Effect of ground cover changes on solar radiation absorption in Three Northeastern Provinces of China

Background,aim,and scope Solar radiation is the main source of energy for terrestrial ecosystems.Small changes in the absorption of solar radiation at the ground surface can have a significant impact on the climatic environment.Natural and anthropogenic changes in ground cover are important factors affecting the absorption of solar radiation at the ground surface.This phenomenon is particularly pronounced in the mid and high latitudes.In order to quantify the inf luence of surface cover change on the absorption of solar radiation at the surface and to provide a scientific basis for changes in the climatic environment,this paper analyzed ground cover change,ground absorbed solar radiation change and the effect of ground cover change on ground absorbed solar radiation in the Three Northeastern Provinces of China from 2001 to 2018.Materials and methods In this study,the Three Northeastern Provinces of China were used as the study area.Firstly,satellite remote sensing data were used to obtain land cover data and albedo data for Aug.1st of each year in 2001,2005,2010,2015 and 2018.The albedo data were further used to calculate the absorbed solar radiation data at the ground surface.Next,the land cover data were used to count the area changes and shifts of different land classes over the five-year period.The land cover data were overlaid with the surface absorbed solar radiation data to obtain the mean and standard deviation of radiation absorption for different ground classes.The surface absorbed solar radiation data were subtracted to obtain the changes in surface absorbed solar radiation for 2001-2005,2005-2010,2010-2015 and 2015-2018.Ultimately,we used a combination of shifted changes in ground classes and changes in surface absorbed solar radiation data,with unchanged ground classes as a baseline and data such as slope orientation as an aid.We analyzed the effect of ground cover change on surface absorbed solar radiation at regional and pixel point scales.Results(1)The area of woodland and waters in the Three Northeastern Provinces of China increased and then decreased from 2001 to 2018,with an overall increase of 3.96%and 10.51%respectively.Cropland decreased and then increased,with a total decrease of 1.22%.Grassland continued to decrease,with an overall decrease of 19.36%.Building sites increased all the time,with a total increase of 11.08%.The main types of ground cover shifted were woodland,cropland and grassland.The main factors for the change in ground cover were China’s woodland protection policy and the saturation of the total woodland stock.(2)The five ground types absorb solar radiation in the order of waters>building sites>woodland>grassland>cropland.The surface absorption of solar radiation in the Songnen Plain,the Sanjiang Plain and the Songhua River Basin flowing through the Songnen Plain and the Sanjiang Plain varies significantly,by more than 25 W·m^(-2).(3)Changes in the ground cover type affected the absorption of solar radiation energy by the ground surface.There was a clear trend of interconversion between waters and cropland/grassland,cropland and woodland/grassland.In particular,the conversion of waters to both cropland and grassland radiation absorption values decreased significantly,while the opposite increased.The absolute difference between waters and cropland was a maximum of -156.66 W·m^(-2)in 2010-2015,and between waters and grassland was a maximum of 102.36 W·m^(-2) in 2005-2010.The radiative absorption values of woodland and grassland reclamation declined and conversely increased.The absolute difference between woodland and cropland was a maximum of-13.94 W·m^(-2) in 2010-2015 when woodland converted to cropland,and between grassland and cropland was a maximum of 22.36 W·m^(-2) in 2001-2005 when cropland converted to grassland,respectively.Discussion Ground cover changes in the Three Northeastern Provinces of China from 2001-2018 were inextricably linked to natural factors and the inf luence of Chinese national policies.The main inf luencing factors were China’s woodland protection policy,restoration of woodland fire sites,saturation of total woodland,optimization of cropland patterns,sanding of grassland,expansion of water conservancy projects,and urbanization expansion.There were differences in the radiation absorption characteristics of different ground cover types.This was due to the nature of the ground type itself and the regional environment.When ground cover types changed,their ability to absorb solar radiation also changed.The degree of change could be inf luenced by different ground types and different environmental factors.Different spatial scales can also produce variability.We need to consider the effects of ground cover change on the absorption of solar radiation at the surface in an integrated and comprehensive way.Conclusions The Three Northeastern Provinces of China had frequent changes in ground cover from 2001-2018,with the area of grassland decreased by almost 20%.These changes were due to natural environmental change and policies issued by China since the 21st century.The extent to which solar radiation was absorbed by different ground cover types was different,with grassland being the strongest and cropland the least.In the past few years,the Songnen Plain and Sanjiang Plain regions were the most significant changes in the absorption of solar radiation by the ground cover.The change in ground cover type led to a change in solar radiation absorption at the ground surface,with the conversion of waters to cropland or grassland and the conversion of cropland to woodland or grassland showing the greatest change in radiation absorption values,and vice versa.Of these,the absolute difference in the conversion of waters to cropland amounts to-156.66 W·m^(-2) in 2010-2015.The variation in the absorption of solar radiation at the ground surface was related to the characteristics of the ground class itself,but was also limited by the regional environment.Recommendations and perspectives This study showed that surface cover change can affect the absorption of solar radiation at the surface to varying degrees.The unchanged land classes were used as a comparative analysis in this paper,and it was clear from the paper that some of the unchanged land classes showed significant changes in radiation absorption that should be of interest in future studies.

