GEM: Response of Global Ionospheric Currents to Substorms: Implication for the Electric Field Penetration to the Inner Magnetosphere

GEM：全球电离层电流对亚暴的响应：对电场穿透内磁层的影响

• 批准号: 1502700
• 负责人: Shinichi Ohtani
• 金额: $ 29.82万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-05-15 至 2022-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1502700&HistoricalAwards=false
• 关键词: GEM; Response; Global; Ionospheric; Currents

This proposal builds on surprising evidence from an earlier study by this group that perturbations in the equatorial electrojet (a narrow ribbon of strong dayside ionospheric current flowing along the magnetic dip equator) may actually be caused by bursts of auroral activity called substorms on the nightside at polar latitudes. During substorms, strong currents are diverted from large radial distances in the extended tail of the magnetosphere along magnetic field lines into and through the ionosphere on the nightside. The ionospheric segment of the current is seen as a strong auroral electrojet (AEJ) at polar latitudes. The equatorial electrojet (EEJ), on the other hand, is generated as a result of the interaction between neutral winds flowing away from a region of strong solar heating while dragging ions across magnetic field lines, and the unique geometry of strictly horizontal magnetic field lines at the dip equator. The association between these electrojets implies that electric fields are penetrating from the polar region as far as the dip equator during substorms. Even though weak by the time they reach the equatorial region, their signatures can be observed in the modulation of the intense equatorial electrojet. This is a proposal to investigate more completely the response of the equatorial electrojet to substorms and determine its global closure. The penetration of the auroral electric field to low-latitudes, and the shielding that inhibits or prevents this penetration, are open and compelling questions for understanding and more accurately predicting space weather, which ultimately has benefits to society. Significant broader impacts include the participation of high-school teachers and students during the summer in research associated with this project.To accomplish the goals of this project, the proposers will address two questions: (1) how does the auroral electrojet respond to substorms, and (2) how is the substorm-related change of the dayside EEJ connected with the nightside AEJ.They will use data from a network of ground magnetometers, which includes 7 ground stations around the dip equator and a meridional chain of stations, along with auroral images from the Polar and IMAGE satellites. To answer question 1, they will use publicly-available lists of substorms, along with these observations, to determine statistically how often the EEJ responds to substorm onsets either by intensifying or weakening, the magnetic local time dependence of the response, and whether it is changed by the preceding level of geomagnetic activity. To answer question 2, they will examine the magnetic deflection (a measure of electric current intensity) as a function of solar zenith angle and magnetic latitude to test the idea that the EEJ and AEJ are connected by meridional currents that flow around the terminator. This is a new idea and a unique aspect of this proposal.

这一建议建立在该小组早期研究的令人惊讶的证据基础上，即赤道电射流（一条沿着磁倾赤道流动的强昼侧电离层电流的狭窄带状物）的扰动实际上可能是由极光活动的爆发引起的，称为极纬度夜侧的亚暴。 在亚暴期间，强电流从磁层延伸的尾部的大径向距离处沿着沿着磁场线转向进入并穿过夜侧的电离层。 电流的电离层部分被视为极纬地区的强极光电射流（AEJ）。 另一方面，赤道电射流（EEJ）是由于中性风从强太阳能加热区域流出，同时将离子拖过磁场线，以及倾角赤道处严格水平磁场线的独特几何形状之间的相互作用而产生的。 这些电射流之间的关联意味着电场穿透从极地地区，直到倾角赤道亚暴期间。尽管当它们到达赤道地区时很弱，但它们的特征可以在强烈的赤道电射流的调制中观察到。 这是一个建议，更全面地调查赤道电急流的响应亚暴，并确定其全球关闭。 极光电场向低纬度的渗透，以及抑制或防止这种渗透的屏蔽，是理解和更准确地预测空间天气的开放和令人信服的问题，最终将造福于社会。 重要的更广泛的影响包括高中教师和学生在夏季参与与该项目相关的研究。为了实现该项目的目标，提案人将解决两个问题：（1）极光电喷流对亚暴的响应，以及（2）与亚暴相关的昼侧EEJ变化如何与夜侧AEJ相联系。他们将使用来自地面磁力计网络的数据，其中包括7个围绕倾角赤道的地面站和一个沿赤道的台站链，沿着有来自极地和IMAGE卫星的极光图像。为了回答问题1，他们将使用公开可用的亚暴列表，沿着这些观测结果，以统计方式确定EEJ通过增强或减弱对亚暴爆发的响应频率，响应的磁当地时间依赖性，以及它是否被先前的地磁活动水平改变。 为了回答问题2，他们将检查磁偏转（电流强度的测量）作为太阳天顶角和磁纬度的函数，以测试EEJ和AEJ由绕着终结器流动的纬向电流连接的想法。 这是一个新的想法，也是这项建议的一个独特方面。