GEM: Ionospheric Control of the Nightside Magnetosphere-Ionosphere (M-I) Coupling

在地球极光区域沿磁力线流动的电流系统和产生可见极光的粒子的加速是密切相关的。这种联系提供了磁层-电离层(M-I)耦合的最重要方面之一。最近的研究发现，在夜间，冬季(黑暗)半球的极光加速往往比夏季(阳光充足)半球更强烈。这种差异在午夜前区域最为明显，并与向上区域-1(R1)场向电流(FAC)系统(向下流动的电子)有关。电子的加速与电流量之间的关系，奈特关系，意味着冬半球的场向电流一定更强。这一暗示似乎是自相矛盾的，因为由于光致电离的增加，夏季半球的电导率更高。本项目将检验这一明显悖论的三种可能解释：(1)尽管总体电导率较低，但FAC确实在冬半球更强烈；(2)FAC在冬半球更局限于纬度，因此平均电流密度在冬半球变得比夏半球更大；(3)在冬半球，向上的FAC结构比夏半球更精细，从而产生了较强的局地FAC。DMSP卫星的磁场和粒子降水数据将用于该项目。将对数据集应用识别FAC结构的自动程序，这将创建一份近300,000个FAC过境点的清单。FAC强度和密度将分别检验(1)和(2)。实际数据和拟合数据之间的差异将被用作内部结构的幅度的测量，这将被检查以进行测试(3)。这些事件将根据电离层状况(有阳光或黑暗)根据电离层脚点处的太阳天顶角进行分类。该项目将比较每个当地时间扇区的R1和R2电流的日光事件和黑暗事件之间的这些特征。一项初步研究表明，(1)的结果是积极的，但这不排除其他两种解释也适用的可能性。我们将研究粒子降水数据，以检验电子降水的半球间不对称性过度补偿了太阳照明引起的背景电导率不对称性的想法。这项研究将基于有史以来用于研究大规模FACS的最大数据集。此外，PI将参与马里兰大学的倡议，支持地球空间科学研究中代表人数不足的群体的学生。

The system of currents flowing along magnetic field lines in Earth's auroral region and the acceleration of particles that produces the visible aurora are closely related to each other. This connection provides on of the most important aspects of the magnetosphere-ionosphere (M-I) coupling. Recent research has found that on the night side, auroral acceleration tends to be more intense in the winter (dark) hemisphere than in the summer (sunlit) hemisphere. The difference is most pronounced in the pre-midnight sector and is related to the upward region-1 (R1) field-aligned current (FAC) system (downward flowing electrons). A relation between the acceleration of electrons and the amount of current, the Knight relation, implies that the field-aligned current must be more intense in the winter hemisphere. This implication seems paradoxical because the electrical conductivity in the summer hemisphere is higher due to the increased photo ionization. This project will test the three possible explanations of this apparent paradox: (1) The FAC is indeed more intense in the winter hemisphere, despite the fact that the overall conductivity is lower; (2) The FAC is more localized in latitude in the winter hemisphere so that the average current density becomes larger in the winter hemisphere than in the summer hemisphere;(3) In the winter hemisphere the upward FAC is more finely structured than in the summer hemisphere, creating strong local FACs. Magnetic field and particle precipitation data from the DMSP satellites will be used for this project. An automatic procedure to identify FAC structures will be applied to the data sets, which will create a list of nearly 300,000 FAC crossings. The FAC intensity and density will be examined to test (1) and (2), respectively. The difference between the actual and fitted data will be used as a measure of the amplitude of internal structures, which will be examined for testing (3). The events will be classified in terms of the ionospheric condition (sunlit or dark) based on the solar zenith angle at the ionospheric foot point. The project will compare those characteristics between sunlit and dark events for both R1 and R2 currents in each local-time sector. A preliminary study has suggested a positive result for (1), but that does not exclude the possibility that the other two explanations may also apply. Particle precipitation data will be examined to test the idea that the interhemispheric asymmetry of the electron precipitation overcompensates for the asymmetry of the background conductivity due to the solar illumination. This study will be based on the largest data set ever used for studying large-scale FACs. In addition, the PI will participate in the University of Maryland's initiative for supporting students from underrepresented groups in geospace science research.