Impacts Of Dynamic Aerodynamic And Thermodynamic Parameters Over Rainfed Maize Agroecosystem On Simulating Land Surface Process

Surface albedo (a) controls directly distribution of solar radiation energy between the earth surface and atmosphere, and it is a very important thermal parameter used to calculate exchanges of energy and materials between terrestrial ecosystems and atmosphere. Aerodynamics roughness (z0) and zero plane displacement (d) are significant dynamic parameters influencing flux exchanges bwteeen terrestrial ecosystems and atmosphere. Accurate description of these parameters can improve simulation accuracy of the exchanges of energy and materials between terrestrial ecosystems and atmosphere as well as meteorological elements. Usually, a,zo and d are expressed with fixed value during the same kind of underlying surface in existing land surface models, and do not consider the change with time. Rainfed maize agroecosystem is a typical and representative underlying surface type in northeast China because its extreme changes in surface construction and properties including canopy height (h), leaf area index (LAI) and vegetation coverage (FVEG) with growth of maize cause variations of a, zo and d and then lead to changes in a series of physical process such as distributing and transferring processes of radiation, water and heat. Based on continuous observation data of land-atmosphere flux exchanges, meteorological and biological elements during2006-2008from Jinzhou agricultural ecosystem research station, dynamic characteristics and relationships with relevant influence factors of a,zo and d in rainfed maize whole growth period are analyzed and their dynamic parameterization schemes are set up and used to improve BATSle. At the last, the effect of improved model on simulating land surface process is investigated. The main conclusions are listed as follows.(1) Revealing the sensitivity of BATSle to dynamic LAI, FVEG, a and z0. BATSle is able to simulate reasonable daily pattern and interdiurnal change of surface soil temperature(Tg), net absorbed solar energy flux(Frs) and sensible heat flux(Hs) as well as undesirable surface soil water content(SWC) and latent heat flux(λE) especially on no-precipitation day. The simulation errors is greater and decreasing when LAI and FVEG are smaller and approaching ground truth, indicating that it is very necessary for increase simulation precision to use more real parameter settings in the model. Dynamic assignment of zo, LAI and FVEG plays an important role in improving simulation precision respectively to Tg, Hs and Tg, Hs, λE, SWC and Tg, frs, Hs, SWC. On the whole, every variable is sensitive to parameter dynamic when rainfed maize ecosystem surface change from bare soil to vegetation. In addition, a assigned with dynamic value affects to varying degrees to simulation of Tg, λE and Hs, especially the latter.(2) Developing a dynamic parameterization scheme of a based on solar altitude(ho), SWC and LAI. The bare soil a scheme founded considering respectively logarithm and linear relationship between a and he and SWC is better than those considering other relationships and is able to simulate diurnal pattern of a with smaller error in most of the non-growing season except early spring. In the growing season, the simulation precision of a scheme founded with statistical regression method considering respectively logarithm, linear and exponential relationship between a and he, SWC and LAI those play an important role to a is higher than those considering other relationships. For the limitation of data, the scheme underestimates evidently a in most of the study periods especially in vegetative growth phase of maize. As FVEG is introduced and used to bestow weighing to soil and vegetation, the synthesis model whose simulation error decreases significantly in whole growing season especially in vegetative growth phase is able to reflect seasonal variation of a and has dynamic simulation ability, which change an untrue hypothesis that vegetation a is only fixed value in many land surface model and makes the model universal-adapted to simulate dynamic a in different phases of rainfed maize ecosystem. Compared with the double-layer and simplified double-layer model of a, simulation ability of the synthesis model is stronger than that of another two in most of time expect in later growing period when is weaker than that of simplified double-layer model.