Trends in Global Solar Radiation and Sunshine Duration in Past Two Decades in Japan

Global solar radiation (GSR) is an essential physical quantity for agricultural management and designing infrastructures. Because GSR has often been modeled as a function of sunshine duration (SD) and day length for a given set of locations and calendar days, analyzing interannual trends in GSR and SD is important to evaluate, predict or regulate the cycles of energy and water between geosphere and atmosphere. This study aimed to exemplify interannual trends in GSR and SD, which had been recorded from 2001 to 2022 in 40 meteorological stations in Japan, and validate the applicability of an SD-based model to the evaluation of GSR. Both the measured GSR and SD had increased in many of the stations in the study period with averaged rates of 0.252 [W·m−2·y−1] and 0.015 [h·d−1·y−1], respectively. The offset and the slope of the SD-based model were estimated by fitting the model to the measured data sets and were found to have been almost constant with the averages of 0.201[-] and 0.566[-], respectively, indicating that characteristics of the SD-GSR relation had not varied for the 22-year period and that the model and its parameter set can be stationarily applicable to the analyses and predictions of GSR in recent years. The stable trends in both parameters also implied that the upward trend in SD can be a main explanatory factor for that in the measured GSR. The upward trend in SD had coincided with the increase in the frequency of heavy-shortened rains, suggesting that the time period of each rainfall event had gradually decreased, which may be attributable to the obtained upward trend in SD. Further studies are required to clarify if there is some cause-effect relation between the changes in rainfall patterns and the standard level of solar radiation reaching the land surface.

Interdecadal Variability in Surface Solar Radiation over Northwest China and Its Possible Cause

The present study investigates the interdecadal variability of seasonal mean surface solar radiation over Northwest China using station observations from 1961-2003. Spring and summer surface solar radiation over Northwest China was lower in the late 1970s through 1990s than in the 1960s through the mid-1970s, and fall and winter surface solar radiation displayed similar patterns. These results indicate that the decrease in spring and summer surface solar radiation may be associated with increased low-cloud cover over Northwest China. Rainfall anomalies were closely related to the low-cloud cover over Northwest China and with the Northern Hemisphere circumglobal teleconnection in spring, summer, and winter.

