本文關鍵詞： 地表湍流熱通量 誤差 中國西部 渦動相關法 變分法 Noah-MP陸面模式 集合卡爾曼濾波　出處：《蘭州大學》2017年博士論文　論文類型：學位論文

【摘要】：地表湍流熱通量是陸面過程中關鍵物理量之一,對它準確計算是大氣、水文和農(nóng)業(yè)等學科必需的。伴隨著天氣和氣候模式物理過程的不斷改進以及時空分辨率的快速提高,為模式提供高精度的地表湍流熱通量下邊界顯得尤為重要。根據(jù)觀測資料和下墊面的不同,目前存在多種計算地表湍流熱通量的方法,影響計算精度的不確定因素也不盡同。中國西部地區(qū)下墊面種類復雜,地形起伏較大,各類方法在該地區(qū)應用時的具體表現(xiàn)可能不盡相同。因此,本文從方法論的角度出發(fā),評估四類代表性估算地表湍流熱通量方案在西部地區(qū)的性能,它們是渦動相關法(EC)、變分法、陸面模式Noah-MP的模擬方法和集合卡爾曼濾波(EnKF)數(shù)據(jù)同化方法;重點分析可能存在的誤差源并針對部分方案提出改進措施,以期提升不同方法估算地表湍流熱通量的精度。主要結果如下:(1)針對西北地區(qū)一類特殊的非均勻綠洲下墊面上單站點EC法求解地表湍流熱通量存在較大的不確定性問題,論文進行了定量誤差源分析。首先,利用單點觀測資料計算EC湍流熱通量并探究低估原因。單站點EC湍流熱通量的誤差部分來源于綠洲上空較大的平均垂直速度(VA)能量輸送以及下沉氣流,尤其在中午前后,其中VA感熱輸送(潛熱輸送)對感熱通量(潛熱通量)日均方根平均值貢獻約為16.5%(7.4%)。其次,為了彌補上述單一站點資料分析結果的代表性不足問題,借助WRF-LES大渦模擬手段研究理想帶狀非均勻綠洲沙漠下墊面上不同位置處EC熱通量的空間代表性。綠洲不同位置EC觀測對區(qū)域平均熱通量的代表性空間差異較大,原因各點受下墊面上空湍流有組織結構(TOS)和次級環(huán)流(SC)的影響不同;由TOS與SC引起的熱通量與區(qū)域平均熱通量的比值在邊界層中上層較大,從而單站點EC熱通量觀測很難代表區(qū)域平均值,部分位置處甚至出現(xiàn)嚴重低估。(2)針對西部地區(qū)部分下墊面(綠洲和高原凍土)存在較大能量存儲進而影響變分法求解精度的問題,論文在變分法中提出兩種能量存儲方案:第一種方法為利用觀測資料計算,第二種方法為分段線性擬合能量存儲。最后,利用地處甘肅省張掖綠洲上大滿站(有植被能量存儲和灌溉造成的較大土壤熱存儲)和青藏高原上安多站(土壤凍融會伴隨大量熱量吸收/排放)的資料,對所提兩類方案進行驗證,并與EC觀測的熱通量進行比較,結果表明:兩種方法都提高了熱通量估計精度;相對而言,第一種方法結果較好,尤其在中午或邊界層強不穩(wěn)定條件下。此外,在沒有足夠觀測資料計算這些能量存儲時,還可以把已有能量存儲項“移植”到同一地區(qū)其他觀測時段用于熱通量的估算,從而增大了方法的適用范圍。(3)利用甘肅張掖綠洲大滿站觀測資料,利用陸面模式Noah-MP求解地表熱通量,并仔細分析誤差源。若只采用默認參數(shù)化方案,模式能夠較好地模擬晴天凈輻射、感熱通量和潛熱通量,但在晴天中午前后模擬的峰值明顯低于觀測值,并且高估土壤蒸發(fā)比和低估植物蒸騰。其次,通過相關物理過程分析和不同的參數(shù)化方案的替換試驗探尋誤差源。采用Cai11地表反照率方案和/或Jarvis氣孔阻抗方案替代默認方案可以部分解決模擬的凈輻射通量和潛熱通量偏低的問題,同時也使土壤蒸發(fā)和植物蒸騰的分配比例更為合理,地表輻射溫度更接近觀測值;采用Alpha方案可解決原有SZ09方案土壤蒸發(fā)過大問題,減少土壤蒸發(fā)的比例。(4)利用地處甘肅省榆中縣原生植被下墊面上的SACOL站觀測資料,開展EnKF同化試驗來改善地表熱通量的計算。相對于沒有進行同化的陸面模式模擬結果,同化表層土壤濕度觀測可以有效地克服感熱通量模擬偏高、潛熱通量模擬偏低的問題,其中在9:00-12:00 LT改進最大。最后,采用敏感試驗方法,探究觀測誤差和背景場誤差對EnKF估算的影響:當觀測誤差減小(增大),感熱通量和潛熱通量估算值均方根誤差也減小(增大);EnKF估算值隨著背景場方差放大系數(shù)的增大而增大。因此,高質量的觀測資料和能真實反映背景場誤差協(xié)方差的樣本是提升地表熱通量估算精度的關鍵�？傊�,上述四類求解地表湍流熱通量的方法各有優(yōu)缺點,雖然在西部地區(qū)能較好地估算地表湍流熱通量,但是由于所用觀測資料來源和性質不同,難于對它們估算結果進行優(yōu)劣比較,在實際中可根據(jù)觀測資料性質和不同下墊面特點進行針對性地選用。
[Abstract]:The surface turbulent heat flux is one of the key physical quantity in the land surface process, it is necessary to accurately calculate the atmospheric, hydrological and agricultural science. With the rapid increase of continuous improvement of weather and climate model and spatial resolution, it is especially important to provide high precision surface turbulent heat flux boundary appears as a model. According to the observation data and the different underlying surfaces, there many methods to calculate surface turbulent heat fluxes at present, influence the precision of calculating uncertainties are not the same. The western region China surface species complex, undulating terrain, the specific performance of various methods in the area of the application may not be the same. Therefore, this article from the methods on the basis of evaluation of four representative types of performance estimation of surface turbulent heat flux in the western region, which is the eddy correlation method (EC), variational method, land surface model Noah-MP model Quasi Calman method and set filter (EnKF) data assimilation method; focus on the analysis of error sources may exist and put forward the improvement measures for the part of the program, in order to improve the different methods of estimation of surface turbulent heat flux precision. The main results are as follows: (1) in the Northwest region of a special kind of non uniform underlying surface on a single site in Oasis EC method for solving the surface turbulent heat flux is a big uncertainty problem, the quantitative analysis of error sources. Firstly, calculate EC turbulent heat flux and explore the reasons of underestimation by the single point observation data. The error sources of single site EC turbulent heat fluxes over the oasis in larger average vertical velocity (VA) of energy transfer and sinking air, especially at noon, which VA sensible heat fluxes (latent heat transfer) of sensible heat fluxes (latent heat flux) the average root mean square average contribution is about 16.5% (7.4%). Secondly, in order to make up for the single A lack of representation of the site data analysis results, with the help of WRF-LES large eddy simulation method to study the non ideal zonal spatial representation of different positions of EC heat flux uniformity