Dawn-dusk difference of periodic oxygen EUV dayglow variations at Venus observed by Hisaki
Dawn-dusk difference of periodic oxygen EUV dayglow variations at Venus observed by Hisaki
复制标题
久崎观测到的金星周期性氧极紫外日光变化的黎明-黄昏差异
DOI：
10.1016/j.icarus.2016.12.027
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发表时间：
2017
期刊：
影响因子：
3.2
通讯作者：
and I. Yoshikawa
中科院分区：
文献类型：
--
作者：
Masunaga;K.;K. Seki;N. Terada;F. Tsuchiya;T. Kimura;K. Yoshioka;G. Murakami;A. Yamazaki;C. Tao;F. Leblanc;and I. Yoshikawa
我们报告了2015年Hisaki航天器在金星上层大气中观测到的氧气EUV日光（OII 83.4 nm，OI 130.4 nm和OI 135.6 nm）周期性变化的黎明-黄昏差异。观测结果表明，日辉的周期性变化主要受太阳极紫外辐射通量的控制。此外，我们还观察到OI 135.6 nm亮度的特征性周期性为0.01天和0.04天。黄昏侧以0.1天周期为主，黎明侧以0.4天周期为主。尽管2.1天周期的驱动因素仍然不确定，但我们认为2.4天周期是由中层大气传播的重力波引起的。热层亚太阳-反太阳流和重力波主要增强黎明侧的涡动扩散，由于超旋转大气风速的大周期调制，涡动扩散系数每隔204天变化一次。由于黎明侧的104天调制没有被连续观测到，可能是由于波源高度的变化，热层与中层大气之间存在间歇性耦合。此外，如果中层或低热层风速存在变化，由于临界能级的周期性消失，即使在黄昏侧，重力波也可能偶尔传播到热层，并出现周期为104天的O原子调制。因此，我们的观测结果表明，极紫外日光的104天周期可能反映了金星中层大气的动力学。我们还研究了太阳风对日光变化的影响，将太阳风的测量从地球转移到金星。我们没有发现它们之间有明显的相关性。然而，由于金星没有太阳风的本地测量，太阳风对日光的影响仍然不确定。
We report a dawn-dusk difference of periodic variations of oxygen EUV dayglow (OII 83.4 nm, OI 130.4 nm and OI 135.6 nm) in the upper atmosphere of Venus observed by the Hisaki spacecraft in 2015. Observations show that the periodic dayglow variations are mainly controlled by the solar EUV flux. Additionally, we observed characteristic ∼1 day and ∼4 day periodicities in the OI 135.6 nm brightness. The ∼1 day periodicity was dominant on the duskside while the ∼4 day periodicity was dominant on the dawnside. Although the driver of the ∼1 day periodicity is still uncertain, we suggest that the ∼4 day periodicity is caused by gravity waves that propagate from the middle atmosphere. The thermospheric subsolar-antisolar flow and the gravity waves dominantly enhance eddy diffusion on the dawnside, and the eddy diffusion coefficient changes every ∼4 days due to large periodic modulations of wind velocity of the super-rotating atmosphere. Since the ∼4 day modulations on the dawnside are not continuously observed, it is possible that there is an intermittent coupling between the thermosphere and middle atmosphere due to variations of wave source altitudes. Moreover, if there are variations of the wind velocity in the mesosphere or lower thermosphere, it is possible that gravity waves occasionally propagate to the thermosphere even on the duskside due to periodic disappearance of the critical level and the ∼4 day periodic O atomic modulations occur. Thus, our observations imply that the ∼4 day periodicity of the EUV dayglow may reflect the dynamics of the middle atmosphere of Venus. We also examined the effects of the solar wind on the dayglow variations by shifting the solar wind measurements from earth to Venus. We did not find clear correlations between them. However, since there are no local measurements of the solar wind at Venus, the effect of the solar wind on the dayglow is still uncertain.