Pakhotin I P, Mann I R, Xie K, Burchill J K, Knudsen D J
Department of Physics, University of Alberta, Edmonton, Alberta, Canada.
University of Calgary, Calgary, Alberta, Canada.
Nat Commun. 2021 Jan 8;12(1):199. doi: 10.1038/s41467-020-20450-3.
Terrestrial space weather involves the transfer of energy and momentum from the solar wind into geospace. Despite recently discovered seasonal asymmetries between auroral forms and the intensity of emissions between northern and southern hemispheres, seasonally averaged energy input into the ionosphere is still generally considered to be symmetric. Here we show, using Swarm satellite data, a preference for electromagnetic energy input at 450 km altitude into the northern hemisphere, on both the dayside and the nightside, when averaged over season. We propose that this is explained by the offset of the magnetic dipole away from Earth's center. This introduces a larger separation between the magnetic pole and rotation axis in the south, creating different relative solar illumination of northern and southern auroral zones, resulting in changes to the strength of reflection of incident Alfvén waves from the ionosphere. Our study reveals an important asymmetry in seasonally averaged electromagnetic energy input to the atmosphere. Based on observed lower Poynting flux on the nightside this asymmetry may also exist for auroral emissions. Similar offsets may drive asymmetric energy input, and potentially aurora, on other planets.
地球空间天气涉及能量和动量从太阳风转移到地球空间。尽管最近发现了极光形态以及南北半球发射强度之间的季节性不对称，但电离层的季节性平均能量输入通常仍被认为是对称的。在此，我们利用“蜂群”卫星数据表明，在450公里高度处，电磁能量输入在白天和夜晚都更倾向于进入北半球，这是季节性平均的结果。我们认为这是由磁偶极偏离地球中心所解释的。这在南半球造成了磁极与旋转轴之间更大的间距，使得南北极光区的相对日照不同，从而导致电离层对入射阿尔文波的反射强度发生变化。我们的研究揭示了季节性平均电磁能量输入到大气中的一个重要不对称性。基于在夜侧观测到的较低坡印廷通量，这种不对称性可能在极光发射中也存在。类似的偏移可能在其他行星上驱动不对称的能量输入，并可能引发极光。
