Sunlight effects on the 3D polar current system determined from low Earth orbit measurements
Sunlight effects on the 3D polar current system determined from low Earth orbit measurements
复制标题
根据近地轨道测量确定太阳光对 3D 极流系统的影响
DOI：
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发表时间：
2016
期刊：
影响因子：
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通讯作者：
N. Olsen
中科院分区：
文献类型：
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作者：
K. Laundal;C. Finlay;N. Olsen
太阳风和地球磁层之间的相互作用与极纬电离层中的大规模电流有关，这些电流沿着磁场线（伯克兰电流）和水平方向流动。这些当前的系统紧密相连，但它们的全局行为很少一起分析。在本文中，我们提出了估计的平均全球伯克兰电流和水平电离层电流从同一组磁场测量。来自低地球轨道Swarm和CHAMP卫星的磁场测量值用于共同估计磁扰动场的极向和环形部分，以磁顶点坐标表示。顶点坐标的使用减少了地球主磁场的纵向和半球变化的影响。我们提出了全球电流从两个半球在不同的阳光条件。结果表明，Birkeland电流随电导率而变化，电导率最强烈地依赖于太阳在昼侧的EUV辐射和午夜前的磁性当地时间的粒子降水。在阳光下，水平等效电流在两个单元中流动，类似于相反的电离层对流模式，这意味着它是由霍尔电流占主导地位。通过结合Birkeland电流图和等效电流，我们能够计算总水平电流，而无需对电导率进行任何假设。我们表明，总的水平电流是接近于零的极冠时，它是黑暗的。这意味着由地面磁力计感测的等效电流在很大程度上被Birkeland电流的水平闭合所抵消。
Interaction between the solar wind and the Earth’s magnetosphere is associated with large-scale currents in the ionosphere at polar latitudes that flow along magnetic field lines (Birkeland currents) and horizontally. These current systems are tightly linked, but their global behaviors are rarely analyzed together. In this paper, we present estimates of the average global Birkeland currents and horizontal ionospheric currents from the same set of magnetic field measurements. The magnetic field measurements, from the low Earth orbiting Swarm and CHAMP satellites, are used to co-estimate poloidal and toroidal parts of the magnetic disturbance field, represented in magnetic apex coordinates. The use of apex coordinates reduces effects of longitudinal and hemispheric variations in the Earth’s main field. We present global currents from both hemispheres during different sunlight conditions. The results show that the Birkeland currents vary with the conductivity, which depends most strongly on solar EUV emissions on the dayside and on particle precipitation at pre-midnight magnetic local times. In sunlight, the horizontal equivalent current flows in two cells, resembling an opposite ionospheric convection pattern, which implies that it is dominated by Hall currents. By combining the Birkeland current maps and the equivalent current, we are able to calculate the total horizontal current, without any assumptions about the conductivity. We show that the total horizontal current is close to zero in the polar cap when it is dark. That implies that the equivalent current, which is sensed by ground magnetometers, is largely canceled by the horizontal closure of the Birkeland currents.