On atmospheric updating, attenuation, and thermospheric phases in infrasonic wave-trains

Because of the dramatic increase in temperature in the thermosphere, thermospheric phases are ubiquitous, despite the fact that they are less often detected than are stratospheric phases. In the thermosphere, the density of the atmosphere is very low so that, as a propagation medium, the thermosphere is very non-linear and very attenuating. Atmospheric specifications of the lower thermosphere are not well constrained by data. This can lead to significant errors in modeling propagation along thermospheric paths. Methods for generating corrections to specifications of the thermosphere from infrasonic data are described. Further, using a non-linear ray theory model we find that non-linear effects in the thermosphere, in particular, period lengthening, mitigate against attenuation. Finally, we show that it is possible to use thermospheric returns to simultaneously update the atmospheric specifications while determining source yield.