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1.
Annemiek I. Stegehuis Robert Vautard Philippe Ciais Adriaan J. Teuling Martin Jung Pascal Yiou 《Climate Dynamics》2013,41(2):455-477
The occurrence and intensity of heatwaves is expected to increase with climate change. Early warnings of hot summers have therefore a great socio-economical value. Previous studies have shown that hot summers are preceded by a Southern European rainfall deficit during winter, and higher spring temperatures. Changes in the surface energy budget are believed to drive this evolution, in particular changes in the latent and sensible heat fluxes. However these have rarely been investigated due to the lack of long-term reliable observation data. In this study, we analyzed several data-derived gridded products of latent and sensible heat fluxes, based on flux tower observations, together with re-analyses and regional climate model simulations over Europe. We find that warm summers are preceded by an increase in latent heat flux in early spring. During warm summers, an increase in available energy results in an excess of both latent and sensible heat fluxes over most of Europe, but a latent heat flux decrease over the Iberian Peninsula. This indicates that, on average, a summertime soil-moisture limited evapotranspiration regime only prevails in the Iberian Peninsula. In general, the models that we analyzed overestimate latent heat and underestimate sensible heat as compared to the flux tower derived data-product. Most models show considerable drying during warm seasons, leading to the establishment of a soil-moisture limited regime across Europe in summer. This over-estimation by the current generation of models of latent heat and hence of soil moisture deficit over Europe in summer has potential consequences for future summertime climate projections and the projected frequency of heat waves. We also show that a northward propagation of drought during warm summers is found in model results, a phenomenon which is also seen in the flux tower data-product. Our results lead to a better understanding of the role of latent and sensible heat flux in summer heatwaves, and provide a framework for benchmark of modeling studies. 相似文献
2.
采用北京大学三维的复杂地形中尺度模式,结合陆面过程模式(SiB),模拟了草原和沙漠并存的下垫面的边界层大气运动.利用SiB模式计算了地表辐射、感热、潜热通量,并且预报地表温度.中尺度模式则模拟了沙漠地区受热抬升,形成的辐合运动,垂直速度的分布,不同高度上水平流场的变化以及中尺度动量和热量通量,把中尺度通量跟湍流通量进行了比较,以确定这种中尺度运动在GCM模式的参数化过程中的重要性.试验表明中尺度通量尤其是热量通量要比湍流通量大很多. 相似文献
3.
Connection between atmospheric latent energy and energy fluxes simulated by nine CMIP5 models 
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下载免费PDF全文 The atmospheric latent energy and incoming energy fluxes of the atmosphere are analyzed here based on the historical simulations of nine coupled models from the Coupled Model Intercomparison Project Phase 5(CMIP5)and two reanalysis datasets.The globally averaged atmospheric latent energy is found to be highly correlated with several types of energy flux,particularly the surface latent heat flux,atmosphere absorbed solar radiation flux,and surface net radiation flux.On the basis of these connections,a hydrological cycle controlled feedback(HCCF)is hypothesized.Through this feedback,the atmosphere absorbed solar radiation is enhanced and causes intensification of the surface latent heat flux when the atmospheric latent energy is abnormally strong.The representativeness of the HCCF during different periods and over different latitudinal zones is also discussed.Although such a feedback cannot be confirmed by reanalysis,it proves to be a common mechanism for all the models studied. 相似文献
4.
During slightly unstable but still very close to neutral conditions new results from two previous investigations have shown
a significant increase of sensible and latent heat fluxes over the sea. The vertical heat transport during these conditions
is dominated by detached eddies originating at the top of the boundary layer, bringing relatively cold and dry air to the
surface. This effect can be described in numerical models by either enhanced heat transfer coefficients for sensible and latent
heat (Stanton and Dalton numbers respectively) or with an additional roughness length, added to the original roughness lengths
for heat and humidity. Such new expressions are developed using turbulence measurements from the Baltic Sea valid for wind
speeds up to 14 m s−1. The effect of including the increased heat fluxes is investigated using two different numerical models: a regional three-dimensional
climate model covering northern Europe, and a process-oriented ocean model for the Baltic Sea. During periods of several days,
the latent heat flux can be increased by as much as 100 W m−2. The increase in sensible heat flux is significantly smaller since the process is only of importance in the very near-neutral
regime where the sensible heat flux is very small. The long-term average effect over the Baltic Sea is of the order of several
W m−2. 相似文献
5.