of oasis desert surfaces. The representative of the regional differences in the average heat flux space oasis EC different position observation points by reason of large surface over turbulent structure (TOS) and secondary circulation (SC) the effect of different heat flux ratio; the average heat flux and area caused by TOS and SC in the boundary layer in the upper is larger, so the single site EC heat flux is difficult to represent the Qu Yuping mean, part of position or even seriously underestimated. (2) according to the the western part of the surface area (oasis and permafrost) there are large energy storage and variational method to solve the accuracy problem, the two energy storage scheme is proposed by the first method for using observation The data calculation, second kinds of methods for piecewise linear fitting energy storage. Finally, the Gansu province is located in Zhangye oasis on the full station (with larger energy storage and heat storage of soil vegetation caused by irrigation) and Tibetan Plateau (Amdo station soil freezing and thawing with lots of heat absorption / emission) data to validate the two kind of scheme, and heat flux and EC observation were compared, the results show that the two methods can improve the estimation accuracy of heat flux; relatively good results, the first method, especially at noon or in the boundary layer instability conditions. In addition, there is not enough data for calculating the energy storage, but also the existing energy storage "transplant" to the same area of other observation period for estimating heat flux, thereby increasing the scope of the method. (3) by Gansu Zhangye oasis over the station observation data of land use planning Type Noah-MP to solve the surface heat flux, and careful analysis of error sources. If only using the default parameter scheme model can better simulate the net radiation, sensible heat flux and latent heat flux, but the peak at noon before and after the simulation was significantly lower than the observed value, and overestimate the soil evaporation and plant transpiration than underestimated. Secondly, explore through the test error source replacement parameterization scheme analysis of relevant physical processes and different surface albedo. The Cai11 scheme and / or Jarvis stomatal resistance alternative default scheme can partly solve the simulation of net radiation flux and the latent heat flux is low, but also the proportion of soil evaporation and plant transpiration is more reasonable. The surface radiation temperature is closer to the observation; using Alpha scheme can solve the original SZ09 scheme of soil evaporation is too large, reduce soil evaporation ratio. (4) the Gansu province is located in Yu The observation data of earth's surface SACOL station in the county of native vegetation, carry out calculation EnKF Assimilation Experiment to improve the surface heat flux. Compared with the land surface model without assimilation of simulation results, assimilation of surface soil moisture observations can effectively overcome the simulated sensible heat flux is high, the problem of low heat flux simulation, the biggest improvement in 9:00-12:00 LT. Finally, the sensitive test method, explore the observation error and background field error on EnKF estimation when the observation error decreases (increases), sensible heat flux and latent heat flux estimates of root mean square error also reduced (increased); EnKF value increases with the increase of background estimation field variance amplification factor. Therefore, the observation data of high quality and can reflect the background error covariance of the sample is to enhance the surface heat flux estimation accuracy of the key. In short, the above four kinds of solving methods of surface turbulent heat flux Each has advantages and disadvantages, although better estimation of surface turbulent heat fluxes in the western region, but due to the source of the observed data and the different nature of them difficult to estimate the results of comparative advantages and disadvantages in practice, according to the nature of observations and different surface features are targeted to choose.

【學位授予單位】：蘭州大學
【學位級別】：博士
【學位授予年份】：2017
【分類號】：P425.2

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