【作者】 谷骏；

【导师】 蔡红涛；

【作者基本信息】 武汉大学 ， 空间物理学， 2023， 博士

【摘要】 E层占优电离层（E-Layer Dominated Ionosphere,ELDI）是近年来发现的一种新的电离层异常垂直结构,表现为电离层E层电子密度峰值超过F层峰值、在垂直结构中占主导地位。对ELDL的研究能够加深我们对电离层异常及其背后物理过程的认识,是电离层物理研究的重要内容,对空间天气的预报和电离层短波通讯有着非常重要的意义。本文利用CHAMP/GRACE等电离层掩星观测数据和EISCAT/ESR非相干散射雷达数据系统分析了ELDI的分布特征和形态学特征,并进一步分析了极区ELDI期间的电离层参数变化,结合相关卫星及其他地面设备的协同观测数据研究了ELDI的形成机制。本文的主要研究工作和创新结果包括:一、基于掩星观测的ELDI全球时空分布特征利用CHAMP（2002-2008年）和GRACE（2007-2017）掩星观测提供的电子密度垂直剖面资料,分别考察了太阳活动高/低年期间ELID发生率的时空分布特征,以及其对极区地磁活动（AE指数）的响应特征,主要结果如下:（1）ELDI的全球时空分布特征:ELDI事件主要在夜间被观测到,其在太阳活动低年的发生率要高于太阳活动高年;ELDI发生率表现出明显的季节效应:冬季发生率明显高于夏季,且在太阳活动高年更加突出;ELDI集中发生在高纬地区,南半球的发生率高于北半球,在太阳活动高年表现的更为明显。（2）ELDI对极区地磁活动表现出明显依赖特征:ELDI发生率与AE指数表现出高度的正相关;随着AE指数的增加,太阳活动水平对ELDI发生率的控制作用逐渐减弱。二、基于地面非相干散射雷达观测的极区ELDI形态学特征地面非相干散射雷达可以对同一区域电离层进行长时间的连续观测,这为我们研究ELDI的形态学及其演化特征提供了机会。掩星观测表明ELDI主要发生在高纬地区,因此,本文利用位于北半球极区的EISCAT/ESR雷达在2000-2020年间的电离层观测资料,分析了极区ELDI形态学及其对太阳活动水平的响应特征。主要研究结果如下:（1）ELDI发生率的日变化表现出明显的地域差异:极光椭圆区ELDI的高发区主要集中在夜间;极尖/极隙区的ELDI则主要出现在磁正午前后;日变化分布特征对太阳活动水平的响应并不明显。（2）部分ELDI的形态学参量表现出太阳活动水平依赖:太阳活动低年ELDI期间,极光椭圆区电离层Hm E更低、ELDI的持续时间更长;极尖/极隙区电离层E层厚度更厚、Nm E/Nm F₂更低。三、极区ELDI期间的电动力学效应及机理研究极区电动力学过程是磁层-电离层/热层耦合的重要途径,对极区乃至中低纬电离层形态和演化起着支配作用。E层占优（ELDI）势必会改变极区局地的电离层电导率,进而影响极区电动力学过程。本文以极区电离层电导率为观测量,重点考察了极区低太阳活动水平条件下与ELDI相伴随的电动力学效应。主要结果如下:（1）ELDI事件可以分为以E层密度增强为主的I型ELDI和以F层密度耗空为主的II型ELDI两种类型。在极光椭圆区和极盖区夜间,以I型ELDI为主,电离层Hall、Pederson电导率显著增强,平均增幅分别超过700%和500%;（2）在极尖/极隙区纬度,Ⅰ型ELDI事件高发于夜晚时段,对电导率的增加起主要贡献;Ⅱ型ELDI事件高发于磁正午前后,对电离层电Hall和Pederson导率的贡献较弱。上述结果表明,ELDI对极区电动力学的影响主要集中在夜间。极区高能粒子沉降是电离层E层高度的重要附加电离源,也被认为是ELDI重要形成机制。然而,粒子沉降无法合理解释Ⅱ型ELDI的形成。为此,本文详细剖析了一次持续2.3 h的ELDI事件,探寻其可能的产生机制。根据电子密度变化的不同特征,此ELDI事件可分为两个阶段。主要研究结果如下:（1）第一阶段表现为E层增强,此时F层等离子体温度和密度未发生明显变化,E层电子温度也没有明显变化。E层离子温度大幅上涨超过200%,DMSP卫星也观测到了高能的沉降离子。因此离子沉降是第一阶段ELDI形成的主要原因;（2）第二阶段表现为F层耗空,此时E层等离子体温度和密度较第一阶段未发生明显变化,DMSP卫星观测到高能沉降离子的通量较低而等离子体的水平漂移速度超过了1000 m/s。Super DARN雷达也在ESR雷达附近观测到超过600m/s的等离子体对流,结合前人等离子体对流对F区密度耗空的模拟结果,增强的等离子体对流是第二阶段ELDI形成的主要原因。更多还原

