M-I Coupling: Summer-Winter Asymmetry of Nightside Field-Aligned Currents

M-I 耦合：夜间场对准电流的夏季-冬季不对称性

• 批准号: 0101086
• 负责人: Shinichi Ohtani
• 金额: $ 16.5万
• 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: 2001
• 资助国家: 美国
• 起止时间: 2001-09-01 至 2004-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0101086&HistoricalAwards=false
• 关键词: Coupling; Summer; Winter; Asymmetry; Nightside

The field-aligned current (FAC) and the auroral acceleration are related to each other and are most important in the magnetosphere-ionosphere (M-I) coupling. The recent studies have found that on the nightside, auroral emission and electron precipitation tend to be more intense in the winter (dark) hemisphere than in the summer (sunlit) hemisphere.The observed asymmetry of auroral emission, suggests that the field-aligned current is more intense in the winter hemisphere, even though auroral regions in two hemispheres are connected by the magnetic field line, and the background ionospheric conductance is lower in the winter hemisphere. The proposed project seeks to study this paradoxical problem by observationally testing three possible explanations. Those explanations are (1) The upward FAC is more confined or structured in latitude in the winter hemisphere creating locally more dense currents; (2) The enhanced electron precipitation in the winter hemisphere overcompensates for the asymmetry of ionospheric conductance due to solar illumination; and (3) The region 1 currents in the summer and winter hemispheres have different sources in the magnetotail, and the M-I coupling takes place separately in each hemisphere.Magnetometer data from the DMSP-F7, F12, and F13 satellites and Geotail data will be used to examine FACs above the ionosphere. An automatic procedure to identify FAC structures will be applied to those data sets, and the characteristics of FACs such as current intensity, current density, latitudinal thickness of FAC sheets, and spatial irregularity will be quantitatively determined. The project will compare those characteristics between the summer (sunlit) and winter (dark) hemispheres.The proposed project will be the first comprehensive study of the summer-winter asymmetry of nightside FACs and will shed new light on the role of the ionospheric conductance in the M-I coupling.

场向电流（FAC）和极光加速度相互关联，在磁层-电离层（M-I）耦合中起着至关重要的作用。 最近的研究发现，在夜面，极光发射和电子沉降在冬季（黑暗）半球比在夏季（阳光）半球更强烈。极光发射的不对称性表明，尽管两个半球的极光区由磁场线连接，但场向电流在冬季半球更强烈。在冬季半球，背景电离层电导较低。 该项目试图通过观察测试三种可能的解释来研究这个矛盾的问题。 这些解释是：（1）在冬季半球，向上的FAC在纬度上更加局限或结构化，产生了局部更密集的电流：（2）冬季半球增强的电子沉降过度补偿了太阳光照引起的电离层电导的不对称性;夏、冬半球的1区电流在磁尾有不同的来源，来自DMSP-F7、F12和F13卫星的磁强计数据和Geotail数据将用于检查电离层上方的FAC。 一个自动程序，以确定FAC结构将被应用到这些数据集，和FAC的特性，如电流强度，电流密度，纬向厚度的FAC片，和空间不规则性将被定量确定。 该项目将比较夏季（阳光照射）和冬季（黑暗）半球的这些特征，拟议的项目将是对夜侧FAC的夏季-冬季不对称性的第一次全面研究，并将对电离层电导在M-I耦合中的作用提供新的认识。