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

这一建议建立在该小组早期研究的令人惊讶的证据之上，该研究表明，赤道电喷流（沿磁倾斜赤道流动的白天电离层电流的窄带）的扰动实际上可能是由极地纬度的夜间极光活动（称为亚暴）爆发引起的。在亚暴期间，强电流沿着磁场线从磁层延伸尾部的大径向距离转移到并穿过夜侧的电离层。电流的电离层部分在极地纬度被看作是一个强极光电喷流（AEJ）。另一方面，赤道电喷流（EEJ）是由从强烈太阳加热区域流出的中性风在拖拽离子穿过磁力线的过程中，与赤道倾斜处严格水平磁力线的独特几何形状相互作用产生的。这些电喷流之间的联系表明，在亚暴期间，电场从极区一直渗透到赤道底端。尽管在到达赤道区域时，它们的信号很弱，但它们的特征可以在强烈的赤道电喷流的调制中观察到。这是一个更完整地研究赤道电喷流对亚暴的响应并确定其全球闭合的建议。极光电场对低纬度地区的渗透，以及抑制或阻止这种渗透的屏蔽，是理解和更准确地预测空间天气的开放和引人注目的问题，最终对社会有益。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。为了实现这个项目的目标，提议者将解决两个问题：(1)极光电喷如何响应亚暴，(2)与亚暴相关的白天侧电喷的变化如何与夜晚侧电喷联系起来。他们将使用地面磁力计网络的数据，该网络包括沿倾角赤道的7个地面站和一个经向站链，以及极地卫星和IMAGE卫星的极光图像。为了回答问题1，他们将使用公开的亚暴列表，以及这些观测结果，从统计上确定EEJ对亚暴发作的反应频率，是通过增强还是减弱，磁场本地时间的依赖性，以及它是否被之前的地磁活动水平所改变。为了回答第2个问题，他们将检查磁偏转（一种测量电流强度的方法）作为太阳天顶角和磁纬度的函数，以验证EEJ和AEJ是由流经终端的子午电流连接起来的这一观点。这是一个新的想法，也是这个提议的一个独特的方面。

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.