Analysis of the Seasonal Cycle Within the First International Urban Land-Surface Model Comparison 总被引：1，自引：0，他引：1
A number of urban land-surface models have been developed in recent years to satisfy the growing requirements for urban weather and climate interactions and prediction. These models vary considerably in their complexity and the processes that they represent. Although the models have been evaluated, the observational datasets have typically been of short duration and so are not suitable to assess the performance over the seasonal cycle. The First International Urban Land-Surface Model comparison used an observational dataset that spanned a period greater than a year, which enables an analysis over the seasonal cycle, whilst the variety of models that took part in the comparison allows the analysis to include a full range of model complexity. The results show that, in general, urban models do capture the seasonal cycle for each of the surface fluxes, but have larger errors in the summer months than in the winter. The net all-wave radiation has the smallest errors at all times of the year but with a negative bias. The latent heat flux and the net storage heat flux are also underestimated, whereas the sensible heat flux generally has a positive bias throughout the seasonal cycle. A representation of vegetation is a necessary, but not sufficient, condition for modelling the latent heat flux and associated sensible heat flux at all times of the year. Models that include a temporal variation in anthropogenic heat flux show some increased skill in the sensible heat flux at night during the winter, although their daytime values are consistently overestimated at all times of the year. Models that use the net all-wave radiation to determine the net storage heat flux have the best agreement with observed values of this flux during the daytime in summer, but perform worse during the winter months. The latter could result from a bias of summer periods in the observational datasets used to derive the relations with net all-wave radiation. Apart from these models, all of the other model categories considered in the analysis result in a mean net storage heat flux that is close to zero throughout the seasonal cycle, which is not seen in the observations. Models with a simple treatment of the physical processes generally perform at least as well as models with greater complexity. 相似文献
6.
Kenneth R. Sperber Silvio Gualdi Stephanie Legutke Veronika Gayler 《Climate Dynamics》2005,25(2-3):117-140
The Madden-Julian oscillation (MJO) dominates tropical variability on timescales of 30–70 days. During the boreal winter/spring,
it is manifested as an eastward propagating disturbance, with a strong convective signature over the eastern hemisphere. The
space–time structure of the MJO is analyzed using simulations with the ECHAM4 atmospheric general circulation model run with
observed monthly mean sea-surface temperatures (SSTs), and coupled to three different ocean models. The coherence of the eastward
propagation of MJO convection is sensitive to the ocean model to which ECHAM4 is coupled. For ECHAM4/OPYC and ECHO-G, models
for which ~100 years of daily data is available, Monte Carlo sampling indicates that their metrics of eastward propagation
are different at the 1% significance level. The flux-adjusted coupled simulations, ECHAM4/OPYC and ECHO-G, maintain a more
realistic mean-state, and have a more realistic MJO simulation than the nonadjusted scale interaction experiment (SINTEX)
coupled runs. The SINTEX model exhibits a cold bias in Indian Ocean and tropical West Pacific Ocean sea-surface temperature
of ~0.5°C. This cold bias affects the distribution of time-mean convection over the tropical eastern hemisphere. Furthermore,
the eastward propagation of MJO convection in this model is not as coherent as in the two models that used flux adjustment
or when compared to an integration of ECHAM4 with prescribed observed SST. This result suggests that simulating a realistic
basic state is at least as important as air–sea interaction for organizing the MJO. While all of the coupled models simulate
the warm (cold) SST anomalies that precede (succeed) the MJO convection, the interaction of the components of the net surface
heat flux that lead to these anomalies are different over the Indian Ocean. The ECHAM4/OPYC model in which the atmospheric
model is run at a horizontal resolution of T42, has eastward propagating zonal wind anomalies and latent heat flux anomalies.
However, the integrations with ECHO-G and SINTEX, which used T30 atmospheres, produce westward propagation of the latent heat
flux anomalies, contrary to reanalysis. It is suggested that the differing ability of the models to represent the near-surface
westerlies over the Indian Ocean is related to the different horizontal resolutions of the atmospheric model employed. 相似文献
7.
