EPP

As one of the most important dynamic processes in the middle and upper atmosphere, gravity waves (GWs) play a key role in determining the global atmospheric circulation. Gravity wave potential energy (GW Ep) is an important parameter that characterizes GW intensity, so understanding its global distribution is necessary. In this paper, a deep learning algorithm (DeepLab V3+) is used to estimate the stratospheric GW Ep. The deep learning model inputs are ERA5 reanalysis datasets and GMTED2010 terrain data. The output is the estimated GW Ep averaged over 2030 km from 60°S60°N. The GW Ep averaged over 20~30 km calculated by COSMIC radio occultation (RO) data is used as the measured value corresponding to the model output. The results showed that (1) this method can effectively estimate the zonal trend of GW Ep. However, the errors between the estimated and measured value of Ep are larger in low-latitude regions than in mid-latitude regions. The large number of convolution operations used in the deep learning model may be the main reason. Additionally, the measured Ep has errors associated with interpolation to the grid, the error tends to be amplified in low-latitude regions because the GW Ep is larger and the RO data are relatively sparse, which affects the training accuracy. (2) The estimated Ep shows seasonal variations, which are stronger in the winter hemisphere and weaker in the summer hemisphere. (3) The effect of quasi-biennial oscillation (QBO) can be clearly observed in the monthly variation in the estimated GW Ep, and its QBO amplitude may be less than that of the measured Ep.

There are many active faults in the southeast margin of Tibetan Plateau, where three large active faults zones, the Longmenshan, Xianshuihe and Anninghe, merge to form a "Y" shape. Strong crustal deformation and a complicated fault distribution accompany strong earthquake activity in this zone. In this paper, we investigate a multi-scale gravity anomaly in the southeastern margin of the Tibetan Plateau using the wavelet transform; we find that the pattern of the gravity field is closely related to the fault system in the study area. Analyzing the characteristics of this Bouguer gravity anomaly at different orders indicates that the eastern Himalayan syntaxis has produced a strong eastward push during its northward movement, resulting in a shortening of the crust from west to east and a rapid uplift of the Tibetan Plateau. The Songpan–Garzê and Sichuan–Yunnan blocks have been forced to slip and extrude southward and eastward laterally. The distributions of seven large earthquakes from 1970 to 2018 reflects the relationship between large earthquakes and characteristics of the gravity anomaly. Comparing the tectonic backgrounds of several earthquakes reveals that the large earthquakes occur usually in the high gravity anomaly gradient zone, which corresponds in general to the boundary zones of the blocks. We infer that large earthquakes occur primarily in high Bouguer gravity anomaly zones in the upper crust, while low Bouguer gravity anomalies encompass the lower crust and the uppermost mantle.