Solar Radiation Estimation Based on a New Combined Approach of Artificial Neural Networks (ANN) and Genetic Algorithms (GA) in South Algeria

When designing solar systems and assessing the effectiveness of their many uses,estimating sun irradiance is a crucial first step.This study examined three approaches(ANN,GA-ANN,and ANFIS)for estimating daily global solar radiation(GSR)in the south of Algeria:Adrar,Ouargla,and Bechar.The proposed hybrid GA-ANN model,based on genetic algorithm-based optimization,was developed to improve the ANN model.The GA-ANN and ANFIS models performed better than the standalone ANN-based model,with GA-ANN being better suited for forecasting in all sites,and it performed the best with the best values in the testing phase of Coefficient of Determination(R=0.9005),Mean Absolute Percentage Error(MAPE=8.40%),and Relative Root Mean Square Error(rRMSE=12.56%).Nevertheless,the ANFIS model outperformed the GA-ANN model in forecasting daily GSR,with the best values of indicators when testing the model being R=0.9374,MAPE=7.78%,and rRMSE=10.54%.Generally,we may conclude that the initial ANN stand-alone model performance when forecasting solar radiation has been improved,and the results obtained after injecting the genetic algorithm into the ANN to optimize its weights were satisfactory.The model can be used to forecast daily GSR in dry climates and other climates and may also be helpful in selecting solar energy system installations and sizes.

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.

Theoretical and Experimental Quantification of Solar Radiation through a Tracking System

This work deals with the estimation of solar radiation through a solar tracker aimed at evaluating the effect of solar tracking on the solar deposit in Burkina Faso. Using a two-axis solar tracking system, we experimentally measured solar radiation at our Joseph KI-ZERBO University site and compared it with that obtained by a numerical simulation run using Fortran programming software based on a mathematical model by Brichambaut. The results obtained from the mathematical and experimental studies show that, with a solar tracker, on a clear-sky day, solar irradiation is between 800 W·m−2 and 1000 W·m−2 between about 8 a.m. and 4 p.m., i.e. a duration of 8 hours of insolation. Analysis of the numerical and experimental results shows very good quantitative and qualitative agreement, with an average relative error of 18%.

Effects of solar radiation and fine roots on suction of Amorpha fruticose-vegetated soil

The thickness of shallow landslides is generally less than 2 m,which is of the same order of magnitude as the growth range of vegetation roots.Vegetation roots can improve the stability of shallow soil through mechanical and hydraulic effects.Therefore,the landslide process is closely related to the plant roots growing on the slope surface.Plant roots play a dominant role in the regulation of soil suction through solar radiation induced transpiration.However,little is known about the correlation between cumulative solar radiation and soil suction.Moreover,the specific effects of fine roots on the suction distribution are not clear in most previous studies.In this study,a vegetated soil of a drought-tolerant and water-tolerant shrub,namely Amorpha fruticose,was adopted.The suction and volumetric water content of bare and vegetated soils were monitored under natural conditions for 4 months.The results demonstrate that there is a nearly linear relationship between cumulative solar radiation and suction ranging from zero to 100 kPa.Regarding the modeling of the soil-plant-atmosphere interactions,this relationship could serve a significant role in calculating the root water uptake under given solar radiation conditions.In addition,higher suctions were observed at the lower layer of the vegetated soil than those at the middle layer,which is different from the results of vegetated soil from previous investigations.This is due to the fact that the root area index(RAI)of fine roots at the lower layer is twice that of the middle layer.Importantly,the higher concentration of fine roots at the lower layer of vegetated soil sample resembles the root distribution of shrub near the soil-bedrock interface on shallow bedrock landslides.The fine roots would increase soil suction through transpiration,and hence reduce the permeability and increase shear strength of landslides.Eventually,these new findings serve as a preliminary step on the evaluation of the stability of this common type of landslides.

Value-Added Products Derived from 15 Years of High-Quality Surface Solar Radiation Measurements at Xianghe,a Suburban Site in the North China Plain

Surface solar radiation(SSR) is a key component of the energy budget of the Earth’s surface, and it varies at different spatial and temporal scales. Considerable knowledge of how and why SSR varies is crucial to a better understanding of climate change, which surely requires long-term measurements of high quality. The objective of this study is to introduce a value-added SSR dataset from Oct 2004 to Oct 2019 based on measurements taken at Xianghe, a suburban site in the North China Plain;two value-added products based on the 1-minute SSR measurements are developed. The first is clear sky detection by using a machine learning model. The second is cloud fraction estimation derived from an effective semiempirical method. A “brightening” of global horizontal irradiance(GHI) was revealed and found to occur under both clear and cloudy conditions. This could likely be attributed to a reduction in aerosol loading and cloud fraction. This dataset could not only improve our knowledge of the variability and trend of SSR in the North China Plain, but also be beneficial for solar energy assessment and forecasting.