Effects of Sky Conditions Measured by the Clearness Index on the Estimation of Solar Radiation Using a Digital Elevation Model

This study evaluated the effects of sky conditions (measured by the clearness index, KT) on the estimation of solar radiation and its components. Solar radiation was calculated by a digital elevation model derived from the Shuttle Radar Topography Mission (SRTM). The calculated radiation was parameterized and validated with measured solar radiation from two stations inside the urban perimeter of the city of Cuiabá, Brazil, during 2006 to 2008. The measured solar radiation varied seasonally, with the highest values in December-March and the lowest in June-September. Comparisons between calculated and measured values for two sites in Cuiabá demonstrate that the model is accurate for daily Rg estimates under clear sky conditions based on Root Mean Square Error, Mean Bias Error and Willmott’s index. However, under partially cloudy and cloudy sky conditions the model was not able to provide robust estimates. Spatially, the highest values of incident Rg occurred on strands with North, Northeast and Northwest orientations and were lowest on those oriented to the South, Southeast and Southwest.

Estimation of Evapotranspiration by Various Net Radiation Estimation Formulae for Non-Irrigated Grass in Brazil

The objective of this study was to assess the accuracy of estimating evapotranspiration (ET) using the FAO-56 Penman-Monteith (FAO-56-PM) model, with measured and estimated net radiation (Rnmeasured and Rnestimated, respectively), the latter obtained via five different models. We used meteorological data collected between August 2005 and June 2008, on a daily basis and on a seasonal basis (wet vs. dry seasons). The following data were collected: temperature;relative humidity;global global solar radiation (Rs);wind speed and soil heat flux. The atmospheric pressure was determined by aneroid barograph, and sunshine duration was quantified with a Campbell-Stokes recorder. In addition to the sensor readings (Rnmeasured), five different models were used in order to obtain the Rnestimated. Four of those models consider the effects of cloud cover: the original Brunt model;the FAO-24 model for wet climates;the FAO-24 model for dry climates, and the FAO-56 model. The fifth was a linear regression model based on Rs. In estimating the daily ET0 with the FAO-56-PM model, Rnmeasured can be replaced by Rnestimated, in accordance with the FAO-24 model for dry climates, with a relative error of 2.9%, or with the FAO-56 model, with an error of 4.9%, when Rs is measured, regardless of the season. The Rnestimated obtained with the fifth model has a relatively high error. The original Brunt model and FAO-24 model for wet climates performed more poorly than did the other models in estimating the Rn and ET0. In overcast conditions, the original Brunt model, the FAO-24 model for wet climates, the FAO-24 model for dry climates, the FAO-56 model and the model of linear regression with Rs as the predictor variable tended to overestimate Rn and ET, those estimates becoming progressively more accurate as the cloud cover diminished.

旱区地膜与种植密度对棉花冠层光分布及产量的影响

棉花冠层光合有效辐射截获率(PARI)是影响干物质积累和产量形成的重要因素,然而对于不同覆膜方式下种植密度对棉花冠层光分布的影响尚未明确。在旱区一膜三行的机采种植模式下,设2种覆膜方式(有膜和无膜)与5种种植密度(D1:9×10^(4)株/hm^(2),D2:13.5×10^(4)株/hm^(2),D3:18×10^(4)株/hm^(2),D4:22.5×10^(4)株/hm^(2),D5:27×10^(4)株/hm^(2)),研究不同覆膜方式下种植密度对棉花冠层PARI的影响。结果表明,在全生育期,有膜处理下棉花冠层光合有效辐射(PAR)的截获能力较强;冠层PARI与种植密度呈显著正相关关系,不同种植密度之间PARI存在差异;叶面积指数(LAI)随生育进程推进呈单峰曲线。有膜处理下,不同种植密度LAI在第94~98天达到峰值;无膜处理下,不同种植密度LAI在第109~113天达到峰值;随着种植密度的增加干物质积累量减少,其生殖器官生物量有所下降。种植密度为18×10^(4)株/hm^(2)下的产量显著高于其他处理(有膜为5805.07 kg/hm^(2),无膜为5436.96 kg/hm^(2)),研究结果为旱区合理密植、构建合理的冠层结构提供理论依据。

