H-Component Variations Induced by Geomagnetic Storms during Solar Cycle 24: Insights from TAM Observatory

Abstract

Geomagnetic storms (GSs), driven by solar activity, produce significant disturbances in the Earth’s magnetic field—particularly in its horizontal component (H). This study investigates the response of the H-component to GSs during solar cycle 24 (2009–2019), using ground-based magnetometer data recorded at the TAM observatory in Tamanrasset, Algeria (22.79° N, 5.53° E), part of the INTERMAGNET network. A total of 130 storms were identified based on Dst-index thresholds and classified into 104 moderate (–100 nT < Dst ≤ –50 nT) and 26 intense (Dst ≤ –100 nT) events. The H-component was derived from the orthogonal north and east components (X, Y) of the geomagnetic field. The results reveal a gradual upward trend in the H-component over the solar cycle, consistent with secular geomagnetic field variations. However, during storm periods, the H-component exhibited significant decreases. These disturbances were quantified using the maximum deviation parameter ΔH_max, which displayed a statistically significant positive correlation with storm intensity (r = 0.71). Notably, the correlation was stronger for intense storms (r = 0.75) than moderate ones (r = 0.38). These results highlight the greater sensitivity of low-latitude geomagnetic observatories to high-intensity storms and demonstrate the diagnostic value of ΔH_max for space weather monitoring.