The ionospheric Sq current system obtained by spherical harmonic analysis

Abstract

[1] An earlier comprehensive analysis of geomagnetic tides by Winch is revisited to display changes in the current systems with season and longitude. The data used come from the quiet Sun years [1964][1965]. We choose to present some total equivalent current systems, being the sum of the external and internal parts derived in the spherical harmonic analysis. The latitudes and local times of the current system foci are generally in agreement with other workers. The amplitudes of the current system vortices follow an annual variation with maximum in summer. The longitude variations of the vortex amplitudes vary as the inverse of the magnetic field strength at both equinoxes but have different variations at the solstices. Other longitude maxima which have been reported in the equatorial electrojet intensity were not found. We examine in detail the "invasions" of the summer current systems across the equator, identifying these as signatures of field-aligned currents (FACs). The tilting of current contours with respect to the equator is interpreted as being due to midday FACs. As others have found, the identification of afternoon FACs is more difficult. The seasonal swap-over of FAC directions occurs not in September but in October-November.Citation: Stening R. J., and D. E. Winch (2013), The ionospheric Sq current system obtained by spherical harmonic analysis,

Sq and EEJ—A Review on the Daily Variation of the Geomagnetic Field Caused by Ionospheric Dynamo Currents

“…54a. Interestingly, some features are in agreement with satellite measurements by Pedatella et al (2011) and others features are in agreement with ground measurements by Stening and Winch (2013). For the Northern Hemisphere, the model predicts strong Sq currents over the American sector throughout the year, which is consistent with the ground measurements.…”

“…The longitudinal variation of the main field B modulates the U × B field and ionospheric conductivities (see (4)- (8)), causing the longitudinal variation in the dynamo-region currents as well as inter-hemispheric field-aligned currents (Stening 1971;Le Sager and Huang 2002b). The longitudinal variation of the Sq current intensity was recently presented by Pedatella et al (2011) based on satellite magnetometer data and by Stening and Winch (2013) based on ground magnetometer data. Figure 54 compares the two results, revealing significant differences in the pattern of the longitudinal variation.…”

“…3, where the current intensity in the summer hemisphere is approximately three times stronger than that of the winter hemisphere. The Sq currents in the winter hemisphere are sometimes so weak that the "disappearance" of the current whorl occurs (e.g., Campbell et al 1993;Rastogi 1993;Stening and Winch 2013).…”

“…Pedatella et al (2011) used the CHAMP vector magnetometer observations during , while Stening and Winch (2013 used magnetic data from 130 ground stations during 1964-1965, originally analyzed by Winch (1981). For the baseline of Sq, Pedatella et al (2011) used the POMME6.1 geomagnetic field model , while Stening and Winch (2013) used the daily mean value. Moreover, Fig.…”

Geomagnetic observatory monthly series, 1930 to 2010: empirical analysis and unmodeled signal estimation

“…This highlights the difficulty of modeling globally the complex magnetic fields at high latitudes from monthly values. A strategy similar to that presented here could be followed for hourly values if one were to also model Sq variations (see Stening and Winch 2013). This would not only have implications for the analysis of annual and semiannual signals; indeed, it would also require accounting for periodic fields at higher frequencies (see Love and Rigler 2014).…”