## 5 Conclusions
Moreover, in the altitude range of 25-35 km of the middle and high latitudes, GW Ep values generally show significant negative trends in almost all months, and the values of the negative trends become smaller in the region closer to the poles. A similar pattern is also shown in the distribution of the deseasonalized trends of monthly zonal-mean GW Ep time series during the 14 years from 2007 to 2020. Furthermore, some prominent features, which are almost symmetric between the NH and the SH, can be figured out in the distributions of the GW Ep trends of different months when taking into consideration the six months shift in the atmospheric conditions between the two hemispheres. On the whole, the gravity wave activities are declining from 2007 to 2020 over the globe. The analyses concerning the responses of the global GW activities in 20-35 km to solar activity, QBO, and ENSO during 2007 to 2020 reveal that the responses of GW Ep values to solar activity are mostly positive. The latitude-height distribution of the areas with significant responses are very similar to that of the deseasonalized trends of the GW Ep, and the positive responses of the GW Ep to solar activity become stronger in the regions closer to the poles. The comparison between the distribution pattern of the deseasonalized trends of the GW activities and that of the response of GW activities to solar activity indicates that the sharp decline in solar activity from 2015 to 2017 might contribute to the overall attenuation of gravity wave activity during the 14 years from 2007 to 2020. Furthermore, significant negative responses of the GW activities to QBO are found in 30-35 km over the latitudes of 30\({}^{\circ}\) S-25\({}^{\circ}\) N, and the negative responses extend to the mid and high latitudes in the SH at 20-30 km. Meanwhile, the responses of GW activities to QBO change to be significantly positive in 20-30 km over the latitudes of 15\({}^{\circ}\) S-15\({}^{\circ}\) N, which demonstrates that the variation in the zonal wind field should be the main factor affecting the GW activities in 20-30 km over the tropics. The responses of GW activities to ENSO at 20-35 km are found to be positive over the latitudes of 15\({}^{\circ}\) S-15\({}^{\circ}\) N, while at 30-35 km over 15\({}^{\circ}\) N-30\({}^{\circ}\) N and at 20-35 km near the latitude of 50\({}^{\circ}\) N, significant negative responses of GW activities to ENSO exist. **Author Contributions:** Conceptualization, X.X. ; Investigation, J.L. and J.H. ; Methodology, J.H. ; Project administration, J.L. and X.X. ; Supervision, J.L. and X.X. ; Writing--original draft, J.L. and J.H. ; Writing--review and editing, X.X. All authors have read and agreed to the published version of the manuscript. **Funding:** This work is supported by the National Natural Science Foundation of China (Grant Nos. 41774033, 41774032, and 42074027). **Data Availability Statement:** The data used in the manuscript are all public data. The atmPrf data of the RO missions, including CHAMP, COSMIC, GRACE, and METOP-A/B/C, were downloaded from the CDAAC Data Center: [[https://cdaac-www.cosmic.ucar.edu/cdac/products.html](https://cdaac-www.cosmic.ucar.edu/cdac/products.html)]([https://cdaac-www.cosmic.ucar.edu/cdac/products.html](https://cdaac-www.cosmic.ucar.edu/cdac/products.html)) (last accessed on 27 August 2021).