# Equinoctial Asymmetry in Solar Quiet Fields along the 120\({}^{\circ}\) E Meridian Chain
## 5 Conclusions  
In this study, measurements of the H component of the geomagnetic field acquired at six magnetometer observatories along the 120\({}^{\circ}\) E meridian chain in the years 1957-2013 were used to investigate the Sq range equinoctial asymmetry. Monthly values of the SqH range dA show large year-to-year variations at each observatory, but yearly averaged Sq range values (\(R\)) are comparable at all observatories. Equinoctial asymmetry is generally significant and positively correlated with geographic latitude. We identify three main features. First, the sign of the equinoctial asymmetry is opposite on the northern and southern sides of the Sq current focus, but the asymmetry is consistent at all observatories on the same side of the focus. SqH range maxima occur in spring at southern observatories but in autumn at northern observatories. Second, equinoctial asymmetry varies linearly with geographic latitude, increasing with increasing distances from the Sq current center, and its sign reverses at around 28.1\({}^{\circ}\) N, located near the focus of the average Sq current. This reversion latitude fluctuates in a range of 18 to 38 degrees when different confidence intervals of asymmetry coefficients are considered in the fitting procedure, reflecting the variability of the reversal latitude under different levels of the equinoctial asymmetry of the SqH. Third, the range and sign of the SqH equinoctial asymmetry do not appear to depend on solar activity. This suggests a possible origin in regional factors related to the ionospheric dynamo process. Further research is needed to investigate such issues as the latitudinal properties of the asymmetry at other longitudes or mechanisms that determine the sign of the asymmetry.  
Conceptualization, Y.W. and L.L.; methodology, Y.W.; software, Y.W.; validation, Y.W., L.L. and Z.R.; formal analysis, Z.R.; investigation, Y.W.; resources, Y.W.; data curation, Y.W.; writing--original draft preparation, Y.W.; writing--review and editing, L.L. and Z.R.; visualization, Y.W.; supervision, L.L.; project administration, Y.W.; funding acquisition, Z.R. All authors have read and agreed to the published version of the manuscript.  
This research was funded by the National Key R&D Program of China (Grant No. 2018 YFC1503504-03), IEF Grant of CEA (Grant No. 2021 IEF0709), and the APSCO Earthquake Research Project Phase II and ISSI-BJ project: Integrating Satellite and Ground Observations for Earthquake Signatures and Precursors, the National Natural Science Foundation of China (417/4161), the Open Research Project of Large Research Infrastructures of CAS--\"Study on the interaction between low/mid-latitude atmosphere and ionosphere based on the Chinese Meridian Project\", and the Meridian Project of China provided funding in the geomagnetic chain, respectively.  
Not applicable.  
The data used in this study are available from the World Data Centre for Geomagnetism in Kyoto, Edinburgh, and GFZ: [[http://wdc.kugi.kyoto-u.ac.jp](http://wdc.kugi.kyoto-u.ac.jp)]([http://wdc.kugi.kyoto-u.ac.jp](http://wdc.kugi.kyoto-u.ac.jp)), ftp.mnh.ac.uk, and ftp.gfz-potsdam.de/pub/home/obs/Kp_ap_Ap_SN_F107 (accessed on 18 September 2021).  
The authors are grateful for all available data from the respective organizations. We thank [PERSON] of IGGCAS for his comments and suggestions, and we are sincerely grateful to the reviewers for their time, effort, and constructive remarks regarding the improvement of our work.  
The authors declare no conflict of interest.