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王伟,申双和,刘寿东,张弥,肖薇,王咏薇,李旭辉.太湖生态系统能量闭合特征及其影响因素.生态学报,2017,37(18):5935~5950 本文二维码信息
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太湖生态系统能量闭合特征及其影响因素
Mechanistic analysis of the observed energy imbalance of Lake Taihu
投稿时间:2016-06-30  修订日期:2017-07-20
DOI: 10.5846/stxb201606301346
关键词太湖  能量不闭合  涡度相关  湍流交换  大气稳定度
Key WordsLake Taihu  energy imbalance  eddy covariance  turbulence exchange  atmospheric stability
基金项目国家自然科学基金青年项目(41505005);江苏省自然科学基金青年项目(BK20150900);国家自然科学基金面上项目(41475141,41575147,41275024);南京信息工程大学人才启动经费(2014r046);教育部长江学者和创新团队发展计划(PCSIRT);江苏高校优势学科建设工程(PAPD);南京信息工程大学2015年度大学生实践创新训练计划项目(201510300023)
作者单位E-mail
王伟 南京信息工程大学, 气候与环境变化国际合作联合实验室大气环境中心, 南京 210044;南京信息工程大学, 气象灾害预报预警与评估协同创新中心/气象灾害教育部重点实验室, 南京 210044 wangw@nuist.edu.cn 
申双和 南京信息工程大学, 江苏省农业气象重点实验室, 南京 210044  
刘寿东 南京信息工程大学, 气候与环境变化国际合作联合实验室大气环境中心, 南京 210044;南京信息工程大学, 气象灾害预报预警与评估协同创新中心/气象灾害教育部重点实验室, 南京 210044  
张弥 南京信息工程大学, 气候与环境变化国际合作联合实验室大气环境中心, 南京 210044;南京信息工程大学, 气象灾害预报预警与评估协同创新中心/气象灾害教育部重点实验室, 南京 210044  
肖薇 南京信息工程大学, 气候与环境变化国际合作联合实验室大气环境中心, 南京 210044;南京信息工程大学, 气象灾害预报预警与评估协同创新中心/气象灾害教育部重点实验室, 南京 210044  
王咏薇 南京信息工程大学, 气候与环境变化国际合作联合实验室大气环境中心, 南京 210044  
李旭辉 南京信息工程大学, 气候与环境变化国际合作联合实验室大气环境中心, 南京 210044  
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摘要:
地表能量不闭合不仅限制了涡度相关观测数据在陆面模型发展和验证等应用性研究中的价值,还给生态系统CO2源汇特征辨析带来不确定性。基于太湖避风港站2012年涡度相关通量、辐射、气象和水温梯度观测数据,分析了太湖能量闭合的多尺度(小时、日和月)时间变化特征,阐述了大气稳定度、摩擦风速和湖风对太湖能量闭合状况的影响。结果表明:太湖小时尺度的能量闭合度为0.59,且昼夜差异较小;日尺度的能量闭合度为0.73,在内陆水体观测结果中处于中等水平;月平均能量闭合度呈现冬季高、夏季低的季节变化特征;年平均时太湖仍有27%的能量不闭合。因摩擦风速减小,太湖能量闭合度在大气极不稳定条件下要比弱不稳定条件下结果低0.3;对于太湖这类大型浅水湖泊,其能量闭合度全天都受动力湍流交换强度制约,能量闭合度随摩擦风速增大而显著提高;虽然湖风发生使太湖小时尺度的能量闭合度降低了0.1,但其影响在日尺度上并不明显。
Abstract:
Surface energy imbalance not only imposes constraints on the application of eddy covariance observations in research on land surface model development and evaluation, but also creates uncertainty regarding measurements of long-term net ecosystem CO2 exchange. Lakes are a main component of the climate system and their surface energy balance is the dominant driver of biophysical and biogeochemical processes in lake ecosystems. In this study, observations of energy fluxes, radiation components, micrometeorological conditions, and water temperature profile were used to investigate the energy balance closure of Lake Taihu on different temporal scales (e.g., hourly, daily, and monthly). Energy balance closure was evaluated by linear regression of turbulent energy fluxes (sensible heat flux plus latent heat flux) against available energy (net radiation minus heat storage in water volume) and by calculating the energy balance ratio, the ratio of turbulent heat fluxes to available energy. Furthermore, the effects of three mechanisms-the stability of boundary layer atmosphere, friction velocity, and lake-breeze-on energy imbalance were analyzed quantitatively. The results showed that the heat storage in lake water volume had a diurnal variation similar to that of net radiation with comparable magnitudes, reaching a maximum at noontime. Both the sensible and latent heat flux showed much smaller diurnal variations and peaked in the morning and afternoon, respectively. Energy balance closure was observed at only 0.59 for the smooth Lake Taihu with half-hour averages, but increased to 0.73 using daily averages. Compared to land observations, there was less obvious diurnal variation in energy balance closure at Lake Taihu due to its aerodynamically smoother surface. Throughout the year, energy balance showed an obvious deficit during the warming months but perfect closure during the winter months. At an annual scale, the energy imbalance was 27%, which is comparable to values reported from eddy covariance observations on land and a few field surveys of lakes. The energy balance closure significantly improved with friction velocity during both daytime and nighttime, which indicates that mechanical turbulence is the main constraint on energy balance at Lake Taihu. The energy balance closure was approximately 0.7 for less unstable conditions (atmospheric stability parameter— -0.1), but was only 0.4 for very unstable conditions (atmospheric stability parameter— -1.5). Our results indicated that the poorer closure for very unstable conditions compared with less unstable conditions was due to reduced friction velocity (from 0.25 to 0.1). Although lake-breeze reduced the energy balance closure by 0.1 on an hourly scale, this was indiscernible on a daily scale. In addition, large-scale atmospheric motion, the stratification of lake water, and the source area mismatch between turbulent heat fluxes and available energy also contributed to the observed energy imbalance at Lake Taihu. Cospectra analysis showed that large-scale atmospheric motion was obvious at Lake Taihu, particularly during stable conditions, which may be filtered by a half-hour block average. Good energy balance closure was achieved when water thermal convection occurred with a 100 cm depth water temperature higher than that at 20 cm depth. The footprint of turbulent heat fluxes was much larger than that for available energy, and also varied with atmospheric stability and surface roughness. However, it is difficult to qualify the energy imbalance resulting from footprint mismatch.
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