利用1979—2005年OAFlux (Objectively Analyzed air-sea Fluxes) 观测资料以及CMIP5的15个耦合模式的模拟结果,评估了BCC_CSM1.1(m) 模式对热带太平洋年平均潜热通量气候态和变化趋势的模拟能力,并分析造成趋势偏差的可能原因。结果表明:BCC_CSM1.1(m) 模式模拟热带太平洋年平均潜热通量气候态在各纬度上差异较大, 其中在赤道的模拟能力较佳,而在10°N和8°S附近模拟偏差较大;BCC_CSM1.1(m) 模式对热带太平洋年平均潜热通量趋势的模拟能力一般,造成趋势偏差的主要原因是该模式低估了风速对潜热通量的局地贡献以及它对风速的非局地贡献的模拟存在较大偏差。此外,该模式未能较好地模拟出风速对全球变暖响应。因此,BCC_CSM1.1(m) 模式对热带太平洋年平均潜热通量趋势模拟的改进需加强其对风速模拟的改进。 相似文献
8.
The estimation of the sensible heatflux from thermal infrared temperature requires anestimate of the excess resistance to be added to theaerodynamic resistance to the transfer of heat fromthe surface. This excess resistance can be expressedin terms of kB-1. An earlier studysuggested that the sensible heat flux over semi-aridregions could be derived from satellite thermalinfrared temperature using a value of kB-1= 7. Values of kB-1 were derived frommeasurements of sensible heat flux, radiometricsurface temperature, air temperature and wind speedtaken over millet, savannah and open forest sitesduring HAPEX-Sahel. These were comparable to valuesderived over similar sites during a previous study. Sensible and latent heat fluxes were estimated usingno excess resistance, kB-1 = 7 andkB-1 set to the values derived from theHAPEX-Sahel data set. There was an improvement on theestimated fluxes when an excess resistance wasincorporated. However, there was no apparentdifference between the errors in the estimated fluxeswith kB-1 set to either the derived orfixed values. This provides additional support forthe use of kB-1 = 7 in the derivation ofsurface fluxes from satellite data for sparsecanopies. 相似文献
9.
模式评估是模式发展中的重要一环。本文利用来自FLUXNET2015数据集的30个站点的涡动相关系统观测数据,重点关注能量通量,对通用陆面模式（Common Land Model version 2014,CoLM2014）在不同典型下垫面的模拟能力进行评估。结果表明,模式总体上能抓住感热、潜热和净辐射通量在日、季节和年平均等不同时间尺度上的变化特征,对感热、潜热和净辐射通量都有较好的模拟能力,净辐射的模拟效果最好,潜热通量次之。季节变化模拟中,感热、潜热通量在夏季不同植被型下站点的空间离散程度大于冬季,不同站点间模拟效果相差较大,净辐射多站点标准差变化幅度要小于感热、潜热,不同站点间模拟效果偏差较小。CoLM在常绿针叶林、稀树林地、草地、农田模拟感热、潜热通量的效果相对较好,在永久湿地、落叶阔叶林下模拟感热通量较差。本研究对CoLM2014在未来的改进和发展中提供了有用的参考。 相似文献
10.
NIM陆面过程模式的研究Ⅱ：青藏高原夏季陆面过程的数值模拟 总被引：4，自引：1，他引：4
采用南京气象学院（NIM）5层陆面过程模式，利用1979年5－8月“青藏高原气象科学实验”资料模拟和分析了夏季青藏高原不同地区的陆面特征和地表能量特征。并将模拟值与根据观测资料计算得到的感热和潜热以及观测得到的净辐射、土壤温度、土壤热通量进行了对比。结果表明，NIM5层陆面过程模式可以模拟青藏高原夏季不同下垫面情形下的能量交换过程。 相似文献
11.
