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

地球极光区中沿沿着磁场线流动的电流系统和产生可见极光的粒子加速相互密切相关。这种联系提供了磁层-电离层（M-I）耦合最重要的方面之一。最近的研究发现，在夜晚一侧，极光加速在冬季（黑暗）半球比在夏季（阳光照射）半球更强烈。这种差异在午夜前的扇区中最为明显，并且与向上区域-1（R1）场向电流（FAC）系统（向下流动的电子）有关。电子加速度与电流量之间的关系，即奈特关系，意味着场向电流在冬季半球一定更强。这似乎是自相矛盾的，因为在夏季半球的电导率较高，由于增加的光电离。本项目将检验对这一明显矛盾的三种可能的解释：（1）尽管总的电导率较低，但FAC在冬季半球确实更强;（2）FAC在冬季半球更局限于纬度，因此平均电流密度在冬季半球比在夏季半球更大;（3）在冬季半球，向上的FAC结构比夏季半球更精细，形成了较强的局地FAC。该项目将使用来自DMSP卫星的磁场和粒子沉降数据。将对这些数据集采用一种自动程序，以确定最后一道防线的结构，这将产生一份近300 000个最后一道防线过境点的清单。将分别检查FAC强度和密度以进行测试（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振幅的度量，将在测试中对其进行检查（3）。将根据电离层足点的太阳天顶角，按照电离层状况（日照或黑暗）对这些事件进行分类。该项目将比较每个当地时间扇区中R1和R2电流的日照事件和黑暗事件之间的这些特征。初步研究表明（1）的结果是肯定的，但这并不排除其他两种解释也可能适用的可能性。粒子沉淀数据将被检查，以测试的想法，即半球间的不对称性的电子沉淀过度补偿的背景电导率的不对称性，由于太阳照射。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将参与马里兰州大学的倡议，支持来自地球空间科学研究中代表性不足群体的学生。

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.