Characteristics Of Surface Energy And Parameters In Gurbantunggut Desert

The Gurbantunggut Desert is the largest fixed and semi-fixed desert in China.Its underlying surface has the characteristics of stable snow cover in winter,vigorous growth of short-lived plants in spring,and abundant shrubs in summer.The non-uniformity of the underlying surface makes it have special laws in terms of land-air energy and material exchange,and has an important impact on Central Asia and even the global climate.This paper uses the 2017 data from the land-atmosphere interaction observation station in the Kelamei area in the hinterland of the Gurbantunggut Desert to analyze the changes in the surface radiation budget of the desert under different time scales and different weather conditions.The turbulence flux data is used to evaluate the energy balance closure degree and analyze the flux source area.On this basis,the characteristics of the desert surface energy balance and energy distribution change are analyzed.Finally,the surface albedo,surface roughness,and overall transportation are given.The characteristics of surface characteristic parameters such as coefficients provide a scientific basis for the subsequent improvement of the desert land process parameterization scheme and the development of a land surface model suitable for the desert.the result shows:(1)The surface radiation budget of the Gurbantunggut Desert has obvious diurnal and seasonal changes.The daily variation of the various components of the surface radiation budget is single-peaked.The maximum daily peak of total solar radiation appears in May(905.7 W·m^-2),and the reflected short-wave radiation appears in March(416 W·m^-2).Both the surface and atmospheric long-wave radiation appeared in July(611.5 W·m^-2 and 385.3 W·m^-2).There are obvious seasonal changes in the various components of the surface radiation.The average exposure of total solar radiation is shown as:growth period>snow cover period>withering period,and reflected shortwave radiation is shown as:snow cover period>growth period>withering period,the surface and the atmosphere The long-wave radiation is all expressed as:growth period>withering period>snow period.The maximum monthly exposures of total solar radiation,surface and atmospheric long-wave radiation all appeared in July,which values are 842.5,1342.43 MJ·m^-2 and 988.89 MJ·m^-2,respectively.The reflected short-wave radiation appeared in March,which value is 312.6 MJ·m^-2.(2)Different weather conditions and rapid snow melting in the Gurbantunggut Desert have a significant impact on the surface radiation budget.The daily variation of the various components of the surface radiation budget on sunny days is a smooth inverted U-shaped curve,while cloudy,rainy and snowy days are not as smooth as sunny days.The total solar radiation,reflected short-wave radiation and net radiation are more sensitive to clouds and precipitation,while the surface and atmospheric long-wave radiation are less affected by clouds and precipitation.The surface albedo and reflected short-wave radiation are greatly reduced during the rapid snow melting,while the surface and atmospheric long-wave radiation will increase in magnitude after the snow is completely melted.(3)The surface energy balance closure rate of the Gurbantunggut Desert in 2017 was higher in the growth period,and lower in the snow-packed period and withered period.The monthly average daily changes of each component of the energy balance from March to October are in a unimodal pattern.The maximum daily peaks of net radiation,latent heat flux,and surface soil heat flux all appear in the first half of May,which are 513.9W·m^-2,respectively.92.7 W·m^-2 and 140.4 W·m^-2,while the sensible heat flux appears in the second half of July(232.6 W·m^-2).The energy distribution is dominated by sensible heat flux during the day,and by the surface soil heat flux at night.The maximum values of daytime H/R_net,LE/R_net,and G₀/R_net occurred in the second half of July,the second half of April,and the first half of April,respectively,which were 53%,24.3%,and 28%.(4)Different weather conditions and the heterogeneous characteristics of the underlying surface of the Gurbantunggut Desert have significant effects on the energy balance and energy distribution characteristics of the surface.In terms of different weather,the sensible heat flux and surface soil heat flux are expressed as:sunny days before rain>sunny days after rain>rainy days,and latent heat fluxes are expressed as:sunny days after rain>rainy days>sunny days before rain.From the second half of March to the first half of May,the snow cover of the Gurbantonggut Desert gradually melts,and the short-lived vegetation grows and flourishes.This causes the latent heat flux and its ratio to the net radiation to be higher than other months.Among them,March Latent heat flux and its ratio to net radiation are higher than sensible heat flux and surface soil heat flux.(5)The daily variation of the surface albedo of the Gurbantunggut Desert from April to November is a"U"-shaped curve.The annual average value of the surface albedo is0.367,and the monthly average value is 0.233—0.766.From January 1 to March 15,the surface is always covered with snow,and the daily average value is higher than 0.7,resulting in an average surface albedo of 0.7 during the snow cover period.The surface dynamic roughness has a relatively low value in the downward dominant wind,and a high value in other wind directions.k B^-1 showed diurnal changes of low morning and evening and high at noon in the non-snow season,and there was no obvious diurnal variation in the snow season.The monthly medians of momentum and sensible heat exchange coefficient are 3.378×10^-3—6.76×10^-3 and 1.32×10^-3—3.46×10^-3,respectively.The size of the former is about 2×10^-3 higher than the latter.