engleski

Cosmic Ray modulation by Solar Wind Disturbances

The relationship between solar wind parameters and ground-based modulation of cosmic rays was analysed. A total of 26 periods with Forbush decreases (FD) between 1998 and 2005 were selected. For each 21-day period an average cosmic ray count rate of 3-4 neutron monitor stations of similar rigidity at different longitudes was calculated, using hourly averaged data corrected for atmospheric pressure. In such way daily variations were eliminated. The in situ solar wind data were taken from the Advanced Composition Explorer (ACE) database. In 26 chosen periods Solar wind disturbances were identified as increases of Solar wind speed, IMF and magnetic field fluctuations. FD data were sorted by several criteria (origin, shock and overrecovery existence). FD magnitude correlated well with increase in IMF(B) and fluctuations(dB), the correlation coefficients being r=0.74 and r=0.75 respectively. A strong correlation was found for product of FD magnitude and duration for ICME with solar wind parameters products (e.g. IMF increase with ICME duration, r=0.79). FD magnitude showed two types of IMF increase dependence.

solar-terrestrial connection ; cosmic rays

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