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Transient Weakening of Earth’s Magnetic Shield Probed by a Cosmic Ray Burst

P. K. Mohanty, K. P. Arunbabu, T. Aziz, S. R. Dugad, S. K. Gupta, B. Hariharan, P. Jagadeesan, A. Jain, S. D. Morris, B. S. Rao, Y. Hayashi, S. Kawakami, A. Oshima, S. Shibata, S. Raha, P. Subramanian, and H. Kojima
Phys. Rev. Lett. 117, 171101 – Published 20 October 2016
Physics logo See Synopsis: A Crack in Earth’s Protective Shield

Abstract

The GRAPES-3 tracking muon telescope in Ooty, India measures muon intensity at high cutoff rigidities (15–24 GV) along nine independent directions covering 2.3 sr. The arrival of a coronal mass ejection on 22 June 2015 18:40 UT had triggered a severe G4-class geomagnetic storm (storm). Starting 19:00 UT, the GRAPES-3 muon telescope recorded a 2 h high-energy (20GeV) burst of galactic cosmic rays (GCRs) that was strongly correlated with a 40 nT surge in the interplanetary magnetic field (IMF). Simulations have shown that a large (17×) compression of the IMF to 680 nT, followed by reconnection with the geomagnetic field (GMF) leading to lower cutoff rigidities could generate this burst. Here, 680 nT represents a short-term change in GMF around Earth, averaged over 7 times its volume. The GCRs, due to lowering of cutoff rigidities, were deflected from Earth’s day side by 210° in longitude, offering a natural explanation of its night-time detection by the GRAPES-3. The simultaneous occurrence of the burst in all nine directions suggests its origin close to Earth. It also indicates a transient weakening of Earth’s magnetic shield, and may hold clues for a better understanding of future superstorms that could cripple modern technological infrastructure on Earth, and endanger the lives of the astronauts in space.

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  • Received 16 June 2016

DOI:https://doi.org/10.1103/PhysRevLett.117.171101

© 2016 American Physical Society

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Synopsis

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A Crack in Earth’s Protective Shield

Published 20 October 2016

Observations with India’s cosmic-ray telescope indicate that Earth’s magnetic field weakened during a 2015 geomagnetic storm, allowing cosmic rays to pass through.

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Authors & Affiliations

P. K. Mohanty, K. P. Arunbabu, T. Aziz, S. R. Dugad, S. K. Gupta*, B. Hariharan, P. Jagadeesan, A. Jain, S. D. Morris, and B. S. Rao

  • Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India†

Y. Hayashi and S. Kawakami

  • Graduate School of Science, Osaka City University, 558-8585 Osaka, Japan†

A. Oshima and S. Shibata

  • College of Engineering, Chubu University, Kasugai, Aichi 487-8501, Japan†

S. Raha

  • Bose Institute, 93/1, A.P.C. Road, Kolkata 700009, India†

P. Subramanian

  • Indian Institute of Science Education and Research, Pune 411021, India†

H. Kojima

  • Faculty of Engineering, Aichi Institute of Technology, Toyota City, Aichi 470-0392, Japan†

  • *gupta.crl@gmail.com
  • The GRAPES-3 Experiment, Cosmic Ray Laboratory, Raj Bhavan, Ooty 643001, India.

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Issue

Vol. 117, Iss. 17 — 21 October 2016

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