| 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. |
