Geospace Drivers For The Variations Of Auroral Particle Energy Deposition

The auroral oval is located between 60° and 80° MLAT,where auroral particles precipitate into the ionosphere with subsequent auroral emissions.The precipitating particle producing aurora is called auroral particles.In addition to auroral oval,there exist some localized auroras,which are medium-scale and separated from the main auroral oval.The precipitating particle connects magnetosphere and ionosphere.Investigation on auroral oval and localized aurora is fundamental in understanding the solar wind,magnetosphere and ionosphere coupling.Due to limited observations,previous studies failed to investigate the mechanism responsible for precipitating particle energy such as the dependences of auroral energy flux distribution over the oval on solar wind,IMF and geophysical conditions,as well as the relative influences of solar and geomagnetic activities on the aurora.In the recent years,the ultraviolet imagers on board the TIMED and DMSP satellites provided spatial coverage of auroral observations in the polar region for carrying out investigations mentioned above.The global imaging observations detected different types of localized aurora,including the detached aurora.Investigating this localized aurora would provide a good opportunity for studying solar wind,magnetosphere and ionosphere coupling processes.In this thesis,we combined different imaging observations for auroral studying,such as TIMED/GUVI,DMSPF16/SSUSI,F17/SSUSI and F18/SSUSI.This study focused on the auroral energy distributions inside and outside the auroral oval,and the main results are summarized as follows:(1)The effects of geomagnetic activity was isolated from those of solar flux on the nightside auroral precipitation by combining imaging data from multi-satellites.Using the long-term auroral energy data observed by TIMED/GUVI and DMSP/SSUSI,the calibration coefficients between these imagers were acquired and these observations were combined together.The observations were binned into different geomagnetic and solar activity levels.The results showed that the nightside auroral power was reduced significantly in solar maximum(F10.7=200 SFU)with respect to that under solar minimum(F10.7=70 SFU)for the Kp=1 condition,and this changing rate became less obvious for the Kp=3 condition.(2)The nightside auroral distributions with respect to seasons,geomagnetic and solar activities were investigated.The average auroral energy flux data for the southern hemisphere in 2004-2015 were taken from the DMSP F16/SSUSI.It is found that the auroral energy flux distribution depended strongly on geomagnetic activities under Kp<=4 conditions.As Kp increased,more auroral energy in local winter tended to be deposited in the post-midnight sector.In local summer,the auroral energy flux was mainly influenced by solar activities.It is found that the pre-midnight and post-midnight aurorae responded differently to solar activities,i.e.the pre-midnight aurora increased significantly with increasing solar F10.7 index,whereas the post-midnight aurora depended weakly on solar activities.These results showed that the auroral energy over the nightside oval was redistributed on the average as the season,solar flux and geomagnetic activity change.This would substantially affect the thermosphere and ionosphere at high latitudes.(3)This study reported a subauroral detached proton aurora during the recovery phase of a moderate storm by combining the auroral emission,wave observation and theoretical modeling and revealed the possible wave-particle process for the detached aurora.The aurora was observed under northward IMF Bz condition,occurring between 60° and 65° MLAT simultaneously in both hemispheres,and was located at subauroral latitudes.It was observed by DMSP F16 and POES 19 satellites at the same time.We further analyzed the in situ data from these two satellites and the EMIC wave observed by ground station,modeling the plasmasphere density during the detached aurora event.It is found that the detached aurora in both hemispheres was expected to be conjugate.Interestingly,the detached aurora was dominated by protons/ions with energies ranging from around 20 keV to several hundreds of keV,without obvious electron precipitations.It is suggested that the increasing solar wind pressure compressed the energetic protons of the ring current and excited EMIC waves which are interacting with hot ions in the ring current during the recovery phase of a storm.By losing energy to EMIC waves the energetic protons(>20 keV)were scattered into the loss cone and produced the rarely observed detached proton auroras.The present work provides a new understanding for the auroral particle distribution.The variations of auroral distribution would change Joule heating at the polar region,influencing high-latitude ionosphere and thermosphere effectively.This work gives an important basis for studying the coupling process in solar wind,magnetosphere,ionosphere and thermosphere.It provides instructions for the location to detect strong auroral precipitations outside the oval and constructing precipitating particle models.DMSP and other possible satellites will be used to investigate detached auroras in the future work.The relationships and differences between different types of detached auroras will be explored.We will further investigate the solar wind,magnetosphere and ionosphere coupling through these auroral events.Combining the observations of ionosphere and thermosphere,we will carry out the studies in the change of auroral distribution and the ionosphere/thermosphere responses associated with large-scale auroral arcs.The coupling mechanism among the solar wind,magnetosphere,ionosphere and thermosphere will be examined.