【Abstract】 The E-Layer dominated ionosphere(ELDI)is an anomalous vertical structure of the ionosphere discovered recently,characterized by the peak value of the electron density in E-layer is larger than the peak value of the electron density in F-layer and and dominates the vertical structure.The study of ELD is important aspect of ionospheric physics research,can deepen our understanding of ionosphere anomalous structure and their underlying physical processes.It is of great significance for space weather prediction and ionosphere shortwave communication.This article uses ionosphere occultation observation data of CHAMP/GRACE and incoherent scattering radar data of EISCAT/ESR to analyze the distribution and morphological characteristics of ELDI systematically,analyzes the changes of ionospheric parameters during polar ELDI duration futher,and study the formation mechanism of ELDI by combined with collaborative observation data from relevant satellites and other ground equipment.The main research work and innovative results of this article included:1.The characteristics of ELDI global spatiotemporal distribution based on occultation observationsUsing the vertical profile data of electron density provided by CHAMP(2002-2008)and GRACE(2007-2017)occultation observations,we inspect the spatiotemporal distribution characteristics of ELID occurrence rate during solar maximum and solar minimum respectively,and its response characteristics to polar geomagnetic activity(AE index).The main results are as follows:(1)The global spatiotemporal distribution characteristics of ELDI: ELDI events are observed at night frequently,and the occurrence rate in solar minimum is higher than solar maximum;ELDI exhibits a significant seasonal effect,the occurrence rate of ELDI is larger in winter than in summer,and this seasonal effect is more prominent in solar maximum;ELDI mainly occurs in high latitude regions,and the occurrence of ELDI in the southern hemisphere is higher than that in the northern hemisphere,the characteristics is more visible in solar maximum.(2)ELDI shows a significant dependence on polar geomagnetic activity: The occurrence rate of ELDI is positive correlated with the AE index highly;As the AE index increases,the effect of solar activity level on the occurrence rate of ELDI weakens gradually.2.The morphologicall characteristics of polar ELDI based on incoherent scattering radar observationsIncoherent scattering radar can continuously observe the same area for a long time,which provides the chance for our study in morphological characteristics of ELDI.Occultation observations indicate that ELDI mainly occurs in high latitude regions.Therefore,this article analyzes the morphology characteristics of polar ELDI and its response to solar activity using ionosphere observation data from the EISCAT/ESR radar located in the Arctic region from 2000 to 2020.The main research results are as follows:(1)The daily variation of ELDI occurrence rate shows significant regional differences: the high occurrence rate areas of ELDI in the auroral elliptical region are mainly concentrated at night,the ELDI in the polar cusp mainly occurs around magnetic noon;The response of the daily variation distribution characteristics to the solar activity is not significant.(2)Some morphological parameters of ELDI exhibit significant solar activity dependence: during the solar minimum,the ionosphere Hm E in the auroral elliptical region is lower and the duration of ELDI is longer;The thickness of the ionospheric E-layer in polar cusp is thicker and the Nm E/Nm F2 is lower.3.The electrodynamic effect of E-layer dominated ionosphere in polarThe polar electrodynamic process is an important way of magnetosphere-ionosphere/ thermosphere coupling,plays a dominant role in the morphology and evolution of the ionosphere in polar and even in the middle and low latitudes region.The E-layer dominated ionosphere(ELDI)will change the ionospheric conductivity,and then affect the polar electrodynamic process.This paper takes the polar ionosphere conductivity as the observed measurement,focuses on the electrodynamic effect associated with ELDI under the condition of low solar activity in the polar region,the main results are included as follows:(1)The ELDI events can be divided into Type I ELDI with E layer enhancement and Type II ELDI with F layer depletion.In the auroral elliptical region at night,Type I ELDI is the mainstream,causing the significant increases of Hall and Pederson conductivity,with the mean increases exceeding 700% and500% respectively;(2)In the polor cusp latitude,type I ELDI events occur most frequently at night,making the major contribution to the increase of conductivity;Type II ELDI events occur frequently near magnetic noon and have a weak contribution to ionosphere Hall and Pederson conductivity.The above results indicate that the impact of ELDI on polar electrodynamics is mainly concentrated at night.The high energy particle precipitation in the polar region is important additional ionization source at E-layer ionsphere,and considered as an important mechanism for the formation of ELIDs.However,particle precipitation cannot explain the formation of type II ELDI.Therefore,this paper study an ELDI event that lasted for 2.3 hours in detail and explore its possible formation mechanism.According to the different characteristics of electron density changes,this ELDI event can be divided into two stages.The main results are included as follows:(1)The first stage shows that the E-layer enhancement,while the temperature and density of the F-layer plasma have not changed significantly,and the electron temperature of the E-layer has not changed significantly.The ion temperature of E-layer has increased by over 200%,and the DMSP satellite has also observed high energy ion precipitation.Therefore,ion precipitation is the main cause for the formation of ELDI in the first stage;(2)The second stage shows that the F-layer depletion.At this time,the temperature and density of the E-layer plasma have not changed significantly compared with the first stage.The DMSP satellite observed that the flux of high energy ions is low and the horizontal drift velocity of the plasma exceeds 1000 m/s.The Super DARN radar also observed plasma convection with the speed lager than600 m/s near the ESR radar.Combined with the simulation results of previous plasma convection on the electron density depletion of the F region,the enhanced plasma convection is the main reason for the formation of ELDI in the second stage.更多还原