Characteristics of Seasonal Variation and Solar Activity Dependence of the Geomagnetic Solar Quiet Daily Variation

Abstract

Characteristics of seasonal variation and solar activity dependence of the X and Y components of the geomagnetic solar quiet (Sq) daily variation at Memambetsu in midlatitudes and Guam near the equator have been investigated using long‐term geomagnetic field data with 1 h time resolution from 1957 to 2016. The monthly mean Sq variation in the X and Y components (Sq‐X and Sq‐Y) shows a clear seasonal variation and solar activity dependence. The amplitude of seasonal variation increases significantly during high solar activities and is proportional to the solar F10.7 index. The pattern of the seasonal variation is quite different between Sq‐X and Sq‐Y. The result of the correlation analysis between the solar F10.7 index and the Sq‐X and Sq‐Y shows an almost linear relationship, but the slope of the linear fitted line varies as a function of local time and month. This implies that the sensitivity of Sq‐X and Sq‐Y to the solar activity is different for different local times and seasons. The pattern of the local time and seasonal variations of Sq‐Y at Guam shows good agreement with that of a magnetic field produced by interhemispheric field‐aligned currents (FACs), which flow from the summer to winter hemispheres in the dawn and dusk sectors and from the winter to summer hemispheres in the prenoon to afternoon sectors. The direction of the interhemispheric FAC in the dusk sector is opposite to the concept of Fukushima's model.

Excursions of Interhemispheric Field‐Aligned Currents in Africa

“…Also, it seems that the magnetic effect of the dusk side IHFACs on the ground was not fully canceled out by the effect from its returning current flowing in the ionosphere (Mazaudier & Venkateswaran, ). With this result, we confirmed the previous reports by Park et al (), Lühr et al (), and Shinbori et al () that the excursion of IHFACs is positive in the dusk.…”

“…This would mean that the currents at MPT are not only due to the IHFACs but also contain some Sq current effects (Yamashita & Iyemori, ). Our observed prominent IHFACs in February around dusk at MPT showed good agreement with those obtained from satellite (Lühr et al, ; Park et al, ) and ground‐based observations (Shinbori et al, ).…”

“…Generally, our results are consistent with the findings of Park et al (2011) and Lühr et al (2015) that used satellite magnetic field data to reveal the Northern Hemisphere positive (dawn) and negative (noon and dusk) IHFACs and their opposite excursions in the Southern Hemisphere between May and September. In addition, these results agree with the equatorial and low-latitude IHFACs found from the ground-based magnetometers (Bolaji et al, 2012;Shinbori et al, 2017;Yamashita & Iyemori, 2002). Although, some of these previous studies used different convention for their IHFACs direction (positive values indicate IHFACs from north to south and negative values indicate IHFACs from south to north), our results agree well with their results.…”

“…In contrast to this theoretical prediction, Park et al () found positive IHFACs in the dusk outside the South Atlantic Anomaly between May and September. In addition, Shinbori et al () identified that the direction of the IHFACs in the dusk is opposite to the concept of Fukushima's model. Furthermore, Richmond and Roble (), Takeda (), and Lühr et al () demonstrated that the observed cross‐equatorial currents in the Sq current system are an offshoot of IHFACs.…”

“…Other investigations in regard to the characteristics of the IHFACs had been studied experimentally (ground‐ and space‐based instruments) by Olsen (), Yamashita and Iyemori (), Park et al (), Bolaji et al (), Lühr et al (), and Shinbori et al (). Their studies confirmed the aforementioned theoretical prediction of Fukushima ().…”