## 3 Results
### Distributions of the CCs and RICs of Different Influencing Factors
In addition, due to the possible collinearities among these influencing factors, it is difficult to present the individual contribution of each factor to the LS GW activity objectively through the Pearson correlation coefficient solely. The DA method helps reduce the influence of the possible collinearity among independent variables on the analyzing results, as mentioned in Section 2.4. In [PERSON] et al. [54], the DA method is adopted instead of the Pearson correlation coefficient to quantify the relative importance of different driving factors that affect the density variations of different elements in the Martian upper atmosphere. In the present study, to further quantify the contribution of each factor to the LS GWs over the Indian region, using the DA method, the RICs of each factor over each 2.5\({}^{\circ}\)\(\times\) 2.5\({}^{\circ}\) grid point are calculated, based on which the latitude-longitude distributions of the RICs of the nine factors are obtained, as presented in Figure 3.  
The RICs of the nine factors generally vary between 0 and around 0.55, and the maximum RIC is obtained by the factor of the mean zonal wind shear in the 20-30 km altitude range (Figure 3g) over the Indian Ocean. The distributions of the RICs of different factors demonstrate that over the Indian region, local differences exist in the main factors influencing the LS GW activity. Generally, in the central and northern parts of the Indian Peninsula, the relative importance of the convection (Figure 3i) is the greatest, followed by the mean zonal wind speeds between 15 and 17 km (Figure 3a) and 20 and 30 km (Figure 3e). In the southern part of the Indian Peninsula and over the Indian Ocean, the impact of the mean zonal wind shear between 20 and 30 km (Figure 3g) on the LS GWs is dominant, and the meridional wind speed and the mean zonal wind shear between 15 and 17 km (Figure 3b,c) also have some contributions to the LS GW activities over the Indian Ocean. Over the Bay of Bengal and its surrounding land area, the mean meridional wind speed between 15 and 17 km (Figure 3b) has an important impact on the LS GWs. Figure 3: Latitude–longitude distributions of the RICs of the nine influencing factors of the LS GW activities over the Indian region during December 2019 and November 2021. The nine influencing factors are (**a**) 15–17 km zonal wind speed; (**b**) 15–17 km meridional wind speed; (**c**) 15–17 km zonal wind shear; (**d**) 15–17 km meridional wind shear; (**e**) 20–30 km zonal wind speed; (**f**) 20–30 km meridional wind speed; (**g**) 20–30 km zonal wind shear; (**h**) 20–30 km meridional wind shear; and (**i**) OLR as the proxy of convection activity, respectively. The eastward/northward wind phases are defined as positive of zonal/meridional winds. Specifically, in the central and northern parts of the Indian Peninsula, the factor with the largest RICs is convection, using OLR as the proxy parameter (Figure 3i), and the RICs of convection generally reach above 0.2, even exceeding 0.4 in the southern foothills of the Himalayas. This should be mainly attributed to the fact that the interaction of the Indian summer monsoon circulation and the terrain of the Himalayas results in frequent convective systems over the northern part of the Indian Peninsula, especially in the arc-shaped belt region along the terrain features of the southern Himalayan front [55; 56], which becomes an important source of the GWs here. The factor with the second largest RIC values is the mean zonal wind speed between 15 and 17 km (Figure 3a), which shows that the TE) in the summer season is indeed an important source of the LS GWs over these areas. The RICs of the mean zonal wind speed between 20 and 30 km (Figure 3e) are mainly within the range of 0.15-0.25, which are generally slightly smaller than those of the mean zonal wind speed between 15 and 17 km.