亚热带典型森林下垫面大气层结变化规律及其对潜在蒸散发估算的影响  

Variation of atmospheric stability in a typical subtropical forest and its effects on potential evapotranspiration

作　　者：郭宝 刘梅先 杜虎[2] 林凯荣 罗威 涂新军 Guo Bao;Liu Meixian;Du Hu;Lin Kairong;Luo Wei;Tu Xinjun(School of Civil Engineering,Sun Yat-sen University,Guangzhou 510275,Guangdong,China;Institute of Subtropical Agriculture,Chinese Academy of Sciences,Changsha 410125,Hunan,China)

机构地区：[1]中山大学土木工程学院,广东广州510275 [2]中国科学院亚热带农业生态研究所,湖南长沙410125

出　　处：《地理科学》2024年第2期359-367,共9页Scientia Geographica Sinica

基　　金：国家自然科学基金项目(42371029);广东省基础与应用基础研究基金-卓越青年团队项目(2023B1515040028)资助。

摘　　要：为评估忽略大气稳定性对潜在蒸散发(Potential Evapotranspiration,PET)估算的影响,本文以亚热带森林下垫面为例,结合涡动相关观测及莫宁-奥布霍夫相似原理,探讨了冠层上方大气层结变化规律,比较了基于中性假设和考虑大气稳定性影响的PET之间的差异。结果表明:①中性、稳定和不稳定3种大气层结具有明显的日内与季节变化特征,不稳定层结在中午居多,稳定层结在早晨和傍晚居多,而中性层结在昼间均有分布;同时,春夏两季的不稳定层结高频时段较长,而秋冬两季相对较短;总体上,观测期内不稳定、中性和稳定3种层结平均占比分别为41.4%、34.7%与24.0%。②基于中性假设的空气动力学阻力估算方法在一定程度上高估了空气动力学阻力,导致PET存在低估现象(RMSE=25.82 W/m^(2)),且误差偏离随着PET增大而愈加明显。③在当地条件下当量空气动力学阻力r_(a)与风速呈显著的指数关系(r_(a)=7.83u^(-2.92)+32.66,R^(2)=0.50,P<0.05,N=394),基于该关系估算的PET相对于中性假设而言具有更高的精度(R^(2)提高了3.26%,RMSE降低了19.83%)。Atmospheric turbulence structure and its scalar transfer capacity,generally described using the concept of aerodynamic resistance(denoted as r_(a))in evapotranspiration models,is one of the key factors affecting the accuracy in estimating potential evapotranspiration(denoted as PET).The aerodynamic resistance is significantly affected by the atmospheric stability,however,due to that the atmospheric stability data are not usually available,most of the previous studies estimated r_(a) based on the neutral hypothesis,which would result in uncertainties.This study investigated the atmospheric stability and evaluated the errors brought by the neutral hypothesis in PET estimation in a subtropical forest in southwestern China,based on EC measurements and Monin-Obukhov similarity theory.Results showed that,the neutral,stable and unstable atmospheric stratifications exhibited explicitly diurnal and seasonal patterns,with unstable stratifications being predominant at noon,stable stratifications being more common in the morning and evening,and neutral stratifications being distributed throughout the daytime.Moreover,the high-frequency periods of unstable stability are longer in spring and summer but shorter in autumn and winter.Overall,the mean ratio of unstable,neutral and stable stratifications during the experimental period was 41.4%,34.7%and 24.0%,respectively.Additionally,the aerodynamic resistance estimation based on the neutral assumption tends to overestimate r_(a),while neglecting the impacts of atmospheric stability leads to underestimation of PET with significant errors(RMSE=25.82 W/m^(2)),and the deviation of the error becomes more pronounced with increasing PET.Finally,potential evapotranspiration based on the relationship(denoted as PET_equ)between the equivalent aerodynamic resistance(denoted as r_(a))and wind speed(R^(2)=0.50,P<0.05,N=394)are more accurate in simulation(R^(2)=0.95,RMSE=20.70 W/m^(2)),compared with that based on neutral hypothesis(R^(2)=0.92,RMSE=25.82 W/m^(2)).Important to note that the rela

关 键 词：大气稳定度 潜在蒸散发 空气动力学阻力 莫宁-奥布霍夫相似原理 涡度相关 

分 类 号：P339[天文地球—水文科学] P421[水利工程—水文学及水资源] P426.2[天文地球—地球物理学]