Impacts of canopy structure on the sub-canopy solar radiation under a deciduous forest based on fisheye photographs

Forest canopy in a deciduous forest has significant sheltering effects on the sub-canopy solar radiation,significantly influencing the energy balance of snow and permafrost beneath the forest and their spatial distribution.This study employs a digital camera mounted with a fisheye lens to acquire photographs at various times in a growth cycle of the forest canopy at three selected sites in a deciduous forest near the Greater Khingan Mountains Forest Ecological Station,Northeast China.The vegetation types and conditions at the selected sites include P1 in Ledum-Claopodium-L.dahurica,P2 in Carex tato-L.dahurica,and P3 in Betula fruticosa-L.dahurica.After necessary image processing,these photographs were used to identify the canopy structure and its impacts on the sub-canopy solar radiation.Results show that fisheye photographs can successfully capture the forest canopy structure and are useful in estimating the sub-canopy solar radiation.The order of sheltering effects from the largest to the smallest on sub-canopy solar radiation at three selected sites is P3,P1,and P2,highly depending on the canopy density.Then sub-canopy solar radiation was calculated using fisheye photographs and an algorithm validated by in-situ observed solar radiation beneath the canopy at P1 and P3.The results are reasonable,although the accuracy seems compromised due to the mismatch of conditions for calculation and observation.Results also show that the mean annual solar radiation above the canopy was about 148.3 W/m2 in 2018,and the mean annual solar radiation values beneath the canopy were about 90.0,123.8,and 61.0 W/m2 at P1,P2,and P3,with only 60%,84%,and 42%of the total solar radiation penetrating through the canopy,respectively.Even in winter,when the trees are leafless,the canopy sheltering effects cannot be ignored in dense forests.Despite the limitations,fisheye photographs and related algorithms are useful in investigating the forest canopy structure and its impacts on sub-canopy solar radiation.

Data-Driven Models for Predicting Solar Radiation in Semi-Arid Regions

Solar energy represents one of themost important renewable energy sources contributing to the energy transition process.Considering that the observation of daily global solar radiation(GSR)is not affordable in some parts of the globe,there is an imperative need to develop alternative ways to predict it.Therefore,the main objective of this study is to evaluate the performance of different hybrid data-driven techniques in predicting daily GSR in semi-arid regions,such as the majority of Spanish territory.Here,four ensemble-based hybrid models were developed by hybridizing Additive Regression(AR)with Random Forest(RF),Locally Weighted Linear Regression(LWLR),Random Subspace(RS),and M5P.The base algorithms of the developed models are scarcely applied in previous studies to predict solar radiation.The testing phase outcomes demonstrated that the ARRF models outperform all other hybrid models.The provided models were validated by statisticalmetrics,such as the correlation coefficient(R)and root mean square error(RMSE).The results proved that Scenario#6,utilizing extraterrestrial solar radiation,relative humidity,wind speed,and mean,maximum,and minimum ambient air temperatures as the model inputs,leads to the most accurate predictions among all scenarios(R=0.968–0.988 and RMSE=1.274–1.403 MJ/m^(2)・d).Also,Scenario#3 stood in the next rank of accuracy for predicting the solar radiation in both validating stations.The AD-RF model was the best predictive,followed by AD-RS and AD-LWLR.Hence,this study recommends new effective methods to predict GSR in semiarid regions.

