用ICON/MIGHTI观测资料表征冬至期间热层平均风和环流
Characterization of the Thermospheric Mean Winds and Circulation during Solstice using ICON/MIGHTI Observations
摘要：
利用NASA ICON上MIGHTI仪器的水平中性风观测（电离层连接探测器）航天器的连续覆盖，我们确定的平均纬向和纬向风的气候和相关的平均环流在低至中纬度（$10^\circ$ S-40 $^{\circ}$ N），适用于北半球90 km和200 km高度之间的夏至条件，特别是在2020年6月20日至2020年6月8日至7月7日的一个月期间，以及2019年12月16日至2020年1月31日的北方冬季，为期47天，提供完整的当地时间覆盖。这些数据在适当的高度、经度、纬度、太阳天顶角和当地时间段内进行平均，以产生平均风分布。文中还分析了平均水平环流的地理分布和当地时间的变化。瞬时水平风表现出显著的时空变异性，经常超过$\pm 150 $ m s $^{-1}$。日平均纬向平均风表现出逐日变化。低层热大气中盛行向东的纬向风和向北的纬向风，这为小尺度重力波的东向动量沉积提供了间接的观测证据。平均中性风和环流在较低的热层（90-120公里）中显示出较小的尺度结构，而在较高的热层中则更为均匀，这表明热层的耗散性越来越强。从ICON/MIGHTI测量推断的平均风和环流模式可用于约束和验证大气环流模型，以及数值波浪模型的输入。
英文摘要：
Using the horizontal neutral wind observations from the MIGHTI instrument onboard NASA's ICON (Ionospheric Connection Explorer) spacecraft with continuous coverage, we determine the climatology of the mean zonal and meridional winds and the associated mean circulation at low- to middle latitudes ($10^\circ$S-40$^{\circ}$N) for Northern Hemisphere {summer} solstice conditions between 90 km and 200 km altitudes, specifically on 20 June 2020 solstice as well as for a one-month period from 8 June-7 July 2020 {and for Northern winter season from 16 December 2019-31 January 2020, which spans a 47-day period, providing full local time coverage}. The data are averaged within appropriate altitude, longitude, latitude, solar zenith angle, and local time bins to produce mean wind distributions. The geographical distributions and local time variations of the mean horizontal circulation are evaluated. The instantaneous horizontal winds exhibit a significant degree of spatiotemporal variability often exceeding $\pm 150 $ m s$^{-1}$. The daily averaged zonal mean winds demonstrate day-to-day variability. Eastward zonal winds and northward (winter-to-summer) meridional winds are prevalent in the lower thermosphere, which provides indirect observational evidence of the eastward momentum deposition by small-scale gravity waves. The mean neutral winds and circulation exhibit smaller scale structures in the lower thermosphere (90-120 km), while they are more homogeneous in the upper thermosphere, indicating the increasingly dissipative nature of the thermosphere. The mean wind and circulation patterns inferred from ICON/MIGHTI measurements can be used to constrain and validate general circulation models, as well as input for numerical wave models.
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