A curious case of monsoon low frequency reverberations from the mighty Himalayas

Abstract

This paper presents an investigation of monsoon-generated infrasound events recorded in Islamabad, Pakistan. The majority of these events originate from a specific azimuth band, pointing towards the Himalaya mountain range in the Indian subcontinent. Although the monsoon phenomenon is well-known to develop over the Bay of Bengal and the Arabian sea and enters Pakistan along the foothills of Himalayas and south-eastern areas of Sindh, Pakistan, the associated infrasound signals have a distinct frequency signature that differs from mountain-associated waves (MAW) and microbaroms. While MAW have a frequency of 0.015–0.1 Hz and microbaroms are found in the frequency band 0.13–0.35 Hz, the monsoon-associated signal is mostly observed in the frequency band 0.6–1.1 Hz. This research highlights the potential of studying monsoon-generated infrasound events as an unexplored area of research in the study of the atmosphere and an important weather phenomenon. The paper also reports a strong correlation between these events and rainfall precipitation, which could potentially benefit early weather warning systems, especially in the context of climate change. The MATLAB-based analysis tool, MatSeis, is used for the detection of infrasound events, and the data collected from a four-element seismic acoustic array with Chaparral Physics 50A sensors in Islamabad are analyzed from June to September in the years 2021 to 2022. Overall, this study highlights the significance of monitoring and analyzing monsoon-generated infrasound events in the region.