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Lanzhou University (2018)

Land-atmosphere Interaction and Its Impacts on the Regional Climate in Arid and Semiarid Regions in China


Titre : Land-atmosphere Interaction and Its Impacts on the Regional Climate in Arid and Semiarid Regions in China

Auteur : 苑广辉;

Grade : Doctoral Dissertation 2018

Université : Lanzhou University

Résumé partiel
Energy and water exchanges between the land surface and atmosphere have an important impact on climate change.Strong interactions exist between human activities,underlying surfaces,and climate change in the arid and semiarid regions in China,which are suffering the shortage of water resources,ecological fragility and frequent dusty weather.Researches on the landatmosphere interaction and its impacts on the regional climate in this region have a great significance on improving the simulations of the regional climate,predicting the regional climate change in the future,and selecting regional sustainable development strategies.The observational stations are less distributed in arid and semiarid regions,limiting the research on the land atmosphere interactions over these regions.Moreover,the impact of land surface on temperature and precipitation remains controversial and uncertain.To acquire high quality surface turbulent fluxes over complicated terrain,turbulent data from the Semi-Arid Climate and Environment Observatory of Lanzhou University(SACOL)are used.The applicabilities of different coordinate rotations are analyzed and a parameterization scheme is provided in integral turbulent characteristics test(ITC).The acquiring of high quality surface turbulent fluxes provide basis for subsequent researches on the land atmosphere interactions.At the same time,the effects of soil moisture,net radiation,and vapor pressure deficit on available energy partitioning are compared using data from SACOL and cropland and degraded-grassland in Tongyu.To assess the impacts of initial soil moisture and the vegetation fraction on the diurnal temperature range(DTR)in arid and semiarid regions in China,three simulations using the WRF model are conducted by modifying the soil moisture,surface emissivity and vegetation fraction.Moreover,MODIS data and observational data from SACOL and the Shapotou Desert Research and Experimental Station(SPD)are also used in this research.The impact strength and way of atmospheric moisture fluxes and soil moisture on local precipitation are compared in the arid and semiarid regions and humid and semihumid regions in China.(1)The overall quality after data processing and quality control including sonic temperature correction,coordinate rotations,WPL correction(correction for density fluctuations),stationarity test and ITC test show that about 45%-62%of the total data are of high quality for friction velocity(*u),66-68%for sensible heat flux,62-65%for latent heat flux and 52-54%for CO2 flux.The proportion of the high quality of*u obtained by DR is 17%higher than PF,while the proportion of high quality data of the latter three kinds of fluxes obtained by PF is 2%-3%higher than DR.The differences between PF and FPF are mainly in*u.Comparing the three coordinate rotations in the dominant wind direction,DR still obtain the best quality of*u.The use of DR is recommended in the complicated terrain for reducing calculation and improving the data quality.(2)The Bowen ratio decrease rapidly with increasing soil moisture when soil is dry but is insensitive to the changes in soil moisture whensoil is wet.Net radiation and vapor pressure deficit affect the sensitivity of the Bowen ratio to soil moisture under dry conditions and the soil moisture threshold above which the Bowen ratio become insensitive to soil moisture.The Bowen ratio increase with net radiation,while the Bowen ratio will decrease with net radiation at a high level of net radiation,especially underdrought conditions.Reduced soil moisture enhanced the effects of the net radiation and vapor pressure deficit on available energy partitioning.

Mots clés : land atmosphere interaction; turbulent flux; energy partitioning; soil moisture; vegetation fraction; diurnal temperature range; precipitation; radiation budget; vapor pressure deficit;

Présentation (CNKI)

Page publiée le 9 avril 2019