Eight-year analysis of radiative properties of clouds and its impact on melting on the Laohugou Glacier No. 12, western Qilian Mountains

摘要

Cloud is an active component in the weather-climate system that modulates both the radiation balance and the water cycle of the earth system via physical, chemical, and radiative mechanisms. In this study, we used observations of meteorological variables recorded on the Laohugou Glacier No. 12 in the western Qilian Mountains during 2009-2017 to investigate the radiative properties of cloud and its impact on glacier melting. The quantified cloud fraction showed an evident seasonal cycle. The highest cloudiness typically occurred at 16:00 Beijing time, which was probably associated with the strength of local convection that produced frequent occurrence of low-level cumulus or cumulonimbus clouds. Most heavy precipitation events (14 mm) occurred on overcast days, signified that at least half of the total precipitation could be attributed to transportation from meso- or large-scale atmospheric circulations. Relationships between modelled glacier melting, energy components and cloud fraction showed that clouds could importantly reduce glacier melting, the most important contributor to this process was the clouds impact on net shortwave radiation. Circulation analyses showed that similar to 7.8%, similar to 6.3%, and similar to 18.7% of overcast days could be clearly and uniquely attributed to Arctic air mass events, monsoon events, and westerlies events, respectively. The remaining overcast days (similar to 67.2%) were influenced by multiple circulations, e.g., westerlies-monsoon, westerlies-Arctic air mass, monsoon-Arctic air mass, and westerlies-monsoon-Arctic air mass interactions. Monsoon potentially contributes a lot to precipitation in the western Qilian Mountains, future work should aim to do more atmospheric circulation analyses combining with isotopic tracing when precipitation occurs during overcast days.