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

GEM：夜侧磁层-电离层 (M-I) 耦合的电离层控制

• 批准号: 0503065
• 负责人: Shinichi Ohtani
• 金额: --
• 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: 2005
• 资助国家: 美国
• 起止时间: 2005-06-15 至 2009-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0503065&HistoricalAwards=false
• 关键词: GEM; Ionospheric; Control; Nightside; Magnetosphere

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.

在地球的极光区域，沿着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）耦合的一个最重要的方面。最近的研究发现，在夜间，冬季（黑暗）半球的极光加速度往往比夏季（阳光）半球的极光加速度更强烈。这种差异在午夜前的扇区最为明显，与向上的1区（R1）场向电流（FAC）系统（向下流动的电子）有关。电子加速度和电流之间的关系，即奈特关系，意味着场向电流在冬季半球一定更强。这种暗示似乎是矛盾的，因为夏季半球的电导率由于光电离的增加而更高。本项目将检验这一明显悖论的三种可能解释：(1)尽管整体电导率较低，但冬季半球的FAC确实更强烈；(2)冬季半球FAC在纬度上更加局域化，使得冬季半球的平均流密度大于夏季半球；(3)在冬季半球，向上的FAC比夏季半球结构更精细，形成了较强的局部FAC。DMSP卫星的磁场和粒子降水数据将用于该项目。识别FAC结构的自动程序将应用于数据集，这将创建一个近30万个FAC交叉点的清单。FAC的强度和密度将分别用于测试(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，这将在测试(3)中进行检查。根据电离层足点的太阳天顶角，这些事件将根据电离层条件（阳光或黑暗）进行分类。该项目将比较每个当地时间区域内R1和R2电流的日光和黑暗事件的特征。一项初步研究表明(1)的结果是肯定的，但这并不排除其他两种解释也适用的可能性。粒子沉淀数据将被检验，以验证电子沉淀的半球间不对称性过度补偿了由于太阳光照引起的背景电导率的不对称性。这项研究将基于迄今为止用于研究大规模FACs的最大数据集。此外，PI将参与马里兰大学的倡议，支持来自地球空间科学研究中代表性不足群体的学生。