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Lanzhou University (2015)

Research on Water-heat Exchange between Land and Air in Badain Jaran Desert Based on Observation


Titre : Research on Water-heat Exchange between Land and Air in Badain Jaran Desert Based on Observation

Auteur : 胡文峰

Grade : Doctoral Dissertation 2015

Université : Lanzhou University

The megadune in Badan Jaran Desert is the heightest in the desert of the world, among these megadunes dotted with many lakes, and the megadunes and lakes alternatively distributed in Geomorphology. It is difficult to carry out experiments in hinterland of the desert due to restrictions by the traffic and environment. Lack of relevant scientific data, it is a controversy in the actual evapotranspiration in the region. In this paper, to select a typical lakes and sand hills, use the turbulent data by eddy covariance system, from the perspective of the turbulence, analyzed the turbulent transport and material exchange between the land and atmosphere, and calculated the actual evaporation over the surface of megadune and lake. Hoping to fill the gaps of the research in the area, to do basic work for the next research about the lake water recharge and supply source.To analyze the characteristics of turbulent transport, select observed turbulence data of the same period over the sand hill and lake, to comparative study on the transport parameters and characteristics over the two surface.The results show that the friction velocity has obvious diurnal and seasonal variation over surface of the land and lake, and the friction velocity on the lake was less than that on the land surface. Near surface layer, the atmospheric turbulence field has variation in day and night and seasonal, and the same time, the atmospheric stability was differences. Due to the presence of lakes, it was intensified the instability and enhanced turbulence intensity of the local atmospheric, and changed the air flow field. There were obvious diurnal variation in transfer coefficient of Sensible heat and momentum, and the transfer coefficients of sensible heat were greater than the transfer coefficients of momentum on the same underlying surface, the sensible heat was more active on land surface and the sensible heat transport was more important than the momentum transport on lake. Whether it were the land surface or lake, the standard deviations of three-dimensional wind speed versus stability (Z/L) were agreed with the "1/3" law on megadune and lake, but there were differences in function coefficients, and support the Monin-Obukov similarity theory in desert hinterland, the turbulence were agreed with the local isotropic theory. There were heat and water vapor interaction between the lake and surrounding sand hills.The contribution made by each scale eddies to the water vapor flux was much more than that to the sensible heat flux transport on the lake, but the contribution made by each scale eddies to the sensible heat flux was much more than that to the water vapor flux transport on the megadune. The turbulent transport influence by geomorphological of lakes and megadunes interphase distribution.In order to further explore the land-air interaction, by analyzing the observational data found that it were differences in radiation budget and turbulence heat fluxes on the megadunes and lake. Duo to the different in properties of the surface of megadunes and lake, it was obviously different in shortwave radiation (UR) and longwave radiation (ULR) of underlying surface, lead to a discrepancy in the radiation energy distribution.The ability to store energy of the lake was much larger than that on bare land surface, exacerbated the uneven distribution of surface energy in the region. Remove differences in altitude between the two stations, the lake obtained the net radiation was larger than that on the bare land surface,and the lake had obvious "Oasis effect" in the energy budget in Badain Jaran Desert. The sensible heat flux was large and latent heat flux was small on land surface, but their change trend keep positive correlation. Latent heat flux over the lake was large and the sensible heat flux was small, and their changes were keep negative correlation. From the point of view of energy balance, the land surface absorbed the solar radiation was mainly used to heating the atmosphere and surface soil, but lake absorbed the solar radiation was mainly used to t evaporate. Geomorphological of lakes and megadunes interphase distribution, conducive to the lake water vapor transported to sand hill under the influence of local circulation, the same time, the presence of the surrounding sand hills, also conducive to water vapor entrapping. Soil heat flux accounts for a large proportion of net solar radiation onland surface, and soil thermal storage can not be ignored, energy balance on land surface can reach 80-90%. Turbulence heat flux was greater than the get net solar radiant energy over the lake, the energy which the lake supply brings can not be ignored. It were significant differences in heat-energy exchange between the land and gas on two kinds of land surfaceIn order to study the water vapor exchange between land surface and the air in two underlying, it was quite different in evaporation rates on the megadunes and lake. Geomorphological of lakes and megadunes interphase distribution, lakes would produced "oasis effecf"on local water vapor exchange. Warm and humid air on the lake would transported to the surrounding hills, and strengthened the precipitation onsand hills, but the lake did not directly increased the precipitation and precipitation intensity on the lake.Precipitation on megadunes determined its evaporation size, Rainfall infiltration of sand hills contributed little to groundwater and lake recharge, and lakes supply depends mainly on groundwater recharge. The cumulative amount of evaporation was 1450mm/a on the lake and the complementary model can be used to estimate the evaporation.The regression analysis of day’s evaporation, the best model was:E= e0.1+0.24*(1-RH2)1/2* VPD*u[0.85*u/(u+2)]

Mots clés : Badain Jaran Desert; eddy covariance; land-air exchange; turbulent flux; energy balance; evaporation;

Présentation (CNKI)

Page publiée le 10 février 2017, mise à jour le 15 septembre 2017