Does high-latitude ionospheric electrodynamics exhibit hemispheric mirror symmetry?

IF 1.7 4区 地球科学 Q3 ASTRONOMY & ASTROPHYSICS
Spencer Mark Hatch, Heikki Vanhamäki, Karl Magnus Laundal, Jone Peter Reistad, Johnathan K. Burchill, Levan Lomidze, David J. Knudsen, Michael Madelaire, Habtamu Tesfaw
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引用次数: 0

Abstract

Abstract. Ionospheric electrodynamics is a problem of mechanical stress balance mediated by electromagnetic forces. Joule heating (the total rate of frictional heating of thermospheric gases and ionospheric plasma) and ionospheric Hall and Pedersen conductances comprise three of the most basic descriptors of this problem. More than half a century after identification of their central role in ionospheric electrodynamics, several important questions about these quantities, including the degree to which they exhibit hemispheric symmetry under reversal of the sign of dipole tilt and the sign of the y component of the interplanetary magnetic field (so-called “mirror symmetry”), remain unanswered. While global estimates of these key parameters can be obtained by combining existing empirical models, one often encounters some frustrating sources of uncertainty: the measurements from which such models are derived, usually magnetic field and electric field or ion drift measurements, are typically measured separately and do not necessarily align. The models to be combined moreover often use different input parameters, different assumptions about hemispheric symmetry, and/or different coordinate systems. We eliminate these sources of uncertainty in model predictions of electromagnetic work J⋅E (in general not equal to Joule heating ηJ2) and ionospheric conductances by combining two new empirical models of the high-latitude ionospheric electric potential and ionospheric currents that are derived in a mutually consistent fashion: these models do not assume any form of symmetry between the two hemispheres; are based on Apex magnetic coordinates (denoted Apex), spherical harmonics, and the same model input parameters; and are derived exclusively from convection and magnetic field measurements made by the Swarm and CHAMP satellites. The model source code is open source and publicly available. Comparison of high-latitude distributions of electromagnetic work in each hemisphere as functions of dipole tilt and interplanetary magnetic field clock angle indicates that the typical assumption of mirror symmetry is largely justified. Model predictions of ionospheric Hall and Pedersen conductances exhibit a degree of symmetry, but clearly asymmetric responses to dipole tilt and solar wind driving conditions are also identified. The distinction between electromagnetic work and Joule heating allows us to identify where and under what conditions the assumption that the neutral wind corotates with the Earth is not likely to be physically consistent with predicted Hall and Pedersen conductances.
高纬度电离层电动力学是否表现出半球镜像对称性?
摘要电离层电动力学是一个以电磁力为媒介的机械应力平衡问题。焦耳热(热大气层气体和电离层等离子体摩擦加热的总速率)以及电离层霍尔电导和佩德森电导是这一问题的三个最基本的描述指标。在确定它们在电离层电动力学中的核心作用半个多世纪之后,关于这些量的几个重要问题,包括它们在偶极子倾斜符号和行星际磁场 y 分量符号颠倒(所谓的 "镜像对称")的情况下呈现半球对称的程度,仍然没有答案。虽然可以通过组合现有的经验模型来获得这些关键参数的全球估计值,但经常会遇到一些令人沮丧的不确定性来源:据以推导出这些模型的测量数据(通常是磁场和电场或离子漂移测量数据)通常是单独测量的,不一定一致。此外,需要合并的模型通常使用不同的输入参数、不同的半球对称假设和/或不同的坐标系。我们将两个新的高纬度电离层电动势和电离层电流经验模型结合起来,消除了模型预测电磁功 J⋅E (一般不等于焦耳热 ηJ2)和电离层电导的不确定性来源,这两个模型是以相互一致的方式得出的:这些模型不假定两个半球之间存在任何形式的对称;以 Apex 磁坐标(记为 Apex)、球谐波和相同的模型输入参数为基础;完全根据 Swarm 和 CHAMP 卫星进行的对流和磁场测量得出。模型源代码是开放源代码,可公开获取。比较每个半球的高纬度电磁功分布作为偶极子倾斜和行星际磁场时钟角的函数,表明典型的镜面对称假设在很大程度上是合理的。电离层霍尔电导和佩德森电导的模型预测显示了一定程度的对称性,但也发现了对偶极子倾斜和太阳风驱动条件的明显非对称响应。通过区分电磁功和焦耳热,我们可以确定在哪些地方和哪些条件下,中性风与地球同向的假设不可能与预测的霍尔和佩德森电导在物理上保持一致。
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来源期刊
Annales Geophysicae
Annales Geophysicae 地学-地球科学综合
CiteScore
4.30
自引率
0.00%
发文量
42
审稿时长
2 months
期刊介绍: Annales Geophysicae (ANGEO) is a not-for-profit international multi- and inter-disciplinary scientific open-access journal in the field of solar–terrestrial and planetary sciences. ANGEO publishes original articles and short communications (letters) on research of the Sun–Earth system, including the science of space weather, solar–terrestrial plasma physics, the Earth''s ionosphere and atmosphere, the magnetosphere, and the study of planets and planetary systems, the interaction between the different spheres of a planet, and the interaction across the planetary system. Topics range from space weathering, planetary magnetic field, and planetary interior and surface dynamics to the formation and evolution of planetary systems.
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