GRAvity wave short term Variability In the Thermosphere/Ionosphere induced by GLObalscale Waves (GRAVITIGLOW)

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Vertical coupling between middle atmosphere and thermosphere/ionosphere (T/I) by atmospheric waves plays an important role in the energy and momentum balance of the T/I. These atmospheric waves include global scale waves (planetary waves (PWs), tides) and mesoscale gravity waves (GWs). It has been modeled and observed that during upward propagation, GWs can interact with global scale waves. The modulation of GWs by global scale waves alters the magnitude of GW momentum fluxes, breaking location and saturation altitudes of GWs. This will affect not only the global distribution of GWs in the T/I but also the wave driving of the global circulation in the T/I. Further, by interaction with GWs, global scale waves are themselves affected. Also, global scale waves can be excited in the T/I due to the non-uniformities of the GW distribution that resulted from GW filtering at lower altitudes. Moreover, selective filtering of GWs by background variations, in particular by global scale waves, influences the wave forcing in the T/I during sudden stratospheric warmings (SSWs). Therefore, simultaneous global observations of GWs and global scale waves in the T/I, together with global observations in the middle atmosphere, are needed to better understand these processes in more detail.In this project, we will analyze the short term variability of GWs induced by global scale waves using different satellite measurements, including CHAMP, GOCE, GRACE, SWARM (in the T/I) and SABER, HIRDLS (in the middle atmosphere). In the T/I, in addition to the global distributions of GW, which were successfully derived from CHAMP and GOCE, we will apply the same method to derive GW distributions from mass density, winds and plasma density from SWARM, CHAMP, and GRACE. Further, tidal amplitudes and tidal phases will be derived from mass density, winds, and plasma density from SWARM, CHAMP, GOCE, and GRACE. These simultaneous observations of GWs and tides will be analyzed to estimate the modulation of GWs by tides. Another focus is the variability of GW distribution in the T/I around central date of each SSW event. Further, we will investigate how the modulation of GWs by background variations, in particular by global scale waves, influences the vertical coupling by GWs during SSWs. For these SSWs, observations both in the middle atmosphere and in the T/I will be analyzed with high temporal resolution. Ray tracing will be performed to investigate filtering of GW spectrum in the middle atmosphere during SSWs. Long-term SABER data and combination of SWARM, CHAMP, GOCE, GRACE data provide a comprehensive collection of study cases. Observations of GWs and tides derived by our project are also important for direct comparison with corresponding quantities simulated by general circulation models.