Precise estimation of hourly global solar radiation for micrometeorological analysis by using data classification and hourly sunshine

We have developed a method for estimating hourly global solar radiation (GSR) from hourly sunshine duration data. This procedure requires only hourly sunshine duration as the input data and utilizes hourly precipitation and daily snow cover as auxiliary data to classify time intervals into six cases according to weather conditions. To obtain hourly GSR using a simple algebraic form, a quadratic function of the solar elevation angle and the sunshine duration ratio is used. Daily GSR is given by a sum of hourly GSRs. We evaluated the performance of the newly developed method using data obtained at 67 meteorological stations and found that the estimated GSR is highly consistent with that observed. Hourly and daily root-mean-square misfits are approximately 0.2 MJ/m²/h (~55 W/m²) and 1.4 to 1.5 MJ/m²/day (~16 to 17 W/m²), respectively. Our classification of weather conditions is effective for reducing estimation errors, especially under cloudy skies. Since the sunshine duration is observed at more meteorological stations than GSR, the proposed new method is a powerful tool for obtaining solar radiation with hourly resolution and a dense geographical distribution. One of the proposed methods, GSRgrn, can be applicable to hourly GSR estimations at different observation sites by setting local parameters (the precipitable water, surface albedo, and atmospheric turbidity) suitable to the sites. The hourly GSR can be applied for various micrometeorological studies, such as the heat budget of crop fields.     

A Remote Sensing Model to Estimate Sunshine Duration in the Ningxia Hui Autonomous Region, China

Sunshine duration (SD) is strongly correlated with solar radiation, and is most widely used to estimate the latter. This study builds a remote sensing model on a 100 m × 100 m spatial resolution to est...     

香港地区地闪时空分布特征及其影响因素

通过对香港地区2006—2012年闪电定位数据、气象参数和海拔高度等相关数据的统计及相关性分析,对香港地区的地闪活动时空分布特征及其影响因素进行研究。结果表明,香港地区2006—2012年的地闪发生次数最多的是2010年,最少是2011年,每年地闪高发日的天数对地闪活动年际变化起到了关键性作用。地闪活动的发生主要集中在4—9月,逐月地闪回击次数与气温、相对湿度、降雨量及CAPE均呈现显著的正相关关系。地闪活动的日变化特征主要受到地闪高发日闪电活动、海陆热力差异及太阳辐射变化的综合影响,正、负地闪回击次数的日变化峰值均出现在01时。香港西部地区的正地闪回击密度明显高于东部,而负地闪回击密度的高值中心主要集中在海拔较高的山区。香港地区正、负地闪回击密度均随海拔的升高而有所增加,且六座典型山峰周围的负地闪回击密度与海拔高度在空间分布特征上具有很强的相似性。      

Estimation of Regional Evapotranspiration by Combining Aircraftand Ground-Based Measurements

Two methods are examined for combining measurements from instrumented aircraftand towers to estimate regional scale evapotranspiration. Aircraft data provided spatially averaged values of properties of the surface, the evaporative fraction and maximum stomatal conductance. These quantities are less sensitive to meteorological conditions than the turbulent fluxes of heat and water vapour themselves. The methods allowed aircraft data collected over several days to be averaged and thus to reduce the random error associated with the temporal under-sampling inherent in aircraft measurements. Evaporative fraction is estimated directly from the aircraft data, while maximum stomatal conductance is estimated by coupling the Penman–Monteith equation to a simple model relating surface conductance to the incoming shortwave radiation and specific humidity saturation deficit. The spatial averages of evaporative fraction and maximum stomatal conductance can then be used with routine tower data to estimate the regional scale evapotranspiration. Data from aircraft flights and six ground based sites during the OASIS field campaign in south–east New South Wales in 1995 have been used to check the methods. Both the evaporative fraction and the maximum stomatal conductance derived from the aircraft data give information on the spatial variability of the surface energy budget at scales from 10 to 100 km. Daily averaged latent heat fluxes estimated using these methods for the OASIS study region agree with the available observations in quasi-stationary conditions or in weakly non-stationary conditions when the data from several aircraft flights are averaged to reduce the impact of short term imbalances in the surface energy budget.     

