The estimation of upper atmospheric wind model updates from infrasound data

Abstract

[1] In our recent paper, the sensitivity of infrasound to the upper atmosphere is investigated using impulsive signals from the Tungurahua volcano in Ecuador. We reported on the coherent variability of thermospheric travel times, with periods equal to those of the tidal harmonics. Moreover, it was shown that the error in predicted thermospheric travel time is in accord with typical uncertainties in the upper atmospheric wind speed models. Given the observed response of the infrasound celerities to upper atmospheric tidal variability, it was suggested that infrasound observations may be used to reduce uncertainty in the knowledge of the atmospheric specifications in the upper atmosphere. In this paper, we discuss the estimation of upper atmospheric wind model updates from the infrasound data described in the aforementioned paper. The parameterization of the model space by empirical orthogonal functions is described; it is found that the wind model in the upper mesosphere and lower thermosphere can be described by a four-parameter model. Due to the small dimensionality of the model space, a grid search method can be used to solve the inverse problem. A Bayesian method is used to assess the uncertainty in the inverse solution given the a priori uncertainty in the data and model spaces and the nonlinearity of the inverse problem at hand. We believe that this is the first study in which such methods are applied to real infrasound data, allowing for a rigorous analysis of this inverse problem. It is found that the complexity of the a posteriori model distribution increases for a larger dimensional model space and larger uncertainties in the data. A case study is presented in which the nonlinear propagation from source to receiver is simulated using an updated wind model and nonlinear ray theory. As nonlinear propagation effects further constrain the propagation path, this is a way to check the physical self-consistency of the travel time inversion approach. We obtain excellent agreement between the simulated and observed waveforms.

Evaluation of wind and temperature profiles from ECMWF analysis on two hemispheres using volcanic infrasound

“…As infrasound waves propagate through the atmosphere, the wave characteristics reveal, in addition to information about the source, significant features of the vertical structure of the wind and temperature. The interpretation of these data has motivated studies on sources of infrasonic waves and their propagation in the upper atmosphere as a means to monitor passively stratospheric [Antier et al, 2007;Kulichkov, 2010] and mesospheric-thermospheric [Rind et al, 1973;Le Pichon et al, 2005b;Assink et al, 2013;Chunchuzov et al, 2013] wind and temperature fields. Among others, studies have focused on the influence of geomagnetic fluctuations [Garcés et al, 2002] and atmospheric solar tides on infrasound propagation, which modulates wind speed and direction in the upper atmosphere [Le Pichon et al, 2005a;Green et al, 2012].…”

“…Recently, studies have focused on the development of inverse methods to estimate upper atmospheric wind updates from infrasound data [Le Pichon et al, 2005b;Drob et al, 2010;Lalande et al, 2012;Assink et al, 2013;Arrowsmith et al, 2013]. Inversions for upper atmospheric data using infrasound data are not only useful in further reducing the uncertainty of these parameters but are also beneficial for applications that require a precise modeling, such as for estimation of explosion magnitude [Assink et al, 2013].…”

“…Inversions for upper atmospheric data using infrasound data are not only useful in further reducing the uncertainty of these parameters but are also beneficial for applications that require a precise modeling, such as for estimation of explosion magnitude [Assink et al, 2013]. Atmospheric specifications are based on spatially and temporally averaged measurements that often do not fully explain infrasound observations.…”

“…Instead of a more rigorous inversion procedure that involves propagation paths, travel time, and bearing deviations Lalande et al, 2012;Assink et al, 2013], we simply seek the ensemble of effective sound speed updates that would likely explain the observed spread in trace velocities. As such, we present these results to provide a first order of magnitude estimate of updates.…”

Simulation study for measurement of horizontal wind profiles in the polar stratosphere and mesosphere using ground-based observations of ozone and carbon monoxide lines in the 230–250 GHz region

“…Infrasound measurements are used for investigating wind velocity variations in the stratosphere, mesosphere, and lower thermosphere (e.g. Le Pichon et al, 2010;Assink et al, 2012Assink et al, , 2013Chunchuzov et al, 2015). Over a 14-year period the space-borne high-resolution Doppler imager (HRDI) (Burrage et al, 1996) measured wind velocities typically between 60 • N and 60 • S and down to 50 km and contributed to the Upper Atmosphere Research Satellite (UARS) Reference Atmosphere Project (URAP) (Swinbank and Ortland, 2003) wind climatology.…”