Variation of Low-Frequency Time-Code Signal During Geomagnetic Storm on November 10-15,2025: Observations and Analysis

A geomagnetic storm is a typical solar eruption activity. When high-speed solar wind or coronal mass ejections generated by solar eruptions impact the Earth, it can cause severe disturbances in the Earth's magnetic field within a short period of time, leading to changes in the ionosphere. For low-frequency time-code signals that rely on the ionosphere as a reflecting medium for long-distance propagation, the signal field strength and time deviation will also undergo corresponding changes, which will affect the normal propagation and reception of signal in space. This paper selects the geomagnetic storm phenomenon that occurred from November 10 to 15, 2025, and utilizes a low-frequency time-code signal monitoring system to conduct experimental research on the impact of geomagnetic storms on low-frequency time-code signals. The test group measured and analyzed the signal field strength data and time deviation data during this period, while combining parameters such as solar activity data and geomagnetic data, in an attempt to explore the causes and patterns of signal changes. The results indicate that a geomagnetic fluctuation occurred on November 12, resulting in a decrease in signal field strength over 2.3dBμV/m, time deviation data showed significant fluctuations, increasing by over 2.4ms, exhibiting a highly discrete state. The reason is that when a local geomagnetic storm occurs, the ionization level in the ionosphere increases. When low-frequency time code signals pass through the D layer, the equivalent emission height of the low ionosphere gradually decreases, resulting in signal attenuation and phase delay, which in turn leads to an increase in time deviation.