Time-variability of the ionospheric electric field: solar wind driving and atmospheric feedback

地球大气层是一个复杂的系统，由许多层组成，这些层在控制其全球动态方面相互作用。电离层在这些动态中起着关键作用，将上方地球空间的磁性环境--“磁层”--与下方的中性环境相耦合。地球大气层和太空之间的电磁场和粒子耦合的可变性是造成“空间天气”现象的原因。目前的NERC战略承认这是一种具有严重全球影响的环境危害，但我们对其对大气影响的了解有限，限制了我们的预测能力。尤其是，电离层电场在管理大气动力学方面发挥着重要作用，主要是在150公里以下的热层。英国气象局试图将热层纳入他们的天气和气候模式，将其统一模式(MetUM)的上限从85公里提高到120-140公里的区域，证明了这一点。为了实现这一点，改进的电离层电场模型是必不可少的，因为现有的模型只描述了平均条件，并且没有对先前的可变性历史进行“记忆”。如果要在这些高度对大气动力学做出现实的预测，捕捉到这种可变性是至关重要的。因此，我们将开发下一代全球电离层电场模型，该模型将首次包括其形态和驱动机制的固有时间依赖性。具体而言，我们包括与三个不同来源有关的可变性：(1)太阳风驱动；(2)地球空间的动力过程；(3)大气反馈。我们的模型将与英国气象局合作设计，用于气候和空间天气模拟应用程序，如Metum。为了实现我们的目标，我们将利用来自电离层雷达和地面磁强计的电场和磁场测量的数十年数据集，以及由Fabry-Perot干涉仪进行的中性风测量，以研究电离层的电动力学及其与中性大气的耦合。我们将使用上游行星际航天器数据，不仅根据地球空间中同时存在的条件，而且根据这些条件的时间历史；持续的等离子体和磁场结构以及可变性程度来对我们的观测进行排序。我们还将使用地磁测量来研究时间可变的内部磁层过程的影响。其中包括磁层亚暴，它激发电离层中的对流，向大气中注入高能粒子，并产生可见的极光，即北极光(和南方光)。最后，我们将使用电场和中性风的同时测量来研究中性风发电机的飞轮效应，即中性风在其直接激励平息后维持电离层电场的能力。将所有这些时变效应结合到电离层电场的新经验模型中，将为磁层物理、大气模型和空间等离子体物理理论家提供宝贵的资源。

The Earth's atmosphere is a complex system consisting of many layers that interact in controlling its global dynamics. The ionosphere plays a key role in these dynamics, coupling the magnetic environment of geospace - 'the magnetosphere' - above to the neutral environment below. Variability in the coupling of electromagnetic fields and particles between Earth's atmosphere and space are responsible for the phenomenon of 'space weather'. This is recognised by current NERC strategy as an environmental hazard with serious global impacts, but limitations in our understanding of its effects on the atmosphere constrain our prediction capability. Ionospheric electric fields, in particular, play an important role in governing atmospheric dynamics, primarily in the thermosphere below 150 km. This is demonstrated by the UK Met Office seeking to include the thermosphere in their weather and climate model, raising the upper boundary of its Unified Model (MetUM) from 85 km to the region of 120-140 km. In order to achieve this, improved ionospheric electric field models are essential, since existing models characterise only average conditions and have no 'memory' of the prior history of variability. Capturing this variability is critical if realistic predictions of atmospheric dynamics are to be made at these altitudes. We will therefore develop the next generation model of global ionospheric electric fields that will include, for the first time, the inherent time-dependence of their morphology and driving mechanisms. Specifically, we include variability associated with three distinct sources: (i) solar wind driving (ii) dynamical processes in geospace and (iii) atmospheric feedback. Our model will be designed in collaboration with the UK Met Office, for use in their climate and space weather modelling applications such as MetUM.To achieve our goals we will utilise multi-decadal datasets of electric and magnetic field measurements from ionospheric radars and ground magnetometers, and neutral wind measurements by Fabry-Perot interferometers, to study the electrodynamics of the ionosphere, and its coupling to the neutral atmosphere. We will use upstream interplanetary spacecraft data to order our observations not only by the concurrent conditions in geospace, but by the time history of these conditions; persistent plasma and magnetic field structures, and the degree of variability. We will also use geomagnetic measurements to investigate the effects of time-variable internal magnetospheric processes. These include magnetospheric substorms, which excite convection in the ionosphere, inject energetic particles into the atmosphere, and produce the visible aurora, or northern (and southern) lights. Lastly, we will use simultaneous measurements of the electric field and neutral wind to investigate the 'flywheel' effect of the neutral wind dynamo; the ability of neutral winds to maintain the ionospheric electric field after their direct excitation subsides. Incorporating all of these time-variable effects into a new empirical model of the ionospheric electric field will provide a valuable resource for magnetospheric physics, atmospheric modellers, and space plasma physics theorists.