Observational Characteristics Of Dayside Poleward Moving Auroral Forms And Its Generation Mechanisms

Solar wind energy and momentum can access the magnetosphere via the daysidepolar region, where field lines map directly to the dayside magnetopause and boundarylayers and various auroral transients occur with different spectrum, luminosity anddynamics. These dynamic processes manifest the intrinsic relation between the auroralcharacteristics and magnetospheric boundary layers.Based on the high temporal resolution auroral observation data obtained from thethree-wavelength all-sky imagers at Yellow River Station in the Arctic, together with thesatellites’ observations for particles and solar wind and the radars’ observations, westudy the dayside poleward moving auroral forms (PMAFs) as well as its generationmechanisms. PMAF is one of the primary auroral forms in the magnetic local time(MLT) range of0900-1500MLT. The main results are summarized as follows:1) We investigated the quantitative relationship between the auroral intensities and theenergy features of the precipitated particles near magnetic noon by using auroraldata and particles data from DMSP satellites. Our statistical results indicated thatthe soft auroral electron precipitation was dominated during10-13MLT,corresponding to630.0nm auroral emissions. The auroral intensity ratioI(630.0nm)/I(427.8nm) decreased as the intensity of427.8nm increased over13-14MLT, suggesting the energy of the precipitated particles increased. In addition, theintensity of427.8nm depended on the total energy flux of the precipitating electronsand the I(630.0nm)/I(427.8nm) ratio related to the average energy. We have built aparameter model of auroral emissions and particle precipitation near magnetic localnoon at YRS, which may benefit monitor the space weather service in the future.2) Using auroral data at YSR together with the ESR radar and SuperDARN radars, weinvestigated the dayside PMAFs and the associated plasma features in the polarionosphere under different interplanetary magnetic field (IMF) conditions, between0900and1010UT on22December2003. Simultaneous optical and ESRobservations revealed that all of these PMAFs were clear associated with pulsedplasma precipitations. During northward IMF, the plasma can precipitate into loweraltitudes and reach the ionopheric E-region, and there is a reverse convection cellassociated with these PMAFs, which is one of the typical signatures in the polarionosphere of the dayside high-latitude (lobe) reconnection. These results indicatethat the PAMFs may due to the high-latitude reconnection. During southward IMF,the PAMFs observed at YRS show larger latitudinal motion, indicating a longermean lifetime, and the associated ionopheric features indicate that the PMAFs were generated by the dayside magnetopause low-latitude reconnection.3) We examined the dependence of the PMAF occurrence on solar wind conditions inthe MLT range of0900-1500MLT. It was found that most PMAF events occurredduring southward IMF and the PMAFs show a tendency to occur preferentiallyunder large IMF|Bx|conditions. The MLT dependence of PMAFs presents aremarkable tendency of decreasing in the midday sector, showing a clear IMFBy-related prenoon-postnoon asymmetry. For the first time, we found, however,that the asymmetry is more evident during conditions of Bz>0than Bz <0,suggesting the importance of the effect of the lobe reconnection. It is worth notingthat the PMAFs occurrence maximized when the IMF clock angle was near90°inthe prenoon and near270°in the postnoon, which might due to theprenoon/postnoon anti-parallel reconnection. We also found that62.12%PMAFsoccurred during the clock angle of90°-270°in the midday sector, which might dueto component reconnection.The dependence of PMAFs in the midday sector mightdue to component reconnection. Our statistical results suggest that the PMAFs arenot caused by the solar wind pressure pulses, but by bursts of magneticreconnection.4) Further, we statistically investigated the dependence of location of PMAFs on theIMF Bz and By components as a function of MLT and MLAT under stable IMFconditions. It was found that more PMAFs occurred in lower latitude for Bz <0andthere was less evident IMF By-related prenoon-postnoon asymmetry for Bz>0than for Bz <0. We found that the PMAFs distributed over a wide range of MLTwhen Bz <0, which indicates that the reconnection X-line might spread like an ‘S’shape. However, during northward IMF, PMAFs were observed predominantlyprenoon for IMF By>0and postnoon for IMF By <0associating with the effect ofthe high-latitude reconnection, which is highly consistent with the theoreticalconvection model.In this thesis, the features and mechanism of the PAMFs have been systematicallystudied. We revealed some new features and formed some new understanding aboutPMAFs. It is so complicated for the dayside PMAFs and their dynamic effect that thefine structures, detailed evolution and the associated polar ionosperic responses stillneed to be further studied.