,城市生态系统已成为影响全球气候变化的热点区域。但是,城市草地作为城市生态系统的重要组成部分,其对土壤—大气CO_(2)和CH_(4)交换过程的影响尚不明确。为此,本文依托北京城市绿地生态系统定位观测研究站,采用静态暗箱—气相色谱方法对三种典型城市草地类型[即以C_(4)草种(光合作用中CO_(2)被固定为三碳和四碳化合物)为主的暖季草地和以C_(3)草种(光合作用中CO_(2)被固定为三碳化合物)为主的冷季草地与林下地被]的土壤CO_(2)排放和CH_(4)吸收通量及其辅助环境因子进行了一个完整周年的田间原位观测研究。结果表明,三种城市草地类型的土壤CO_(2)排放和CH_(4)吸收通量在整个观测期内具有相似的季节变化动态。城市草地土壤CO_(2)排放的季节变化主要受土壤温度和土壤水分含量变化的影响,二者的协同作用可以解释土壤CO_(2)排放变化的77%~87%;而城市草地土壤CH_(4)吸收通量的变化主要受土壤水分含量的影响,且两者之间呈显著负相关关系。在全年尺度上,三种城市草地类型的土壤CO_(2)年排放量在12.1~15.2 t C ha^(-1)a^(-1)之间,其土壤CH_(4)年吸收量范围为3.71~4.27 kg C ha^(-1)a^(-1)。尽管城市草地非生长季的低温通常会抑制微生物活性而降低土壤呼吸和CH_(4)吸收强度,但结果显示非生长季土壤CO_(2)排放和CH_(4)吸收量分别占全年总量的10%~18%和39%~51%,突出了开展完整周年观测研究的重要性。对比三种城市草地类型,以C_(4)草种为主的暖季草地相较于冷季草地和林下地被(二者均以C_(3)草种为主)具有明显较高的土壤CO_(2)年排放量,同时显著降低了土壤CH_(4)年吸收量,这与各草地植被特性以及土壤性质的差异有关。综上,该研究结果表明种植C_(3)草种有利于城市草地土壤—大气CO_(2)和CH_(4)交换过程的减排增汇,这将有助于合理规划和利用城市草地,以缓解快速城市化对气候变化所带来的影响。展开更多
基于2024年5月10日和20日在丹江口水库汇水区开展的针对气溶胶和积层混合云的两次飞机观测,利用机载探测资料,分析了水库汇水区气溶胶和云微物理量的垂直分布特征。结果表明,气溶胶数浓度总体随高度的增加呈下降趋势,与白天相比,夜晚近...基于2024年5月10日和20日在丹江口水库汇水区开展的针对气溶胶和积层混合云的两次飞机观测,利用机载探测资料,分析了水库汇水区气溶胶和云微物理量的垂直分布特征。结果表明,气溶胶数浓度总体随高度的增加呈下降趋势,与白天相比,夜晚近地层气溶胶浓度更高,最高达4000 cm^(-3)。中低层气溶胶中值体积直径约为0.2~0.3μm,有效直径约为0.6~0.8μm。气溶胶粒子主要集中在小粒径段,粒子谱为多峰分布,第一峰值直径为0.14μm。云内气溶胶浓度基本都略低于云外,而更强的吸湿增长作用导致气溶胶粒径更大。气团后向轨迹分析结果表明,近地层气溶胶粒子主要来自局地排放,高层粒子主要来自远距离传输,5月10日观测点周围人为排放产生的污染性细颗粒物是造成近地层气溶胶浓度高于5月20日的主要原因。两次观测的积层混合云内的云滴有效直径整体均在25μm以内,云滴数浓度最大值分别为118 cm^(-3)和205 cm^(-3),5月10日和20日云内液水富集层分别在6100 m和5500 m左右,液水含量最大值分别为0.44 g m^(-3)和0.78 g m^(-3)。由于气溶胶粒子竞争水汽的作用,云底附近的较高气溶胶浓度使得云滴浓度出现高值,同时云滴直径减小。小云滴阶段粒子谱为单峰分布,不同高度的峰值粒径略有差异,主要集中在11~25μm,雨滴和冰晶阶段粒子谱转变为多峰分布。展开更多
基金National Natural Science Foundation of China(42575091)Marine Meteorological Science and Data Center Program (2024B1212070014)。
文摘In this study, the ground potential rise(GPR) phenomenon caused by a lightning current injected into a field-shaped artificial grounding grid, as well as the potential difference between two different nodes at the edge of the grounding grid, was observed and analyzed under artificially triggered lightning conditions. Based on circuit theory and measured current data, a π-equivalent circuit was established to simulate the transient response of the grounding grid.Nineteen return strokes from three artificially triggered lightning events were analyzed. The peak currents of the 19 return strokes range from -6.7 to -25.1 kA, and the mean value was -14.3 kA. The GPR decreased rapidly and formed a subpeak after reaching the initial peak, with the mean value of the initial peak being -148.65 kV and the mean value of the subpeak being -92.87 kV. The GPR induced by the triggered lightning currents exhibited a subpeak phenomenon. Simulation results indicate that the subpeak phenomenon is related to localized corrosion of the vertical grounding electrode. The potential difference at the grounding grid edge exhibited a multi-pulse waveform with alternating polarity, dominated by positive pulses. The peak values of both the positive and negative polarity pulses gradually decreased, with the first positive pulse displaying a significantly higher intensity than that of subsequent pulses.
