This paper presents an overview of results obtained during the solar activity cycle 23 up to minimum phase of solar cycle 24 on short term cosmic ray intensity decreases and how it relate to solar flares and interplanetary shocks. For this work we have obtained the data of cosmic ray intensity decreases and other parameters from ground-based neutron monitors (NMs) and NCEI respectively. we observed that 47 symmetric cosmic ray decreases in cosmic ray intensity in our list out of which 42 (89.36%) have been identified as being associated with X ray solar flares of different categories. Out of 42, most of the symmetric cosmic ray decreases are associated with M (42.86%) class and C (45.24%) class solar flares. Further out of 47 symmetric cosmic ray intensity decreases, 22 (46.81%) have been found to be associated interplanetary shocks. The associated interplanetary shocks are forward shocks out which arrival time of 17 (77.27%) interplanetary shocks have been found after the onset time of symmetric cosmic ray intensity decreases, The arrival time of 05 (22.72%) interplanetary shocks have been found before the onset time of symmetric cosmic ray intensity decreases. We perform a statistical analysis to find out the relation between cosmic ray intensity decreases with solar flares of different categories and obtain the correlation coefficient of 0.26, 0.14 and -0.34 for M, C and B class x-ray solar flares respectively.
Keywords: – cosmic ray intensity, symmetric cosmic rays, solar flares, interplanetary shocks.Shiva Soni*