Six large Forbush decrease (FD) events of solar cycles 24 and 25 from 2008 to 2021 were recorded from five neutron monitoring stations in Rome, Moscow, Fort smith, Oulu, and Thule around the world. These events were recorded on (November 3, 2021, July 15, 2017, September 6, 2017, June 21, 2015, September 11, 2014, and March 7, 2012). An investigation has been carried out in an effort to comprehend the possible factors that played a role in the occurrence of the large FD. During the investigation, various extreme solar and interplanetary events were analyzed. These include sunspot numbers, the disturbance storm time (Dst) index, and the Ap index. We also analyzed the solar wind parameters like speed, density, temperature, and interplanetary magnetic field (IMF) Bz component. During the event period, there is a sudden decrease in the Dst index similar to the Forbush decrease. The increase in the number of sunspots that occurred prior to the beginning of the FD provides evidence that this phenomenon may be connected to the occurrence of solar flares, which further influences the variation in cosmic rays. It is found a substantial southerly Bz dip, a sharp increase in solar wind temperature and speed, and no discernible density influence was seen in any significant FD.