复杂地形对计算地表太阳短波辐射的影响

首先利用数字高程数据(DEM)、大气辐射传输模式6S以及野外观测资料计算了复杂地形(青藏高原)上地表入射太阳辐射,然后计算不考虑地形产生的地表辐射的计算误差,对误差进行归一化后得到相对辐射误差.结果显示,相对辐射误差的标准差(即相对地表辐射计算误差绝对值的统计平均值) Se随太阳天顶角的增加呈指数增长,随高度标准差的增加几乎呈线性增长,随数字高程数据的分辨率(或卫星资料的分辨率)降低而降低.利用分步拟合方法拟合了Se随太阳天顶角、高度标准差和数字高程分辨率的变化.利用拟合方程可以计算任意地形条件下,不同分辨率的卫星(或数字高程)资料在不同太阳天顶角情况下,不考虑地形复杂性产生的平均地表入射太阳辐射的计算误差,结果表明,使用中分辨率的卫星(如MODIS)资料计算地表太阳净辐射时,需要考虑地形复杂性.     

DEM-based delineation for improving geostatistical interpolation of rainfall in mountainous region of Central Himalayas,India

In mountainous region with heterogeneous topography, the geostatistical modeling of the rainfall using global data set may not confirm to the intrinsic hypothesis of stationarity. This study was focused on improving the precision of the interpolated rainfall maps by spatial stratification in complex terrain. Predictions of the normal annual rainfall data were carried out by ordinary kriging, universal kriging, and co-kriging, using 80-point observations in the Indian Himalayas extending over an area of 53,484 km². A two-step spatial clustering approach is proposed. In the first step, the study area was delineated into two regions namely lowland and upland based on the elevation derived from the digital elevation model. The delineation was based on the natural break classification method. In the next step, the rainfall data was clustered into two groups based on its spatial location in lowland or upland. The terrain ruggedness index (TRI) was incorporated as a co-variable in co-kriging interpolation algorithm. The precision of the kriged and co-kriged maps was assessed by two accuracy measures, root mean square error and Chatfield’s percent better. It was observed that the stratification of rainfall data resulted in 5–20 % of increase in the performance efficiency of interpolation methods. Co-kriging outperformed the kriging models at annual and seasonal scale. The result illustrates that the stratification of the study area improves the stationarity characteristic of the point data, thus enhancing the precision of the interpolated rainfall maps derived using geostatistical methods.     

A Model to Estimate Global Radiation in Complex Terrain

Global radiation is an important parameter necessary for most ecological models. However, in situ data barely meets the needs of modelling mountainous ecosystems since most field stations are located in flat areas. Consequently, it is usually necessary to extrapolate radiation measurements obtained from an adjacent flat area to the complex terrain of concern. The distribution of radiation in complex terrain depends upon two factors: the local atmospheric conditions, which determine the radiation potentially available to a supposed flat surface in a given location, and the topographic effects on this possible radiation. The latter have been included in detail in most radiation models for complex terrain, but the former are often only simply treated as constant or estimated by over-simplified empirical algorithms. In this paper we propose a novel model that uses a parametric atmospheric model to calculate the potential radiation for a supposed flat surface in a given location, and then account for topographic effects. Direct radiation, diffuse radiation and reflected radiation are calculated separately in the model due to the distinctive characteristics of and the effects by topography. Based on the parametric model, this paper has investigated the relationship between radiation transmittance, clearness indices and altitude under a series of water vapour content and turbidity conditions. This combines three ratios, R _b, R _d, and R _r, defined as the direct radiation, diffuse radiation and reflected radiation received by the arbitrary surface, respectively, to their counterparts in the horizontal surface, to estimate the global radiation for any given location. The model has been validated with data from measurements in National Park Berchtesgaden, Germany, where six measurement sites with various altitudes and topographic characteristics have been deployed. The r ² of modelled and measured hourly global radiation are greater than 0.90 in all six sites, with RMSE varies from 16 to 100 W m⁻². Sensitivity analysis revealed that the model was not sensitive to change in water vapour content, which suggests the possibility to use an exponential algorithm of water vapour content when there is no in situ water vapour content information in complex terrains. The NRMSE was only reduced by 0.04, on average, in five of the six sites when water vapour content information was calculated from the in situ air temperature and relative humidity measurements.     

