Abstract. Terrestrial ecliptic dayside observations of the exospheric Lyman-α column intensity between 3–15 Earth radii (R_e) by UVIS/HDAC at CASSINI have been analysed to derive the neutral exospheric H-density profile at the Earth's ecliptic dayside in this radial range. The data were measured during CASSINIS's swing by manoeuvre at the Earth on 18 August 1999 and are published by (Werner et al., 2004). In this study the dayside HDAC Lyman-α observations published by (Werner et al., 2004) are compared to calculated Lyman-α intensities based on the 3D H-density model derived from TWINS Lyman-α observations between 2008–2010 (Zoennchen et al., 2015). It was found, that both Lyman-α profiles show a very similar radial dependence in particular between 3–8 R_e. Between 3.0–5.5 R_e impact distance Lyman-α observations of both TWINS and UVIS/HDAC are existing at the ecliptic dayside. In this overlapping region the cross-calibration of the HDAC profile against the calculated TWINS profile was done, assuming, that the exosphere there was similar for both due to comparable space weather conditions. As result of the cross-calibration the conversion factor between counts/s and Rayleigh f_c = 3.285 [counts/s/R] is determined for these HDAC observations. Using this factor the radial H-density profile for the Earths ecliptic dayside was derived from the UVIS/HDAC observations, which constrained the neutral H-density there at 10 R_e to a value of 35 cm⁻³. Furthermore, a faster radial H-density decrease was found at distances above 8 R_e (≈ r⁻³) compared to the lower distances 3–7 R_e (≈ r^−2.37). This increased loss of neutral H above 8 R_e might indicate a higher rate of H ionization in the vicinity of the magnetopause at 9–11 R_e (near sub solar point) and beyond, because of increasing charge exchange interactions of exospheric H atoms with solar wind ions outside the magnetosphere.

中文翻译：

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在3-15地面exospheric向阳面H-密度分布ř _ë从UVIS / HDAC和TWINS莱曼-α数据相结合

摘要。已经分析了 CASSINI 的 UVIS/HDAC对 3-15 个地球半径 ( R _e )之间的外层层 Lyman-α 柱强度的陆地黄道日侧观测，以推导出地球黄道日侧在这个径向范围内的中性外层外 H 密度剖面。这些数据是在卡西尼号于 1999 年 8 月 18 日在地球机动摆动期间测量的，并由（Werner 等人，2004 年）发表。在这项研究中，将（Werner 等人，2004 年）发表的日侧 HDAC Lyman-α 观测值与基于 2008-2010 年间 TWINS Lyman-α 观测值得出的 3D H 密度模型计算的 Lyman-α 强度进行了比较（Zoennchen 等人，2004 年）等，2015）。结果发现，这两个莱曼-α曲线显示在特定3-8之间一个非常类似的径向相关性[R _È. 之间3.0-5.5 ř _Ë双胞胎和UVIS / HDAC的冲击距离莱曼-α的观察是在黄道向阳面现有。在这个重叠区域，HDAC 剖面与计算出的 TWINS 剖面进行了交叉校准，假设由于可比的空间天气条件，两者的外逸层相似。作为交叉校准的结果， 为这些 HDAC 观测确定了counts/s 和 Rayleigh f _c = 3.285 [counts/s/R]之间的转换因子。使用这个因素，地球黄道日侧的径向 H 密度剖面来自 UVIS/HDAC 观测，这将那里的中性 H 密度限制在 10 Re _e值为 35 cm ^-3. 此外，更快的径向H-密度下降，发现在上述的距离8 - [R _È（≈  - [R ^-3）相比较低的距离3-7 - [R _È（≈  - [R ^{- 2.37}）。该增加的8以上中性H的损失ř _Ë可能在9-11表明在磁层附近的较高速率ħ电离的ř _ë（近日下点）及以后，因为增加了与exospheric H原子的电荷交换的相互作用，磁层外的太阳风离子。