Initial C-response estimation from 2010–2022 Hovd geomagnetic station data, western Mongolia

<jats:p>Geomagnetic depth sounding (GDS) is an electromagnetic induction method that uses long-period natural variations of the geomagnetic field to investigate the electrical conductivity structure of the lithosphere and upper mantle. In Mongolia, the use of geomagnetic observatory data for deep electromagnetic induction studies remains limited. This study applies the standard GDS methodology to long-term geomagnetic observations from the Hovd geomagnetic station and evaluates the feasibility of estimating the C-response from Mongolian geomagnetic data. To validate the methodological implementation, several representative 1-D synthetic electrical conductivity models of the lithosphere and upper mantle were tested. These models were designed to examine how different geo-electrical conditions, including a shallow conductive layer, a resistive lithosphere, and a conductive upper mantle, affect the real and imaginary components of the C-response. Continuous H, D, and Z geomagnetic field components recorded at the Hovd station during 2010–2022 were processed using standard procedures, including time synchronization, quality control, trend removal, filtering, resampling, and spectral analysis. Frequency-domain transfer functions and complex C-responses were then estimated from the processed data. The results show that, for periods longer than 7 days, the squared coherence reaches 0.7–0.9, indicating stable transfer-function estimates. The real and imaginary components of the observed C-response show a physically consistent trend that agrees with the general behavior predicted by the synthetic models. This study provides an initial methodological assessment of C-response estimation using long-term geomagnetic observations from the Hovd station. Because no electrical conductivity inversion was performed, the obtained C-responses are not directly interpreted in terms of specific geological structures or conductive anomalies. Instead, the results demonstrate the feasibility of applying standard GDS processing to Mongolian geomagnetic data and provide a methodological basis for future multi-station GDS studies and 2-D or 3-D electrical conductivity inversion in Mongolia.</jats:p>