Cluster observations of quasi‐periodic impulsive signatures in the dayside northern lobe: High‐latitude flux transfer events?

Abstract

We report on a series of quasi‐periodic reversals in GSM BZ observed by the four Cluster spacecraft in the northern dayside lobe poleward of the cusp on 23 February 2001. During an interval of about 35 min, multiple reversals (negative to positive) in BZ of approximately 1‐min duration with an approximate 8‐min recurrence time were observed. The individual structures do not resemble low‐latitude flux transfer events (FTE) [Russell and Elphic, 1979] but the 8‐min recurrence frequency suggests that intermittent reconnection may be occurring. Measurements (appropriately lagged) of the solar wind at ACE show that the IMF was southward‐oriented with a strong BX and that a modest dynamic pressure increase occurred as the events started. The multi‐point observations afforded by the Cluster spacecraft were used to infer the motion (direction and speed) of the observed magnetic field reversals. The associated currents were also calculated and they are consistent with the spatial confinement of the observed magnetic field reversals. We propose that the observed reversals are due to flux tubes reconnecting with closed field lines on the dayside. Ancillary data from the Cluster Ion Spectrometry (CIS) and Plasma Electron And Current Experiment (PEACE) instruments were used to develop a physical picture of the reversals.