The Acceleration of Outer-Belt Electrons by Localized Electric Fields

To explain the populations of the outer-belt energetic electrons, including relativistic electrons, that sporadically appear in the magnetosphere, a mechanism was proposed long ago for the acceleration of those electrons by short-term bursts of the electric field, which appear on the night side during substorm disturbances (Kropotkin, 1996). This mechanism can be substantially specified if the modern concepts of bursty bulk flows in the geomagnetic tail, the occurrence of dipolarization fronts, and the excitation of localized field-aligned-resonant poloidal Alfvén oscillations involving a strong component of the electric field in the dawn-dusk direction are taken into account.

Intense dB/dt variations driven by near-Earth Bursty Bulk Flows (BBFs): A case study

<p>During geomagnetically disturbed times the surface geomagnetic field often changes abruptly, producing geomagnetically induced currents (GICs) in a number of ground based systems. There are, however, few studies reporting GIC effects which are driven directly by bursty bulk flows (BBFs) in the inner magnetosphere. In this study, we investigate the characteristics and responses of the magnetosphere-ionosphere-ground system during the 7 January 2015 storm by using a multi-point approach which combines space-borne measurements and ground magnetic observations. During the event, multiple BBFs are detected in the inner magnetosphere while the magnetic footprints of both magnetospheric and ionospheric satellites map to the same conjugate region surrounded by a group of magnetometer ground stations. It is suggested that the observed, localized substorm currents are caused by the observed magnetospheric BBFs, giving rise to intense geomagnetic perturbations. Our results provide direct evidence that the wide-range of intense dB/dt<strong> </strong>(and dH/dt) variations are associated with a large-scale, substorm current system, driven by multiple BBFs.</p>

Statistical properties of ions in bursty bulk flows

<p>With the observations of THEMIS and MMS Mission, we have investigated the properties of ions in bursty bulk flows (BBFs). Based on analysis of 315 BBF events, we can obtain the statistical features of ions in the BBFs. The results can be summarized as follows: (1) the occurrence rate of BBFs is related with AE index, which is also confirmed by previous studies; (2) the ion number density in the duskside is nearly at the same level with that in the dawnside; (3) in the region -10<em>R<sub>E</sub></em> > <em>X<sub>GSM</sub></em>> -15<em>R<sub>E</sub></em>(where <em>R<sub>E</sub></em>is the earth radius), the ion temperature in the duskside is much higher than that in the dawnside; (4) the ion temperature anisotropy <em>T</em><sub>⊥</sub>/<em>T</em><sub>∥ </sub>is weaker as BBFs close to the Earth; (5) corresponds to cold electrons (<em>T<sub>e</sub></em> < 1.5 keV), the ratio of the ion and electron temperature <em>T</em><sub>i</sub>/<em>T</em><sub>e</sub> can reach 10-15 and the temperature of ions and electrons have a linear correlation.</p>

Intense dB/dt variations driven by near-Earth Bursty Bulk Flows (BBFs): A case study

<p>During geomagnetically disturbed times, geomagnetically induced currents (GICs) flow in power systems potentially causing damage to the system. The largest GICs are often produced when the surface geomagnetic field abruptly changes (for example, an induced rate of change of the horizontal magnetic field component, dH/dt). It is well established that intense dB/dt variations take place in the main phase of a geomagnetic storm, particularly while magnetic substorms occur during the active period. However, there are currently few studies that report intense dB/dt variations which are directly driven by bursty bulk flows (BBFs) at geosynchronous orbit. In this study, we investigate the characteristics and response in the magnetosphere-ionosphere system during the recovery phase of a geomagnetic storm that occurred on 7 January 2015 by using a multi-point approach combining space-borne Cluster and SWARM measurements, and a group of ground-based magnetometer observations. The locations of Cluster and SWARM map to the same conjugate region as the magnetometer ground stations at the time of the BBF. The measurements show that corresponding signals in all measurements occur simultaneously in this region. Our results suggest that the most intense dB/dt (dH/dt) variations are associated with R1-type FACs that are driven by BBFs at geosynchronous orbit around substorm onset.</p>