梅雨期持续性暴雨过程云—辐射—降水的关系

本文利用站点观测数据以及ERA5再分析资料分析了2006—2020年14次长江中下游地区梅雨期持续性暴雨的基本特征以及过程中云—辐射—降水的关系。结果表明,在梅雨期持续性暴雨过程中,降水呈纬向分布;云量分布随高度向南倾斜,中云分布与降水分布对应良好,高云分布在降水区南侧;降水发生时,梅雨锋北侧中低云增加,南侧高云增加,北侧中低云辐射降温以及南侧高云温室效应和暖平流共同作用造成梅雨锋两侧温差增大,锋面加强使得持续性暴雨得以维持。

近几十年青藏高原与华北地区地表太阳辐射变化特征及其影响因素的对比分析

地表太阳总辐射具有较大的时空变化特征,不同地区的影响因素也存在显著差异。本文利用1961—2016年青藏高原与华北地区的地表太阳总辐射资料,在进行严格的质量控制和均一化处理的基础上,深入分析了两个地区总辐射的年际变化趋势,同时结合云量和气溶胶光学厚度观测资料,探讨了两个地区总辐射变化的影响因素。结果表明:(1)1961—2016年青藏高原和华北地区总辐射总体呈下降趋势,但2008年后青藏高原西部和东部地区总辐射变化趋势相反,而华北地区站点总辐射均呈上升趋势。(2)青藏高原西部地区总辐射的下降主要受到云量变化的影响,而东部地区低云量和气溶胶的下降是总辐射上升的重要原因。(3)在2006—2016年,华北地区总辐射的变化受气溶胶的影响更加显著。

A comparative study of the land-atmosphere energy and water exchanges over the Tibetan Plateau and the Yangtze River Region

正确认识不同区域能量和水分循环特征是研究局地地气相互作用及准确预测区域天气,气候变化的关键.为了研究属于干旱/半干旱气候的青藏高原(TP)和湿润/半湿润气候的长江流域(YRR)之间地表能量和水分交换的异同,本文对比分析了两个区域8个不同地表类型(包括高山荒漠,高山草地,(平原)城市和(平原)草地等)观测站点的地表辐射和能量通量数据.结果显示:(1)TP由于高原大气层稀薄且空气洁净,年平均入射短波辐射为251.3W m^(-2),是YRR的1.7倍.加之高原地表反照率高导致反射辐射(59.6 W m^(-2))是YRR的2.87倍.入射及出射的长波辐射为231.5和338.0 W m^(-2),分别为YRR的0.64和0.83.而两个区域的净辐射差异不大;(2)草地站更多的潜热释放使得地表总加热效率高于城市和高山荒漠,TP和YRR的草地站的年平均潜热分别为35.0和38.8 W m^(-2),而植被稀疏且土壤干燥的高山荒漠地区感热最大,年平均感热为42.1 W m^(-2);其次是城市下垫面,其年平均感热为37.7 W m^(-2).研究结果揭示了不同气候背景下典型下垫面地气相互作用特征,为地气相互作用过程深入分析奠定了基础.

青海湖流域不同下垫面类型对地表温度的生物物理影响

本研究选取青海湖流域亚高山灌丛和温性草原两个不同土地覆盖类型的站点,利用湍流通量数据和自动气象站数据对比生长季和非生长季两个站点的微气象要素和地表能量平衡收支,评估土地利用/土地覆盖变化(Land Use/Land Cover Changes,LULCC)对地表温度的生物物理影响。亚高山灌丛相比温性草原具有更低的地表温度、气温和土壤温度,在生长季两个站点的地表温度、气温和土壤温度的差异更为明显,而非生长季相对湿度的差异更为明显。根据直接分解温度理论(Direct Decomposed Temperature Metric,DTM),分析不同下垫面对地表温度的生物物理影响。结果表明:白天灌丛相比草原的冷却作用主要贡献因素是短波辐射、地表土壤热通量和感热通量项,其中短波辐射在灌丛的冷却中起到正反馈作用,而后两者起到负反馈作用。夜间灌丛的冷却作用主要贡献因素是地表土壤热通量项。在相同气候和天气背景下,不同下垫面确实会对地表温度有明显的生物物理反馈作用。

