Available energy and energy balance closure at four coniferous forest sites across Europe

The available energy (AE), driving the turbulent fluxes of sensible heat and latent heat at the earth surface, was estimated at four partly complex coniferous forest sites across Europe (Tharandt, Germany; Ritten/Renon, Italy; Wetzstein, Germany; Norunda, Sweden). Existing data of net radiation were used as well as storage change rates calculated from temperature and humidity measurements to finally calculate the AE of all forest sites with uncertainty bounds. Data of the advection experiments MORE II (Tharandt) and ADVEX (Renon, Wetzstein, Norunda) served as the main basis. On-site data for referencing and cross-checking of the available energy were limited. Applied cross checks for net radiation (modelling, referencing to nearby stations and ratio of net radiation to global radiation) did not reveal relevant uncertainties. Heat storage of sensible heat J _H, latent heat J _E, heat storage of biomass J _veg and heat storage due to photosynthesis J _C were of minor importance during day but of some importance during night, where J _veg turned out to be the most important one. Comparisons of calculated storage terms (J _E, J _H) at different towers of one site showed good agreement indicating that storage change calculated at a single point is representative for the whole canopy at sites with moderate heterogeneity. The uncertainty in AE was assessed on the basis of literature values and the results of the applied cross checks for net radiation. The absolute mean uncertainty of AE was estimated to be between 41 and 52 W m^?2 (10–11 W m^?2 for the sum of the storage terms J and soil heat flux G) during mid-day (approximately 12% of AE). At night, the absolute mean uncertainty of AE varied from 20 to about 30 W m^?2 (approximately 6 W m^?2 for J plus G) resulting in large relative uncertainties as AE itself is small. An inspection of the energy balance showed an improvement of closure when storage terms were included and that the imbalance cannot be attributed to the uncertainties in AE alone.     

Energy balance storage terms in a mature mixed forest at Petawawa,Ontario — A case study

The energy storage terms for a mature mixed forest at Petawawa, Ontario are reported for 38 days in the summer of 1982 when the forest was in full leaf. Hourly, daily and daytime values of the storage terms are documented. The biomass storage term, Q _v , should be calculated from measurement of biomass temperature change. For hourly periods, the storage terms can be of significant size with respect to net radiation, Q ^*. This is especially the case at night, in the early morning after sunrise, and near sunset. The importance of the storage terms is still pronounced when daytime totals are considered — the ratio of the total storage (Q _s ) to Q ^* varied from 1 to 15% for the whole sample, but is typically between 5 and 10%. For daily totals when the canopy is dry and the net radiation high, Q _s is typically 2 to 3 % of Q ^*. However, it can be up to 10% of Q ^* under particular conditions (overcast days, or during or immediately following rainfall).     

A two-dimensional energy balance climate model including radiation and ice caps-albedo feedback

A simplified two-dimensional energy balance climate model including the solar and infrared radiation transports, the turbulent exchanges of heat in vertical and horizontal directions and the ice caps-albedo feedback is developed The solutions show that if the atmosphere is considered as a grey body and the grey coefficient depends upon the distributions of absorption medium and cloudiness, both horizontal and vertical distributions of temperature are identical to the observation.On the other hand, comparing the models that the atmosphere is considered as a grey body with ones that the infrared radiation is parameterized as a linear function of temperature, as was considered by Budyko, Sellers(1969), then the results show that even though both of them can obtain the earth's surface temperature in agreement with the observation, the sensitiv ity of the climate to the changes of solar constant is very different. In the former case,the requirement for the ice edge to move southward from the normal 72°N to 50°N(i.e. where the glacial climate would take place) is that the solar constant should decrease by 13% to 16%. However, in the latter case, the climate is highly sensitive to the changes of solar radiation. In this case, the requirement of solar radiation occurring in the glacial climate should decrease by 2% to 6%. According to the investigations mentioned above we must be careful when the parameterizations of the radiation and other processes are conducted in a climate model, otherwise the reliability of the results is suspicious.     

Crop residue effects on surface radiation and energy balance — review

Summary Crop residues alter the surface properties of soils. Both shortwave albedo and longwave emissivity are affected. These are linked to an effect of residue on surface evaporation and water content. Water content influences soil physical properties and surface energy partitioning. In summary, crop residue acts to soil as clothing acts to skin. Compared to bare soil, crop residues can reduce extremes of heat and mass fluxes at the soil surface. Managing crop residues can result in more favorable agronomic soil conditions. This paper reviews research results of the quantity, quality, architecture, and surface distribution of crop residues on soil surface radiation and energy balances, soil water content, and soil temperature.With 6 Figures     

