_____________________________________________________________________________________________________ *Corresponding author: E-mail: kfdarlene@gmail.com; Physical Science International Journal 24(6): 44-55, 2020; Article no.PSIJ.58988 ISSN: 2348-0130 Heliospheric Modulation of GCR at Mid and High Latitudes Kingsley Chukwudi Okpala 1 , Darlene Florence Kalu 1* and Nnaemeka Onyekachi Njoku-Achu 1,2 1 Department of Physics and Astronomy, University of Nigeria, Nsukka, Enugu State, Nigeria. 2 NASRDA, Centre for Basic Space Science, Nsukka, Enugu State, Nigeria. Authors’ contributions This work was carried out in collaboration among all authors. Author KCO designed the study, performed the statistical analysis, wrote the protocol and wrote the first draft of the manuscript. Authors DFK and NONA managed the analyses of the study and the literature searches. All authors read and approved the final manuscript. Article Information DOI: 10.9734/PSIJ/2020/v24i630198 Editor(s): (1) Dr. Lei Zhang, Winston-Salem State University, USA. (2) Dr. Thomas F. George, USA. Reviewers: (1) Roshni Dave, India. (2) Jan Louis Raath, North-West University, South Africa. (3) Caio Lagana Fernandes, University of Sao Paulo, Brazil. (4) Mukesh K. Jothe, Barkatullah University Institute of Technology, India. (5) Abdelmadjid Maireche, University of M'sila, Algeria. Complete Peer review History: http://www.sdiarticle4.com/review-history/58988 Received 23 May 2020 Accepted 29 July 2020 Published 07 August 2020 ABSTRACT The variations of Galactic Cosmic Ray (GCR) as compared with the behaviour of various solar activity indices, heliospheric parameters and the geomagnetic index Ap during 1999-2015, which covers part of cycles 23 and cycle 24 have been studied. Two sets of data were considered, consisting respectively of all days of the month and the five quietest days. Neutron Monitor Stations of Moscow and Rome (mid latitude stations) and Inuvik and Oulu (High latitude stations) were employed. Cosmic Ray (CR) wave characteristics were obtained by the harmonics method. The mean, diurnal amplitude of the first, second, and third harmonics were calculated and profiled. Furthermore, correlation analysis was carried out to determine the association between parameters. Results showed that the total magnetic field B T and the sunspot number (SSN) showed the strongest association with CR in both quiet conditions and all day conditions considered. The higher harmonics showed a slightly stronger association with CR than lower Original Research Article