Effects of Cloud Cover on Surface Sublimation at 4,817 m a.s.l. on the Flat-Top August-One Glacier of the Northern Tibetan Plateau

As a crucial role in earth's energy budget, cloud cover exerts great effects on climate change. Although existing sublimation studies across High Mountain Asia (HMA) glaciers have identified the importance of cloud cover in limiting sublimation, the primary/main factors limiting sublimation under high cloud cover conditions are unknown. Based on the 5-year meteorological observation at the top of August-one glacier in the northern Tibetan Plateau (TP), we analyzed the role of cloud cover on meteorological variables and sublimation. The cloud cover over this glacier was found to have distinct effects on the primary meteorological variables, causing the generally negative and positive temperature gradients in clear-sky and overcast conditions, respectively. Additionally, the increase in cloud cover is associated with decreased near-surface humidity gradient and wind speed, which is unfavorable for sublimation. Glacier sublimation was limited in overcast conditions, whereas the sublimation rate was about two-and-half times higher in clear-sky conditions. We noted that the specific humidity gradient and wind speed combined as a more important role in determining sublimation based on the multiple linear regression analysis. Overall, on this westerly dominated glacier, the weak sublimation in overcast conditions was primarily associated with the combined effect of significantly higher air moisture and decreased wind speed. These results contribute to a better understanding of the link between near-surface water vapor exchange between glaciers and the atmosphere.