Accurate estimates of extreme ultraviolet (EUV) irradiance are needed in order to understand the dynamical, chemical, and plasma processes occurring in planetary upper and tenuous atmospheres. Most studies rely on irradiance measurements made at Earth, which are extrapolated to the location of interest. The Mars Atmosphere and Volatile Evolution (MAVEN) orbiter includes the Extreme Ultraviolet Monitor (EUVM) instrument to measure the solar EUV irradiance in situ at Mars, which is used in this study to quantify the error introduced when phase‐shifting EUV measurements from Earth to other locations in the solar system. The MAVEN/EUVM solar soft X‐Ray (SXR) and Lyman‐α measurements are compared with analogous measurements made from Earth to characterize the typical error introduced when phase‐shifting solar EUV irradiance measurements made from Earth to other points in the solar system according to the 27.27 day synodic solar rotation period. The phase‐shifting error, ε_ps, measured at SXR and Lyman‐α wavelengths are extrapolated to the full EUV spectrum by assuming it is proportional to the variability that occurs over the 27‐day timescale of solar rotation. Values for ε_ps as a function of wavelength are reported and used to find the typical error for estimates of photoionization frequencies of some major species found in planetary upper atmospheres. Measuring EUV irradiance in situ reduces the random uncertainty by approximately half of that expected from phase shifting irradiances to the point of interest from Earth. These findings indicate that estimates of EUV induced variability in planetary atmospheres are highly uncertain at timescales of ∼10 days for large phase angles.

中文翻译：

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用于行星研究的太阳极端紫外线辐照度不确定度

为了了解在行星上层和弱层大气中发生的动力学，化学和等离子体过程，需要准确估计极端紫外线（EUV）的辐照度。大多数研究都依赖于在地球上进行的辐照度测量，这些测量被推断到感兴趣的位置。火星大气与挥发性演化（MAVEN）轨道器包括用于测量火星原位太阳EUV辐照度的极紫外监测仪（EUVM），该仪器在本研究中用于量化EUV测量值从地球移至地面时引入的误差。太阳系中的其他位置。MAVEN / EUVM太阳软X射线（SXR）和莱曼α将测量结果与地球进行的类似测量结果进行比较，以表征根据27.27天的同步太阳旋转周期将地球进行的太阳EUV辐照度测量相移至太阳系中其他点时引入的典型误差。移相误差，ε _PS，在SXR和Lyman-测量α波长被假设它正比于发生在太阳能旋转27天时间尺度的可变性外推到满EUV光谱。值ε _PS报告了作为波长函数的函数，并用于发现典型误差，以估计行星高层大气中某些主要物种的光电离频率。在原位测量EUV辐照度可将随机不确定性降低大约一半，该不确定度是从相移辐照度到地球关注点的期望值的一半。这些发现表明，对于大相角，EUV引起的行星大气变率的估计在约10天的时间尺度上是高度不确定的。