Electrodynamical characteristics of the polar ionosphere over the auroral and polar cap regions based on incoherent scatter radar measurements

Abstract

Electrodynamical characteristics of the polar ionosphere over the auroral and polar cap regions are examined based on incoherent scatter radar measurements particularly in terms of electric field and ionospheric conductivity. For this purpose, 43 and 109 days of measurements from the Chatanika and Sondrestrom incoherent scatter radars, respectively, are utilized. The ionospheric current density inferred from the radar measurements of ionospheric conductance and electric field is compared with the corresponding ground magnetic disturbance. Also estimated is the global field-aligned current (FAC) that affects the ground magnetic disturbance, particularly of the D component. Several interesting characteristics about the polar ionosphere are emerging from this study: (1) the sun determines largely the conductance over the Sondrestrom radar, while the nighttime conductance distribution over the Chatanika radar is significantly affected by auroral precipitation. (2) The regions of the maximum N–S component of the electric field over the Chatanika radar are located approximately at the dawn and dusk sectors, while they tend to shift towards dayside over the Sondrestrom radar with the N–S component over Sondrestrom being slightly stronger than Chatanika. However, the E–W component over Chatanika is negligible compared to that of Sondrestrom. (3) The E–W component of the ionospheric current, J E, over Chatanika flows dominantly in the night hemisphere while it flows in the sunlit hemisphere over Sondrestrom. The N–S component of the ionospheric current, J N, over Chatanika flows prominently in the dawn and dusk sectors, while a strong southward current flows over Sondrestrom in the pre-noon sector. (4) The assumption of infinite sheet current approximation is far from realistic, underestimating the current density by a factor of 2 or more. It is particularly serious at higher latitudes. (5) The correlation between Δ H and J E is higher than the one between Δ D and J N indicating that FAC affects significantly Δ D. (6) The total upward and downward FAC are quite comparable and they are approximately 5.9×10 5 and 2.2×10 5 A over Chatanika and Sondrestrom, respectively. With enhancement of magnetic activity, FAC increases drastically over Chatanika by a factor of 4 or 5 while it is insignificant over Sondrestrom.