资源环境科技发展态势分析平台

More than 2 years of magnetic and electric field measurements by the Van Allen Probes are analyzed with the objective of determining the average effects of magnetic activity on the electric drift below L=3. The study finds that an increase in magnetospheric convection leads to a decrease in the magnitude of the azimuthal component of the electric drift, especially in the nightside. The amplitude of the slowdown is a function of L, magnetic local time, and Kp, in a pattern consistent with the storm time dynamics of the ionosphere and thermosphere. To a lesser extent, magnetic activity also alters the average radial component of the electric drift below L=3. A global picture for the average variations of the electric drift with Kp is provided as a function of L and magnetic local time. It is the first time that the signature of the ionospheric disturbance dynamo is observed in near-equatorial electric drift measurements.

Plain Language Summary Maps are developed to best describe what surrounds us. That is true on the ground, and it is also true in space. Some of the most interesting maps are of traffic conditions, that is, maps that tell us how fast transport is, and in what direction the flow is, depending on location, even weather conditions. In space, the only difference is we are dealing with plasma transport, ions, and electrons, rather than flows of cars and trucks. To detail traffic in space, we must know both the magnetic field and the electric field: How strong are they? In what direction are they pointing? But unlike the magnetic field, the electric field is very difficult to measure, especially close to Earth. The instruments onboard the Van Allen Probes are the first to be accurate enough to measure plasma electric drift very close to Earth. In this work, we examine for the first time how electric drift varies with magnetic activity below three Earth radii. (Akin to measuring the impact of weather on traffic.) The results underline the important role played by the ionosphere. They offer new context to existing theories, and they provide a starting point to better mapping space dynamics.