Research Article

Local environmental effects on cosmic ray observations at Syowa Station in the Antarctic: PARMA-based snow cover correction for neutrons and machine learning approach for neutrons and muons

¹ National Institute of Polar Research, Tachikawa, Tokyo 190-8518, Japan
² The Graduate University for Advanced Studies, Tachikawa, Tokyo 190-8518, Japan
³ Okinawa Institute of Science Technology Graduate University, Onna-son, Okinawa 904-0495, Japan
⁴ Japan Atomic Energy Agency, Tokai, Ibaraki 319-1184, Japan
⁵ Shinshu University, Matsumoto, Nagano 390-8621, Japan
⁶ Polar Environment Data Science Center, Joint Support-Center for Data Science Research, Research Organization of Information and Systems, Tachikawa, Tokyo 190-0014, Japan
⁷ National Institute of Technology (KOSEN), Hitachinaka, Ibaraki 312-8508, Japan

^* Corresponding author: kataoka.ryuho@nipr.ac.jp

Received: 8 July 2022
Accepted: 5 October 2022

Abstract

Solar modulation of galactic cosmic rays around the solar minimum in 2019–2020 looks different in the secondary neutrons and muons observed at the ground. To compare the solar modulation of primary cosmic rays in detail, we must remove the possible seasonal variations caused by the atmosphere and surrounding environment. As such surrounding environment effects, we evaluate the snow cover effect on neutron count rate and the atmospheric temperature effect on muon count rate, both simultaneously observed at Syowa Station in the Antarctic (69.01° S, 39.59° E). A machine learning technique, Echo State Network (ESN), is applied to estimate both effects hidden in the observed time series of the count rate. We show that the ESN with the input of GDAS data (temperature time series at 925, 850, 700, 600, 500, 400, 300, 250, 200, 150, 100, 70, 50, 30, and 20 hPa) at the local position can be useful for both the temperature correction for muons and snow cover correction for neutrons. The corrected muon count rate starts decreasing in late 2019, preceding the corrected neutron count rate which starts decreasing in early 2020, possibly indicating the rigidity-dependent solar modulation in the heliosphere.