(3) Evaluating the simulation of improving BATSle model through introducing the synthesis model and dynamic LAI. The results show that the improving model realizes dynamic simulation of a whose annual simulation error decreases obviously and the simulation value is more accurate for dynamic LAI introduced in growing season, which improves the simulation precision of radial component such as frs whose annual improving quantity(IQ) accounts for1.7percent of annual global radiation, net absorb long wave radiation(frl) in May and June when FVEG changes quickly and nr in growing season and daytime,respectively. IQ of yearly and monthly Tg is0.62K and above1K, respectively. Concidering difference of canopy heat flux between bare soil and vegetation, their simulation results analyzed respectively show that simulation process of heat flux by the improve model is more close to the fact including Hs whose improvement is the most obvious, especially in the growing season in June and August when underlying surface characteristics change evidently than in non-growing season, and λE whose improvement is less than the former and circumstance is consistent mainly with Hs, but simulation error is large because of notable underestimation of SWC on no precipitation day, which demonstrates that expression of soil water content of BATSle must be improved, as well as soil heat flux(G) whose simulation precision is higher in the non-growing season than in the growing season and the explaining ability of simulation to observation increases4%. Yet simulation process of the primary model is consistent with the fact in trend seen from the outside but is an indisguise in facts.(4) Establishing dynamic parameterization schemes of zo and d by the optimization methods. It is found that zo from bulk Rickardson number (Ri) considering different heights combination is discrepant, decrease with increasing Ri and is reasonable simulated with the height combination of2m and10m. z0is smaller than0.2m before tasseling stage and comes to the maximum about0.4m before and after milk stage. d value begins to appear10days after jointing when h is1.4m height and at this time its height is0.8to1m then1to1.4m after tasseling stage. For magnitude and change trend, zo and d in this study are consistent with related research results. Before d appears, negative exponent and positive linear relationships between zo and wind speed, LAI, h are found. Simulation precision of zo parameterization scheme considering accumulation form of the effect of h and wind speed on zo is highest. After d appears, relationship between wind speed and zo+d is more notable than those between wind speed and zo or d. At the same time, positive exponent relationships between zo or d and LAI or h are found. LAI and h have more influence to zo than d and zo+d for the former greater than the latter. In addition, d/h and zo/h is0.4to0.54and0.1to0.14respectively. Before h comes to the maximum, d/h and zo/h are decreasing and increasing with LAI respectively. Simulation precisions of z0and d parameterization model considering multiplicative form of exponent relationships between zo and LAI, wind speed as well as d and h, wind speed respectively are highest, respectively. When h is invariable, simulation precisions of d and zo parameterization model is decreasing and can't be simulated respectively as a result of small variation of LAI and greater measure error of wind speed for the former and smaller diurnal variation for the latter.(5) Evaluating the simulation of improving BATSle model through introducing dynamic aerodynamic parameter scheme. The simulation precision of each component of land surface heat flux is in different degree improved with the order of G, Hs and λE whose growing season IQ account for1.24,0.36and0.19percent of global radiation respectively when original BATSle model is modified with newly-built dynamic zo and d parameterization scheme. IQ of G, Hs and λE are larger in July and August, in August and September, in July and August accounting for2.35and3.36,1.68and0.4as well as0.67and2.29percent of monthly global radiation respectively than in other months. Furthermore, we come to a conclusion that d is able to be ignored when that is smaller than1.6m because of slow response from BATSle model.(6) Evaluating the simulation of improving BATSle model through introducing dynamic aerodynamic and thermodynamic parameter scheme. Simulation precision of a, nr and Tg are improved when original BATSle model is simultaneously modified with newly-built dynamic a, zo and d parameterization scheme. As a result, simulation of each component of land surface heat flux is improved with the order of Hs, G, and λE. Considering contribution of each parameter, a dynamic parameterization contributes more than that of z0and d to nr and Hs, on the contrary, z0and d dynamic parameterization contribute more than that of a to simulation of Tg, λE and G. Simulation precision of λE decreases in some periods though that parameterization of a, zo and d are improved, which is owed to SWC unreasonably simulated by original BATSle model. Those show that simulation of some variables may be improved but those of another deteriorative when one or several parameters are mended because the fictitious balance situation canceling out simulation errors between different variables and making simulation result seem to be true is destroyed by improving of some variables, which leads error to amplify. But, the model is being more reasonably improved. As a result, enlargement of simulation error does n't absolutely represent that the improvement of model is invalid. Altogether, many processes in land surface model are still not perfect and in need to be improved...