Evidence for the braking of flow bursts as they propagate toward the Earth

Abstract

AbstractIn this article we use energy conversion arguments to investigate the possible braking of flow bursts as they propagate toward the Earth. By using E·J data (E and J are the electric field and the current density) observed by Cluster in the magnetotail plasma sheet, we find indications of a plasma deceleration in the region −20 RE < X < − 15 RE. Our results suggest a braking mechanism where compressed magnetic flux tubes in so‐called dipolarization fronts (DFs) can decelerate incoming flow bursts. Our results also show that energy conversion arguments can be used for studying flow braking and that the position of the flow velocity peak with respect to the DF can be used as a single‐spacecraft proxy when determining energy conversion properties. Such a single‐spacecraft proxy is invaluable whenever multispacecraft data are not available. In a superposed epoch study, we find that a flow burst with the velocity peak behind the DF is likely to decelerate and transfer energy from the particles to the fields. For flow bursts with the peak flow at or ahead of the DF we see no indications of braking, but instead we find an energy transfer from the fields to the particles. From our results we obtain an estimate of the magnitude of the deceleration of the flow bursts, and we find that it is consistent with previous investigations.