A. J. Pitman A. Henderson-Sellers C. E. Desborough Z.-L. Yang F. Abramopoulos A. Boone R. E. Dickinson N. Gedney R. Koster E. Kowalczyk D. Lettenmaier X. Liang J.-F. Mahfouf J. Noilhan J. Polcher W. Qu A. Robock C. Rosenzweig C. A. Schlosser A. B. Shmakin J. Smith M. Suarez D. Verseghy P. Wetzel E. Wood Y. Xue 《Climate Dynamics》1999,15(9):673-684
Using atmospheric forcing data generated from a general circulation climate model, sixteen land surface schemes participating
in the Project for the Intercomparison of Land-surface Parametrization Schemes (PILPS) were run off-line to equilibrium using
forcing data from a GCM representative of a tropical forest and a mid-latitude grassland grid point. The values for each land
surface parameter (roughness length, minimum stomatal resistance, soil depth etc.) were provided. Results were quality controlled
and analyzed, focusing on the scatter simulated amongst the models. There were large differences in how the models’ partitioned
available energy between sensible and latent heat. Annually averaged, simulations for the tropical forest ranged by 79 1 3;W m-2 for the sensible heat flux and 80 W m-2 for the latent heat flux. For the grassland, simulations ranged by 34 W m-2 for the sensible heat flux and 27 W m-2 for the latent heat flux. Similarly large differences were found for simulated runoff and soil moisture and at the monthly
time scale. The models’ simulation of annually averaged effective radiative temperature varied with a range, between all the
models, of 1.4 K for tropical forest and 2.2 K for the grassland. The simulation of latent and sensible heat fluxes by a standard
‘bucket’ models was anomalous although this could be corrected by an additional resistance term. These results imply that
the current land surface models do not agree on the land surface climate when the atmospheric forcing and surface parameters
are prescribed. The nature of the experimental design, it being offline and with artificial forcing, generally precludes judgements
concerning the relative quality of any specific model. Although these results were produced de-coupled from a host model,
they do cast doubt on the reliability of land surface schemes. It is therefore a priority to resolve the disparity in the
simulations, understand the reasons behind the scatter and to determine whether this lack of agreement in de-coupled tests
is reproduced in coupled experiments.
Received: 15 October 1997 / Accepted: 22 April 1999 相似文献
12.
A physically-based solar radiation transmission model and a slope energy budget model were available which used climatic observations, averaged over 10-deg north-south latitude bands. This made possible the systematic examination of the diurnally changing energy budget components of net radiation, conduction, sensible, and latent heat flux occurring at all slope angles (0 to 90 deg) and slope directions (south-, west-, and north-facing). The present analysis utilized two contrasting landscapes along a latitudinal transect of the east coast of the Americas (northern hemisphere). Among the results, the maximum net radiation for all slope angles and directions occurred at noon on a 40-deg, south-facing slope for latitude 60. Generally, latent and sensible heat fluxes were similar in trend and magnitude between latitudes 0 and 35. Poleward, sensible heat flux increased with advancing latitude at the expense of latent heat flux. A great diversity in net radiation, sensible, and latent heat flux was obtained between different slopes and their orientation at a paniculate latitude. In addition to hourly rates of the energy budget components, daily positive sums of net radiation, sensible, and latent heat flux were examined. It is assumed that the portrayed patterns are general enough to add to our increasing understanding of the contrasts possible in a real-world north-south transect. 相似文献
13.
Isabel L. Pilotto Sin Chan Chou Paulo Nobre 《Theoretical and Applied Climatology》2012,110(3):437-456
This work evaluates the added value of the downscaling technique employed with the Eta model nested in the CPTEC atmospheric general circulation model and in the CPTEC coupled ocean?Catmosphere general circulation model (CGCM). The focus is on the austral summer season, December?CJanuary?CFebruary, with three members each year. Precipitation, latent heat flux, and shortwave radiation flux at the surface hindcast by the models are compared with observational data and model analyses. The global models generally overestimate the precipitation over South America and tropical Atlantic. The CGCM and the nested Eta (Eta + C) both produce a split in the ITCZ precipitation band. The Eta + C produces better precipitation pattern for the studied season. The Eta model reduces the excessive latent heat flux generated by these global models, in particular the Eta + C. Comparison against PIRATA buoys data shows that the Eta + C results in the smallest precipitation and shortwave radiation forecast errors. The Eta + C comparatively best results are though as a consequence of both: the regional model resolution/physics and smaller errors on the lateral boundary conditions provided by the CGCM. 相似文献
14.
