Sensitivity of simulated frozen ground temperatures to different solar radiation and air temperature products-a case study in the Qilian Mountains in West China

Downward solar radiation (DSR) and air temperature (Ta) have significant influences on the thermal state of frozen ground. These parameters are also important forcing terms for physically based land surface models (LSMs). However, the quantitative influences of inaccuracies in DSR and Ta products on simulated frozen ground temperatures remain unclear. In this study, three DSR products (CMFD-SR, Tang-SR, and GLDAS-SR) and two Ta products (CMFD-Ta and GLDAS-Ta) were used to force an LSM model in an alpine watershed in Northwest China, to investigate the sensitivity of simulated ground temperatures to different DSR and Ta products. Compared to a control model (CTRL) forced by in situ observed DSR, ground temperatures simulated by the experimental model forced by GLDAS-SR are obviously decreased because GLDAS-SR is much lower than in situ observations. Instead, simulation results in models forced by CMFD-SR and Tang-SR are much closer to those of CTRL. Ta products led to significant errors in simulated ground temperatures. In conclusion, both CMFD-SR and Tang-SR could be used as good alternatives to in situ observed DSR for forcing a model, with acceptable errors in simulation results. However, more care need to be paid for models forced by Ta products instead of Ta observations, and conclusions should be carefully drawn.