A study of the effect of global radiation and other factors on seasonal maximum frozen depth in the Tibetan Plateau

In this study, monthly average daily global radiation of 22 radiometric stations across the Tibetan Plateau were utilized to determine the coefficients of monthly Angström-Prescott´s model for estimating global solar radiation from sunshine duration. Using the model, global solar radiations of another 116 meteorological stations across the Tibetan Plateau were estimated. Combined with frozen ground data measurement at 75 stations, global radiation effects on the maximum frozen depth of active layer were discussed. The result showed that the global radiation in cold season (from October to February the next year) had much influence on maximum frozen depth of the active layer. The relationship between them in three typical stations showed a marked negative correlation. As a whole, the maximum frozen depth of the active layer in nearly 80% of all investigation stations had the same relationship with the global solar radiation, while the others showed a positive correlation. This indicated that the maximum frozen depth of the active layer was the result of combined effects of several other factors other than global radiation. Of these influencing factors, such as global solar radiation, local latitude, longitude, altitude, air temperature in cold season, relative humidity, accumulation of precipitation in cold season, etc., only local latitude, altitude, global solar radiation and air temperature showed high correlation with frozen depth. Essentially, the influences of local latitude and altitude can be regarded as the effects of global radiation indirectly. As the local latitude and altitude influenced the distribution of global radiation, so the global radiation was an important affecting factor on the maximum frozen depth of the active layer.