Geomagnetic field variations due to solar tides at the Indian Observatories

Abstract This study investigates the response of solar (S) tidal signatures on the horizontal component of the geomagnetic field at two observatories in India during 1980–2002 over solar cycles (SC) 21–23: Hyderabad (HYB), located in the low-latitude region, and Ettaiyapuram (ETT), situated at the magnetic equator. HYB represents the characteristics of solar quiet (Sq), while ETT is under the equatorial electrojet (EEJ) effect. Our results show the additional information about ter (S3), and quarta-diurnal (S4) tidal signatures of Sq and EEJ, along with diurnal (S1) and semi-diurnal (S2) at both observatories. In Sq solar tide, the average amplitude of S1 tide is consistently higher than that of EEJ tide by ~ 10%. During the same period, the S2, S3, and S4 tidal signatures of Sq are weaker than EEJ by ~ 2%, 5%, and 2.5%, respectively. During solar cycle maxima, the amplitude of the Sq tide is higher in SC-21 than in SC-22 and SC-23 by ~ 13% and 16%, while SC-22 has higher EEJ tidal amplitudes than other SCs by ~ 9%. We observe that the tidal signatures of Sq and EEJ closely follow the trend of solar radio flux ( $$\sqrt{F10.7}$$ F 10.7 ), except for S4 of Sq. The Pearson correlation coefficients (P) between $$\sqrt{F10.7}$$ F 10.7 and Sq/EEJ tidal amplitudes exhibit negative to positive correlation coefficients during different phases of SCs. The solar tidal amplitudes of Sq/EEJ (S1-S4) with $$\sqrt{F10.7}$$ F 10.7 during D, E, and J seasons have varying correlation coefficients, indicating that each tide has a distinct response on the geomagnetic field. Graphical Abstrac

One second vector and scalar magnetic measurements at the low-latitude Choutuppal (CPL) magnetic observatory

One second measurements of the geomagnetic field variations, which meet INTERMAGNET quality and transmission specifications, require very special conditions to be maintained at the observatories over sustained periods of time, which pose serious challenges for the operators, particularly when infrastructural and environmental conditions are far from ideal. This work presents the progressive steps, which led to the successful setup of such measurements at the new magnetic observatory of the Council of Scientific and Industrial Research (CSIR)-National Geophysical Research Institute (NGRI) in the Choutuppal (CPL) campus, Hyderabad (HYB), India. The 1 s magnetic measurements in trial mode commenced in 2015 using the newly developed observatory-grade 1 s fluxgate magnetometer, GEOMAG-02MO, from Research Centre GEOMAGNET (GM), Ukraine, and the Overhauser proton precession magnetometer, GSM-90F1, along with the data acquisition system, Magrec-4B from Mingeo, Hungary. Iterative tuning of the setup led to the generation of good quality data from 2016 onward. The processes of commissioning this setup in low-latitude conditions, with the aim of producing 1 s definitive data, and the characteristics of the data from this new instrument are presented here