Observational Study Of Surface Energy Balance And Energy Closure In The Farmland Ecosystems In Huaihe River Basin

In the context of three years（July2007July-2010July） eddy covariance data of theShouxian National Climatological Observatory,an intensive study is performed to an-alyze the exchange charaeteristics of energy and matter in air-land interaction overthe farmland ecosystems in Huaihe River Basin.Especially emphasizing on the issueof energy balance unelosure in observation experiment of land surface,not only thecondition of energy balance unelosure and all the factors affecting it have been analy-zed in detail by using the eddy covariance data,but also provides the basis forAccurately evaluation energy and matter in air-land interaction over the wheat andrice Field ecological system. The following are the main conclusions:（1）turbulent fluxes and available energy near surface farmland have obviouslycharaeteristies of diurnal and seasonal variation,They also have obvious diumalvariation which shows “U”type Net radiation （Rn）, latent heat flux （LE） and sensibleheat flux （H）, generally appear in peak change12:00-14:00, Soil heat flux peak timelag of1²hours. Net radiation, the heat and latent heat flux annual monthly averageare positive value, and monthly average of Soil heat flux is negative value. In the fourseasons latent heat flux share of the net radiation ratio is greater than the sensible heatflux proportion,especially in summer, autumn season,This suggests that the sensibleheat flux is the largest ratio of the net radiation over the farmland ecosystems in thehuaihe river basin.Throughout the year, albedo rate the day in surface rate changes has the obvious"U" type, The albedo of the seasonal average size performance of different underlyingsurface of the mean size of the performance of autumn <spring <summer <winter, thebare <paddy <wheat field <snow.Wheat and rice during the growing season, surfacealbedo rates at first increase and then decrease trend.（2）CO₂flux and sensible heat, latent heat flux are a significant negativecorrelation,CO₂and LE fitting curve is ywheat=-172.08x+16.713,yrice=-56.676x-4.2884，CO₂and H fitting curve is ywheat=-184.24x-52.905, yrice=-35.718x+13.906。（3）Energy balance conditions of the farmland ecosystems in Huaihe River Basinhave Obviously charaeteristies of diurnal and seasonal variation, Energy closedrates progressively smaller,from big to small sort: autumn>winter> summer>spring.Spring energy closed rate is only0.53. OLS slope of daytime and OLS slope of allday are similar, were1.05and1.06,R₂²are0.72and0.80, the day closed rate is0.91;The night closed rate is0.11,R₂²is only0.05, closed rate of only0.24, the day of energy balance significantly better than closed rate closed at night. diurnal variation ofbowen ratio is an inverted "U" shape, and it reaches its maximum at noon, alternatingday and night time Bowen is relatively small. The residual amount of energy duringthe day showes a single peak curve, daytime energy residual is greater than its at night,when the available energy measurement is accurate, reflects the eddy covariancemethod to express the turbulent energy is underestimated. From the energy balanceresidual relative frequency distribution maps also proved turbulent energy has beenunderestimated. Each quarter of the residual energy from small to big sort: autumn<winter <summer <spring.（4）different sizes of Flux source areas is the reason of the energy unclosure of thethe Shouxian farmland ecosystem.The perennial main wind direction of the Shouxianis NE, the average size of the source area is34400m², The average energy closure rateof0.76; the main wind direction in June is SSE,it’s the source area of14200m²,energyclosure rate is0.93. stable and unstable layer formed rice growing season range ofsource area is26000m²、48800m², while the wheat growing season, the source area is38000m²、10800m²， The interim period of the source area is49600m²、24000m². Itshows the source area of the wheat growing season measured by eddy covariancemethod is greater than the rice, the interim period is greater than the growing season;stable stratification is less than the unstable stratification.energy closure after correction byWang Jieming teacher Edire software is higherthan before the amendment. Which WPL correction, coordinate rotation correctionand frequency correction improve the energy closure rate of0.01, the planar fitcorrection do not significantly improve energy closure rate.（5）Friction velocity and atmospheric stability affect the OLS slope and energyclosure rate, night OLS slope changes significantly by Friction velocity increasingduring the day,OLS slope increases relatively stable by Friction velocity. In springOLS slope in the low-friction velocity （U^*<0.2m/s） is only0.1, the high-frictionvelocity it reaches0.7. It continues increasing in autumn and winter, LS slope is from0.01to0.21by the of friction velocity from low to high level.Unstable stratification （ζ<0）, the OLS slope and energy closure rate is greater thanthe stable stratification （ζ>0）, the OLS slope and energy closure rate, and the OLSslope is more significantly reduced and energy balance closure rate decreases with theinstability stratification weakened.