Effect of the Non‐Dipole Field on the Seasonal Variation of the Geomagnetic Sq(Y)

Abstract

It is well known that the solar quiet daily geomagnetic variation (Sq) at mid-low latitudes primarily originates from the dayside ionospheric E-region dynamo (Matsushita, 1967;Forbes & Lindzen, 1976;Richmond, 1979;Yamazaki & Maute, 2017). According to the classical dynamo theory, the distribution of the geomagnetic field, the tidal wind, and the ionospheric conductivity control the behavior of the Sq type variation (Campbell, 1982). In particular, the geomagnetic field not only modulates the conductivity through its dependence on the electron and ion gyrofrequencies but also controls the dynamo electric field (Le Sager & Huang, 2002;Stening, 1971;Takeda, 1996). The modulation on the conductivity is mainly through the change in the gyrofrequencies of the electrons and ions in the ionospheric dynamo region. At the regions with weaker geomagnetic field strength, such as the South Atlantic Ocean anomaly region (SAA), both the electron and ion gyrofrequencies are lower than those at other regions. The lower boundary of the dynamo region, which is defined by the altitude where the electron gyrofrequency is equal to the electron-neutral collision frequency, is higher at the SAA region. This is also the case at the upper boundary, which is defined by the altitude where the ion gyrofrequency is equal to the ion-neutral collision frequency. The dynamo region will upward shift at the SAA region, and thus they are located at altitudes where the electron density is larger. This upward shift causes the enhancement of both the height integrated Pedersen (Σ P ) and Hall conductivities (Σ H ). Using a numerical calculation, Takeda (1996) estimated the height of integrated Pedersen and Hall conductivities for different geomagnetic field strengths. He found that the Σ P and Σ H are 42 and 26 times stronger at the regions with 10% of the normal geomagnetic field strength, respectively. As a consequence of these factors, the Sq electric current systems show a remarkable dependence on season, solar activity,

A Simulation Study of the Modulation of the Geomagnetic Field Configuration on the Seasonal Variation of Ionospheric Sq Currents

“…In regions with strong magnetic fields like Eurasian magnetic anomaly region, the annual mean appears smaller; however, it is larger in regions such as South Atlantic anomaly region indicating an inverse relationship between geomagnetic field strength and the annual mean of Δ K qλ . This conclusion has been validated through observational studies (Takeda, 2013a; Tian et al., 2022). Notably, a significant anomalous weakening of Δ K qλ has been observed in Northern Hemisphere corresponding to South Atlantic anomaly region which may be attributed to conjugate structure of magnetic fields showing positive correlation between conjugate points' magnetic anomalies and Sq current.…”

“…Tian et al. (2022) suggest a positive correlation between the annual variation of geomagnetic perturbation (Sq1) and geomagnetic fields in the Northern Hemisphere. The Sq1 in magnetic anomaly regions is mainly attributed to interhemispheric field‐aligned currents.…”

“…The role of inter‐hemisphere coupling as a contributing factor to the semiannual variation of ionospheric electric field has in previous simulation studies (Yu et al., 2006). The long‐term analysis (Tian et al., 2022) revealed a more pronounced semiannual variation in the South Atlantic anomaly region, indicating an asymmetry in magnetic field structure between hemispheres that drives a stronger inter‐hemisphere field‐aligned current. This impact is further accentuated in the presence of intensified solar radiation.…”

“…In previous studies, the daily variation of Sq(Y), representing the difference between the maximum and minimum values of the geomagnetic Y component, has been identified as a readily observable parameter that characterizes ionospheric geomagnetic perturbations (Takeda, 2002(Takeda, , 2013a(Takeda, , 2013bTian et al, 2022). In the Northern Hemisphere, eastward geomagnetic perturbations occur at dawn and westward geomagnetic perturbations take place at dusk, corresponding to a northward current on the dawn side and a southward current on the dusk side, respectively.…”

“…Previous studies focused on the local geomagnetic anomalies affecting the seasonal variation characteristics of Sq current but did not entirely exclude the global influence caused by the tilt angle of geomagnetic field (Le Sager & Huang, 2002;Takeda, 2013aTakeda, , 2013bTian et al, 2022). Two hypothetical geomagnetic field configurations are employed in our simulation study to address this issue.…”