Middle‐Atmosphere Dynamics Observed With a Portable Muon Detector

Abstract

In the past years, large particle physics experiments have shown that muon rate variations detected in underground laboratories are sensitive to regional, middle‐atmosphere temperature variations. Potential applications include tracking short‐term atmosphere dynamics, such as Sudden Stratospheric Warmings. We report here that such sensitivity is not only limited to large surface detectors under high‐opacity conditions. We use a portable muon detector conceived for muon tomography for geophysical applications, and we study muon rate variations observed over 1 year of measurements at the Mont Terri Underground Rock Laboratory, Switzerland (opacity of ~700 meter water equivalent). We observe a direct correlation between middle‐atmosphere seasonal temperature variations and muon rate. Muon rate variations are also sensitive to the abnormal atmosphere heating in January–February 2017, associated to a Sudden Stratospheric Warming. Estimates of the effective temperature coefficient for our particular case agree with theoretical models and with those calculated from large neutrino experiments under comparable conditions. Thus, portable muon detectors may be useful to (1) study seasonal and short‐term middle‐atmosphere dynamics, especially in locations where data are lacking such as midlatitudes, and (2) improve the calibration of the effective temperature coefficient for different opacity conditions. Furthermore, we highlight the importance of assessing the impact of temperature on muon rate variations when considering geophysical applications. Depending on latitude and opacity conditions, this effect may be large enough to hide subsurface density variations due to changes in groundwater content and should therefore be removed from the time series.

Development of Scintillator‐Based Muon Detectors for Muography

“…Since the overburden acts as a "high-energy-pass filter", it has been also possible to study the variation in time of the high-energy muon flux and its correlation with the temperature variations at the top of the atmosphere. In particular, a very promising correlation has been pointed out with brief events, referred to as sudden stratospheric warmings (SSW), where the atmosphere's density decreases quickly, resulting in a sharp increase of the muon flux (Tramontini et al, 2019).…”

Muographic monitoring of hydrogeomorphic changes induced by post-eruptive lahars and erosion of Sakurajima volcano

“…Changes in atmosphere’s thermal state affect the muon production 59 , 60 that has to be taken into account in muographic monitoring 40 . The F change from the F muon flux due to pressure and temperature changes can be quantified with the following empirical formula: where is the barometric coefficient, p is the pressure change from the average pressure that is measured at the observational site, is the temperature coefficient that depends on amount of transferred materials and T is the weighted average of temperatures measured under different atmospheric pressures.…”

Atmospheric & Geodesic Controls on Muon Rate: A Numerical Study Based on CORSIKA

“…The sensitivity of the technique relies on the model's accuracy, which should take into account the experimental conditions in the most realistic possible way. For instance, it has been shown in Jourde et al [11] and Tramontini et al [12] that atmospheric conditions (pressure and temperature) are strongly correlated with the muon flux. It is also clear that the geomagnetic field may play a significant role by deflecting charged particles toward the poles [13], which leads to a decrease in the flux at the equator and an increase at high latitudes.…”