The diurnal and latitudinal variation of auroral zone ionospheric conductivity

Abstract

The great spatial and temporal variability of auroral ionospheric conductivity significantly influences the ionospheric closure path for high‐latitude, field‐aligned currents. Because these closure paths can extend to low latitudes, changes in auroral zone conductivity can influence the global electric field distribution. In this paper, synoptic Chatanika radar observations of auroral zone conductivity that cover ∼62° to 68° geomagnetic latitude are presented. They are representative of quiet winter, active winter, and equinoctial conditions. During the daytime the solar contribution to the height‐integrated conductivity is well represented by Σ P,H ≃ (5, 10) cos 1/2 (χ), where χ is the solar zenith angle. The nighttime, height‐integrated Pedersen and Hall conductivities (Σ P and Σ H ) in the electron density trough are, at times, below our detection threshold of ∼0.5 mho. Following magnetic substorm onset, enhanced conductivity regions move southward and intensify. As the recovery phase begins, the conductivity pattern recedes northward and diminishes. The onset and cessation of precipitation associated with these events can be as abrupt as a few minutes. In one example the behavior of Σ P and Σ H are examined in the vicinity of the Harang discontinuity, which was quite sharp (≲30 min) in local time. At the Harang discontinuity on that day, the ratio of Σ H to Σ P decreased, indicating a softening of the precipitating energy distribution.