Global-Scale, Nonlinearly-Generated Waves in the Space-Atmosphere Interaction Region

Understanding of the space-atmosphere interaction region spanning from 60 km to 500 km altitude is becoming increasingly important for satellite operations. Significant variability in this region is induced by global-scale atmospheric tides and planetary waves generated in the lower atmosphere, which can vertically propagate with increasing amplitude. Past studies have suggested that these global scale waves may nonlinearly interact to produce additional secondary waves and thus, introduce further variability in the region This dissertation investigates the secondary waves that are produced during a nonlinear interaction between the quasi two-day wave and the migrating diurnal tide, two of the largest global-scale waves in the upper atmosphere. Theoretically, this nonlinear interaction should produce the 16hrW4 and 2dayE2 secondary waves. The main goal is to characterize the secondary wave forcing region and understand how this relates to their manifestation throughout the atmosphere. The first portion of this dissertation applies the Fast Fourier Synoptic Mapping technique to present new observational evidence of secondary waves in the mesosphere-lower thermosphere region. The results demonstrate that the secondary waves are significant at altitudes above 80 km, and do not necessarily coincide with the regions where the interacting primary waves are largest. In order to further understand the secondary wave generation process, numerical experiments with a linearized tidal model are conducted. First, short-term primary wave estimates are extracted from the NOGAPS-ALPHA reanalysis model and are utilized to derive observationally-based nonlinear forcing quantities for the 16hrW4 and 2dayE2 secondary waves. The nonlinear forcing values are then implemented in a linear tidal model that is modified to compute secondary wave responses from the surface to the upper thermosphere. Numerical experimental results demonstrate that the magnitude of the secondary wave response in the mesosphere-lower thermosphere region is dependent on factors such as the spatial distribution and location of the forcing, and the secondary wave frequency and vertical wavelength. Additional experiments simulating the interaction between the quasi two-day wave and the migrating semidiurnal tide suggest that certain secondary waves may be able to propagate far into the thermosphere and hence, introduce significant variability within the space-atmosphere interaction region