Study On Morphological Character Of Dayside Diffuse Aurora

Diffuse aurora mostly appears at the equatorward of aurora oval ofmidnight-morning-midday, which was believed that more than half ofthe polar auroral energy has relation with. Study of the diffuse auroracan help us to understand the polar space weather process comp-rehensively, and it is also very important to establish and improve thedynamics models of space physics. Using the long-time continuousobservation data obtained at Yellow River Station (YRS), we will makestatistical and case studies on the dayside diffuse aurora. The mainresults are summarized as follows:The typical morphological classification of dayside diffuse auroraAccording to the dayside diffuse auroral morphology, we dividedinto four primary categories:1) Veiling Diffuse Aurora (VDA), whichhas no obvious morphological structure and clear boundaries, sometimeslike a thick cloud cover the entire sky;2) Patch Diffuse Aurora (PDA),which usually occurred accompany with pulsating aurora. PDA occurredwith vary scale in size, mostly in~10-100km diameter width, occasio-nally size will reach hundreds kilometer, which often appeared in the su-rrounding VDA background;3) Diffuse Aurora Arc (DAA), which hasobvious difference from the discrete auroral arcs in morphology. Theluminosity of DAA is weaker than that of discrete auroral arc. It oftenappears with fuzzy boundary;4) Pulsating Aurora (PA), occurred withsparkling forms. When the PDA and DAA occurred, the luminousintensity showed a periodic change.Morphology distribution and distribution character research ofdayside diffuse auroraWe statistically studied the occurrence rate of the different kinds of diffuse aurora with MLT and found that the occurrence of each type ofdiffuse aurora shows a unimodal distribution. The four peaks of theoccurrence are occurred mostly at cusp region, which are easy to appearat the same time and the patterns are more complex. The duration time ofpulsating aurora were affected by the solar wind, which is markedlydifferent from the nightside pulsating aurora. The nightside diffuseaurora and pulsating aurora were caused by the Chorus scattering. Weinvestigated different diffuse aurora morphology with the differencesinterplanetary magnetic field conditions. We found that the daysidediffuse aurora mostly appear in IMF B_z>0(65%). As B_z and B_ycomponents were predominantly positive and negative, respectively. Itcould be expected that the diffuse auroral configuration would be morelikely observed, especially at the0600-1400MLT. Compared with thesouthward IMF, the northward IMF make field-aligned currents (FACs)are located at the higher latitude; Furthermore, a variational IMF Byassociated with an upward FAC at the lower latitude boundary in thenorthern hemisphere is preferable for the influence of ionospheric pla-sma flows with east-west directions.Dayside diffuse aurora response to an increase of solar winddynamic pressureThe diffuse aurora, which is excited by high-energy particles ofmagnetosphere precipitating into the upper atmosphere and impactingwith the neutral gas, can respond to the solar wind dynamic pressuredisturbance. With the enhancement of the solar wind dynamic pressure,the diffuse aurora on the equatorward of ASI’s field-of-view showed theintensity enhance and the poleward extension on latitude, the geo-magnetic environment also showed a corresponding disturbance at thesame time. We suggested that the dayside magnetopause is compressedbecause of the enhancement of the solar wind dynamic pressure. It canresult in the enhancement of pitch-angle scatter by wave particleinteraction in the magnetosphere. Consequently, the number flux of the high-energy particle scattering the loss-cone and precipitating into theequatorward ionosphere of auroral oval is enhanced, and led the emi-ssion increase of dayside diffuse aurora.