东亚地区的地表面辐射平衡、热量平衡及冷热源问题的研究

本文是<我国辐射平衡、热量平衡及水分平衡的研究>工作中的一部份。根据我国七十多个日射台站1974年前的全部实测资料,推求出适合于我国实际情况的计算方法。计算了我国300多个台站的太阳辐射各分量(直达辐射、散射、辐射、总辐射)数值。同时设计了计算理论公式的计算图,求得了这些台站的有效辐射量,从而得到我国辐射平衡及其各分量。又根据我国六个台站热量平衡观测资料,得到土壤热交换量与气温变化的关系,确定了土壤热交换量。并采用和计算了与我国邻近的国外几十个台站辐射平衡各分量及研究成果。最后分析了东亚地区的辐射平衡、热量平衡及冷热源的时空分布。     

2011年2月—2012年1月东南极高原辐射平衡观测研究

利用东南极高原熊猫-1自动气象站2011年2月—2012年1月观测的辐射资料和相关资料,对辐射分量和辐射平衡的季节变化进行了研究。结果表明,夏季是东南极高原获得太阳能的主要时段,总辐射通量夏季平均为365.0 W/m²,总量达到2752.1 MJ/m²,占全年总辐射量的58%。各个季节均能出现总辐射瞬时值大于大气顶水平总辐射,春季发生频率最高,冬季最小,总辐射平均日变化呈单峰型。大气长波辐射除夏季外,日变化不明显。冰雪面长波辐射除冬季外,各季节平均日变化呈明显的单峰单谷型。净辐射12月和1月为很小的正值,其他月份为负值。年平均净辐射为 -8.7 W/m²,表明地表相对于大气为冷源。该站的辐射平衡特征与其他南极内陆高原站相似,雪面具有强烈的辐射冷却效应,导致净辐射绝对值都小于下降风区。     

A nonlinear stochastic low-order energy balance climate model

The effects of stochastic forcing on a one-dimensional, energy balance climate model are considered. A linear, stochastic model is reviewed in analogy with the Brownian motion problem from classical statistical mechanics. An analogous nonlinear model is studied and shows different behavior from the linear model. The source of the nonlinearity is the dynamical heat transport. The role of nonlinearity in coupling different temporal and spatial scales of the atmosphere is examined. The Fokker-Planck equation from statistical mechanics is used to obtain a time evolution equation for the probability density function for the climate, and the climatic potential function is calculated. Analytical solutions to the steady-state Fokker-Planck equation are obtained, while the time-dependent solution is obtained numerically. The spread of the energy produced by a stochastic forcing element is found to be characterized by movement mainly from smaller to larger scales. Forced and free variations of climate are also explicitly considered.     

Evapotranspiration from a boreal forest drainage basin using an energy balance/eddy correlation technique

Meteorological techniques were used to monitor evapotranspiration (ET) at two sites in a boreal forest drainage basin located in southeastern Manitoba, Canada. An energy balance method was used in which net radiation (R _N ) and ground heat flux (G) were measured directly. Sensible heat flux (H) was measured by the eddy correlation technique using a propeller anemometer and a fine-wire thermocouple. The energy components were calculated hourly on-line, and data were collected reliably over a five-month period.The R _N and H instruments were mounted above the forest canopy and simultaneous measurements of H at heights of 12 and 6 m were in good agreement. Measurements at an open bare rock site indicated that G could be a substantial fraction of the daily RN at some locations, but over longer time periods, it was a small fraction and, therefore, was ignored.The two measurement locations represented upland (open bedrock/jack pine forest) and lowland (aspen/willow forest) sites in the drainage basin. The mean daily value of R _N - H at the upland site was 0.57 times the value at the lowland location owing to differences in R _N , H, and G. The mean ratio of daily H/R _N was 0.6 for the upland site and 0.4 for the lowland site. A basin-wide ET was calculated by weighting the values for the two sites in proportion to their areas. The measured ET agreed well with precipitation minus runoff for the basin. Differences between these two quantities in summer and fall were attributed to water release and storage by the ground, respectively.Issued as AECL-9153.     

Net radiation,sensible and latent heat flux densities on slopes computed by the energy balance method

Energy balance components obtained over five grass-covered sloping surfaces near Manhattan, KS, using the Bowen ratio energy balance technique with the instruments mounted horizontally were compared with calculated values when the instruments were mounted parallel to the surfaces. Hourly values of the components changed when the instruments were parallel to the surfaces. The changes were larger at low solar angles (spring and fall) and on steeper slopes. An area average of daylight totals, assuming that all aspects were equally represented, changed only 0.1% on June 6 and 2.3% on October 11. The calculations, extended to steeper slopes, indicated small changes in the daylight totals for slopes of less than 10 deg.Supported in part by a grant from NASA NAG 5-901.     

A study of water balance in china

The water balance in C'hina is studied in this paper, which follows the papers on the radiation balance and the heat balance in China. Using the data from more than 200 meteorological stations for 1961-1970 and about 200 hydrometric stations bcforc1972, we, through the equation of water balance, have calculated the monthly and annual amounts of precipitation, evaporation, run-off and soil water variation. The water balance and the hydroclimatological characteristics of China arc given.     