Solar Radiation Prediction Using Satin Bowerbird Optimization with Modified Deep Learning

Solar energy will be a great alternative to fossil fuels since it is clean and renewable.The photovoltaic(PV)mechanism produces sunbeams’green energy without noise or pollution.The PV mechanism seems simple,seldom malfunctioning,and easy to install.PV energy productivity significantly contributes to smart grids through many small PV mechanisms.Precise solar radiation(SR)prediction could substantially reduce the impact and cost relating to the advancement of solar energy.In recent times,several SR predictive mechanism was formulated,namely artificial neural network(ANN),autoregressive moving average,and support vector machine(SVM).Therefore,this article develops an optimal Modified Bidirectional Gated Recurrent Unit Driven Solar Radiation Prediction(OMBGRU-SRP)for energy management.The presented OMBGRU-SRP technique mainly aims to accomplish an accurate and time SR prediction process.To accomplish this,the presented OMBGRU-SRP technique performs data preprocessing to normalize the solar data.Next,the MBGRU model is derived using BGRU with an attention mechanism and skip connections.At last,the hyperparameter tuning of the MBGRU model is carried out using the satin bowerbird optimization(SBO)algorithm to attain maximum prediction with minimum error values.The SBO algorithm is an intelligent optimization algorithm that simulates the breeding behavior of an adult male Satin Bowerbird in the wild.Many experiments were conducted to demonstrate the enhanced SR prediction performance.The experimental values highlighted the supremacy of the OMBGRU-SRP algorithm over other existing models.

Application of Exergy for Research on Increasing the Usefulness of Solar Radiation by Dispersing It into Monochromatic Beams

Energy determines the ability of matter to work. However, in the given environment, the real usefulness to perform work is determined by exergy. This study covers not only solar, but also any monochromatic thermal radiation. The value of such radiation was determined by its exergy and the ratio of its exergy-to-energy. A novelty in this work is to demonstrate by means of exergy that the usefulness of thermal polychromatic radiation can be increased by its dispersion to monochromatic radiation. This effect is the greater, the lower the temperature of the radiation. Analogies of this effect to the exergetic effect of gas separation have been indicated. The effect of the increase in exergy in the process of radiation dispersion was interpreted by means of a cylinder-piston system that explains this effect with the influence of environmental radiation. The concept of quasi-monochromatic and cumulated radiation was introduced into dispersion considerations and the change in the energetic, entropic and environmental components of the exergy of radiation beams was analyzed. Considerations were illustrated with appropriate examples of calculations considering dispersion of high-temperature radiation, such as extraterrestrial solar radiation and dispersion of low-temperature radiation from water vapor.

Comparative analysis of extreme ultraviolet solar radiation proxies during minimum activity levels

Four extreme ultraviolet(EUV)solar radiation proxies(Magnesium II core-to-wing ratio(MgII),Lymanαflux(Fα),10.7-cm solar radio flux(F10.7),and sunspot number(Rz))were analyzed during the last four consecutive solar activity minima to investigate how they differ during minimum periods and how well they represent solar EUV radiation.Their variability within each minimum and between minima was compared by considering monthly means.A comparison was also made of their role in filtering the effect of solar activity from the critical frequency of the ionospheric F2 layer,foF2,which at mid to low latitudes depends mainly on EUV solar radiation.The last two solar cycles showed unusually low EUV radiation levels according to the four proxies.Regarding the connection between the EUV“true”variation and that of solar proxies,according to the foF2 filtering analysis,MgII and Fαbehaved in a more stable and suitable way,whereas Rz and F10.7 could be overestimating EUV levels during the last two minima,implying they would both underestimate the inter-minima difference of EUV when compared with the first two minima.

Evaluation on Solar Radiation Resource and Photosynthetic and Thermal Potential Productivity in Shandong Province

To evaluate scientifically the change of photosynthetic and thermal potential productivity caused by climate variation,based on comparison with mean of previous 30 years(1971-2000),the change of total solar radiation,sunshine hours,photosynthetic active radiation,photosynthetic and thermal potential productivity since 2001 were analyzed through data of radiation,sunshine and temperature in Shandong Province from 1971 to 2007,and the change trend was also tested by Mann-Kendall non-parametric statistical met...

Variation Trend of Total Solar Radiation in Nujiang Basin in Recent 30 Years

Based on the data of sunshine duration,cloud cover and relative humidity from 9 stations in 1981-2008,the spatial and temporal distribution and change trend of total solar radiation in river valley basin of Nujiang were analyzed,as well as its impact factors.The results showed that annual solar radiation decreased obviously in Nujiang basin from 1981 to 1997,with the rate of-161.1 MJ/(m2·10 a),while it went up after 1997 at the rate of 111.3 MJ/(m2·10 a).Annual total cloud cover showed significant decrease trend with the rate of 1.8%/10 a,but annual low cloud cover increased at the rate of 3.2%/10 a.Contrary to the change trend of annual solar radiation,relative humidity rose at the increase of 3.1%/10 a from 1981 to 1997 and decreased significantly at the rate of 5.6%/10 a in 1997-2008.The change of water vapor pressure was consistent with relative humility change.Low cloud cover was the main impact factor of total solar radiation and had a negative correlation with total solar radiation.

