Solar Magnetic Polarity Effect on Neutron Monitor Count Rates from Latitude Surveys Versus Antarctic Stations

Kledsai
Poopakun
Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
Waraporn Nuntiyakul, Department of Physics and Materials Science, Faculty of Science, Chiang Mai University, Chiang Mai 50200, Thailand
David Ruffolo, Department of Physics, Faculty of Science, Mahidol University, Bangkok 10400, Thailand
Paul Evenson, Department of Physics and Astronomy, University of Delaware, Newark, DE 19716, USA
Jiang Peng, Polar Research Institute of China, Pudong, Shanghai 200136, China
Pongpichit Chuanraksasat, National Astronomical Research Institute of Thailand (NARIT), Chiang Mai 50180, Thailand
Marc Duldig, School of Natural Sciences, University of Tasmania, Hobart, Tasmania 7001, Australia
John Humble, School of Natural Sciences, University of Tasmania, Hobart, Tasmania 7001, Australia
Suyeon Oh, Department of Earth Science Education, Chonnam National University, Gwangju 61186, South Korea
Poster
The Galactic cosmic ray spectrum manifests subtle variations over the 22-year solar magnetic cycle in addition to more pronounced variations over the 11-year sunspot cycle. We conducted numerous latitude surveys by operating a neutron monitor onboard an icebreaker that traveled across a wide range of geomagnetic cutoff rigidities. Here we revisit our previous work to study spectral changes using 13 annual latitude surveys from 1994 to 2007 by comparing with neutron monitor data from Mawson instead of McMurdo, which closed in 2017, in order to allow a comparison with more recent latitude surveys. We confirm linear trends between count rates at different geomagnetic cutoff rigidities and changes in slope before and after the polarity reversal in 2000 as an effect of solar magnetic polarity. We performed two more latitude surveys (in 2019 and 2019-20) with a monitor similar to the 3NM64 in the previous surveys but without lead rings around the central tube, a so-called “semi-leaded neutron monitor.” We also found similar results for the relationship between the count rate of the semi-leaded neutron monitor and that of the Jang Bogo and Mawson neutron monitor stations in Antarctica. We acknowledge logistical support from Australia's Antarctic Program. The research is supported in part by Thailand Science Research and Innovation via Research Team Promotion Grant RTA6280002.