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Shao and Lay ( 2016) also found that AWs correlate with convective downdrafts and stratiform regions that may be offset from the most active convection. Indeed, observations reveal correlations between AW occurrences and larger source spatial scales (Lay et al., 2015). ( 2017) support that reflection and resonance processes enhance persistence of AW signatures, especially above larger (more directive) source regions. In addition to filtering via reflection and resonance, the spectral coherence of AWs is enhanced by viscous dissipation and the vertical integration of TEC measurements, which typically limits the observable bandpass to periods longer than 1 min (Zettergren & Snively, 2015). Modeled “updraft” sources, used to demonstrate primary AW and GW observability in the mesospheric hydroxyl airglow by Snively ( 2013) and ionospheric TEC by Zettergren and Snively ( 2013), also excite resonant AWs and GWs similar to those reported in thermospheric observations.

This provides a simple explanation for their observed persistence following seismic events and severe weather (e.g., Matsumura et al., 2012 Nishioka et al., 2013, and references therein). These waves may become trapped below the lower thermosphere, thus forming resonances or ducted modes, while gradually leaking upward into the thermosphere-ionosphere. Tropospheric convective disturbances may impose thermal and mechanical forcing over short periods, leading to the generation of upward propagating AWs and GWs (e.g., Walterscheid et al., 2003 Vadas, 2013). ( 2013), are often observed to persist over long periods of time (hours), likely due to reflection and ducting in addition to the persistence of forcing. Both AWs and GWs, such as reported by Nishioka et al. The AWs in data, with periods ∼1–4 min, are often accompanied by detectable gravity waves (GWs) at greater radii (e.g., Lay et al., 2015), typically with periods of ∼6–30 min. Acoustic waves (AWs) in the ionosphere, thermosphere, and mesosphere (ITM) above convection, while observed for decades (e.g., Georges, 1973), have recently received new attention as their perturbations can be mapped in Global Positioning System (GPS) total electron content (TEC) data (e.g., Nishioka et al., 2013).