海陀山冬奥气象综合观测平台及研究进展

气象保障是历届冬季奥林匹克运动会（冬奥会）成功举办的最重要条件之一。延庆赛区（位于延庆海陀山区）地形复杂、山高坡陡、垂直落差大,因而观测难度大、气象数据稀少,成为影响赛区精细化预报的核心因素,对冬奥气象服务提出了严峻挑战。为此,北京市气象局组织开展了冬奥海陀山综合气象观测,针对该区复杂地形和多尺度气象影响系统构建了包含中、小、微尺度的三维立体实时综合观测平台,观测要素涵盖了三维风场、温湿度场、云和能见度、近地面湍流与辐射等。综合观测将提高对复杂山区高影响天气特征和机理的认知,为改进和提高预报模式提供数据支撑。文中系统介绍了海陀山冬奥气象综合观测平台的科学目标、观测布局、观测内容以及观测平台在降雪过程中的初步应用,最后阐述了基于该观测进一步开展的研究计划。     

地形非均匀性对网格区地面长波辐射通量计算的影响

从理论和数值试验两个方面证明地形的非均匀性(如海拔高度)对网格区地面长波辐射通量的计算有重要影响,海拔高度场的区域平均值及其变差系数是影响网格区地面长波辐射通量的主要因素,仅仅用地表均匀假定下的区域平均参量(如平均海拔高度和平均温度)所计算的网格区地表有效辐射通量值与其真实值之间存在着一定的误差。由于地表有效辐射通量是海拔高度的非线性函数,在特定情况下,其影响相当大,可产生不容忽略的误差。相对而言,海拔高度自身非均匀性对误差的影响远大于地表温度非均匀性项及其混合扰动项所产生的误差。对于不同的地形平均高度,地形非均匀性影响的程度并不相同。平均高度较小时,非均匀性的影响几乎可以忽略,但随着地形平均高度的增加,地形非均匀性的影响程度呈非线性增长趋势。因而,在复杂地形区域,考虑次网格地形的热力作用非常必要。     

起伏地形下浙江省散射辐射时空分异规律模拟

结合影响起伏地形下太阳散射辐射的天空因素与地面因素,通过基于数字高程模型（DEM）数据的起伏地形下天文辐射模型和地形开阔度模型,综合考虑地面因素对散射辐射的影响;基于常规地面气象站观测资料建立的水平面散射辐射模型,考虑天空因素对散射辐射的影响;建立了起伏地形下浙江省散射辐射分布式估算模型;逐月计算了浙江省散射辐射（100m×100m）的空间分布。结果表明：散射分量分布与地理地形因子、季风影响、大气透明程度有关,由高纬向低纬逐渐增加;季节分布特点为,夏季〉春季〉秋季〉冬季;坡度、坡向对散射辐射的分布影响小,但辐射值与开阔度呈正相关,各季辐射最大值分布在开阔度大处,最小值在开阔度最小处,不同季节有所伸缩。计算结果可以为气候变化和环境资源研究提供基础数据。     

太阳直接辐射的分光测量

利用热电式相对日射表和八种有色玻璃滤光片,于1975—1978年先后在我国七个地区(共十个测点)进行了太阳分光辐射的测量,获得了2698组资料。根据这些资料,分析了太阳高度、季节、地理纬度和海拔高度以及气溶胶和水汽等大气成份对各波段的太阳分光辐射的影响。最后,用大气质量、浑浊度系数和地面绝对湿度三个物理量作参数,以表格的形式列出了各波段分光辐射的相对通量值。     

