Trends In Solar Radiation Research Articles

Internal Variability of the Climate System Mirrored in Decadal‐Scale Trends of Surface Solar Radiation

AbstractDecadal‐scale unforced climate variability associated with low‐frequency ocean (or coupled) modes can be identified within the time‐evolving sea surface temperature (SST) pattern. We seek to find a relationship between 12 well‐known climate modes of variability (El Niño–Southern Oscillation, Pacific Decadal Oscillation, Atlantic Multidecadal Oscillation, etc.), which are reflected in the SST pattern, and decadal trends in downwelling shortwave radiation at Earth's surface (surface solar radiation, surface shortwave radiation [SSR]). The analysis is performed using the pre‐industrial control runs (piControl) of 57 models from the Coupled Model Intercomparison Project—Phase 6. We find that regional SSR trends occur during periods when a climate mode is transitioning and show a mirroring pattern (opposite sign SSR trends) when the mode transitions in the opposite direction. Unforced trends in clear‐sky SSR are mostly driven by SST‐induced water vapor changes, while all‐sky SSR trends show a complex spatial structure with trends of different signs in different regions. Unforced SSR trends are generally weaker in simulations with climatological SSTs. The role of natural aerosols as another potentially relevant factor for SSR variability is briefly addressed and we find that constantly higher aerosol loads result in increased variability for clear‐sky conditions, but not for all‐sky conditions. The results from this study suggest that all‐sky dimming and brightening in different parts of the world are enhanced rather than suppressed by internal variability related to an SST‐pattern with the exception of India and China, where both effects are present. A practical application can be the planning of photovoltaic energy facilities given areas where internal variability is generally smaller or affects SSR in opposite directions.

Spatio-Temporal Trend Analysis of Reference Evapotranspiration in Central Luzon, Philippines

Understanding trends in reference evapotranspiration (ETₒ) and their influencing factors is crucial for calculations of irrigation requirements and water management. Meteorological data in Central Luzon (1985–2019) were used to estimate ETₒ using the FAO Penman-Monteith method. Spatial and temporal ETₒ trends were analyzed using the Mann-Kendall test and Sen’s slope estimator. Correlation and sensitivity analyses were conducted to analyze the impact of weather variables on ETₒ. Positive correlations were observed for maximum temperature, solar radiation, and wind speed whereas negative correlations were observed for relative humidity and minimum temperature. In general, ETₒ was statistically dependent and most sensitive to solar radiation, maximum temperature, and relative humidity. ETₒ in the stations surrounded by mountains was consistently lower than the stations in the agricultural areas by 197 and 207 mm for the dry season and annual basis, respectively. The increasing trends with a magnitude of 3.98 mm/yr in annual ETₒ were caused by the rising trend in solar radiation and maximum temperature and a decreasing trend in relative humidity. The decreasing ETₒ trend (–2.6 to –4.63 mm/yr) predominant in the study area was mainly attributed to the decreasing trend of solar radiation and wind speed. Areas with increasing ETₒ trends indicate the need for supplemental irrigation. Decreasing ETₒ trends may indicate climate change, land-use change, or human-related factors.

Prediction of Energy Production Level in Large PV Plants through AUTO-Encoder Based Neural-Network (AUTO-NN) with Restricted Boltzmann Feature Extraction

In general, reliable PV generation prediction is required to increase complete control quality and avoid potential damage. Accurate forecasting of direct solar radiation trends in PV power production could limit the influence of uncertainties on photovoltaics, enhance organizational dependability, and maximize the utilization factor of the PV systems for something such as an energy management system (EMS) of microgrids. This paper proposes an intelligent prediction of energy production level in large PV plants through AUTO-encoder-based Neural-Network (AUTO-NN) with Restricted Boltzmann feature extraction. Here, the solar energy output may be projected using prior sun illumination and meteorological data. The feature selection and prediction modules use an AUTO encoder-based Neural Network to improve the process of energy prediction (AUTO-NN). Restricted Boltzmann Machines (RBM) can be used during a set of regulations for development-based feature extraction. The proposed model’s result is evaluated using various constraints. As a result, the proposed AUTO-NN achieved 58.72% of RMSE (Root Mean Square Error), 62.72% of nRMSE (Normalized Root Mean Square Error), 48.04% of MaxAE (Maximum Absolute Error), 48.66% of (Mean Absolute Error), and 46.76% of (Mean Absolute Percentage Error).

