Probing local wind and temperature structure using infrasound from Volcan Villarrica (Chile)

We use the continuous and intense (similar to 10(7) W) infrasound produced by Volcan Villarrica (Chile) to invert for the local dynamic wind and temperature structure of the atmosphere. Infrasound arrays deployed in March 2011 at the summit (2826 m) and on the NNW flank (similar to 8 km distant at 825 m) were used to track infrasound propagation times and signal power. We model an atmosphere with vertically varying temperature and horizontal winds and use propagation times (ranging from 23 to 24 s) to invert for horizontal slowness (2.75-2.94 s/km) and average effective sound speeds (328-346 m/s) for NNW propagating infrasound. The corresponding ratio of recorded acoustic power at proximal versus distal arrays was also variable (ranging between 0.15 to 1.5 for the peak 0.33-1 Hz infrasound band). Through application of geometrical ray theory in a uniform gradient atmosphere, these 'amplification factors' are modeled by effective sound speed lapse rates ranging from -15 to +4 m/s per km. NNW-projected wind speeds ranging from -20 m/s to +20 m/s at 2826 m and wind gradients ranging from -11 to +10 m/s per km are inferred from the difference between effective sound speed profiles and adiabatic sound speeds derived from local temperature observations. The sense of these winds is in general agreement with regional meteorological observations recorded with radiosondes. We suggest that infrasound probing can provide useful spatially averaged estimates of atmospheric wind structure that has application for both meteorological observation and volcanological plume dispersal modeling.