文摘随着城市人口密度的不断增长和城市化进程的加快,城市生态系统已成为影响全球气候变化的热点区域。但是,城市草地作为城市生态系统的重要组成部分,其对土壤—大气CO_(2)和CH_(4)交换过程的影响尚不明确。为此,本文依托北京城市绿地生态系统定位观测研究站,采用静态暗箱—气相色谱方法对三种典型城市草地类型[即以C_(4)草种(光合作用中CO_(2)被固定为三碳和四碳化合物)为主的暖季草地和以C_(3)草种(光合作用中CO_(2)被固定为三碳化合物)为主的冷季草地与林下地被]的土壤CO_(2)排放和CH_(4)吸收通量及其辅助环境因子进行了一个完整周年的田间原位观测研究。结果表明,三种城市草地类型的土壤CO_(2)排放和CH_(4)吸收通量在整个观测期内具有相似的季节变化动态。城市草地土壤CO_(2)排放的季节变化主要受土壤温度和土壤水分含量变化的影响,二者的协同作用可以解释土壤CO_(2)排放变化的77%~87%;而城市草地土壤CH_(4)吸收通量的变化主要受土壤水分含量的影响,且两者之间呈显著负相关关系。在全年尺度上,三种城市草地类型的土壤CO_(2)年排放量在12.1~15.2 t C ha^(-1)a^(-1)之间,其土壤CH_(4)年吸收量范围为3.71~4.27 kg C ha^(-1)a^(-1)。尽管城市草地非生长季的低温通常会抑制微生物活性而降低土壤呼吸和CH_(4)吸收强度,但结果显示非生长季土壤CO_(2)排放和CH_(4)吸收量分别占全年总量的10%~18%和39%~51%,突出了开展完整周年观测研究的重要性。对比三种城市草地类型,以C_(4)草种为主的暖季草地相较于冷季草地和林下地被(二者均以C_(3)草种为主)具有明显较高的土壤CO_(2)年排放量,同时显著降低了土壤CH_(4)年吸收量,这与各草地植被特性以及土壤性质的差异有关。综上,该研究结果表明种植C_(3)草种有利于城市草地土壤—大气CO_(2)和CH_(4)交换过程的减排增汇,这将有助于合理规划和利用城市草地,以缓解快速城市化对气候变化所带来的影响。
文摘基于2024年5月10日和20日在丹江口水库汇水区开展的针对气溶胶和积层混合云的两次飞机观测,利用机载探测资料,分析了水库汇水区气溶胶和云微物理量的垂直分布特征。结果表明,气溶胶数浓度总体随高度的增加呈下降趋势,与白天相比,夜晚近地层气溶胶浓度更高,最高达4000 cm^(-3)。中低层气溶胶中值体积直径约为0.2~0.3μm,有效直径约为0.6~0.8μm。气溶胶粒子主要集中在小粒径段,粒子谱为多峰分布,第一峰值直径为0.14μm。云内气溶胶浓度基本都略低于云外,而更强的吸湿增长作用导致气溶胶粒径更大。气团后向轨迹分析结果表明,近地层气溶胶粒子主要来自局地排放,高层粒子主要来自远距离传输,5月10日观测点周围人为排放产生的污染性细颗粒物是造成近地层气溶胶浓度高于5月20日的主要原因。两次观测的积层混合云内的云滴有效直径整体均在25μm以内,云滴数浓度最大值分别为118 cm^(-3)和205 cm^(-3),5月10日和20日云内液水富集层分别在6100 m和5500 m左右,液水含量最大值分别为0.44 g m^(-3)和0.78 g m^(-3)。由于气溶胶粒子竞争水汽的作用,云底附近的较高气溶胶浓度使得云滴浓度出现高值,同时云滴直径减小。小云滴阶段粒子谱为单峰分布,不同高度的峰值粒径略有差异,主要集中在11~25μm,雨滴和冰晶阶段粒子谱转变为多峰分布。
