This project will investigate sources of short-period gravity waves at high polar latitudes as well as the atmospheric conditions which influence their propagation. This investigation will utilize measurements of gravity waves and mesospheric wind speeds acquired by an all-sky imager and meteor radar co-located at Rothera on the Antarctic Peninsula. The observed wave data will be analyzed in conjunction with the Navy Operational Global Atmospheric Prediction System Advanced High Altitude (NOGAPS-ALPHA) forecasting and data assimilative model of the upper atmosphere, along with a Fourier ray tracing model for localization of wave source regions. This analysis will result in an identification of dominant wave sources at high latitudes, including an assessment of the importance of orographic waves, as well as a characterization of atmospheric conditions which affect wave ducting and propagation.
Atmospheric gravity waves are disturbances in the atmosphere generated by e.g. thunderstorms and flow over mountains. As these waves propagate through the atmosphere, they grow in amplitude until they break like waves on a beach. The wave breaking act to slow down the upper atmospheric winds and, at times, even reversing the winds. By doing so, the waves are the main cause for a global circulation pattern in the atmosphere. It is of critical importance to correctly implement this circulation properly into global weather and climate models. Unfortunately, these waves are small in nature and it is not feasible at this point in time to implement the waves in our models. Instead, the consequences of the waves are implemented into the models. Therefore, it is essential to have a global understanding on how these waves appear, change, and propagate. This project addressed these items for waves observed over the Antarctic, where our knowledge of the waves until now has been limited. The project utilized ten years of data obtained from a light sensitive imaging system known as an airglow imager. The airglow is an extremely faint natural emission in the high atmosphere (~60 miles high). When a wave passes through the airglow, it perturbs the atmospheric particles and thus the amount of light emitted. Hence, the wave passage looks like bright/dark bands in the airglow (Figure 1). Our study revealed a large of amount of waves over Antarctica, suggesting that these waves are present at most times. Furthermore, the waves at one location, Rothera on the Antarctic Peninsula, had a dominant direction of propagation. This is an important observation as this implies a strong forcing in that same direction when the wave breaks. In contrast, a second observation site (Halley) showed great variability in the wave propagation. The nature of the wave propagation suggested that the waves at Rothera were likely waves related to flow across the peninsula, while the waves over Halley potentially were generated at distances far from Halley. The long-term data set showed a remarkable variation in the observed speed of the waves that resembled the 11-year solar cycle. However, there was a delay of the minima between the wave speed and the solar cycle. This lag remains unexplained. The analyses used in this study utilized novel high altitude weather prediction systems and models to trace waves through the atmosphere. A model was employed to create the waves anticipated to be generated by the Antarctic Peninsula (Figure 2). The model then used the temperature and winds from the weather prediction system to follow the waves as they propagated through the atmosphere. We found that few of the waves managed to reach 60 miles high (Figure 3). These waves showed a remarkable similarity to the waves observed with the imaging system (Figure 4), showing the importance of having these high altitude weather prediction systems. In summary, due to the results of this project, we have significantly improved our knowledge of these waves and how they may impact the atmosphere.