应用城市地表能量平衡方案研究城市冠层结构对城市热岛的热力影响

用南京大学区域边界层模式NJU-RBLM, 通过对一组理想试验的模拟, 研究了TEB方案 (town energy balance) 和SVAT方案 (soil－vegetation－atmosphere transfer) 模拟城市热岛现象的差异及本质原因, 发现TEB方案对城市热岛 (UHI) 尤其是夜间UHI模拟效果更优, 这是由于TEB方案具备较强模拟城市储热项的能力形成的。此外, 深入探讨UHI对大气边界层热力结构的影响, 发现UHI现象使城市和郊区的近地层位温廓线在清晨和傍晚都存在明显差异, 同时使城市区域气温全天高于郊区, 且日间城乡温差能达到的高度明显高于夜间。分析人为热源和建筑物冠层对UHI的影响时发现: 人为热源对UHI的影响在夜间强于白天, 而建筑物对白天城市湍能的影响强于人为热源的作用。     

A 1-D atmospheric energy balance model developed for ocean modelling

Summary We present a simple, deterministic energy balance model. The model is designed to represent the atmospheric component of the coupled atmosphere-ocean system. It is a one dimensional, global model with time and space resolutions of one year and 10° of latitude respectively. The model predicts the surface air temperature and estimates the surface freshwater flux diagnostically. The coupling between the atmospheric model and an ocean model is accomplished by heat and freshwater fluxes at their interface. The heat flux is calculated according to the difference in the surface air temperature and ocean surface temperature, while the freshwater flux is estimated from the latent heat transport in the atmosphere by a diagnostic equation. Two parameterizations for the latent heat transport are proposed, which distinguishes the two versions of the model.Before proceeding with interactive runs, we study the behaviour of the model in a decoupled mode. Some experiments with initial conditions altered and external forcings changed ar carried out to investigate the sensitivity and stability of the model. In particular, the influence of the ice-albedo feedback on model solutions is examined. The results of these experiments may be helpful both in understanding the characteristics of the model and in interpreting results when the model is coupled to an OGCM.With 9 Figures     

A microscale three-dimensional urban energy balance model for studying surface temperatures

A microscale three-dimensional (3-D) urban energy balance model, Temperatures of Urban Facets in 3-D (TUF-3D), is developed to predict urban surface temperatures for a variety of surface geometries and properties, weather conditions, and solar angles. The surface is composed of plane-parallel facets: roofs, walls, and streets, which are further sub-divided into identical square patches, resulting in a 3-D raster-type model geometry. The model code is structured into radiation, conduction and convection sub-models. The radiation sub-model uses the radiosity approach and accounts for multiple reflections and shading of direct solar radiation. Conduction is solved by finite differencing of the heat conduction equation, and convection is modelled by empirically relating patch heat transfer coefficients to the momentum forcing and the building morphology. The radiation and conduction sub-models are tested individually against measurements, and the complete model is tested against full-scale urban surface temperature and energy balance observations. Modelled surface temperatures perform well at both the facet-average and the sub-facet scales given the precision of the observations and the uncertainties in the model inputs. The model has several potential applications, such as the calculation of radiative loads, and the investigation of effective thermal anisotropy (when combined with a sensor-view model).     

Surface energy and radiation budget over a tropical station: An observational study

This study attempts to understand the variations in the radiation and surface energy budget parameters during days of occurrence and non occurrence of convective activity such as thunderstorms at Ranchi (23°25??N, 85°26??E), India using the special experimental data sets obtained during pre-monsoon month of May, 2008. For this purpose five continuous thunderstorm days (TD) of varying intensity, along with three non-thunderstorm days (NTD) preceding the TD are considered. Thunderstorms occurred at site are multi-cellular in nature. Change of wind direction and strong gusty winds are noticed in TD cases. Pre-dominant wind direction is south westerly for the TD; it is northwesterly during NTD. Sudden drop of air temperature and rise of relative humidity and rise/drop in atmospheric pressure is noticed during TD are found to be proportional to the intensity of thunderstorm event. More partitioning of net radiation (QN) is in to latent heat flux (QE) and the contribution of sensible heat flux (QH) and soil heat flux (QG) are same during TD. But in the NTD more partitioning of QN is in to QH followed by QG that of QE. Significant differences in radiation and energy budget components are noticed during TD and NTD events.     

Tests of three urban energy balance models

Observations of surface characteristics, meteorological conditions and energy balance components from Vancouver, B.C. are used to test the validity of the output from three one-dimensional surface energy balance models. The results show that whereas all of the models provide good simulations of net radiation, none can consistently predict the turbulent fluxes of sensible and latent heat using easily available input data. Inability to handle the role of water availability and its impact on evapotranspiration is identified as the principal problem.