| As an important part of the cryosphere,snow has a strong interaction with other components of the cryosphere and has a major impact on regional and global climate change.Due to the special geographical location and altitude of the Qinghai-Tibet Plateau,it is significantly different from other areas.At the same time,the winter and spring snow on the Qinghai-Tibet Plateau has obvious significance for the Asian monsoon precipitation,but the physical mechanism of its influence is still controversial.Therefore,it is of great significance to carry out research on the impact of snow on the land surface process.In this paper,we use the multi-satellite fusion inversion of China's long-term daily snow depth data(1979-2016)to analyze the distribution and variation characteristics of snow cover depth and snow cover days in the Qinghai-Tibet Plateau,and according to the seasonal changes of snow cover.The snow cover period(October to May)is divided into three stages(accumulation period,peak period and ablation period).Combined with ERA-Interim monthly average and 3h reanalysis data,the surface heat conditions such as snow cover and temperature are analyzed.The relationship between soil water content and latent heat flux and other energy transports,preliminary analysis of the role of snow in the plateau land surface process.Considering the difference between the ERA-Interim data itself and the snow-capped data of satellite observation,six sub-regions are selected according to the correlation coefficient distribution of the two to study the influence of snow on surface water and heat parameters.The results show:(1)The spatial and temporal distributions of snow depth and snow days are basically the same,there is no obvious interannual variation law of snow distribution,and the climatic tendency characteristics of the plateau marginal areas such as the western Sichuan Plateau and the plateau main body are reversed.The climatic trends of snow depth and number of days are:-0.30cm/10 a,-3.23 days/10a;there are 5snowy years defined by the original sequence and detrending,and 6 years of less snow,due to the original sequence to a certain extent.Influenced by the climatic tendency characteristics of snow reduction,more(less)snow years are concentrated before 2000(post);ERA-I snow depth is lower than the remote sensing snow depth,the average snow depth of plateau snow is underestimated,and the snow cover is underestimated.The interannual variation amplitude,unable to describe the climatic tendency characteristics of the plateau snow reduction.(2)There are obvious climate climatic trends in surface heat conditions.The temperature(0.29°C/10a)and surface temperature(0.143°C/10a)are most significant in the snow stage,and the soil temperature is warm in the snow melting stage.The most significant increase is that the climatic tendency rates of the first to fourth layers of soil temperature are: 0.127°C/10 a,0.124°C/10 a,0.118°C/10 a,and0.094°C/10a;the soil water content is mainly dry and only at the peak.The soil moisture in the third and fourth layers of the stage has a tendency to dry out;the net short-wave radiation is mainly reduced by the decreasing trend of the downward short-wave radiation,and the sensible heat and latent heat are obviously weakened,and the soil heat flux is There are significant differences between different snow stages and different soil layers.(3)Judging from the correlation coefficient of interannual variation,snow cover plays a role in cooling the surface heat condition,and humidifies the soil water content,and this cooling and humidifying effect is most obvious in the accumulation stage of snow accumulation.The correlation is weakened with the deepening of the soil layer;the snow has a sensible effect on the sensible heat and latent heat transfer to the atmosphere,and its inhibition is mainly reflected in the accumulation stage;the snow has a positive effect on the heat transport of the soil upwards,and its promotion is mainly Reflected in the accumulation phase.(4)The surface heat condition(soil water content)of the snowy year is lower than(higher than)the snow year,and the snow mainly plays the role of cooling(humidification),and its cooling(humidification)effect is most significant at the peak stage;The ablation stage has a significant inhibitory effect on the sensible heat flux,and the snow accumulation stage has a significant inhibitory effect on the latent heat flux;during the accumulation of snow accumulation,the snow has an inhibitory effect on the upward heat input of the soil,while the peak and ablation stages are on the soil upwards.The input heat has a promoting effect.In the process of snow accumulation,the soil freezing time is advanced and the number of complete freezing days is increased when there is more snow.The shallow water layer(0-0.28m)in the ablation stage increases rapidly and even higher than the deep layer(1.0-2.89m)in a period of time.The soil water content has a small amplitude of surface latent heat flux after the average snow cover of the plateau is more than1-2cm,and the weather scale fluctuation of the sensible heat flux during the snow deposition period is opposite to the snow depth;the soil heat flux of each layer in thesnowy year The amount of time from the downward(upper)transport to the upward(lower)transport is less early(late). |
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