We report a thunderstorm-induced muon event (TIME) observed on 20 March 2020 using the GRAPES-3 muon telescope in Ooty, India. This event was investigated using complementary data from the INSAT-3DR satellite, the Indian lightning location network, and ground-based electric field measurements. A 1.4% suppression in muon flux ($12.4\sigma$ significance) was detected in the southeast sector, coinciding with intense upward-directed electric fields ($-5\mathrm{kV}/\mathrm{m}$) and elevated lightning activity. These observations support the hypothesis that upward electric fields cause energy losses in positive muons, resulting in reduced ground-level flux. The event provides evidence for the directional sensitivity of cosmic-ray secondaries to storm-time electric fields and highlights the unique capability of muon telescopes in probing high-altitude atmospheric electrodynamics. This study illustrates the value of integrating particle physics with atmospheric science, leveraging ground- and space-based observations to deepen our understanding of energetic atmospheric processes and their connections to space weather phenomena.

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• Atmospheric science
• Cosmic ray & astroparticle detectors
• Particle astrophysics