Infrasonic observation of microbarom signals in the middle latitude: An investigation of summer and winter season on the upper atmosphere

We report the result of infrasound observation applied to microbaroms between peak winter and summer season of 2018, obtained from ambient noise. For our study several infrasound sensor over Shikoku island was used, which had been installed since 2015. Observation of our microbaroms shows regular pressure variations of a few milliPascals at around 0.2 Hz produced by the incoming of infrasound arrived from the ocean fields. As the result, their amplitudes show prominent greatly in winter time expect to depend on the appearance of the atmospheric sound ducts between the surface and the level at certain altitudes. These ducts depend on the wind structure and vertical temperature of the atmosphere. For our station close to the ocean, sound ducting from the oscillation wave of the ocean surface, requires strong contribution westerly winds at certain upper reflection point. With a global reanalysis horizontal wind assimilation, the seasonal wind structure at our geographical study, near 33° N, is shown to distinguish and to account for the observed profiles of microbaroms. Finally, we suggest that use of our network of infrasound sensors would provide a global complementary result to monitor the upper atmosphere conditions in the middle latitude regions.