Study on 2015 June 22 Forbush decrease with the muon telescope in Antarctic

TL;DR

This study analyzes a significant Forbush decrease event in June 2015 using data from a newly installed Antarctic muon telescope and other cosmic ray detectors, revealing complex features in cosmic ray fluctuations.

Contribution

First surface muon telescope in Antarctica used to study cosmic ray variations during a major Forbush decrease event, highlighting differences in detection timelines and event profiles.

Findings

Delayed FD onset at Zhongshan muon telescope by 2.5 hours

FD profile exhibited a four-step decrease

Traditional classification methods were insufficient to explain the observed FD

Abstract

By the end of 2014, a cosmic ray muon telescope was installed at Zhongshan Station in Antarctic and has been continuously collecting data since then. It is the first surface muon telescope to be built in Antarctic. In June 2015, five CMEs were ejected towards the Earth initiating a big large Forbush decrease (FD) event. We conduct a comprehensive study of the galactic cosmic ray intensity fluctuations during the FD using the data from cosmic ray detectors of multiple stations (Zhongshan, McMurdo, South Polar and Nagoya) and he solar wind measurements from ACE and WIND. A pre-increase before the shock arrival was observed. Distinct differences exist in the timelines of the galactic cosmic ray recorded by the neutron monitors and the muon telescopes. FD onset for Zhongshan muon telescope is delayed (2.5h) with respect to SSC onset. This FD had a profile of four-step decrease. The traditional one- or two-step classification of FDs was inadequate to explain this FD.