Intense Db/Dt Variations Driven By Near-Earth Bursty Bulk Flows (Bbfs): A Case Study

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 January 7, 2015 storm by using a multipoint 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 (and dH/dt) variations are associated with a large-scale, substorm current system, driven by multiple BBFs.Plain Language Summary The geomagnetically induced currents (GICs) produced on the ground result from rapid fluctuation of the surface geomagnetic field. The intense GICs can cause dramatic effects on man-made technological systems, and these effects can in turn lead to severe economic losses. Generally, the high rates of change of the geomagnetic field (dB/dt) are employed as a proxy for the GICs. In Earth's magnetosphere (a region of space surrounding Earth which is controlled by the Earth's magnetic field), transient ion flow bursts called bursty bulk flows (BBFs), are transient structures with typical ion velocities larger than 150 km/s. It is believed that the intense dB/dt are associated with BBFs. However, there are currently few studies reporting the direct proof of intense dB/dt driven by BBFs in the near-Earth region. In this work, we reported multiple BBFs events in the near-Earth region and revealed its magnetospheric driving effects on the intense geomagnetic field perturbations during the January 7, 2015 storm by analyzing multipoint measurements of satellites, and a group of ground-based magnetometer observations. Our field confirms that the field-aligned currents connect directly intense dB/ dt on the ground with the BBFs in the near-Earth region.