Unmasking the Effects of Aerosols on Greenhouse Warming Over Europe

AbstractAerosol optical thickness (AOT) has decreased substantially in Europe in the summer half year (April–September) since 1980, with almost a 50% reduction in Central and Eastern Europe, according to Modern‐Era Retrospective analysis for Research and Applications, Version 2 (MERRA‐2) reanalysis. At the same time, strong positive trends in ERA5 reanalysis surface solar radiation downward for all‐sky and clear‐sky conditions (SSRD and SSRDc, respectively) and temperature at 2 m are found for Europe in summer during the period 1979–2020. The GEBA observations show as well strong increases in SSRD during the latest four decades. Estimations of changes in SSRDc, using the Santa Barbara DISORT Atmospheric Radiative Transfer (SBDART) model, show similarly strong increases when fed by MERRA‐2 AOT. The estimates of warming in this study, caused by increases in SSRD and SSRDc, are based on energy budget approximations and the Stefan Boltzmann law. The increases in near surface temperature, estimated both for clear‐sky and all‐sky conditions, are up to about 1°C for Central and Eastern Europe. The total warming over large parts of this region for clear‐sky conditions is however nearly double the global mean temperature increase of 1.1°C, while somewhat less for all‐sky conditions. The effects of aerosols on warming over the southerly Iberian Peninsula are weaker compared to countries further north. The rapid total warming over the Iberian Peninsula is probably caused by greenhouse warming, drier surface conditions, and to some degree decline in aerosols. Reduced cloud cover is found for large parts of Europe in summer during the latest four decades.

Interactions of genotype, environment and management on wheat traits and grain yield variations in different climate zones across China

CONTEXTConcerns about the effects of global warming on crop yields have risen due to stagnating yield progress in recent years. Understanding crop traits and grain yield variations in different climate zones is critical to gain insights into crop response and adaptation mechanisms to ongoing climate change. However, the interactions of genotype, environment and management on crop traits and historical yield progress are lacking. OBJECTIVEThis study is to investigate the variations and trends in wheat traits in different climate zones across China, trade-offs among phenological and yield-related traits, the effects of genotype, environment and management interactions on wheat traits, as well as the contributions of traits, management, climate and genetic changes to grain yield. METHODSThe genotype, environment and management interactions on wheat traits and grain yield variations were analyzed based on long-term field trials during 2003–2016 at five representative stations across China. And then, a machine learning method was applied to quantify the relative contributions of these factors to wheat traits and grain yield variations. RESULTS AND CONCLUSIONSA significant warming trend during the reproductive growth period and a decreasing trend in solar radiation were observed. Significant trends and variations in wheat traits and significant interactions between genotype, station and year were discovered. Compared with fertilization, grain yield under no-fertilization was significantly lower by 80.3% at five representative stations across China. With local farmer's practices, about 3.5–40.9%, 19.6–58.3% and 0.1–8.2% of the yield variations were associated with agricultural management practices, climate change and cultivar shifts, respectively, contradicting some previous studies which highlight the weight of genetic yield improvement. SIGNIFICANCEThe findings are valuable for understanding the mechanisms underlying crop traits and grain yield variations, for breeders to breed desirable traits, and for agronomists to adopt suitable cultivars and agricultural management practices.

Decadal trends in surface solar radiation and cloud cover over the North Atlantic sector during the last four decades: drivers and physical processes

Satellite-derived products and reanalyses show consistent increases in downward surface solar radiation (SSR) and decreases in cloud cover over North America and Europe from the 1980s to 2010s. These trends show a strong seasonality, with the largest changes in boreal summer. A set of timeslice experiments with an atmospheric general circulation model (AGCM) forced with prescribed changes in sea surface temperature/sea ice extent (SST/SIE), greenhouse gas (GHG) concentrations, and anthropogenic aerosol (AA) emissions, together and separately, is performed to assess the relative roles of different forcings in these observed trends. The model reproduces the main observed features over Europe and North America, including the seasonality of trends, suggesting a dominant role of forced changes in the recent trends in SSR and cloud cover. Responses to individual forcings indicate that recent decadal trends in SSR over Europe are predominantly driven by AA emission reductions, with an additional influence from SST/SIE and GHG changes. In contrast, changes in AA, SST/SIE, and GHG contribute more equally to simulated decadal trends in SSR and cloud cover over North America, although SST/SIE play the most important role. In our simulations, responses of SSR to AA emission reductions are primarily governed by aerosol-radiation interactions. Responses to SST/SIE and GHG changes are predominantly due to cloud cover changes, which are driven by atmospheric circulation and humidity changes. This process level understanding of how different forcing factors influence decadal trends in SSR and cloud cover is valuable for understanding past changes and future projections in global and regional surface energy budgets, surface warming, and global and regional hydrological cycles.

