## 7 Discussions and Conclusions  
If migrating and non-migrating tides are correctly simulated in numerical weather and climate models, it means that both radiative and dynamic processes are correctly taken into account and can somehow validate models on hourly scales. The ERA5 model is currently one of the most sophisticated representations of our atmosphere for weather and climate forecasting. The analysis of the new data from the European center ERA5 allows us to develop a new methodology to separate migrating tides from non-migrating tides by an objective analysis of histograms by longitude where migrating tides by definition must have similar characteristics. It appears that the characteristics of the migrating modes are in fairly good agreement up to 60 km, even if the amplitudes at mid-latitudes remain twice as large compared to the simulations with the GSWM model, as already reported by previous studies. This is not surprising because daily comparisons with the observations showed that the variability in the upper part of the model was clearly damped and permanently close to the climatology [32; 49]. Although non-migrating modes appear to exist at all latitudes in the model, the largest amplitudes appear around the equator where the water vapor content may be regionally very important due to convection. However, at the present time, no data are available to validate their characteristics. This study is a preliminary approach showing that migrating and non-migrating tidal components co-exist in the model. It is likely that more sophisticated statistical methods can be used to extract the global tidal modes and anomalies associated with non-migrating local effects. Lack of knowledge of tidal characteristics is a problem in the middle atmosphere for monitoring issues, but also because tides induce spectrum aliasing effects and thus undesirable fluctuations occur during data assimilation processes, for example. The use of a satellite constellation could partially solve this weakness. Constellations are only feasible if several small satellites are deployed simultaneously at low cost. With the limb observations, it is possible to derive temperature profiles with a good vertical resolution (1-2 km). This technique can be developed within small satellites like CubeSat and can then be deployed through a large constellation that can provide several observations each day over a single location, allowing us to take into account tidal fluctuations. These data would provide global coverage with an improved sampling rate, which could be incorporated into meteorological models. This will be crucial for providing accurate mesospheric temperature information. Space observations could be supplemented by specific continuous observations of the tides from the ground in convective regions to observe local non-migrating tides. Therefore, the microwave technique, which is not affected by clouds, allows us to provide continuous observations in convective regions. Ozone and water vapor profiles can be derived with microwave spectrometers [12] and, more recently, wind and temperature profiles have also been produced with similar methods [50]. This issue needs to be taken into account when building infrastructure dedicated to middle atmosphere observation networks. The international NDACC network [39] has suggested the use of microwave spectrometers to monitor composition changes, and it is possible to derive diurnal changes due to photo-dissociation over some ground-based locations. More recently, instrumental developments performed within the European ARISE network [38] have extended observations to the wind parameters and thus atmospheric tides in dynamic parameters. Such international efforts to provide continuous observations of the middle atmosphere need to continue over more locations in conjunction with the setting of a space constellation. More local observations are required over the tropical band.