Study On Low-and Mid-latitudinal Ionospheric Irregularity Based On Ground-based And Satellite Observations

In this dissertation,we combined ground-based two Digisonde,a VHF radar,and a GPS-TEC monitor from Chinese Meridian Project,and the Communication/Navigation Outage Forecasting System(C/NOFS)satellite,and used plenty of airglow data from an all-sky airglow imagers(ASAIs)network to study low-latitudinal equatorial plasma bubbles(EPBs)and mid-latitudinal mesoscale traveling ionospheric disturbance structures(MSTIDs)occurring in China.This dissertation mainly includes three parts:In part one,we study evolution processes of a group of EPB depletions simultaneously observed by two ASAIAs,one at Dax,Guangxi,and one at Quj,Yunnan.The Digisonde and VHF radar in Fuk,Hainan,and C/NOFS satellite were also used to study this event.The EPB event generated in local geomagnetic equatorial region and extended poleward at sunset.In the almost same time spans and geographical longitudes,C/NOFS observed a periodic plasma density depletion structures(PDDs)with a wavelength of 450 km and a longitudinal extension of 2250 km at the geomagnetic conjugation part of the EPB airglow structures.In this event,a southwestward motion of an extremely bright airglow region(SMEBAR)was first found.This structure was a high plasma density enhanced region living in the equatorial ionization anomaly(EIA)crest or EIA crest itself.However,characteristics of this SMEBAR are different from that of the plasma blobs in previous literature.The averaged electron density of the SMEBAR increased by only 50% of the background.The SMEBAR propagated southwestward,but the reported blobs propagated eastward.Both EIA crest and SMEBAR can have eroded the EPB airglow depletion structures.They can feed high plasma density into the EPB airglow depletions,and made depletions became bright airglow structures or disappeared eventually.When the periodic EPB airglow depletions passed over the Digisonde,periodic satellite traces(ST)occurred.Occurrences of STs suggest that the EPB event could develop from ionospheric bottomside large-scale wave-like structures(LSWS).C/NOFS observations also indicate that post-sunset rise(PSSR)cannot play a dominant role in triggering this event.This is the first time that the simultaneous ASAIs,Digisonde,VHF radar,and C/NOFS satellite are used to study a large-scale EPB event likely resulted from the bottomside LSWS.In part two,airglow data collected by four ASAIs located at Fuk,Hainan,Dax and Guip,Guangxi,and Quj,Yunnan during 2012-2014 was used to do the statistical study of EPBs.This statistic includes: daily and seasonal variations of EPB occurrence,EPB eastward drift velocities,EPB poleward magnetic latitudinal extensions(PMLEs),spacing between adjacent EPB depletions,longitudinal extension of an EPB group,and EPB tilt characteristics.EPBs mainly occur during21:00-00:00 local time(LT)in equinoxes.There is an asymmetry in occurrence rates between March(June)and September equinoxes(December solstices).Most EPBs occur in groups of two to six depletions.The distance between adjacent EPB depletions is ~100-700 km,and the average is 200-300 km.The zonal extension of an EPB group is usually less than 1500 km but can reach 3000 km.EPBs usually have a maximum drift velocity near 100 m/s at 21:00-22:00 LT in 9.5°-1.5° geomagnetic latitude and then decrease to 50-70 m/s toward sunrise.The averaged westward tilt angle of most EPBs(with respect to the geographic north-south)increased from5°-10° to 23°-30° with LT between 20:00 and 03:00 LT,then decreASAIng to10°-20° toward sunrise.The EPB occurrence patterns and zonal drift velocities are significantly different from those at Kolhapur,India,which locates west to our stations by 20.0°-32.0° in longitude.The significance of this study is that we first systemically investigate statistical features of EPB airglow structures by using an all-sky imager network in the ASAIan region.In addition,this study helps us understanding the formative and evolutionary process of EPBs.In part three,we used the ASAI and Fabry-Perot Interferometer(FPI)at Xinglong,the Digisonde at Shisanling,GPS-TEC monitor at Nanmeng(BJNM),Beijing to study a MSTID event accompanying with mesoscale field-aligned irregularity structures(FAIs)(~ 150 km).The mesoscale FAIs were generated in anairglow depletion front of the MSTIDs propagating southwestward.The airglow depletion front occurred in an ionospheric uplifted region,and a depleted region of GPS-TEC oscillation structure with a period of 2.0 hour.The mesoscale FAIs resulted in a GPS-TEC high-frequency oscillation with a period of 15.0 min.Two-dimensional normalized cross-correlation analysis indicates that the FAIs had a relative velocity almost parallel to the depletion front of the MSTIDs.Relationship of the mesoscale FAIs with MSTIDs is the same as that of meter-scale FAIs with MSTIDs in previous radio wave studies.Note that this is the first time to directly grasp FAIs with scale of150 km from airglow images by using picture technique in the word.This study helps us furthermore understanding the formative mechanism of ionospheric irregularity at mid-latitude.