This paper reports on measurements of sensible and latent heat and CO2 fluxes made over an irrigated potato field, growing next to a patch of desert. The study was conducted using two eddy correlation systems. One measurement system was located within the equilibrium boundary layer 800 m downwind from the edge of the potato field. The other measurement system was mobile and was placed at various downwind positions to probe the horizontal transition of vertical scalar fluxes. Latent (LE) and sensible (H) heat fluxes, measured at 4 m above the surface, exhibited marked variations with downwind distance over the field. Only after the fetch to height ratio exceeded 75 to 1 didLE andH become invariant with downwind distance. When latent and sensible heat fluxes were measured upwind of this threshold, significant advection of humidity-deficit occurred, causing a vertical flux divergence ofH andLE.The measured fluxes of momentum, heat, and moisture were compared with predictions from a second-order closure two-dimensional atmospheric boundary layer model. There is good agreement between measurements and model predictions. A soil-plant-atmosphere model was used to examine nonlinear feedbacks between humidity-deficits, stomatal conductance and evaporation. Data interpretation with this model revealed that the advection of hot dry air did not enhance surface evaporation rates near the upwind edge of the potato field, because of negative feedbacks among stomatal conductance, humidity-deficits, andLE. This finding is consistent with results from several recent studies. 相似文献
15.
Alpine wetland is one of the typical underlying surfaces on the Qinghai–Tibet Plateau. It plays a crucial role in runoff regulation. Investigations on the mechanisms of water and heat exchanges are necessary to understand the land surface processes over the alpine wetland. This study explores the characteristics of hydro-meteorological factors with in situ observations and uses the Community Land Model 5 to identify the main factors controlling water and heat exchanges.Latent heat flux and therm... 相似文献
16.
夏季青海湖局地环流及大气边界层特征的数值模拟 总被引：13，自引：8，他引：5
使用美国NCAR新版MM5V3.6非静力模式,采用两重嵌套方法,模拟了青海湖区域的局地环流及大气边界层特征,并且与无湖试验进行了比较。结果表明:白天由于青海湖的存在有很好的降温作用,夜晚则有保温效应,表现出明显的冷(暖)湖效应;青海湖对感热和潜热的影响有很强的日变化,白天湖面感热、潜热都小,夜间情况相反,这使得白天青海湖是冷干岛,夜间是暖湿岛;青海湖使得白天湖面边界层顶低,陆面边界层顶高,夜间相反。这样的边界层顶高度和温度、地面能量通量相配合,形成了一个很好的保护机制,对青海湖的水土保持和生态环境的维持有正效应;青海湖使得湖面上空大气下沉,陆面上空大气上升,从而产生了湖面上空大气冷干,陆面上空大气暖湿的边界层特征;青海湖边缘的陆面形成的较大的湿气柱围绕着湖面,起到了保护湖面的作用;青海湖低空白天有明显的湖面向四周的辐散气流,而夜间则为从北偏东方向来的陆风。 相似文献
17.
Th. Burkhardt 《Meteorology and Atmospheric Physics》1991,46(3-4):155-168
Summary A diagnostic model for complete heat budgets in the free atmosphere is presented and is applied to the African-Atlantic sector between 35°S–30°N for May 1979. The model is based on the conservation equations for latent and sensible heat. These are evaluated in a form integrated over 24 hours in time and over atmospheric boxes of 2.5°×2.5° in horizontal and 100 hPa in vertical direction. Grid-scale input data are the 3D-ECMWF-diagnoses of the FGGE period plus parameterized fields of surface rain, evaporation and sensible Heat flux. This leads to an overspecification of latent and sensible heat budgets for any atmospheric column between surface and top of the atmosphere and thus yields an objective column imbalance. In order to separate the vertical subscale fluxes of rain, moisture and heat in the free atmosphere the model uses a closure assumption for the coupling between moisture and sensible heat flux as well as one for the vertical imbalance profiles; it is demonstrated that the budgets are not too sensitive with respect to these parameterizations.Results are presented in terms of vertical profiles of the subscale vertical fluxes of rain, moisture and heat. These are interpeted as measures of convective activity, with particular emphasis on the ITCZ. May 1979 averages as well as results for a respresentative single day are discussed. The imbalance (=the error) can be sufficiently well separated from the signal. It is shown that the low-level mass flux divergence does not coincide with the position of the ITCZ while the maximum of the subscale fluxes does coincide. Over the continent, it is not the horizontal mass flux convergence which feeds the ITCZ and the rainbelt but rather the subscale moisture flux and its convergence in the vertical. Over the Saharan latitudes, there is considerable convective flux of sensible heat, but not of latent heat. Over the ocean, deep convection in the ITCZ is weaker than over Africa, and it is consistently correlated with upward converging subscale moisture flux. The fields of the subscale vertical fluxes are coherent in space and time. It is argued from these results that the presented diagnostic model is potentially useful for testing parameterizations of convection in general circulation and climate models.With 19 Figures 相似文献
18.
