The Cosmic Rays after being originated by their sources are modulated within the intergalactic regions. Within the solar system, Sun being, the solely active star. Further Changing condition over the solar disc will lead to small and large scale variation in the interplanetary region.
Sun influential region is inter stellar medium is known as Heliosphere, Heliosphere boundary are directly or indirectly related with sun and its outputs.
Sun spot numbers are normally being used as easily available parameters of solar activity, which shows 11 years periodicity.
Besides this many other solar indices have been used to study their relationship with various interplanetary geomagnetically parameters and also for CR intensity variations.
These CR variations are carried away be the solar winds with frozen-in solar magnetic fields. This leads to the two major types modulation in Cosmic Rays as detected by ground based instrumentation.