Application of recording films of solar radiation for environmental and ecological research

Global solar radiation is recorded by fading of the colored film into which azo-dye is impregnated with use of organic solvent. Oil Red O, Sudan I, Sudan IV and Pyridylazonaphthol are used as the azo dye. These films can be applied to measure the solar radiation in many kinds of environmental or ecological conditions. The merits of the film compared with usual measurements are to be: unnecessary of any electric sources; cheap and mass-productive easily; suitable to integrate solar radiation for long time; easy dealing in out-door or underwater conditions; possible to use on leaves of any plants because of light weight; possible to use in a lot of points at the same time.

Neural Network for Estimating Daily Global Solar Radiation Using Temperature, Humidity and Pressure as Unique Climatic Input Variables

Solar radiation is one of the most important parameters for applications, development and research related to renewable energy. However, solar radiation measurements are not a simple task for several reasons. In the cases where data are not available, it is very common the use of computational models to estimate the missing data, which are based mainly on the search for relationships between weather variables, such as temperature, humidity, precipitation, cloudiness, sunshine hours, etc. But, many of these are subjective and difficult to measure, and thus they are not always available. In this paper, we propose a method for estimating daily global solar radiation, combining empirical models and artificial neural networks. The model uses temperature, relative humidity and atmospheric pressure as the only climatic input variables. Also, this method is compared with linear regression to verify that the data have nonlinear components. The models are adjusted and validated using data from five meteorological stations in the province of Tucumán, Argentina. Results show that neural networks have better accuracy than empirical models and linear regression, obtaining on average, an error of 2.83 [MJ/m2] in the validation dataset.

Sensitivity of the Upper Ocean Temperature and Circulation in the Equatorial Pacific to Solar Radiation Penetration Due to Phytoplankton

Solar radiation penetration in the upper ocean is strongly modulated by phytoplankton, which impacts the upper ocean temperature structure, especially in the regions abundant with phytoplankton. In the paper, a new solar radiation penetration scheme, based on the concentration of chlorophyll-a, was introduced into the LASG/IAP （State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics/Institute of Atmospheric Physics） Climate system Ocean Model （LICOM）. By comparing the simulations using this new scheme with those using the old scheme that included the constant e-folding attenuation depths in LICOM, it was found that the sea surface temperature （SST） and circulation in the central and eastern equatorial Pacific were both sensitive to the amount of phytoplankton present. Distinct from other regions, the increase of chlorophyll-a concentration would lead to SST decrease in the central and eastern equatorial Pacific. The higher chlorophyll-a concentration at the equator in comparison to the off-equator regions can enlarge the subsurface temperature gradient, which in turn strengthens the upper current near the equator and induces an enhancing upwelling. The enhancing upwelling can then lead to a decrease in the SST in the central and eastern equatorial Pacific. The results of these two sensitive experiments testify to the fact that the meridional gradient in the chlorophyll-a concentration can result in an enhancement in the upper current and a decrease in the SST, along with the observation that a high chlorophyll-a concentration at the equator is one of the predominant reasons leading to a decrease in the SST. This study points out that these results can be qualitatively different simply because of the choice of the solar radiation penetration schemes for comparison. This can help explain previously reported contradictory conclusions.

Effects of temperature and solar radiation on yield of good eating-quality rice in the lower reaches of the Huai River Basin,China

We studied the effects of temperature and solar radiation on rice yield with the aim of understanding the temperature and solar radiation requirements for high yield rice production in the lower reaches of the Huai River,China.Field experiments were conducted with two medium-maturing japonica rice(MMJR)varieties and four late-maturing japonica rice(LMJR)varieties in 2017 and 2018.Seeds were sown on May 10(T1),May 17(T2),May 24(T3),May 31(T4),June 7(T5),June 14(T6),and June 21(T7).The whole growth duration(WGD)of rice was shortened when sowing date was delayed,especially for the duration from sowing to heading(S–H).The effective accumulated temperature(EAT),mean daily temperature(Tmean),cumulative solar radiation(CSR),and mean daily solar radiation(Rmean)over the WGD decreased when sowing date was delayed.Compared with T1,yields in T2,T3,T4,T5,T6,and T7 decreased by 0.12–0.35,0.45–0.89,0.74–1.56,1.41–2.24,2.16–2.90,and 2.69–3.64 t ha^(-1),respectively.There was a significant positive correlation between rice yield and EAT in different growth stages.Temperature was the main factor that affected the yield of good eating-quality rice in the lower reaches of the Huai River.We found that a relatively high yield can be obtained when the optimal Tmean for medium-maturing japonica rice(MMJR)and late-maturing japonica rice(LMJR)was 25.8–27.0℃and 26.6–27.1℃in the stages from sowing to heading(S–H),and 20.3–23.3℃and 20.3–22.1℃in the stages from heading to maturity(H–M),respectively.The optimal sowing dates for MMJR and LMJR in the lower reaches of the Huai River were May 15–31 and May 15–18,respectively.

