Vector measurement of the midlatitudeSqionospheric current system

Abstract

This paper reports the results of two flights of vector magnetometer systems designed to measure the magnitude and direction of the ionospheric current system responsible for the solar quiet daily geomagnetic variation. The measurements were obtained from cesium vapor magnetometers with bias coils flown aboard sounding rockets from Wallops Island, Virginia. Instrumental difficulties on both flights limited the resolution of measurement, but the data indicated that current sheets were penetrated on both flights. These current sheets were observed to be thinner and more intense than those measured by previous investigators, and were confined to the lower edge of the altitude range over which currents have usually been observed. The unusual altitude profiles on both flights and an anomalously large current magnitude with a fluctuating direction observed on the second flight are attributed to localized enhancement of ionospheric electron concentration in sporadic E layers observed in ionograms taken during the flights. Because of disturbed ionospheric conditions and unknown boundary effects due to horizontal localization of the sporadic E layer, it is difficult to evaluate the validity of theoretical conductivity models. However, calculations of the conductivity profile required by the current position and intensity indicate that the observed current structure requires electron concentration enhancement compatible with that experimentally observed in sporadic E layers. Previous theoretical work also predicts a localized enhancement of the Sq current confined to the horizontal extent of the sporadic E layer, although such a large enhancement as was observed is not easily explainable.