Forcing for Multidecadal Surface Solar Radiation Trends Over Northern Hemisphere Continents

AbstractThe long‐term variation of North Pacific and North Atlantic sea surface temperatures (SSTs) is shown to be associated with multidecadal trends of surface solar radiation in North America, Europe, and Asia. Long‐term, large‐scale warm SST anomalies lead to a mid‐level planetary wave anomaly pattern of geopotential height ridges over the warm water and dynamically‐induced lower heights on either side, sometimes extending over adjacent continents. Geopotential height troughs over the continents encourage more cloud cover and dimming of surface solar radiation. Conversely, cool SST anomalies correspond to a pattern of lower mid‐level geopotential heights over the cool water and compensating high pressure on either side that encourages decreasing cloud cover and brightening over the continents, if the wave positioning is favorable. Additionally, these effects are observed to be latitude dependent, showing stronger SST‐geopotential height associations in the northern half of the Northern Hemisphere. The change from continental dimming to brightening and the reversal of North Pacific SST trends are nearly simultaneous. A similar SST‐geopotential height association is seen in the North Atlantic and leads to brightening and dimming in Europe and North America, but there is a ∼12‐year lag between the transition of dimming to brightening and SST reversals there, which is yet unexplained. The next step is to support these connections and their latitudinal dependence with carefully designed numerical experiments that consider variable greenhouse gas and aerosol concentrations.

Observations and Implications of Diurnal Climatology and Trends in Direct and Diffuse Solar Radiation Over China

AbstractSolar radiation received at the Earth's surface (Rs) is comprised of two components, the direct radiation (Rd) and the diffuse radiation (Rf). Rd, the direct beam from the sun, is essential for concentrated solar power generation. Rf, scattered by atmospheric molecules, aerosols, or cloud droplets, has a fertilization effect on plant photosynthesis. But how Rd and Rf change diurnally is largely unknown owing to the lack of long‐term measurements. Taking advantage of 22 years of homogeneous hourly surface observations over China, this study documents the climatological means and evolutions in the diurnal cycles of Rd and Rf since 1993, with an emphasis on their implications for solar power and agricultural production. Over the solar energy resource region, we observe a loss of Rd which is relatively large near sunrise and sunset at low solar elevation angles when the sunrays pass through the atmosphere on a longer pathway. However, the concentrated Rd energy covering an average 10‐hr period around noon during a day is relatively unaffected. Over the agricultural crop resource region, the large amounts of clouds and aerosols scattering more of the incoming light result in Rf taking the main proportion of Rs during the whole day. Rf resources and their fertilization effect in the main crop region of China further enhances since 1993 over almost all hours of the day.

Evaluation of surface solar radiation trends over China since the 1960s in the CMIP6 models and potential impact of aerosol emissions

Accurate representation of surface solar radiation (SSR) trends is an important indicator for global climate models (GCMs) to correctly reproducing the historical climate evolution. This study examines the annual mean SSR trends in China under all-sky and clear-sky conditions for the period 1961–2014 in 34 Coupled Model Intercomparison Project Phase 6 (CMIP6) models using the latest homogenized in-situ SSR dataset. The site-observed annual mean SSR over China shows a significant decadal decline during 1961–2005 but an uptrend during 2006–2014, with the trends being −6.4 (−8.6) W m−2 and + 2.5 (+5.9) W m−2 per decade under all-sky (clear-sky) condition, respectively. All CMIP6 models simulate the sustained decline in SSR over China for the period 1961–2005 but significantly underestimate the dimming. The model results show trends of −1.9 ± 0.5 W m−2 and -2.5 ± 0.7 W m−2 per decade during 1961–2005 under all-sky and clear-sky conditions, respectively, which are around one third of the observed results. Furthermore, the models fail to capture the reversal of SSR trends in China during 2006–2014, with the trends being −1.1 ± 1.7 W m−2 and -2.2 ± 0.9 W m−2 per decade under all-sky and clear-sky conditions, respectively. We infer that the underestimation of anthropogenic aerosol emissions, especially absorbing black carbon emissions cause the underestimated simulation of SSR in dimming period over China. After 2005, the unseasonal increase in carbonaceous aerosol emissions and the weaker decline of sulfur dioxide emissions in China in the models result in an opposite SSR trends relative to the trends based on the site-observations. Our results suggest that improving the anthropogenic aerosol emissions inventory will be useful for generating a more accurate reproduction of the regional SSR evolution over China in GCMs.

