The Pierre Auger Observatory scaler mode for the study of solar activity modulation of galactic cosmic rays (original) (raw)
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Study of intensity fluctuations in cosmic rays during Forbush-decreases
2011
Abstract: A fast decreases of GCR intensity during one-two days and then it's gradually recovery in 5–7 days are called the Forbush decreases (Fds). They are formed after the outstanding flares on the Sun and intensive solar cor-onal mass ejecta. These phenomena appear randomly in time, sporadically without any regularity, increasing its fre-quency in maxima of the solar activity. The strong shocks propagating in the interplanetary medium sweep out ener-getic cosmic rays and this effect is known as Forbush decrease of the cosmic ray intensity. Studying the cosmic ray spectrum during the times of Forbush decreases would provide a tool for probing large scale interplanetary irregulari-ties. The present study dealt with the relationship between Interplanetary Coronal Mass Ejections (ICMEs) and the count rate decrease detected by the muon detector/neutron monitor. The emphasis is given on the analysis of the solar event, studying data from the Interplanetary medium to identify the i...
Journal of Geophysical Research, 2009
a Forbush decrease observed at Polar in the Earth's magnetosphere was also seen at the INTEGRAL spacecraft outside the magnetosphere during a very active time in the solar wind. High-resolution energetic particle data from ACE SIS, the Polar high-sensitivity telescope, and INTEGRAL's Ge detector saturation rate, which measures the galactic cosmic ray (GCR) background with a threshold of $200 MeV, show similar, short-period GCR variations in and around the Forbush decrease. Focusing upon the GCR intensity within a 3-day interval from 19 August 2006 to 21 August 2006 reveals many intensity variations in the GCR on a variety of time scales and amplitudes. These intensity variations are greater than the 3s error in all the data sets used. The fine structures in the GCR intensities along with the Forbush decrease are propagated outward from ACE to the Earth with very little change. The solar wind speed stays relatively constant during these periods, indicating that parcels of solar wind are transporting the GCR population outward in the heliosphere. This solar wind convection of GCR fine structure is observed for both increases and decreases in GCR intensity, and the fine structure increases and decreases are bracketed by solar wind magnetic field discontinuities associated with interplanetary coronal mass ejection (ICME) magnetosheath regions, clearly seen as discontinuous rotations of the field components at ACE and at Wind. Interestingly, the electron heat flux shows different flux tube connectivity also associated with the different regions of the ICME and magnetosheath. Gosling et al. (2004) first discussed the idea that solar energetic particle intensities commonly undergo dispersionless modulation in direct association with discontinuous changes in the solar wind electron strahl. The observations show that the intensity levels in the GCR flux may undergo a similar partitioning, possibly because of the different magnetic field regions having differing magnetic topologies.
Research in Astronomy and Astrophysics, 2021
Forbush decrease (FD), discovered by Scott E. Forbush about 80 years ago, is reffered to as the non-repetitive short-term depression in galactic cosmic ray (GCR) flux, presumed to be associated with large-scale perturbations in solar wind and interplanetary magnetic field (IMF). It is the most spectacular variability in the GCR intensity which appear to be the compass for investigators seeking solar-terrestrial relationships. The method of selection and validation of FD events are very important to cosmic ray scientists. We have deployed a new computer software to determine the amplitude and timing of FDs from dailyaveraged cosmic ray (CR) data at OULU neutron monitor station. The code selected 230 FDs between 1998 and 2002. In an attempt to validate the new FD automated catalog, the relationship between the amplitude of FDs, and IMF, solar wind speed (SWS) and geomagnetic storm indices (Dst, kp, ap) is tested here. A two-dimensional regression analysis indicates significant linear relationship between large FDs (CR(%) ≤ −3) and solar wind data and geomagnetic storm indices in the present sample. The implications of the relationship among these parameters are discussed.