Ionospheric signatures of Bursty Bulk Flows in the 6D Vlasiator simulations

Bursty Bulk Flows (BBFs) are high-speed plasma flows that occur within the magnetotail plasma sheet. BBFs are known to play a crucial role in transporting energy, mass, and magnetic flux across the magnetotail, as well as to the coupled ionosphere. Understanding the ionospheric signatures of BBFs is therefore essential to advance our understanding of the coupling processes between the Earth’s magnetosphere and ionosphere. Currently, most insights into the ionospheric signatures of BBFs come from individual case studies that include simultaneous observations of BBFs in the magnetotail and field-aligned currents (FACs) in the nightside ionosphere. In this study, we utilized the 6D Vlasiator simulations to study the ionospheric signatures of BBFs in the near-Earth magnetotail. Vlasiator is a global hybrid-Vlasov model designed to simulate near-Earth space plasmas and has recently been complemented with an ionosphere model, allowing the study of magnetosphere-ionosphere coupling.

In the magnetotail, the simulation results show that a BBF with V_x ≥400,km/s emerges shortly after magnetic reconnection occurs on the dusk-side at a radius between 11 and 14 R_E (where R_E= 6371 km, radius of the Earth) in the current sheet plane. As the BBF moves Earthward and azimuthally dusk-ward (as seen from above the current sheet plane), clockwise (counterclockwise) flow vortices are induced on the dawn(dusk) sides of it. These vortical flows generate FACs flowing upward (out of the current sheet plane) on the dawn-side and downward (into the current sheet plane) on the dusk-side flanks, respectively.

The mapping of BBF structures onto the ionosphere shows that BBFs are primarily aligned in the East-West direction, with their ionospheric signatures appearing as enhancements in FACs, ionospheric conductances, horizontal ionospheric currents, and the formation of localized plasma flow channels. The upward and downward FACs associated with BBFs in the magnetotail consistently map to enhanced Region 2 (R2) and Region 1 (R1) FAC structures at ionospheric altitude, which are then closed in the ionosphere by north-west flowing Pedersen currents. The Earthward motion of the BBF maps to an equator-ward flow channel, while the dusk-side counterclockwise (and dawn-side clockwise) magnetotail vortical flows correspond to evening-side clockwise (and midnight-side counterclockwise) flow channels in the ionosphere. Overall, the Vlasiator simulation results show that the emergence of BBFs in the near-Earth magnetotail drives enhancements in the currents and conductances of the nightside ionosphere, while the westward drift of these enhanced structures corresponds to the dusk-ward movement of BBFs in the magnetotail.