Abstract
AbstractBased on magnetic field data from the Swarm satellite constellation advanced estimates of field‐aligned and radial currents at middle and low latitudes can be derived. Detailed results have been obtained for low‐latitude (14°–35° magnetic latitude) interhemispheric field‐aligned currents related to the solar quiet (Sq) current system. The continuous data set of five years allows resolving the dependences on local time, season, and longitude. We confirm the known current flow from the southern to the northern hemisphere around June solstice. Unexpected results are obtained for the months following December. Stratospheric sudden warming events are suggested as a reason for that. These phenomena are known to amplify lunar tides and atmospheric planetary waves. Furthermore, we investigated the mean characteristic of the meridional current systems connected to the wind‐driven F region dynamo above the magnetic equator. Typical features of radially downward currents around noon and upward currents in the evening sector could be confirmed. From a detailed analysis of the connected field‐aligned current distribution we deduced that the mean altitude of the dynamo region is higher in the evening than around noon. And it appears also at greater heights in the western hemisphere than in the eastern. Special current configurations are encountered in the longitude range containing the South Atlantic Anomaly. Here summer‐like conditions are prevailing through all seasons. This infers that the ionospheric conductivity is significantly enhanced in this region of weak magnetic field strength.
Highlights
Ground‐based magnetometers regularly observe a diurnal waveform at middle and low latitudes during daytime
Detailed results have been obtained for low‐latitude (14°–35° magnetic latitude) interhemispheric field‐aligned currents related to the solar quiet (Sq) current system
The aim of this study is to find out the true average characteristics of interhemispheric field‐aligned currents (IHFACs) and F region dynamo currents by resolving the details of the various dependences
Summary
Ground‐based magnetometers regularly observe a diurnal waveform at middle and low latitudes during daytime This is commonly termed the solar quiet (Sq) variation (for reviews, see Campbell, 1989; Yamazaki & Maute, 2017). The difference in solar zenith angle between the two hemispheres, in particular during solstices, leads to asymmetries in ionospheric conductivities. All these effects may cause differences in the efficiencies of the wind dynamos at magnetically conjugate points in the two hemispheres (e.g., van Sabben, 1964). Fukushima (1979) proposed a set of IHFACs that should be suitable to remove the differences of the Sq systems According to his model most intense IHFACs connect the Sq foci in the two hemispheres (near 35° magnetic latitude (MLat)) around noontime. For June solstice conditions these authors could confirm in principle the predictions of Fukushima (1979, 1994) except for the evening hours, where they found IHFACs from the summer to the LÜHR ET AL
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