## 3 Results  
### Variations in Climatic Elements  
The strength of land-atmosphere coupling in a climate region is closely linked to both the patterns of atmospheric circulation and the magnitude of the surface energy fluxes and the SM. The Bowen ratio (BR) is an important parameter representing the proportions of energy allocation and provides information on surface dryness or wetness. Understanding the statistical characteristics of the land surface and atmospheric climatic elements contribute to our understanding of the climatic background of land-atmosphere coupling in the study region. Table 1 presents the statistical values of Ta, major surface energy fluxes, shallow and deep SM, EF, and BR recorded at the SACOL site during the seasons of vegetation growth (April-September) from 2007 to 2012. The average Ta during the growing season was 15.8 \({}^{\circ}\)C, with a daily average variance of 4.7 \({}^{\circ}\)C. The mean values of the SH, LE, and Rn were 42.2, 47.4, and 103.8 W m\({}^{-2}\), respectively, with daily average variances of 23.2, 24.6, and 44.7 W m\({}^{-2}\), respectively. It is evident that large fluctuations in the daily surface energy fluxes were the main reason for the large daily variations in Ta in the transitional climate zone. The annual average values of the SM in a depth range of 0-40 cm varied by a range of 0.109 to 0.153 m\({}^{3}\) m\({}^{-3}\), with a daily average variance of 0.038 m\({}^{3}\) m\({}^{-3}\). The annual average values of the SM varied from 0.092 to 0.148 m\({}^{3}\) m\({}^{-3}\) in a depth range of 40-80 cm, with a daily average variance of 0.032 m\({}^{3}\) m\({}^{-3}\). This indicates that the values of the SM and the amplitude of fluctuations in the deeper layer (40-80 cm) were smaller than those in the shallower layer (0-40 cm) in the transitional climate zone. The mean values of the BR during the growing season fluctuated between 1.22 and 2.27, with a daily mean variance of 1.66, while those of the EF ranged from 0.36 to 0.56, with a daily mean variance of 0.20 (Table 1). The surface heat flux is transported upward to the atmosphere through turbulent processes and has a direct feedback effect on the atmosphere. Changes in the surface heat flux, regardless of whether it increased or decreased, had a direct impact on the state of the atmosphere. This is a key component of the process of land-atmosphere coupling and plays a determining role in the coupling between the ET and the SM. Figure 2 shows the analysis of the variations in the Ta, Rn, and surface heat flux during the growing season from 2007 to 2012. The six-year averages show that the SH in the transitional climate zone generally exhibited a fluctuating trend of decrease in the growing season (April to September) (Figure 2a). The LE gradually increased, reaching its maximum from late August to early September, and then gradually decreased (Figure 2b). The variations in the Rn and Ta were relatively consistent, and both showed an increase to their maximum values in late July to early August, followed by a gradual decrease (Figure 2c,d). The interannual fluctuations in the Rn and SH were most pronounced in July, with values of 47.3 and 15.0 W m\({}^{-2}\), respectively. The interannual fluctuation in the LE was most pronounced in July, with a value of 45.7 W m\({}^{-2}\). This indicates that significant interannual variations in precipitation in the transitional climate zone in July induce substantial differences in the surface moisture necessary for the latent heat process. Consequently, this impacts latent heat flux and exerts a significant influence on it [13]. The seasonal variations in the SM in the transitional climate zone in the depth range of 0-40 cm revealed distinct patterns. The average annual SM gradually decreased before mid\(-\)May and began to gradually increase from then on (Figure 3a). This reflects the characteristics of increased atmospheric precipitation and significant interannual differences in the transitional climate zone beginning in mid\(-\)May.