## 4 Discussion  
### Quantification of the Impacts of Selected Factors on LS GW Activities in the Indian Region  
As mentioned in Section 2.4, the sum of the RICs of all factors equals to the total \(R^{2}\) of the MLR model. The determination coefficient \(R^{2}\) may vary between 0 and 1, and the closer \(R^{2}\) is to 1, the better the independent variable set \(\mathbf{X}\) in the MLR model can explain the dependent variable \(Y\). Figure 4 presents the spatial distribution of the sums of the RICs of all the nine considered factors, and the closer the sum of the RICs to 1, the greater the combined influence of these factors is. As can be seen, except for the latitude band between 25\({}^{\circ}\)N and 30\({}^{\circ}\)N in the northern part of the Indian region, where the sums of the RICs vary between 0.4 and 0.6, the sums of the RICs are generally higher than 0.7 in the Indian Peninsula, the Bay of Bengal and its surrounding land area, and the Indian Ocean. This demonstrates that the factors considered in the present study, including the TEJ with its jet core in the height range of 15-17 km, the air flows between 20 and 30 km, and the convections that are closely related to the Indian summer monsoon are, indeed, the main factors affecting the LS GWs in most part of the Indian region. This is also consistent with previous studies [30; 39; 53]. The latitude band of around \(5^{\circ}\) in the northern part of the region, where the summed RICs are generally lower, is mainly the Himalayas and Qinghai-Tibet Plateau with large terrain heights. Both the distributions of the CCs shown in Figure 2 and those of the RICs shown in Figure 3 demonstrate that the LS GWs in this area are mostly affected by the convective activity, while they are less affected by the TEJ and the air flows between 20 and 30 km. Analysis of the Impacts of Zonal Wind Speeds and Wind Shears on the LS GWs in Different Local Regions  
The results presented in Section 3 demonstrate that over the Indian region, the wind flows and the wind shears in the two height ranges, 15-17 km (TEJ) and 20-30 km, and the convection are generally the main factors influencing the LS GWs, while over different local areas, differences exist in which factors are the dominant ones. More specifically, among the wind-related factors, the influences of the zonal wind-related factors are greater than those of the meridional wind-related factors in most local areas, while regional differences exist on which zonal wind-related factors are the dominant ones. This aspect and the possible mechanisms will be further discussed in this section, and two grid points are selected as the representatives for different geographic locations. As presented in Figure 5, grid point A (\(77.5^{\circ}\)E, \(10^{\circ}\)N) is located at the southern end of the Indian Peninsula, and grid point B (\(80^{\circ}\)E, \(22.5^{\circ}\)N) is located in the middle of the Indian Peninsula. According to the distributions of the RICs of each factor presented in Figure 3, the zonal wind shear between 20 and 30 km plays a dominant role in influencing the LS GWs at grid point A, while at grid point B, the zonal wind speeds between 15 and 17 km and 20 and 30 km both have relatively important impacts on the LS GWs. Figure 4: Latitude–longitude distribution of the sums of the RICs of all the nine influencing factors over the Indian region during December 2019 and November 2021. Figure 5b-g show the altitude-time distributions of the GW Ep, the zonal wind speeds, and the zonal wind shears over these two grid points. As we can see in Figure 5d,e, during JJA of 2020 and 2021, the westward wind phases appear at altitudes higher than 10 km  
Figure 5: Geographic locations of two representative grid points in the Indian Region (**a**), and the altitude-time distributions of GW Ep (**b,c**), zonal wind speeds (**d,e**), and zonal wind shears (**f,g**) over the two grid points during December 2019 to November 2021. The eastward wind phases are defined as positive of zonal wind speed and zonal wind shear.