Estimates of the field-aligned current density in current-carrying filaments using auroral zone ground-based observations

Abstract

Abstract.We described the ground signatures of dynamic substorm features as observed by the imaging riometer, magnetometers and all-sky camera (ASC) at Kilpisjärvi, Finland on 5 and 25 October 1999 during the late evening hours. The magnetometer data was consistent with the motion of upward field-aligned currents (FACs) associated with absorption patches moving within the field of view of the riometer. We used riometer data in order to estimate the intensity of FACs associated with these local current-carrying filaments. It is shown that during these events, the estimated FAC intensity exceeds a threshold value that corresponds to the excitation of the low-frequency turbulence in the upper ionosphere. As a result, a quasi-oscillating regime of anomalous resistivity on the auroral field lines can give rise to the burstlike electron acceleration responsible for simultaneously observed auroral forms and bursts of Pi1B pulsations.

Statistical Correlation Analysis of Field‐Aligned Currents Measured by Swarm

“…Although the Pi1B waves observed on the ground have maximum amplitude when they lie underneath active auroral forms (Arnoldy et al, ; Bösinger & Wedeken, ; Danielides et al, ; Haldoupis et al, ; Milling et al, ), thereby suggesting they were locally generated (Posch et al, ). A number of studies have mentioned that Pi1B waves can extend in latitude and longitude/MLT (e.g., 12° in latitude and 20° in longitude, as mentioned by Arnoldy et al, ; 7°of magnetic latitude and 4 hr of MLT, as mentioned by Posch et al, ; 5° in latitude and less than 30° in longitude, as mentioned by Parkhomov & Rakhmatulin, ) For these extended distributions, only the brightest auroral onsets can be associated with Pi1B observations at more than 5° in latitude and 2 hr in MLT distance.…”