全ピッチ角領域をカバーした宇宙線ミューオン観測ネットワークによる 地磁気嵐前兆現象の観測

*宗像 一起[1], 桑原 孝夫[1], 服部 哲弥[1]
井上 和也[1], 安江 新一[1], 加藤 千尋[1]
藤井 善次郎[2], Marcus L. Duldig[3]
Nelson J. Schuch[4], John W. Bieber[5]

信州大学理学部[1]
名古屋大学太陽地球環境研究所[2]
Australian Antarctic Division, Australia[3]
National Institute for Space Research, INPE, Brazil[4]
Bartol Research Institute, University of Delaware, USA[5]

A prototype muon detector network covering a full range of cosmic ray pitch angles

*Kazuoki Munakata[1] ,Takao Kuwabara [1],Tetsuya Hattori [1]
Kazuya Inoue [1],Shin-ichi Yaue [1],Chihiro Kato [1]
Zenjirou Fujii [2],Marcus L. Duldig [3]
Nelson J. Schuch [4],John W. Bieber [5]
Faculty of Science, Shinshu University[1]
STE Lab., Nagoya University[2]
Australian Antarctic Division, Australia[3]
National Institute for Space Research, INPE, Brazil[4]
Bartol Research Institute, University of Delaware, USA[5]

A systematic survey of cosmic ray precursors of geomagnetic storms recorded by muon detector network showed that 89% of large storms were associated with precursors seen in the pitch-angle distribution of cosmic-ray intensity in space (Munakata et al., JGR, 105, A12, 27457, 2001). The network at that time, however, had a big gap in directional coverage over the Atlantic and European regions and we were not able to analyze 43.6% of storms. To fill this gap, we recently installed a prototype multi-directional muon detector in southern Brazil and started a preliminary measurement. In this report, we will report on the performance of this new instrument, particularly focusing on its directional coverage over the gap mentioned above. We will also analyze the new network data and examine the expected appearance of muon precursors over a full range of pitch angle.

We analyze the pitch angle distributions observed by a prototype muon detector network covering a full pitch angle range. The network includes a new muon detector installed at Sao Martinho in Brazil. Sample pitch angle distributions are obtained from preliminary analyses for periods including the Easter ground level enhancement (GLE) on April 15 and a large geomagnetic storm on March 31, 2001. It is confirmed in both sample distributions that the pitch angle coverage by the network is greatly improved by the new detector installed in Brazil. The pitch angle distribution showed no systematic intensity excess from 0° pitch angle (sunward IMF) direction immediately after the onset of the Easter GLE, but the network observed an enhancement of the first order anisotropy preceding the onset of GLE. No clear loss-cone precursor was found during a period preceding the geomagnetic storm on March 31, but the network observed instead intensity excesses around 0° pitch angle, half a day ahead the storm onset. We disc ss these results taking account of the possible contribution from the atmospheric temperature effect. It is concluded that extension of the Brazilian detector in size is required for more precise and reliable observations.