Item

Abstract

It is well known that ionospheric currents in the dynamo region (ca 90-150 km) are responsible for the daily variation of the geomagnetic field on the ground. The global-scale current system that dominates geomagnetic daily variations at middle and low latitudes is referred to as solar quiet (Sq). Geomagnetic signatures of Sq can be measured not only by ground-based magnetometers but also by magnetometers onboard low-Earth-orbit satellites. This presentation describes a recent effort to characterize Sq using high-precision magnetometer data from the Swarm mission. Internal and external equivalent Sq current systems are estimated based on the spherical harmonic analysis of Swarm geomagnetic field data. The internal Sq current system can be regarded as a superposition of ionospheric dynamo currents and induced underground currents. The external Sq current system at a satellite altitude (~500 km) is derived for the first time. The results suggest that the external Sq current system is due to interhemispheric field-aligned currents at low and middle latitudes.