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，高能电子在地球磁层和磁尾中加速，并在高纬度地区沉淀到大气中。与最丰富的N2、O2和O的初级碰撞过程导致主要在中间层和上层热层（70-150公里）形成一氧化氮，并开始影响许多其他微量成分的离子和中性化学反应。在冬季，氮氧化物可以在极地纬度的大规模下降运动中被输送到海拔45公里以下的平流层，并在催化循环中破坏那里的臭氧，即所谓的“高能粒子降水间接效应”。由于臭氧是平流层辐射加热和冷却的关键物质之一，其成分的变化直接影响平流层温度，并启动一系列影响大气温度和大气环流的动力耦合机制。由于其对冬季和春季天气系统的明显重要性，特别是在北方高纬度地区，现在建议，例如，由世界气候计划WCRP发起的模式研究，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-气候模式研究。然而，最近对基于卫星电子通量观测的这类模式研究提供的大气电离率的分析表明，这些速率存在很大的缺陷，特别是对具有高能电子降水（HEEP）的大型地磁风暴期间和之后的大气电离率的低估，高能电子降水在平流层和60公里以下的中下层特别大。在本项目框架内，我们将通过结合大型HEEP事件观测所得的大气电离率、1961年以来的长期气球数据集以及最近对平流层和中间层微量成分的卫星观测结果，研究HEEP事件对中层大气（平流层和中间层，10-90公里）化学成分、温度和动力学的影响。从一维离子化学模式、中性模式和辐射对流模式到全球化学-气候模式。特别是，我们将解决以下两个问题：•高能电子沉淀对中层大气化学成分的长期影响是什么，由于哪些过程？•最近的结果表明，对推荐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WCRP （https://www.wcrp-climate.org）、SPARC HEPPA/SOLARIS （http://solarisheppa.geomar.de）和SCOSTEP （http://www.yorku.ca/scostep）等国际项目具有重要意义。

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).