What can we learn from the Van Allen probe measurements of the electric drift E × B/B² in the inner magnetosphere? — An update

摘要

Although electric fields play a fundamental role in space physics, they are difficult to observe experimentally. This is particularly true close to Earth, because of accuracy issues around spacecraft perigee. Yet, to improve our understanding of the plasmasphere dynamics, ground-truth about the low-L convection field could be key. With that in mind, we developed a unique database of equatorial electric drifts E × B/B² below L= 3, using more than two years of magnetic and electric field measurements from the two Van Allen Probe spacecraft. In previous work, we demonstrated that the Van Allen Probes had the accuracy required to provide reliable measurements of the electric drift close to spacecraft perigee. We performed a first statistical analysis of the database and we derived typical values of the electric drift below L= 3, in both radial and azimuthal directions. We studied the dependences of the electric drift on radial distance, magnetic local time, and geographic longitude. Then we investigated the Van Allen Probe electric drift database with a focus on anomalous behavior, i.e., with a focus on those electric drifts that significantly diverge from expectations. We will present the results of our investigation. The circumstances that lead to such anomalous values together with the consequences on the overall dynamics of the plasmasphere will be assessed. To our best knowledge, this work represents the most comprehensive observational description of the electric drift around magnetic equator below L~3. It can be used for example to question the suitability of different electric field models in the low L-region.