Fine‐scale transient arcs seen in a shock aurora

Abstract

AbstractWe report, for the first time, fine‐scale transient arcs that emerged successively within the initial 1–2 min evolutionary interval of a postnoon shock aurora on 14 July 2012. Data were acquired from ~2 Hz temporal resolution imaging of dayside aurora with a white light all‐sky camera (ASC) at South Pole Station (magnetic latitude = −74.3°, magnetic local time = UT −3.5 h). Just after 1809:50 UT at which the initial response to an interplanetary (IP) shock was detected in the postnoon geosynchronous magnetic field, the ASC observed three successive transient arcs of which the locations shifted equatorward with an abrupt jump by ~0.2° in latitude. All of the transient arcs occurred in a closed field line region, ~1.0°–1.5° equatorward of the polar cap or open/closed field line boundary inferred from the intensity ratio of I630.0/I557.7 but just poleward of the shock‐induced proton and diffuse‐type electron aurorae. Each of the transient arcs had a latitudinal width of ~0.1° and a short lifetime of ~20–30 s. Although the obvious mechanism has still remained unclear, possible interpretations of the fine‐scale transient arc features are discussed in terms of a local process of each of the magnetospheric origin (mode conversion) and ionospheric origin (feedback interaction) that may be induced by IP shock.