Study On The Characteristics And Influencing Factors Of Sensible Heat Flux Over The Desert Steppe In Inner Mongolia

To evaluate the road surface process over a desert steppe area and its influence and adaptation to climate change,it is necessary to understand the characteristics of energy exchange between a desert steppe ecosystem and atmosphere.In this study,the desert steppe ecosystem in Inner Mongolia was taken as the research object,and the large aperture scintillometer was used as the main measurement method,and the footprint model and path analysis method were introduced.Combined with the corresponding meteorological and environmental observation data,the variation characteristics,source area distribution and environmental control mechanism of sensible heat flux over the desert steppe in Inner Mongolia were analyzed.The main results are as follows:（1）Average diurnal variations of sensible heat flux over the desert steppe in Inner Mongolia in 2022 showed a unimodal trend,the peak value appeared at about 13:30,the daytime flux symbol was positive,and the nighttime flux symbol was negative.The diurnal variation curve of cloudy and overcast days is more complicated by the influence of clouds.The strength of sensible heat exchange in sunny days was stronger than that in cloudy and overcast days.The monthly average daily dynamic curve of sensible heat flux was the highest peak value in May and the lowest in November.From June to August,it entered the vegetation growth season,and the peak value of the curve decreased significantly.In the subsequent decline,September（the end of the growing season）showed a peak recovery.In 2021,the sensible heat exchange in July was the weakest during the vegetation growth season,and this phenomenon was delayed to August in2022.Affected by net radiation,rainfall and vegetation conditions,the change curve of the daily accumulated value of sensible heat flux in the study period is approximate“S”type,and it is approximately a unimodal trend in 2022.The total daily sensible heat exchange was between-1.57MJ·m^-2·d^-1and 13.79 MJ·m^-2·d^-1.The daily accumulated sensible heat flux was negative for 14 days throughout the year.The total accumulated sensible heat exchange in summer and spring was similar,which was much larger than that in autumn and winter.The sensible heat flux in the growing season was about 60%more than that in the non-growing season.In 2022,the underlying surface of unit square meter over the desert steppe in Inner Mongolia transmitted sensible heat to the atmosphere by 1673.05 MJ,which was higher than that in the previous year.（2）The source area of the sensible heat flux observation of the large aperture scintillometer over the desert steppe in Inner Mongolia was not the same.They were distributed according to the upward wind direction of the scintillometer light path.The closer to the light path,the greater the contribution to the flux.The diurnal variation of the source area of sensible heat flux was basically consistent with the change of atmospheric stability.The monthly flux source area varies from 225000 to 372000 m².From January to December,the range of source area showed a trend from large to small and then to large.The source area of flux in the whole growing season was smaller than that in the non-growing season.The source area of LAS flux observation in 2022 was314500m²,with a length of about 730m from east to west and about 630m from north to south.It was mainly distributed on both sides of the light path,and the area of the northwest side was larger than that of the southwest side.The important factors affecting the distribution of source area of flux were atmospheric stability and wind direction.Atmospheric stability determined the size of the source area,wind direction determined the orientation and extension of the source area of flux,which could also affect the size of the range.（3）The meteorological factors that significantly affect the sensible heat flux in the desert steppe ecosystem of Inner Mongolia were global solar radiation,air temperature,vapour pressure deficit and wind speed.The sensible heat flux was mainly affected by the global solar radiation,and the correlation coefficient is greater than 0.93,followed by the vapour pressure deficit,and the influence of air temperature and wind speed was weak.The influence of global solar radiation on sensible heat flux was mainly reflected in the direct effect positively.The vapour pressure deficit,air temperature and wind speed mainly affected the sensible heat flux indirectly through the global radiation path.The factors that have a significant effect on the sensible heat flux in the underlying surface properties were surface temperature,soil water content at 10cm depth and ground-air temperature differentials.The ground-air temperature differentials had the greatest influence on sensible heat flux,and the correlation was above 0.88,followed by surface temperature,and soil water content had the weakest influence.The ground-air temperature differentials mainly positively affected the sensible heat flux in a direct way.The surface temperature mainly affected the sensible heat flux indirectly through the ground-air temperature differentials path and the soil water content path.There was not a significant correlation of sensible heat flux with aboveground biomass.