一次大磁暴主相期间ENA氧与氢的分离及分布特征——TWINS卫星观测

ENA-H and ENA-O separation and their distribution features during the main phase of a great magnetic storm——TWINS satellite observation

本文采用基于ENA(Energetic Neutral Atoms)次生电子起始脉冲高度分布,统计拟合分离中能段ENA两种主要成分氢和氧的方法,研发了实现ENA氢与氧分离的TWINS卫星原始数据处理软件;其中所需要的脉高分布模型,参照已有理论公式,利用TWINS(Two Wide-angle Imaging Neutral-atom Spectrometers)卫星标定数据进行拟合确定未知参数,再加以计算得到.将上述方法用于TWINS卫星实测数据,分离得到一次大磁暴主相期间ENA-H和ENA-O微分通量随观测视线的分布及其随主相增长的变化.分析发现:(1)ENA-H与ENA-O微分通量的强度和随观测视线的分布特征都有明显差别,从某种角度反映出ENA之源的O^+与H^+离子强度和分布之间的差异;(2)接近主相极大时,ENA-H有很强的低高度发射(LAE,Low Altitude Emission),出现在磁地方时午夜前极光和亚极光纬度区,意味着该区域较强的等离子片和环电流质子沉降,进入到外层基底以下较低高度大气层;而ENA-O则未有明显LAE产生;ENA-O强通量观测视线主要穿过广大环电流区,磁地方时主要在午夜之后以及黄昏前和黎明前后;(3)在磁暴主相快速增长期,ENA-O平均总通量持续增大,而ENA-H同步减小,ENA-O与ENA-H平均总通量的比率随环电流指数Dst绝对值的增大而大致成正比增长.

Applying the method of statistical fitting based on the probability distribution features of start pulse height （STPH） excited by ENA＇s secondary electron, a set of programs has been developed to process the TWINS （Two Wide-angle Imaging Neutral-atom Spectrometers） satellite Level-0 data aiming to separate compositions of oxygen and hydrogen in ENA. Therein a model of STPH distribution needed for making the separation is set up by fitting the satellite calibration data to the theoretic formula in being. Implementing the separation method to the TWINS satellite measured data during a great magnetic storm, the respective ENA-H and ENA-O differential flux distributions with line-of-sight （LOS） have been obtained, as well as their evolution with the storm main phase growth. It is found that： （1） There are obvious differences in both magnitudes and distributions of differential fluxes between ENA-H and ENA-O, implying from a certain angle the differences between fluxes of energetic O＋ and H＋ ions as ENAs＇ sources. （2） During the period approaching the storm main phase, ENA-H displays intense Low Altitude Emissions （LAEs） which appear in the aurora and sub-aurora region before midnight, suggesting strong proton precipitation coming from plasma-sheet and RC （ring current） region into the lower atmosphere below exobase; while the oxygen has no obvious LAEs, but showing intensive fluxes along LOSs that traverse extensive RC region located mainly in the magnetic local time sectors of post-midnight, pre-dusk and around dawn. （3） During the rapid growth of the storm main phase, the averaged total flux （ATF） of ENA-O continues to increase, while the ENA-H to decrease synchronously. Correspondingly, the ATF ratio of ENA-O to ENA-H grows in a way of being roughly proportional to the increase of the absolute value of the ring current index Dst.