High-energy Electron Precipitation Into the atmosphere: an assessment based on balloon-borne observations and model Calculations

在极光亚暴和地磁暴期间，地球磁层和磁尾中加速的高能电子沉淀到高纬度的大气中。与最丰富的物种N2、O2和O的初级碰撞过程导致一氧化氮的形成，主要在中间层和高层热层(70-150公里)，并启动离子和中性化学反应，影响许多其他痕量组分。冬季，氮氧化物可以在极地纬度上以大规模下沉运动的形式向下输送到45公里高度以下的平流层，并在催化循环中破坏那里的臭氧，即所谓的“高能粒子沉淀间接效应”。由于臭氧是平流层辐射加热和冷却的关键物种之一，其组成的变化直接影响平流层的温度，并启动一系列动力耦合机制，影响到对流层以下大片区域的大气温度和环流。由于高能粒子降水对冬季和春季天气系统，特别是对高纬度地区的冬季和春季天气系统的明显重要性，现在建议，例如，对于世界气候方案发起的模型研究，将高能粒子降水作为气候系统自然太阳强迫的一部分，纳入化学-气候模型研究。然而，最近对基于卫星电子通量观测的这种模式研究提供的大气电离率的分析表明，这些电离率存在很大的不足，特别是在具有高能电子降水的大型地磁风暴期间和之后，大气电离率被低估了，高能电子降水在平流层和60公里以下的中间层低层特别大。在这个项目的框架内，我们将研究高能电子降水事件对中间大气(平流层和中间层，(10-90公里)，将从观测大型HeEP事件得出的大气电离率与追溯到1961年的长期气球数据集与最近对平流层和中层微量成分的卫星观测相结合，并与从一维离子化学、中性和辐射对流模型到全球化学-气候模型的不同复杂程度的中间大气模型相结合。我们将特别讨论以下两个问题：·高能电子沉淀对中层大气化学成分的长期影响是什么，是由于哪些过程？·最近的结果所表明的对建议电离率的明显低估对中层大气的组成、温度和动力学有什么影响？该项目的结果将对诸如WCRP(https://www.wcrp-climate.org)，SPARC HEPPA/SOLARIS(http://solarisheppa.geomar.de)和SCOSTEP(http://www.yorku.ca/scostep).))等国际计划具有重要意义

Energetic electrons accelerated in the terrestrial magnetosphere and magnetotail during auroral substorms and geomagnetic storms precipitate into the atmosphere at high latitudes. Primary collision processes with the most abundant species N2, O2, and O lead to the formation of nitric oxides primarily in the mesosphere and upper thermosphere (70—150 km), and start ion- and neutral chemistry reactions affecting many other trace constituents. Nitric oxides can be transported down into the stratosphere below 45 km altitude in large-scale downward motions over polar latitudes during winter, and destroy ozone there in catalytic cycles, the so-called “Energetic particle precipitation indirect effect”. As ozone is one of the key species in radiative heating and cooling of the stratosphere, changes in its composition directly affect stratospheric temperatures and start a chain of dynamical coupling mechanisms affecting atmospheric temperatures and circulation over large areas down to the troposphere. Because of its apparent importance for winter and spring weather systems particularly at high Northern latitudes, it is now recommended, e.g., for model studies initiated by the World Climate Programme WCRP to include energetic particle precipitation in chemistry-climate model studies as part of the natural solar forcing of the climate system. However, recent analyses of the atmospheric ionization rates provided for such model studies based on satellite-based electron flux observations suggest large deficits in these rates, in particular, an underestimation of the atmospheric ionization during and after large geomagnetic storms with high-energy electron precipitation (HEEP) which is particularly large in the stratosphere and lower mesosphere below 60 km.In the frame of this project, we will investigate the impact of HEEP events on the chemical composition, temperatures and dynamics of the middle atmosphere (stratosphere and mesosphere, (10—90 km) by combining atmospheric ionization rates derived from observations of large HEEP events with a long-time balloon data-set going back to 1961 with recent satellite observations of stratospheric and mesospheric trace constituents, and with models of the middle atmosphere of different complexity going from 1-dimensional ion-chemistry, neutral, and radiative-convective models to global chemistry-climate models. In particular, we will address the following two questions:• What is the long-term impact of high-energy electron precipitation on the chemical composition of the middle atmosphere, and due to which processes?• What is the impact of the apparent underestimation of recommended ionization rates as suggested by the recent results on the composition, temperature and dynamics of the middle atmosphere?Results of the project will be of importance for international programs such as WCRP (https://www.wcrp-climate.org), SPARC HEPPA/SOLARIS (http://solarisheppa.geomar.de) and SCOSTEP (http://www.yorku.ca/scostep).