大气电场倒转与突发钠层及突发E层的相关性

突发钠层(Sporadic Sodium Layer, Na_S)是中高层大气金属层最为显著的一种现象,其发生机制目前尚无定论。突发E层(Sporadic E layer, E_S)是等离子体密度异常增大的薄层,被认为与Na_S密切相关。为进一步研究Na_S及E_S事件之间相关性及影响因素,利用中国科学院“子午工程”2010～2018年合肥科大站宽带钠荧光共振激光雷达观测结果,并结合武汉左岭镇站数字测高仪及九峰站大气电场仪数据,分析大气电场倒转(即北向电场)对Na_S以及E_S事件的影响。在统计的91例Na_S事件中,发生于大气电场倒转时的比例为20/91; 同时,在发生Na_S事件的事例中,E_S消失或中断的比例较大(14/20),表明E_S可能以提供钠源的形式转化为Na_S。此外,在分析武汉左岭镇站数字测高仪数据的同时进行概率统计,结果表明:当大气电场倒转时,E_S临界频率减小甚至消失的概率较大(187/242),少数情况下可能造成临界频率增大甚至激发E_S生成(55/242); E_S虚高消失比例为179/242,E_S不变比例为27/242,E_S上升比例为23/242。综上所述,大气北向电场在一定程度上对E_S事件的发生有抑制作用,并对E_S事件的发生高度有明显影响。最后,对一种与电场倒转相关的突发钠层机制也进行了讨论。

Correlation Between Atmospheric Electric Fields Overturning and Mesospheric Sporadic Thin Layers

Sporadic sodium layer(Na_S)is the most significant phenomenon in the metallic layer of the middle and upper atmosphere, whose mechanism has not been determined. Sporadic E layer(E_S)is a thin layer with abnormal increase of plasma density on the ionospheric E layer, which is considered to be closely related to Na_S. For further study of influence factors and correlation between Na_S and E_S, the observation results of a fluorescent scattering LIDAR and a nearby narrowband temperature/wind LIDAR at Hefei station by Chinese Meridian Project, combined with an ionosonde at Zuolingzhen station and an atmospheric mill at Jiufeng station in Wuhan, were used to analyze the effects of atmospheric electric field overturning(i.e. northward electric field)on Na_S and E_S. Among the 91 Na_S events, the ratio of atmospheric electric field overturning is 20/91. At the same time, in the cases of Na_S occurrence, the ratio of E_S disappearance or interruption is higher(14/20), suggesting that E_S may be converted into Na_S in the form of sodium source. In addition, the data from the ionosonde at Zuolingzhen station in Wuhan were analyzed and the probability statistics were made. The results show that when the atmospheric electric field is overturned, the critical frequency of E_S has a large probability of reduction or disappearance(187/242), and in a few cases, it may even incite E_S production(55/242).The visual height of E_S disappears at a ratio of 179/242, the constant ratio is 27/242, and the increasing ratio is 23/242.The statistical results show that the atmospheric northward electric field can inhibit the E_S occurrence to a certain extent, and has a significant effect on the occurrence height of E_S. Finally, a mechanism related to electric field overturning for Na_S is discussed.