电离层热层对太阳耀斑的耦合响应

Solar flares disturb significantly the space environment. Sudden increases in X-ray and EUV radiation during a solar flare would change the ionosphere, which is one of the key topic researches of the ionospheric physics. Solar flare effect on the thermosphere also draws attention of the researchers. We plan to study the coupling variation of the ionosphere and thermosphere during super solar flares. Under the idea of coupling variation of the ionosphere and thermosphere, we explore the cause for the faster and stronger thermospheric responses to a solar flare than expected before, which may be due to the effect from the ionospheric variation. We also explore the cause for the long time ionospheric responses, which may be due to the effect from the thermospheric variation. Use both observations and simulations, we study the relationship between the ionospheric responses and thermospheric responses. By the case-controlled simulations, we continue to study the dependence of the responses on the flare class, solar activity, local time and latitude. In addition, we would also particularly study the dynamic process's effect on the low-latitude responses to solar flares, topside ionospheric responses, as well as the behaviors of the ionosphere and thermosphere during the extreme enhancements in solar radiation. Finally, we construct an empirical model of solar radiation during a solar flare by statistically analyzing the data of solar radiation. Through this program, we can further understand the coupling between the ionosphere and thermosphere.

太阳耀斑事件会对空间环境产生显著影响。耀斑期间X射线和极紫外辐射剧烈的短时变化引起的电离层变化，这一直是电离层物理的研究热点之一，最近人们还开始关注耀斑的热层响应。本项目拟研究大耀斑事件期间电离层/热层的变化特征，在考虑电离层/热层耦合的理念下，探讨热层耀斑响应要比早期预期的迅速和强烈的原因，是否主要来自电离层变化对热层所引起的次级影响，以及一些大耀斑期间电离层长时间响应是否来自热层变化的次级影响。通过观测分析，并结合耦合模式模拟，考察电离层变化与热层变化的关联，避免以往以孤立分析为主。在此基础上,研究这些变化与耀斑等级，以及太阳活动水平、地方时、纬度等的关系,进而着重研究动力学对低纬电离层热层扰动的影响、顶部电离层在耀斑期间的响应特征以及极端太阳辐射条件下电离层热层状态。最后构建耀斑期间电离层热层响应的经验模式。通过此研究，可深化对电离层热层耦合变化的认识。

在以往的电离层、热层对耀斑响应的研究中，大部分是分别研究电离层响应、热层响应，对于电离层热层之间的耦合变化则并不清楚。基于大量电离层/热层观测数据，并利用实验室自主开发的全球电离层-热层耦合模式，本项目重点研究了耀斑爆发的极紫外辐射突然增强条件下，电离层与热层响应特征，特别是电离层热层耦合响应。模拟结果揭示出热层对耀斑的响应呈现全球扰动特征，向日面的能量通过全球大气环流变化向背日面传输。我们的观测统计和模拟研究还揭示热层响应主要受耀斑期间总积分辐射的控制，与电离层响应主要受峰值辐射显著不同。极端事件通常能将一般条件下不易显现的过程放大，利于研究相关理论问题。为了进一步更好的研究电离层耦合变化特征及其机制，我们模拟研究X40级超级耀斑条件下全球电离层热层响应，结果显示电离层扰动持续时间超过5个小时，远超以往纪录。模式试验发现热层的超强扰动是电离层长时间扰动的主要驱动力。我们还进一步通过模拟不同强度耀斑来研究电离层热层响应随耀斑强度的演化过程。我们发现随着耀斑强度增强，电离层热层响应均呈现非线性放大效应，这与以往的认识有很大的差别。观测结果也部分证实了这样一个非线性放大效应。