近43年江西省太阳辐射变化特征及其影响因素研究

基于江西省20个国家站1980—2022年逐日气象数据,利用Mann-Kendall趋势检验法、Pearson相关分析法分析了太阳辐射的长期变化趋势及其与气溶胶光学厚度、整层大气水汽含量、低云量和总云量之间的关系。研究发现:1)近43年来,受气溶胶光学厚度和整层大气水汽含量显著增长的影响,江西省太阳辐射以-5.7×10^(-3) MJ m^(-2) decade^(-1)的速度下降,总云量、低云量的微弱变化对太阳辐射的影响有限;2)夏季、秋季和冬季太阳辐射分别以-24×10^(-3) MJ m^(-2) decade^(-1)、-2.4×10^(-3) MJ m^(-2) decade^(-1)、-2.8×10^(-3) MJ m^(-2) decade^(-1)的速度下降,而春季太阳辐射以11.5×10^(-3) MJ m^(-2) decade^(-1)的速度上升,其中,夏季太阳辐射的下降受气溶胶光学厚度和低云量显著增加的影响,秋、冬季太阳辐射的下降受气溶胶光学厚度显著增加的影响,春季太阳辐射的增长主要取决于总云量的显著下降;3)气溶胶光学厚度和整层大气水汽含量增加导致80%的台站太阳辐射呈下降趋势,总云量和低云量下降导致20%的台站太阳辐射呈上升趋势,而修水、赣州站太阳辐射与4个影响因素的变化趋势相同的原因还需进一步研究。

Evaluating the impacts of land use and land cover changes on surface air temperature using the WRF-mosaic approach

Satellite-derived land surface data in 1980 and 2010 were used to represent land use and land cover（LULC） changes caused by the rapid economic development and human activities that have occurred over the past few decades in East Asia and China. The effects of LULC changes on the radiation budget and 2-m surface air temperature（SAT） were explored for the period using the Weather Research and Forecasting（WRF） model. The mosaic approach, which considers the N-most abundant land use types within a model grid cell（here, N = 3） and precisely describes the subgridscale LULC changes, was adopted in the integrations. The impacts of LULC changes based on two 36-year integrations showed that SAT generally decreased, with the sole exception being over eastern China, resulting in decreased SAT in China（-0.062 °C） and East Asian land areas（EAL,-0.061 °C）. The LULC changes induced changes in albedo, which influenced the radiation budget. The radiative forcings at the top of the atmosphere were-0.56 W m-2 across the whole of China, and-0.50 W m-2 over EAL. Meanwhile, the altered roughness length mainly influenced near-surface wind speeds, large-scale and upward moisture fluxes, latent heat fluxes, and cloud fractions at different altitudes. Though the impacts caused by the LULC changes were generally smaller at regional scales, the values at local scales were much stronger.

发动机缸盖罩结构声辐射特性优化分析

发动机是船舶动力系统的重要组成部分,是振动噪声的源头之一,发动机缸内噪声通过缸体和缸盖罩向外辐射。以发动机缸盖罩为研究对象,通过有限元建模分析其模态,并进行试验验证。以缸盖罩结构的表面振速和辐射声功率为目标,采用有限元与边界元相结合的方法对缸盖罩结构进行声辐射特性优化设计。研究结果表明:通过结构优化设计,在缸盖罩内部两侧添加等腰三角形加强筋,可使得10Hz~4000Hz频段内发动机缸盖罩辐射声功率平均降低2.10dB(A)。研究结果可为发动机缸盖罩结构的设计提供借鉴。

