Wavelet Analysis of Forbush Decreases at High-Latitude Stations During Geomagnetic Disturbances

We analyzed the behavior of Cosmic-Ray (CR) intensity during five geomagnetic events over 9-day periods of varying disturbance, using ground-based CR measurements from the Bartol Research Institute neutron-monitor program that occurred on 25th October – 2nd November 2003, 23rd – 31st July 2004, 13th – 21st May 2005, 13th – 21st Mar 2015, and 19th – 27th June 2015. A nine-day time frame gives us a reasonable time interval for data analysis before, during, and after the main event(s). These events have been deliberately chosen, intending to track Forbush Decreases (FDs) at high-latitude stations following geomagnetic storms of different intensity and duration from the perspectives of their origin and geoeffectiveness. FDs are observed when the magnetic fields entangled in and around a Coronal Mass Ejection (CME) exert a deflecting effect on galactic cosmic radiation, resulting in a sudden reduction in their intensities. The results revealed that the CR intensity dropped by 4 – 17% in the chosen events. The FDs examined were not typical, with multistage decrement during the event period. Furthermore, we have used the Discrete Wavelet Transform (DWT) technique to detect a singularity on the CR intensity at the stations described. The first three decomposition levels have proved sufficient to isolate the transients in CR intensity in conjunction with varying nature and intensities, ranging from intense to superintense geomagnetic storms to a high-intensity long-duration continuous auroral electrojet activity (HILDCAA) event. Finally, the findings of the detrended crosscorrelation technique showed a good association of percentage decrease in cosmic-ray intensity with the Dst index during the process. No noticeable lag has been found between the parameters discussed, which indicates a strong correlation between the IMF-Bz and the Dst index and the FD.