Heliospheric Modulation of Galactic Cosmic Rays During Solar Cycle 23
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Galactic cosmic rays (GCRs) encounter an outward-moving solar wind with cyclic magnetic-field fluctuation and turbulence. This causes convection and diffusion in the heliosphere. The GCR counts from the ground-based neutron monitor stations show intensity changes that are anti-correlated with the sunspot numbers with a lag of a few months. GCRs experience various types of modulation from different solar activity features and influence space weather and the terrestrial climate. In this work, we investigate certain aspects of the GCR modulation at low cut-off rigidity (R c≈1 GV) in relation to some solar and geomagnetic indices for the entire solar cycle 23 (1996 – 2008). We separately study the GCR modulation during the ascending phase of cycle 23 including its maximum (1996 – 2002) and the descending phase including its minimum (2003 – 2008). We find that during the descending phase, the GCR recoveries are much faster than those of the solar parameters with negative time-lag. The results are discussed in light of modulation models, including drift effects and previous results.
KeywordsCosmic ray modulation Cosmic rays Interplanetary medium Sun: activity – solar cycles
We thank the anonymous referee for his/her constructive comments. We also acknowledge the NGDC and OMNI web data service for different solar and geomagnetic parameter data and Ilya Usoskin for the Oulu Neutron monitor data. KK wishes to acknowledge the VEGA grant agency, Project 2/0040/13, for support.
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