电离层电子密度剖面和特征参数对两次日食事件的响应研究

Ionospheric electron density profiles and their characteristic parameters in response to two solar eclipse events

本文利用亚洲和美洲地区多个测高仪台站的观测,并结合三维电离层-热层耦合理论模型进行数值模拟,对2020年6月21日和2017年8月21日两次日食事件期间电离层电子密度剖面的变化特征进行分析,并探讨这两次事件中日食效应的异同及形成机制.分析结果表明,在这两次日食期间,位于电离层低高度的E层和F1层的电子密度变化与太阳辐射的变化基本同步;且F1层峰值密度的日食响应幅度大于E层.该结果与以往观测一致,且日食响应无明显的经度变化.进一步地,通过分析观测和模拟结果中电子密度日食衰减效应的高度变化和时延特征,我们发现:(1)观测和模拟结果均表明,食甚时电子密度的最大相对衰减的位置一般不在F1层峰的位置,而是在其上方约几十公里的高度;模拟结果显示该现象是由日食期间F1层上方光化学过程与动力学过程共同作用导致;(2)在中纬地区,在F2层峰附近及以上区域中电离层电子密度最大日食衰减相对太阳辐射变化的时延具有显著的经度变化,其相对衰减在亚洲地区随高度增加而减少,在北美地区随高度无明显变化,与以往报道的欧洲地区随高度增加而增加的趋势也不同;(3)日食电子密度衰减时延的高度变化受到日食发生的地方时的显著影响,如上午时段与午后时段的响应有明显不同.模拟结果表明F2层峰及以上高度的日食效应受到中性风和双极扩散的影响较大,而受电场漂移的影响相对较小;模拟结果同时显示在午后这些动力学输运过程及其日食响应比在午前更强,该现象与午前和午后背景电子密度的大小差异有关.这可能是观测到的日食电子密度衰减时延的高度依赖具有经度变化的原因.

In this work,the ionosonde observations in Asia and North America and the numerical simulations are used to analyze the variation of the ionospheric electron density profiles and their characteristics,in response to the two solar eclipses occurring on June 21,2020and August 21,2017.For these events the similarities and differences in the responses of the ionospheric electron density profiles and their physical mechanisms are discussed.The results show that the variations of the electron density in E and F1layers are synchronous during these two solar eclipses.The relative decrease of the electron density in the E and F1layers during eclipses has a positive correlation with the solar radiation flux changes.These results are consistent with the previous observations and do not show obvious longitudinal variations.In addition,we analyze the altitudinal variations and the time delay of the maximum electron density decrease in response to the peak solar radiation reduction from the observational and simulation results.The main results are summarized as follows.(1)Both the observational and simulation results show that the maximum relative electron density decrease during the solar eclipse generally occurs at a few tens of kilometers above the F1layer peak.(2)The time delay of the electron density reduction in the mid-latitude ionosphere for the altitude near and above the F2layer peak has obvious longitudinal variations.The delayed time decreases with altitude in Asia and has little change with altitude in North America.(3)The delayed time of the electron density in response to the solar eclipse is significantly affected by the local time of the eclipse totality.For example,the response time in the morning and the afternoon is significantly different.The simulation results show that the eclipse effect near and above the F2layer peak is largely caused by plasma drifts due to neutral winds and diffusion,while is less affected by electric field drifts.The simulation results also show that these dynamic processes and their eclipse responses are stronger in the afternoon than in the morning,which is related to the larger magnitude of the background electron densities in the afternoon than in the morning.This may explain why the altitudinal variations and the time delay of the electron density profiles exhibit longitudinal variations in response to the solar eclipse.