Using an oceanic acoustic noise model to evaluate and constrain simulated atmospheric states

Among the different types of atmospheric waves, infrasound corresponds to low-frequency acoustic waves that can propagate over thousands of kilometers within atmospheric waveguides formed between the  surface and the middle-atmosphere (MA, 15-90 km) or the lower thermosphere (90-120 km). Infrasound is a technology used to monitor the atmosphere for the Comprehensive Nuclear-test Ban Treaty (CTBT). Infrasound stations of the International Monitoring System put in place to monitor compliance with CTBT continuously record infrasound waves, which can be seen as a tracer of the MA and lower thermosphere dynamics. At these altitudes, Numerical Weather Prediction (NWP) models are biased, notably due to the lack of observations to assimilate, especially for winds, or for instance due to an approximate representation of the impact of atmospheric gravity waves on the dynamics. We propose a method based on the observation of infrasound of oceanic origin, known as microbaroms, to evaluate and compare the performances of atmospheric models in the middle atmosphere. We present a complete processing chain that simulates microbarom arrivals at an infrasound station and that compares them to observations. It explicitly accounts for both the oceanic source emission mechanism and the atmospheric propagation. Beyond the atmospheric diagnostics enabled by this method, we have implemented our modeling of microbarom arrivals within a variational data assimilation (DA) framework to constrain wind and temperature atmospheric fields in the MA. As proof-of-concept, first DA synthetic experiments were conducted in simplified atmospheric configurations to demonstrate the added value of infrasound observations in constraining the MA dynamics.