Asymmetric Differences in the Effects of Average Air Temperature and Solar Radiation on Early Rice and Late Rice Yield

China is the world’s largest rice producer. Thus, the stability of rice production plays a decisive role in food security. Among the types of rice, double rice (including early rice and late rice) accounts for the largest proportion of rice in China. Climate change is widely expected to affect rice yields. Studying the response of double rice yield to climate change will benefit strategic decisions related to future crop adaptation. In this paper, the relationship between climate factors and the yield of double rice during 1992–2013 in south China was analysed to determine the responses of double rice yield to climate change. The results showed that the daily average air temperature during the early rice and late rice growing seasons increased by 0.34 °C and 0.68 °C, 0.29 °C and 0.67 °C, and 0.11 °C and 0.31 °C per 10-year period in the northern subtropical zone (NST), middle subtropical zone (MST) and south subtropical zone (SST), respectively, in the last 20 years. The change trend in solar radiation was not obvious, but it fluctuated greatly. A 1 °C increase in average air temperatures decreased early rice yield by 5.36% and 2.16% in SST and MST, respectively; decreased late rice yield by 0.75% and 1.43% in MST and NST, respectively; and increased late rice yield by 3.93% in SST. A solar radiation increases of 100 MJ m−2 increased early rice yield by 1.02%, 1.54% and 1.71% in SST, MST and NST, respectively, and decreased late rice yield by 0.89% in SST. We found that annual average temperatures of 17.3 °C and 18.6 °C were the early rice and late rice yield variation thresholds, respectively; in addition, above the background temperature in south China, the early rice yield will decrease and the late rice yield will increase.

Observed increasing water constraint on vegetation growth over the last three decades

Despite the growing interest in predicting global and regional trends in vegetation productivity in response to a changing climate, changes in water constraint on vegetation productivity (i.e., water limitations on vegetation growth) remain poorly understood. Here we conduct a comprehensive evaluation of changes in water constraint on vegetation growth in the extratropical Northern Hemisphere between 1982 and 2015. We document a significant increase in vegetation water constraint over this period. Remarkably divergent trends were found with vegetation water deficit areas significantly expanding, and water surplus areas significantly shrinking. The increase in water constraints associated with water deficit was also consistent with a decreasing response time to water scarcity, suggesting a stronger susceptibility of vegetation to drought. We also observed shortened water surplus period for water surplus areas, suggesting a shortened exposure to water surplus associated with humid conditions. These observed changes were found to be attributable to trends in temperature, solar radiation, precipitation, and atmospheric CO2. Our findings highlight the need for a more explicit consideration of the influence of water constraints on regional and global vegetation under a warming climate.

A new view on the trend of solar radiation in mainland China — based on the optimized empirical model

As a kind of renewable energy, the development and utilization of solar energy are valued by many countries. To accurately provide a basis for the use of solar energy in mainland China, the optimized empirical model is adopted to analyze the variation trends and spatial patterns in solar radiation (SR) during 1961–2016 based on the data of 31 SR sites and 500 sunshine duration (SD) stations. The results indicate that there are obvious discrepancies in the variation trends of annual SR and SD during 1961–2016, with trend conversion occurring in 1992 (SR) and 1980 (SD), respectively. Overall, annual SR decreases at the rate of −3.68 MJ/m2·a in China. Notably, SR declines at the rate of −16.95 MJ/m2·a during 1961–1989 (“dimming” stage), while it increases at the rate of 5.34 MJ/m2·a for 1990–2016 (“brightening” period). In addition, all seasons show a tendency of dimming first and then brightening except for autumn. Compared with SD, SR is more sensitive to changes in pollution, leading to a marked recovery with the reduction of pollution after the 1990s. This study provides a new perspective for the trend difference between SR and SD after the 1990s.