Based on the daily precipitation data taken from 17 stations over South China during the
period of 1961--2003, a sudden change in summer extreme precipitation events over South China in the
early 1990s along with the possible mechanism connected with the anomalies of the latent heat flux
over the South China Sea and the sensible heat flux over the Indochina peninsula are examined. The
results show that both the annual and summer extreme precipitation events have obvious interdecadal
variations and have increased significantly since the early 1990s. Moreover, the latent heat flux
over the South China Sea and the sensible heat flux over the Indochina peninsula also have obvious
interdecadal variations consistent with that of the extreme precipitation, and influence different
months' extreme precipitation, respectively. Their effects are achieved by the interdecadal increases
of the strengthening convection over South China through the South China Sea Summer Monsoon. 相似文献
19.
利用第三次青藏高原大气科学观测试验数据,对高原不同地区感热、潜热交换等湍流输送特征进行了分析,并进一步对比研究了其与气象环境因子的相关关系。结果表明:（1）高原各站之间感热和潜热的差异性较大,但大多在雨季潜热会大于感热。干燥的狮泉河站属于高寒荒漠地区,降水极少,全年感热都远大于潜热,波文比年平均值可达到20.0;湿润的比如站和嘉黎站潜热在4～10月均显著大于感热,波文比在4～10月的数值范围在0.27～0.88。（2）高原感热和潜热通量的季节变化与高原季风所处的地理位置有密切关系,高原中部的感热通量在3～5月达到最大值,而高原西部则在4～6月最大,可能与高原季风的活动有关。（3）通过与气象要素的相关分析表明,高原西部狮泉河站感热与地气温差的正相关关系最为显著,全年的相关系数可以达到0.905,在4个季节相关系数也均大于0.79,这可能与下垫面是裸地有关;高原中部安多站和那曲站感热与风速的正相关在夏季最为显著,比如站感热与风速的正相关在冬季最为明显,而狮泉河站感热与风速在春、夏季均有着十分显著的正相关。 相似文献
20.
青藏高原作为世界第三极,其热力强迫作用不仅对亚洲季风系统的发展和维持十分重要,也会对大气环流场产生深远影响。利用欧洲中期天气预报中心（ECMWF）的ERA-Interim中1979-2016年3-10月青藏高原及其周边地区的地表热通量月平均再分析资料,通过分析得出以下结论:3-5月青藏高原主体由感热占据,感热强度快速上升且呈西高东低的分布态势,潜热强度较小但随时间而增强。季风爆发后的6-8月,青藏高原感热强度减弱,潜热强度迅速增强且呈东高西低的分布特征。季风消退后的9-10月,感热与潜热强度相当,但感热呈现出西高东低的分布特征。过去38年,青藏高原地表感热总体呈现微弱下降趋势,潜热呈较弱上升趋势。青藏高原西部地区感热呈微弱下降趋势,潜热呈上升趋势。东部感热呈较为明显的下降趋势且近年来变化趋势增强,东部潜热通量则呈现较为明显的上升趋势,分析结论与近期全球变暖条件下青藏高原气候变暖变湿这一变化状况一致,通过对青藏高原地表热通量的变化分析为下一步运用第三次青藏高原大气科学试验所获资料分析青藏高原上空大气热源的变化以及地表加热场如何影响大气环流奠定基础。 相似文献