| The land surface albedo is an important surface parameter that affects ground-air interaction and controls the surface radiation energy budget.This paper analyzes the temporal and spatial distribution and dynamic characteristics of land surface albedo over the Tibetan Plateau using MODIS land surface albedo climatic grid products MCD43C3(Collection005)from 2000 to 2016.Then,the main reason for changes of land surface albedo over the Tibetan Plateau in recent 17 years is discussed that based on the data from ECMWF/ERA-Interim reanalysis,temperature,atmospheric precipitable water and MODIS snow cover and vegetation index data.Finally,three common plateau monsoon indices are selected to explore the relationship between the land surface albedo over the Tibetan Plateau and the plateau monsoon.The following conclusions are obtained:(1)The spatial distribution of the average land surface albedo over the Tibetan Plateau has obvious regional differences.Overall,it is low in the southeast and high in the northwest,which is greatly influenced by terrain and surface coverage.Besides,it changes significantly in the four seasons,with the highest values in winter,followed by spring and autumn,and the lowest values in summer.And the land surface albedo of the plateau varies drastically during the year in high altitude mountainous regions and alpine shrub meadows.The land surface albedo changes during the year is between 0· 19 and 0.26.It appears to be a "double-peak single-valley" type to a certain extent.The peak value is at the end of winter,early spring and midautumn,the valley value is at the end of summer.Changes in land surface albedo during the year are closely related to the seasonal changes in land cover types.(2)The annual variation of annual land surface albedo over the Tibetan Plateau is slowly fluctuating and decreases.The average variability is about-0.4×10-3/a,and the reduced area accounts for about 66%of total plateau.Southeast of Sichuan and Tibet are the regions where the land surface albedo decreases most rapidly with the rate of decreasing exceeds 1.0×10-2/a.Land surface allbedo fluctuates significantly in Guoluo,Naqu and Ali.As for the overall plateau,the land surface albedo of the four seasons showes a decreasing trend,and the land surface albedo decreases most quickly in winter,followed by the spring and autumn,and the slowest in the summer.(3)In the past 17 years,The anomalous annual land surface albedo over the Tibetan Plateau is in 2008,and the abnormally weak year is 2010.High altitude areas are always sensitive areas where land surface albedo changes abnormally.(4)In the past 17 years,the climate warming and humidification has been an important factor in reducing the land surface albedo over the Tibetan Plateau,especially in spring,summer and autumn.With the warming and humidification of the plateau climate,the overall reduction of land surface albedo on the plateau is closely related to the ablation of plateau glaciers and the reduction of seasonal snow cover.In addition,the overall improvement of the plateau vegetation coverage is a non-negligible factor that causes the reduction of land surface albedo over the Tibetan Plateau.(5)The land surface albedo in the early November has certain indicative significance for the outbreak of the sumner monsoon over the Tibetan Plateau.The relatively low(or high)land surface albedo in the early November will lead to the early(or late)outbreak of summer monsoon over the Tibetan Plateau.(6)The land surface albedo in the early November is low(high),in April,the main body of the plateau exerted a strong(weak)heat-sensing effect on the atmosphere,the upward movement of the surface layer above the plateau is significantly strengthened(weakened),which(not)facilitated the transmission of heat to the upper air,the troposphere heating effect is strengthened(weakened)and the plateau troposphere temperature is high(low),which makes the monsoon circulation system of the plateau strengthen(weaken),and eventually leads to a seasonal advancement(delay)of the plateau monsoon. |
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