Research On Radiation Balance Of The Laohugou Basin In West Qilian Mountains

Solar radiation is a direct energy source for surface physiography,a major driver of climate change,an important meteorological factor affecting heat exchange and glacial material balance at the glacier surface,and plays an important role in the water cycle in the cryosphere,especially in mountain glacier regions.In the context of climate change,the atmosphere and cryosphere are undergoing rapid changes,and most mountain glaciers in China are in a state of loss,and the rate of loss has accelerated in recent years,especially in the Qilian Mountains.In order to investigate the dynamic change characteristics of mountain glaciers in the context of climate change,researchers have made a large number of observations of the radiation income and expenditure on the glacier surface.However,due to the complex topography and harsh climate in mountainous regions,it is difficult to obtain large scale and long time series of observed datasets.Reanalysis datasets are an effective way to obtain large-scale radiometric datasets on glacier surfaces,which is limited by spatial resolution and difficult to meet the needs of local and basin scale studies in complex mountainous terrain conditions,especially in alpine glacier regions.Therefore,the paucity of long timescale radiation datasets on the glacier surface is a key factor limiting the study of glacier surface variation dynamics.Based on the limited observed datasets,evaluating the applicability of different reanalysis datasets in alpine glaciers and obtaining the optimal reanalysis datasets is one of the possible ways to solve the above problems.To this end,this thesis analyzes the variation characteristics of the four components of radiation in the Laohugou basin at seasonal and interannual scales using upward and downward shortwave radiation and upward and downward longwave radiation datasets from the 4550m automatic weather station in the glacial ablation zone of the LHG basin from July 2010 to December 2015.The applicability of five sets of reanalyzed radiation data,MERRA2,ERA5,HAR v2,JRA55,and NCEP/CFSR,to the glacial zone was evaluated on hourly to seasonal scales.The main conclusions of this thesis are as follows:(1)The downward shortwave radiation trend is relatively consistent with the upward shortwave on a seasonal scale,and the daily variation of shortwave radiation is single-peaked in both summer and winter.The radiation value of downward shortwave radiation is higher in summer than in winter and higher than upward shortwave radiation;in winter,the flux of upward shortwave radiation is higher from 9:00 to 17:00 than in summer,and the flux is smaller than downward shortwave radiation throughout the day.The annually scale downward shortwave radiation exhibits an obvious single-peak type,with the maximum and minimum annually radiation values of 417.82 w/m~2 and 35.53 w/m~2,respectively;the upward shortwave radiation shows a double-peak and double-valley type with large interannual fluctuations,with the maximum value of 316.45 w/m~2 and the minimum value of 6.44 w/m~2 during the observation period.The flux magnitude of downward longwave radiation depends mainly on upward longwave radiation,both of which show a single-peak-single-valley pattern of daily variation in summer and winter.On the annually scale,the upward longwave radiation is single-peaked,with the maximum radiation value of 321.44 w/m~2 and the minimum value of 276.2 w/m~2 during the observation time;the downward longwave radiation is also single-peaked,with the maximum and minimum fluxes of 334.36 w/m~2 and 97.62 w/m~2 in 2011,respectively;the interannual variation of the basin is less volatile,and the long-wave radiation is stable.(2)The net radiation flux is significantly higher in summer than in winter,and the daily variation is single-peak,increasing from around sunrise to a maximum value at 13:00 and then decreasing continuously;the daily average variation of net radiation is consistently positive in summer and negative in winter from October to February.The annual scale is unimodal,rising rapidly from January to June and decreasing rapidly from September,with negative net radiation from October to January and positive from February to September on average during the observation period.The net radiation fluxes in the glacial ablation zone are generally stable with small fluctuations between years,and the radiation fluxes are similar.(3)In areas where there is a lack of observed shortwave radiation datasets,ERA5 reanalysis radiation datasets are recommended first on the hourly scale,and HAR v2 is recommended for downward shortwave radiation on the daily,monthly and annually timescales;ERA5 reanalysis datasets are preferred for upward shortwave radiation on the daily,monthly and annually timescales.(4)For areas where longwave radiation datasets are scarce,ERA5 are preferred for downward longwave radiation at hourly and daily scales,and HAR v2 reanalysis datasets are recommended for monthly and annually scales;and HAR v2 reanalysis datasets are preferred for upward longwave radiation at all time scales.