贵州高原起伏地形下日照时间的时空分布

由于坡度、坡向和地形之间相互遮蔽等局地地形因子的影响, 实际起伏地形下的日照时间与水平面上的日照时间有一定差异。该文建立了一种基于数字高程模型 (DEM) 的起伏地形下日照时间的模拟方法, 计算了起伏地形下贵州高原100 m×100 m分辨率日照时间的时空分布。结果表明:坡度、坡向、地形遮蔽对日照时间的影响较大, 实际起伏地形下日照时间的空间分布具有明显地域特征。1月太阳高度角较低, 坡度、坡向的作用非常明显, 地形遮蔽面积较大, 日照时间的空间差异较多, 日照时间为16~142 h, 最大值约为最小值9倍; 7月太阳高度角较高, 地形遮蔽面积相对较小, 日照时间的空间差异相对较少, 日照时间为133~210 h, 最大值为最小值1.6倍, 但由于7月日照时间相对较多, 局地地形对日照时间影响仍明显。4月、10月日照时间及其变化幅度介于1月和7月之间。     

Parameterizations of surface radiation in the semiarid grasslands of Inner Mongolia under clear-sky conditions using MODIS data

A set of improved and efficient radiation parameterization schemes for surface radiation balance components under clear- sky conditions was developed by using general surface measurements and MODIS data. The set of schemes was then adapted for regions similar to the present study sites under different grazing intensities and varying degrees of drought in the semiarid grasslands of Inner Mongolia. Specifically, we mainly improved two schemes for estimating downward shortwave and longwave radiation at the surface, which could be applied to regions with certain degrees of drought. The validation datasets were from ground-based observations at various grazing sites during the growing season （May to September） of different drought years, 2005 and 2006. Through comparisons of parameterized versus measured radiation values, the increased or modified factors in the original schemes demonstrated improved estimation accuracy, and the rationalities of input parameters and variables were analyzed. The regional instantaneous net radiation estimations had root-mean-square errors of less than 30 W m-2 compared with ground measurements at the sites during the study period. The statistical results showed the improved schemes are suitable for estimating surface net radiation in regional semiarid areas during the growing season. Analyses of the sensitivity of the schemes to corresponding variables were conducted to ascertain the major error sources of the schemes and potential variables for improving the performance of the schemes in agreement with observations.     

Retrieving air humidity,global solar radiation,and reference evapotranspiration from daily temperatures: development and validation of new methods for Mexico. Part II: radiation

We propose a new model to estimate daily global radiation from daily temperature range measurements. This model combines that of Majumdar et al. (Sol Energy 13(4):383–394, 1972) to estimate clear sky radiation with a Gompertz function to estimate the relation between temperature range and cloud transmittance. Model parameters are estimated from historical weather data: maximum and minimum temperatures and, if available, relative humidity; no other calibration is required. The model was parametrized and validated using 788 weather stations in Mexico. When calibrated using historical humidity data, daily global radiation was estimated with a mean root mean square error of 3.06 MJ m^?2 day^?1. The model performed well in all situations, except for a few stations around the Gulf of Mexico and in mountain areas. When using estimated humidity, the root mean square error of prediction was only slightly degraded (3.07 MJ m^?2 day^?1). Possible theoretical basis and applicability of this model to other environments are discussed.     

