Measurements of Forbush Decrease Events at the Center of the South Atlantic Magnetic Anomaly With Muon Detectors

We present the construction and validation of a low‐cost muon detector in Paraguay, located at the center of the South Atlantic Magnetic Anomaly (SAMA), where the geomagnetic cutoff rigidity is 9.63 GV. The detector consists of plastic scintillator plates coupled with silicon photomultipliers for light detection. To verify its performance, we measured the average muon flux rate and investigated its correlation with geomagnetic activity, particularly the disturbance storm time (Dst) index, during the May and October 2024 Forbush Decrease events. Using the Truncated Time‐Shift test—a recent statistical method for comparing time‐series—we found a strong correlation, indicating our detector reliably measures the muon flux over time. Our measurements also allowed us to resolve the detailed morphology of the Forbush decreases, by comparison with local magnetic field fluctuations. These initial results represent a step forward in ground‐level radiation monitoring within the SAMA, and highlight the potential of economical muon detectors as components of early‐stage diagnostic systems for space weather forecasting.