氢高能中性原子从终止激波到地球轨道的存活几率和能量修正
Survival probability and energy modification of hydrogen Energetic Neutral Atoms on their way from the termination shock to Earth orbit
摘要：
内容：随着美国航天局SMEX飞行任务IBEX的即将发射，该飞行任务专门通过现场探测高能中性原子对日光层界面进行成像，认识到这些原子从太阳风的终端激波向地球轨道的传输成为一个重要问题。目的：考虑到可变和各向异性的太阳风和太阳极紫外辐射的影响，研究IBEX（0.01 - 6千电子伏）在终止激波和地球轨道之间可探测的HENA的能量和生存概率的变化。研究方法：原子的能量变化是通过数值模拟从太阳到地球轨道的~100 AU的HENA原子的轨道来计算的，考虑到太阳引力和$α$辐射压力，其随时间变化并且取决于原子的径向速度。为了计算原子在电离作用下的存活概率，基于太阳风和极紫外电离辐射的观测，建立了详细的三维含时HENA电离模型，并利用该模型沿计算轨道进行数值积分，计算了原子的存活概率.结果如下：由于辐射压的作用，除了在太阳活动高峰期能量低于0.1keV的原子外，HENA到达地球轨道几乎没有能量和方向的变化。对于地球轨道上的给定能量，人们期望生存概率的波动从0.01 keV的~20%下降到6 keV的仅几个百分比，并且生存概率的调制是地球轨道上的位置、到达方向的黄道纬度的函数，太阳活动周期的相位，在太阳活动极小期，0.1keV原子的振幅为百分之几十，在太阳活动极大期，6 keV原子的振幅为百分之几。
英文摘要：
Context: With the forthcoming launch of a NASA SMEX mission IBEX devoted to imaging of heliospheric interface by in-situ detection of Energetic Neutral Atoms (ENA) an important issue becomes recognizing of transport of these atoms from the termination shock of the solar wind to Earth orbit. Aims: Investigate modifications of energy and of survival probability of the H ENA detectable by IBEX (0.01 -- 6 keV) between the termination shock and Earth orbit taking into account the influence of the variable and anisotropic solar wind and solar EUV radiation. Methods: Energy change of the atoms is calculated by numerical simulations of orbits of the H ENA atoms from ~100 AU from the Sun down to Earth orbit, taking into account solar gravity and Lyman-$α$ radiation pressure, which is variable in time and depends on radial velocity of the atom. To calculate survival probabilities of the atoms against onization, a detailed 3D and time-dependent model of H ENA ionization based on observations of the solar wind and EUV ionizing radiation is constructed, and wth the use of this model probabilities of survival of the atoms are calculated by numerical integration along the previously calculated orbits. Results: Owing to the radiation pressure, H ENA reach the Earth orbit practically without energy and direction change except the atoms with energy lower than 0.1 keV during high solar activity. For a given energy at Earth orbit one expects fluctuations of survival probability from ~20% at 0.01 keV down to just a few percent at 6 keV and a modulation of survival probability as a function of the location at Earth orbit, ecliptic latitude of the arrival direction, and the phase of solar cycle with an amplitude of a few dozen percent for 0.1 keV atoms at solar minimum to a few percent for 6 keV atoms at solar maximum.
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