Delineating the Migrating Solar and Lunar Semidiurnal Atmospheric Tides in the General Circulation Model

During periods of Sudden Stratospheric Warming (SSW), large disturbances in the lower atmosphere couple to the ionosphere, inducing plasma density fluctuations of 50-150% in the low-latitude F-region. Understanding the mechanisms by which the atmospheric layers couple is important to the prediction of space weather, which affects communications and the operation of satellites in low Earth orbit. Part of this understanding requires the ability to accurately quantify the amplitudes and phases of the solar and lunar migrating semidiurnal tides. In most cases, the solar migrating semidiurnal tide (SW2) is much larger in amplitude than the lunar migrating semidiurnal tide (M2) in the lower thermosphere, but in periods of SSW, M2 is enhanced and becomes comparable in magnitude to SW2. As the two tides have very similar periods, they are difficult to separate. In our method, we first remove SW2 from the data before fitting a function to extract the M2 amplitude and phase. We then compare our results to that of an earlier method used by Maute et al. [2016], which fit a general function to total data without attempting to separate SW2 and M2 first. Results from testing our method for accuracy on synthetic data show that the percent error of M2 amplitudes is 0.33% for data resolution of 30 minutes, and 1.42% for data resolution of 1 hour. We then apply our method to data generated by TIME-GCM. In comparing our results to those of Maute et al., we see good agreement in amplitudes of M2 in the Northern Hemisphere. However, in the Southern Hemisphere, a slight increase (~6.25%) occurs, which is likely due to other effects not accounted for in the scope of this study. With further work on phase recovery and incorporation of other factors affecting the Southern Hemisphere, we believe our method has promise as a clear way to extract M2 amplitudes that yields similarly accurate results as existing methods.