Immel Thomas J, Harding Brian J, Heelis Roderick A, Maute Astrid, Forbes Jeffrey M, England Scott L, Mende Stephen B, Englert Christoph R, Stoneback Russell A, Marr Kenneth, Harlander John M, Makela Jonathan J
Space Sciences Laboratory, University of California, Berkeley, CA, USA.
These authors contributed equally: Thomas J. Immel, Brian J. Harding.
Nat Geosci. 2021 Dec;14:893-898. doi: 10.1038/s41561-021-00848-4. Epub 2021 Nov 29.
Earth's equatorial ionosphere exhibits substantial and unpredictable day-to-day variations in density and morphology. This presents challenges in preparing for adverse impacts on geopositioning systems and radio communications even 24 hours in advance. The variability is now theoretically understood as a manifestation of thermospheric weather, where winds in the upper atmosphere respond strongly to a spectrum of atmospheric waves that propagate into space from the lower and middle atmosphere. First-principles simulations predict related, large changes in the ionosphere, primarily through modification of wind-driven electromotive forces: the wind-driven dynamo. Here we show the first direct evidence of the action of a wind dynamo in space, using the coordinated, space-based observations of winds and plasma motion made by the National Aeronautics and Space Administration Ionospheric Connection Explorer. A clear relationship is found between vertical plasma velocities measured at the magnetic equator near 600 km and the thermospheric winds much farther below. Significant correlations are found between the plasma and wind velocities during several successive precession cycles of the Ionospheric Connection Explorer's orbit. Prediction of thermospheric winds in the 100-150 km altitude range emerges as the key to improved prediction of Earth's plasma environment.
地球赤道电离层在密度和形态上呈现出巨大且不可预测的逐日变化。这给提前24小时为对地球定位系统和无线电通信的不利影响做准备带来了挑战。现在从理论上理解，这种变异性是热层天气的一种表现，其中高层大气中的风对从低层和中层大气传播到太空的一系列大气波有强烈响应。第一性原理模拟预测电离层会发生相关的巨大变化，主要是通过改变风驱动的电动势：风驱动发电机效应。在此，我们利用美国国家航空航天局电离层连接探测器进行的基于空间的风与等离子体运动的协同观测，展示了风发电机效应在太空中作用的首个直接证据。在600公里附近磁赤道处测量的垂直等离子体速度与下方更远处的热层风之间发现了明确的关系。在电离层连接探测器轨道的几个连续进动周期内，等离子体速度与风速之间发现了显著的相关性。预测100 - 150公里高度范围内的热层风成为改善地球等离子体环境预测的关键。