积雪和沙尘对冰封期青海湖辐射和温度的影响

青藏高原广泛而密集地分布着大量湖泊,受高海拔影响,湖泊多季节性冻结且冰封期较长。湖冰可显著改变湖面和水下辐射、能量传输过程,进而影响局地、区域气候及冰下水生生态系统;然而目前对高原湖泊冰封期湖面特征及湖下热力过程的认识尚不明确。因此,本研究于2022年2月6-28日在青藏高原最大湖泊青海湖进行了冰封期多层湖水-湖冰-大气的系统野外观测;利用获取的野外观测数据及视频影像,结合台站降水资料,研究了冰封期青海湖不同冰面覆盖条件对湖水-湖冰-大气辐射和温度的影响。结果表明,降雪、沙尘、大风等不同天气过程可显著改变冰面物质的分布情况,导致青海湖冰面覆盖物和冰层的厚度发生变化。冰面覆盖物的反照率差异及其对太阳辐射的吸收差异使入射到湖表覆盖物上界面、湖冰上界面的短波辐射和湖冰温度日变化存在显著差别。裸冰时反照率较小且上层少有可吸收太阳辐射的覆盖物,冰面温度的日变化较大。积雪的高反射特性和沙尘的强吸收特性均削弱了入射湖冰表面的短波辐射,使得湖冰温度日变化较小。

Separation of Atmospheric Circulation Patterns Governing Regional Variability of Arctic Sea Ice in Summer

In recent decades,Arctic summer sea ice extent(SIE)has shown a rapid decline overlaid with large interannual variations,both of which are influenced by geopotential height anomalies over Greenland(GL-high)and the central Arctic(CA-high).In this study,SIE along coastal Siberia(Sib-SIE)and Alaska(Ala-SIE)is found to account for about 65%and 21%of the Arctic SIE interannual variability,respectively.Variability in Ala-SIE is related to the GL-high,whereas variability in Sib-SIE is related to the CA-high.A decreased Ala-SIE is associated with decreased cloud cover and increased easterly winds along the Alaskan coast,promoting ice-albedo feedback.A decreased Sib-SIE is associated with a significant increase in water vapor and downward longwave radiation(DLR)along the Siberian coast.The years 2012 and 2020 with minimum recorded ASIE are used as examples.Compared to climatology,summer 2012 is characterized by a significantly enhanced GL-high with major sea ice loss along the Alaskan coast,while summer 2020 is characterized by an enhanced CA-high with sea ice loss focused along the Siberian coast.In 2012,the lack of cloud cover along the Alaskan coast contributed to an increase in incoming solar radiation,amplifying ice-albedo feedback there;while in 2020,the opposite occurs with an increase in cloud cover along the Alaskan coast,resulting in a slight increase in sea ice there.Along the Siberian coast,increased DLR in 2020 plays a dominant role in sea ice loss,and increased cloud cover and water vapor both contribute to the increased DLR.

蒙特卡罗方法在高放废物贮存库屏蔽盖板设计中的应用

利用蒙特卡罗方法,分别模拟了屏蔽盖板间缝隙、盖板材料及贮存井壁内部结构对屏蔽效果的影响。通过分析对比,最终提出了一种高放废物贮存井盖板屏蔽设计的解决方案,不仅可满足辐射防护设计安全性的基本要求,而且最大程度地实现了废物库建设经济性的目的。这种贮存井盖板设计方法最终可量化,推广到更多同类型后处理设施的屏蔽设计工作中。

