Ps 6 spatial and temporal structure from STARE and riometer observations

Abstract

At the time of ground‐based observations of Ps 6 events, the two‐dimensional electron drift velocity maps (or the corresponding electric field maps) deduced from the Scandinavian twin auroral radar experiment (STARE) measurements exhibit a characteristic wavelike oscillation pattern. This pattern extends 3–4° in latitude and moves eastward roughly along L shells at a speed typically in the range 800–1300 m/s. The pattern has a precursor, a core, and a recovery zone. In the core, the electron drift attains some of the largest values ever seen by STARE (>2000 m/s). The electric field divergence indicates the presence of an east‐west field‐aligned current (FAC) pair, the more spatially confined leading FAC being downward, the more broadly spread following FAC being upward. A multiple narrow beam 51.4‐MHz riometer at Tromsö indicates a broad absorption zone associated with the trailing upward FAC. By using the Biot‐Savart Law to integrate the magnetic flux density due to the STARE velocity vectors (elemental currents) and by comparing the result with the ground‐based magnetometer records, it can be inferred that the closure current for the FAC pair has both Pedersen and Hall components, thereby indicating the presence of conductivity gradients. Furthermore, the STARE flows predict the observed ground D component variation very well and indicate integrated Hall conductivity of ∼50 mhos.