Long‐Term Density Trend in the Mesosphere and Lower Thermosphere From Occultations of the Crab Nebula With X‐Ray Astronomy Satellites
Long‐Term Density Trend in the Mesosphere and Lower Thermosphere From Occultations of the Crab Nebula With X‐Ray Astronomy Satellites
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DOI：
10.1029/2022ja030797
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发表时间：
2023-01
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通讯作者：
S. Katsuda;T. Enoto;A. Lommen;K. Mori;Y. Motizuki;M. Nakajima;Nathaniel C. Ruhl;Kosuke Sato
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作者：
S. Katsuda;T. Enoto;A. Lommen;K. Mori;Y. Motizuki;M. Nakajima;Nathaniel C. Ruhl;Kosuke Sato
我们根据X射线天文卫星ASCA、RXTE、朱雀、努斯塔和瞳观测到的蟹状星云的大气掩星，呈现了地球高层大气在71至116 km高度的长期密度趋势。五颗卫星的组合提供了从1994年到2022年的28年时间段。为了抑制季节和纬度的变化，我们集中使用了北方半球0° ~ 40 °的秋季（49 < doy < 111）和春季（235 < doy < 297）的资料。有了这个限制，本地时间会自动限制在中午或午夜左右。我们获得了每个海拔层的四组（两个季节×两个当地时间）密度趋势。我们使用线性回归技术考虑了线性趋势和11年太阳周期的变化。因为我们没有看到四个趋势之间的显著差异，所以我们将它们结合起来，以提供趋势斜率的单个垂直剖面。我们发现，在每个海拔高度，密度呈负趋势，约为-5%/十年。这与从高层大气沉降速率的推论是一致的。在100-110 km的高度，我们发现了一个异常高的密度下降，约为-12%/十年。这一峰值可能是110公里附近由于水汽和臭氧导致的强烈冷却的第一个观测证据，这是Akmaev等人在数值模拟中首次发现的（2006，https：//doi.org/10.1016/j.jastp.2006.03.008）。需要进一步的观察和数值模拟与适当的输入参数，以建立这一功能。
We present long‐term density trends of the Earth's upper atmosphere at altitudes between 71 and 116 km, based on atmospheric occultations of the Crab Nebula observed with X‐ray astronomy satellites, ASCA, RXTE, Suzaku, NuSTAR, and Hitomi. The combination of the five satellites provides a time period of 28 years from 1994 to 2022. To suppress seasonal and latitudinal variations, we concentrate on the data taken in autumn (49 < doy < 111) and spring (235 < doy < 297) in the northern hemisphere with latitudes of 0°–40°. With this constraint, local times are automatically limited either around noon or midnight. We obtain four sets (two seasons × two local times) of density trends at each altitude layer. We take into account variations due to a linear trend and the 11‐year solar cycle using linear regression techniques. Because we do not see significant differences among the four trends, we combine them to provide a single vertical profile of trend slopes. We find a negative density trend of roughly −5%/decade at every altitude. This is in reasonable agreement with inferences from settling rate of the upper atmosphere. In the 100–110‐km altitude, we found an exceptionally high density decline of about −12%/decade. This peak may be the first observational evidence for strong cooling due to water vapor and ozone near 110 km, which was first identified in a numerical simulation by Akmaev et al. (2006, https://doi.org/10.1016/j.jastp.2006.03.008). Further observations and numerical simulations with suitable input parameters are needed to establish this feature.