ALBERT

Description: A statistical study of ion upflow and field-aligned currents (FACs) has been performed in the topside ionosphere of both hemispheres for magnetic quiet and disturbed times by using DMSP satellite observations from 2010–2013. Distributions in MLT/MLat reveal that ion upflow occurrence shows a dawn-dusk asymmetry distribution that matches well with the Region 1 FACs. In addition, there are highest occurrence regions near noon and within the midnight auroral disturbance area, corresponding to dayside cusp and nightside auroral disturbance regions, respectively. Both the ion upflow occurrence and FAC regions expand equatorward to a wider area during disturbed times.

Description: Dynamic mesoscale flow channels move across the open field line regions of the polar caps, and then enter the nightside plasma sheet, where they can lead to important space weather disturbances, such as streamers, substorms, and omega bands. We find that the polar cap structures leading to disturbances can have long durations (at least ~1½ to 2 hours), and one flow structure can lead to more than one disturbance as it moves azimuthally within the polar cap. Examples using 630 nm auroral and radar observations indicate that the motion of flow channels within the polar cap may be significantly controlled by the IMF By. This motion appears to possibly be a critical factor in determining when and where a particular disturbance within the nightside auroral oval will be triggered. Also, potentially important is the occasional dramatic azimuthal turning of a flow channel, leading to azimuthal broadening of flow channel contact with the auroral oval and of a subsequent substorm onset. Of additional importance for future understanding of disturbances resulting from polar cap flow channels will be determining conditions along nightside auroral oval field lines (plasma sheet) that interact with an incoming flow polar-cap flow channel to give a particular disturbance. Additionally interesting will be consideration of the generality of geomagnetic disturbances being related to their connections with incoming polar cap flow channels, including the location, time, and type of disturbances, and also whether the duration of the disturbances appears to be related to the duration of an incoming flow channel.

Description: This study addresses whether a series of strong substorm-associated MeV electron injections can be a crucial contributor to outer-radiation belt enhancement events. We examine an event that occurred on July 10, 2019, where ~2 MeV electron fluxes increased by ~3 orders of magnitude in only ~7.5-hrs under 4 repetitive, strong relativistic electron injections. For this examination, it is essential to precisely separate purely temporal flux changes from spatial variations observed as Van Allen Probes move along their orbits (i.e., orbital effect). Employing a new “hourly snapshot” analysis approach, we uncover unprecedented details of electron flux dynamics that indicates that the overall outer belt enhancement for this event was not continuous but composed of 4 large discrete flux increases primarily driven by the strong injections. These injections appear as sharp flux increases at all energies when a spacecraft is located in the injection region, and the inner-most L of the flux increase is located farther out with increasing energy as expected for injections. Earthward of the injection region, by comparing hourly snapshots for different times, we infer injections and infer temporally-stable fluxes between injections, despite strong and continuous chorus emission. The fast and intermittent, large flux growths imply cumulative outer belt enhancement via repetitive inward radial transport associated with injection-induced electric fields.

Description: During the periods of strong northward interplanetary magnetic field (IMF), the polar cap (normally no aurora) often appears clear auroral structures. Their appearance not only directly links to solar wind-magnetosphere-ionosphere coupling processes, but also often results in variable space weather disturbances. However, their formation and evolution are still poorly understood, and there is no forecasting tool to predict either their formation or evolution. Here we summarize the recent new progresses about the formation, evolution and space weather impact of polar cap auroras. 1) A general formation mechanism has been proposed for the formation of transpolar auroral arcs (TPA): strong flow shear sheets in the magnetosphere generate field aligned current (FAC) sheets which field-aligned accelerate electrons through the Knight’s current-voltage process to precipitate into the polar cap ionosphere. 2) A cyclone-shaped aurora has been identified and named as space hurricane above the Earth’s magnetic north pole with strong electron precipitations and a clockwise circulation of the plasma flow, and been. 3) A merging poleward edges of a conjugate horse-collar aurora (HCA) has been identified in both hemispheres’ polar ionosphere, indicating an almost complete disappearance of the open-flux polar cap and a shrunk and nearly closed magnetosphere due to the quasi-steady dual-lobe reconnection continuously eroding the magnetotail open and even closed magnetic field lines that reclosed at the dayside magnetopause under long-time strong northward IMF. These results indicate that there are still significant energy disposition and coupling in the solar wind-magnetosphere-ionosphere interactions under strong northward IMF conditions.