Predicting the upper atmospheric response to extremes of space weather forcing

空间天气描述了太阳活动对地球、大气和空间环境的影响。例如，来自太阳的高能粒子可以撞击和损坏绕地球轨道运行的航天器。由太阳风驱动的电场可以改变高层大气，导致加热并改变通信系统无线电波的传播特性。地球磁场产生的快速变化可以在接地的技术基础设施中感应电流。因此，了解空间天气是一个重要的科学目标，鉴于能够直接测量空间天气影响的天文台相对稀少，显然需要有空间天气模型的能力。为了模拟空间天气对大气的影响，我们需要考虑整个大气。尽管空间天气效应在高海拔地区最为明显，但上层大气——热层和电离层——的动力学是由空间（“自上而下”的强迫）和下面的大气层（“自下而上”的强迫）驱动的。即使在地磁风暴等极端空间天气事件中，模式研究也表明，低层大气的状态可以影响热层的响应。电离层-热层模型中包含电场，将磁层（受太阳风控制的近地空间区域）的动力学与中性大气耦合起来，从而成为空间天气的驱动因素。目前，最先进的全大气模型包括有限的和过时的电离层电场参数化，基于几十年的旧数据集和假设，这些数据集和假设不允许捕捉实际的时间变化或极端事件。我们建议利用我们在探索和模拟电离层-热层电动力学方面的专业知识，将最先进的电离层电场输入引入全大气群落气候模型-扩展（WACCM-X）。我们将通过对预先选择的事件进行模拟来测试新的模型配置，我们已经对电离层和热层的流动、密度和温度进行了观测和测量。最能再现观测结果的模式配置将用于在可变的太阳风强迫和地磁活动间隔期间指定一系列不同空间天气驱动因素的全球热层参数。我们的研究结果将使我们能够解决一些关于热层对空间天气响应的悬而未决的问题，并为下一代的全大气模型和空间天气模型提供信息。

Space weather describes the effects of solar activity on our planet, its atmosphere and space environment. For example, energetic particles from the Sun can impact and damage Earth-orbiting spacecraft. Electric fields driven by solar winds can modify the upper atmosphere causing heating and changing the propagation characteristics of radio waves for communications systems. Rapid changes produced in the Earth's magnetic field can induce electrical currents in grounded technical infrastructure. Understanding space weather is thus an important scientific goal, and given the relatively sparse nature of observatories capable of measuring space weather effects directly, it is clear that a capability to model space weather is required.To model the atmospheric effects of space weather we need to consider the whole atmosphere. Although space weather effects are most apparent at high-altitudes, the dynamics of the upper atmosphere - the thermosphere and ionosphere - are driven both from space ('top-down' forcing) and from the atmospheric layers below ('bottom-up' forcing). Even during extreme space weather events such as geomagnetic storms, model studies have shown that the state of the lower atmosphere can influence the thermospheric response. Electric fields are included in ionosphere-thermosphere models to couple the dynamics of the magnetosphere (the region of near-Earth space controlled by the solar wind), and hence the drivers of space weather, to the neutral atmosphere. Currently, the most state-of-the-art whole atmosphere models include limited and outdated parameterisations of the ionospheric electric field, based on decades old datasets and assumptions, which do not allow for realistic time-variability or extreme events to be captured.We propose to utilise our expertise in exploring and modelling ionosphere-thermosphere electrodynamics to bring state-of-the-art ionospheric electric field inputs to the Whole Atmosphere Community Climate Model - Extended (WACCM-X). We will test the new model configurations by running simulations of pre-selected events for which we have observations and measurements of ionospheric and thermospheric flows, densities, and temperatures. The model configuration that is best able to reproduce the observations will then be used to specify global thermospheric parameters for a range of different space weather drivers during intervals of variable solar wind forcing and geomagnetic activity. Our results will enable us to solve a number of outstanding questions on the thermospheric response to space weather and inform the next generation of whole atmospheric modelling and space weather modelling.