复杂天气和地形下的地表太阳辐射估算模型及其在超短期光伏发电功率预测中的应用

为了研究表面太阳辐射估算模型在超短期光伏功率预测中的应用,并减少多云天气对预测的干扰,利用电荷耦合器件/红外光谱(CCD/IRS)数据对表面太阳辐射估计模型进行了优化,构建了一种有效的超短期光伏功率预测模型,并通过实验证明了它的可靠性。首先介绍了CCD/IRS数据的原理,接着在考虑云量影响的情况下改进了太阳表面辐射估算模型。分别选择了多云和无云2种不同的天气类型来验证估算模型。实验结果表明:与传统算法相比,所提出的地表太阳辐射估算模型在多云天气和复杂地形条件下具有更大的优势,可用于光伏功率预测;基于地表太阳辐射估算模型构建的超短期光伏功率估算模型可用于在无云天气下获得准确有效的预测结果,提出的预测模型在多云天气中的偏差也得到了显着的改进。表面太阳辐射估算模型对于超短期光伏发电量的准确预测和安全运行具有重要的参考价值。

某铀矿山退役治理尾渣库覆土实验

某即将退役铀矿尾渣库面积约14000m^(2)。据监测、取样分析,尾渣库(0~20cm)天然铀含量在(10.5~71.2)mg/kg范围内,平均值为49.8mg/kg;镭-226含量在(984~5027)Bq/kg范围内,平均值为4014Bq/kg。表面氡析出率范围为(3.552~4.889)Bq/(m^(2)·s),平均氡析出率为3.79Bq/(m^(2)·s)γ辐射剂量率范围为(1247~2143)nGy/h。为了给铀矿退役治理工程项目尾渣库退役处置提供基础资料,在尾渣库上进行了现场覆土实验。通过在实验场地覆盖不同厚度的土壤,监测γ辐射剂量率与表面氡析出率在不同土壤覆盖下的变化趋势,从而核算出尾渣库达标退役需要的覆土厚度。

1961—2000年中国太阳辐射区域特征的初步研究

利用中国122个辐射观测站1961—2000年的逐日地面辐射资料,同期729个气象站的逐日云量资料,分析了总辐射、直接辐射和散射辐射年代际距平分布和变化。按照中国地理气候区域的特征并考虑年总辐射,将中国划分为5个不同的辐射区域。分析了各区近40a来总辐射、直接辐射、散射辐射的年际变化。结果表明:①总辐射和直接辐射年曝辐量在1961—1990年之间呈下降趋势,在20世纪80年代达到最低值,以青藏高原西南部地区降幅最明显;在1991—2000年总辐射和直接辐射年曝辐量有回升趋势,其中青藏高原地区回升最显著,但均未达到历史最高水平。5区总辐射近40a来下降率为:-1.24%/10a,-1.66%/10a,-1.60%/10a,-1.89%/10a和-1.93%/10a。②近40a来散射辐射年曝辐量除东北无明显变化外,南疆和青藏高原有降低趋势,而南方有略微增加趋势;通过对云量的分析发现西北地区低云量略增加,而其他地区低云量和总云量都有不同程度的下降趋势,5区总云量近40a来下降率为:-2.99%/10a,-1.68%/10a,-3.10%/10a,-1.17%/10a和-1.01%/10a,低云量变化率为:-1.51%/10a,4.46%/10a,-1.47%/10a,-0.89%/10a和-0.75%/10a。最后对造成辐射长期变化的原因作了初步讨论。

基于不确定理论的光伏出力预测研究

预测光伏出力对光伏发电系统的并网运行具有重要意义。目前很多预测方法中只能得到单一预测结果,缺乏对影响因素不确定性的分析。考虑到太阳辐射和温度是光伏出力的两个最大的影响因素,本文建立了基于不确定理论的太阳辐射值预测模型。首先分析了云量的模糊性和云遮系数的双重随机性,采用双重随机理论计算云量对应云遮系数的期望值和关键值,然后以无云天气计算太阳辐射值的REST模型为基础,用云遮系数对其进行修正,得到太阳辐射值的预测结果,最后得到光伏出力在不同云量下的预测期望值和满足不同置信水平的预测区间。模型选取美国BMS光伏电站的数据,验证了改进后模型的有效性。预测结果表明,该模型能够提供较丰富的信息,具有较好的实用性。