Change of the solar radiation and its causes in the Haihe River Basin and surrounding areas

Solar radiation is an important driving force for the formation and evolution of climate system. Analysis of change in solar radiation is helpful in understanding mechanism of climate change. In this study, the temporal and spatial variations of solar radiation and the cause of the change in solar radiation have been analyzed based on meteorological data from 46 national meteorological stations and aerosol index data from TOMS over the Haihe River Basin and surrounding areas. The results have shown that solar radiation and direct radiation significantly decreased, while scattered radiation increased during the period 1957-2008. Spatially, the decreasing trend of solar radiation was more and more significant from low population density areas to high population density areas. The spatial distribution of increase in aerosol index is consistent with that of decrease in solar radiation. The increase in aerosols resulting from human activities was an important reason for the decrease in solar radiation.

Simulation of astronomical solar radiation over Yellow River Basin based on DEM

Based on the developed distributed model for calculating astronomical solar radiation (ASR), monthly ASR with a resolution of 1 km×1 km for the rugged terrains of Yellow River Basin was calculated, with DEM data as the general characterization of terrain. This model gives an all-sided consideration on factors that influence the ASR. Results suggest that (1) Annual ASR has a progressive decrease trend from south to north; (2) the magnitude order of seasonal ASR is: summer>spring>autumn>winter; (3) topographical factors have robust effect on the spatial distribution of ASR, particularly in winter when a lower sun elevation angle exists; (4) the ASR of slopes with a sunny exposure is generally 2 or 3 times that of slopes with a shading exposure and the extreme difference of ASR for different terrains is over 10 times in January; (5) the spatial differences of ASR are relatively small in summer when a higher sun elevation angle exists and the extreme difference of ASR for different terrains is only 16% in July; and (6) the sequence of topographical influence strength is: winter>autumn>spring>summer.

The effect of solar radiation change on the maize yield gap from the perspectives of dry matter accumulation and distribution

The uneven distribution of solar radiation is one of the main reasons for the variations in the yield gap between different regions in China and other countries of the world.In this study,different solar radiation levels were created by shading and the yield gaps induced by those levels were analyzed by measuring the aboveground and underground growth of maize.The experiments were conducted in Qitai,Xinjiang,China,in 2018 and 2019.The maize cultivars Xianyu 335 (XY335)and Zhengdan 958 (ZD958) were used with planting density of 12×10^(4) plants ha^(–1) under either high solar radiation (HSR)or low solar radiation (LSR,70%of HSR).The results showed that variation in the solar radiation resulted in a yield gap and different cultivars behaved differently.The yield gaps of XY335 and ZD958 were 8.9 and 5.8 t ha^(–1) induced by the decreased total intercepted photosynthetically active radiation (TIPAR) of 323.1 and 403.9 MJ m^(–2) from emergence to the maturity stage,respectively.The average yield of XY335 was higher than that of ZD958 under HSR,while the average yield of ZD958 was higher than that of XY335 under LSR.The light intercepted by the canopy and the photosynthetic rates both decreased with decreasing solar radiation.The aboveground dry matter decreased by 11.1% at silking and 21% at maturity,and the dry matter of vegetative organs and reproductive organs decreased by 9.8 and 20.9%at silking and by 12.1 and 25.5% at physiological maturity,respectively.Compared to the HSR,the root weights of XY335 and ZD958 decreased by 54.6 and 45.5%,respectively,in the 0–60 cm soil layer under LSR at silking stage.The aboveground and underground growth responses to different solar radiation levels explained the difference in yield gap.Selecting suitable cultivars can increase maize yield and reduce the yield gaps induced by variation of the solar radiation levels in different regions or under climate change.