甘肃马衔山区陆面过程与降水的研究

采用定西的麦田微气象观测,定西、兰州的辐射观测和马衔山区34个气象、水文和雨量站的气候资料,结合NOAA-16卫星的AVHRR资料以及反演的地表植被盖度和反射率,并用SEBAL算法推导出夏季地表净辐射、感热、潜热、土壤热通量密度的区域分布特征,并分析陆面过程对降水的影响。结果表明:本区降水的空间分布与夏季植被盖度对应最好,相关系数高达0.722,其次是土壤热通量和潜热通量,相关系数分别为-0.65和0.615。这表明森林通过降低地表反射率和表面温度,不仅增加地表净辐射,而且减少其用于感热和土壤热通量的消耗。由于林区地表水分多,从而将接收较多的太阳辐射能主要用于蒸散,增加边界层中的水汽。故林区降水远大于植被稀疏的半干旱黄土梁。     

珠峰绒布河谷近地面层气象要素及湍流通量变化

利用2006年5～6月和2007年5～6月中国科学院HEST大气科学实验在珠峰绒布寺河谷野外观测期间获得的观测资料,分析了珠峰地区河谷近地层风向、风速、温度、湿度和CO2的日变化特征,讨论了珠峰北坡冰川风和山谷风的特点以及高原地表辐射、地表反照率和近地层湍流通量的变化特征.结果表明:在复杂地形和特殊下垫面影响下,珠峰绒布河谷地区近地面层各个气象要素和湍流通量日变化特征显著,并且明显存在冰川风和山谷风复合的局地环流,冰川风对该地区地气间物质能量交换起着重要作用.     

Spatiotemporal modeling of monthly soil temperature using artificial neural networks

Soil temperature data are critical for understanding land–atmosphere interactions. However, in many cases, they are limited at both spatial and temporal scales. In the current study, an attempt was made to predict monthly mean soil temperature at a depth of 10 cm using artificial neural networks (ANNs) over a large region with complex terrain. Gridded independent variables, including latitude, longitude, elevation, topographic wetness index, and normalized difference vegetation index, were derived from a digital elevation model and remote sensing images with a resolution of 1 km. The good performance and robustness of the proposed ANNs were demonstrated by comparisons with multiple linear regressions. On average, the developed ANNs presented a relative improvement of about 44 % in root mean square error, 70 % in mean absolute percentage error, and 18 % in coefficient of determination over classical linear models. The proposed ANN models were then applied to predict soil temperatures at unsampled locations across the study area. Spatiotemporal variability of soil temperature was investigated based on the obtained database. Future work will be needed to test the applicability of ANNs for estimating soil temperature at finer scales.     

Estimating heat fluxes by merging profile formulae and the energy budget with a variational technique

A variational technique (VT) is applied to estimate surface sensible and latent heat fluxes based on observations of air temperature, wind speed, and humidity, respectively, at three heights (1 m, 4 m, and 10 m), and the surface energy and radiation budgets by the surface energy and radiation system (SERBS). The method fully uses all information provided by the measurements of air temperature, wind, and humidity profiles, the surface energy budget, and the similarity profile formulae as well. Data collected at Feixi experiment station installed by the China Heavy Rain Experiment and Study (HeRES) Program are used to test the method. Results show that the proposed technique can overcome the well-known unstablility problem that occurs when the Bowen method becomes singular; in comparison with the profile method, it reduces both the sensitivities of latent heat fluxes to observational errors in humidity and those of sensible heat fluxes to observational errors in temperature, while the estimated heat fluxes approximately satisfy the surface energy budget. Therefore, the variational technique is more reliable and stable than the two conventional methods in estimating surface sensible and latent heat fluxes.     

地形起伏对模式地表长波辐射计算的影响

初步探讨了数值模式中次网格区地形起伏(高度、坡度)对长波辐射计算的影响。结果表明,地形高度的次网格变化对辐射计算结果的影响较小,其相对误差一般<2%,但不同分辨率的地形高度场会产生不同的坡度计算误差,低分辨率地形资料所计算的坡度分布相差不大,但坡度的量级存在较大偏差。地形的分辨率越高,实际计算结果的偏差越小。而高分辨率地形资料计算实例表明,地形坡度引起的区域相对辐射误差可达到10%以上。因此,在数值模式中,网格区地表长波辐射计算结果对地形起伏的敏感性应给予足够的重视。