Wavelet Coherence Analysis of Magnetic Declination During Quiet and Disturbed Geomagnetic Activity

Abstract

This study investigates characteristics of magnetic declination (D) at the mid-latitude Dusheti Geophysical Observatory and it’s coupling to solar wind during both quiet and disturbed periods, with a specific focus on the intense storm of May 11, 2024. We analyze one-minute resolution geomagnetic and solar wind data from July 2023 to July 2024, . Using power spectral density (PSD) and continuous wavelet transform (CWT), we characterize the spectral behavior of declination. The analysis confirms the persistent presence of diurnal (24h) and semidiurnal (12h) periodicities, characteristic of the quiet time, also a period of 8h, while demonstrating significant spectral broadening during the geomagnetic storm. We then employ wavelet coherence analysis to quantify the coupling between declination and the IMF magnitude (B), its southward component (Bz), and the solar wind velocity (v). The results reveal distinct coupling mechanisms: coherence with B is dependent on storm intensity, being strong only during the intense May 11 storm. In contrast, coherence with Bz is robust and significant during both intense (May 11) and moderate (April 19) storms, highlighting its fundamental role in driving disturbances in geomagnetic data regardless of storm intensity. This work demonstrates the effectiveness of wavelet coherence for evaluating solar wind magnetosphere coupling at different frequencies.