Influence of mixing height and atmospheric stability conditions on correlation of NO2 columns and surface concentrations in a Mexico‐United States border region

AbstractThe objective was to analyze how representative tropospheric NO2 column densities are of surface NO2 measurements under different atmospheric stability conditions in the air basin of two border cities: Calexico, United States, and Mexicali, Mexico. NO2 columns were measured by the Ozone Monitoring Instrument (OMI) on the NASA Aura satellite. NO2 concentrations and meteorological parameters were also measured on the surface for comparison. Specifically, the correlations between OMI and surface NO2 concentrations under different atmospheric stability conditions according to the Pasquill‐Gifford (P‐G) and Monin‐Obukhov (M‐O) classification schemes were determined for 2017 and 2018. During the passage of the satellite through the study area (11:00–13:00 UTC−8), unstable conditions were documented in both years. Good correlation was found between the surface NO2 and OMI NO2 column observations in the second semester of each year, particularly under unstable conditions as diagnosed by the P‐G and M‐O schemes applied in the first and second year, respectively. However, a weakening of these conditions occurs during the autumn–winter period. In both cases, the highest determination coefficients were found for Calexico, with values of 0.48 and 0.36 in 2017 and 2018, respectively; for Mexicali, the determination coefficients were 0.23 and 0.35, respectively. Under each atmospheric stability scheme, the mechanical and convective turbulence caused a decreasing trend in wind speed and solar radiation over the course of second semester of 2017 and in friction velocity, temperature, and sensible heat flux over the course of the same period for 2018. The negative trend of these parameters during the analyzed time frames helped to reduce the influence of unstable atmospheric conditions, favoring better correlations between satellite and surface NO2 measurements. The methodology applied and results obtained herein can enable us to better understand the representativeness of OMI NO2 data in arid border zones with extreme meteorological conditions.

TREND ANALYSIS OF EVAPORATION AND SOLAR RADIATION USING INNOVATIVE TREND ANALYSIS METHOD

Analysis of trends in monthly evaporation and solar radiation in the face of climate change gives useful information for better planning and management of water resources. This paper examines the monthly evaporation and solar radiation trend using the recently developed innovative trend analysis method (ITAM). The monthly evaporation trend result shown that 75% of the months indicated decreasing trend with the month of February, March, August and April decreased significant at 0.1%, 10%, 10% and 5% significance level respectively. As regards solar radiation all the months indicated decreasing trend with January, July and October shown a decreasing trend at 5% significant level. By comparing the Mann-Kendall method with the ITAM the reliability of ITAM was ascertained. Hence, ITAM can be effectively utilized in climate change scenarios where useful information is needed for accurate management and planning of water resources.

Decadal Changes in Soil and Atmosphere Temperature Differences Linked With Environment Shifts Over Northern Eurasia

AbstractThe difference between soil and air temperatures (ΔT) in a specified time is dependent on meteorological conditions, properties of soil and land covers. Understanding ΔT is critical in assessing land–atmosphere thermal interactions in changing environment. However, systematic knowledge of interannual variations and responses of ΔT to the environmental changes (e.g., snow cover and soil moisture) at decadal scales remain limited. Here, variations of the mean annual air and soil temperatures, and ΔT were investigated at 217 sites in northern Eurasia during 1981–2015. It is found that changes in the mean annual air and soil temperatures were inconsistent as the average increase in soil temperature was generally less than that of air. The relationships between trends in soil and air temperatures were significant in the upper ground (0.2 and 0.8 m) over the seasonal frost region but insignificant in the permafrost regions and deeper ground. During the period, widespread changes in ΔT occurred and closely responded to the environmental changes, but the relationships varied with soil depth. Among the tested factors, trends in snow cover thickness dominantly control trends in ΔT, followed by trends in snow cover duration and solar radiation. Both linear and nonlinear analyses indicate enhanced relationships between trends in snow depth and ΔT as depth increases. This study provides the first view of decadal trends in ΔT and conjunctions with the environmental changes during 1981–2015 over northern Eurasia. The findings are relevant to quantify land–atmosphere thermal interactions given impacts of future environmental changes.

Potential Driving Factors on Surface Solar Radiation Trends over China in Recent Years

The annual mean surface solar radiation (SSR) trends under all-sky, clear-sky, all-sky-no-aerosol, and clear-sky-no-aerosol conditions as well as their possible causes are analyzed during 2005–2018 across China based on different satellite-retrieved datasets to determine the major drivers of the trends. The results confirm clouds and aerosols as the major contributors to such all-sky SSR trends over China but play differing roles over sub-regions. Aerosol variations during this period result in a widespread brightening, while cloud effects show opposite trends from south to north. Moreover, aerosols contribute more to the increasing all-sky SSR trends over northern China, while clouds dominate the SSR decline over southern China. A radiative transfer model is used to explore the relative contributions of cloud cover from different cloud types to the all-types-of-cloud-cover-induced (ACC-induced) SSR trends during this period in four typical sub-regions over China. The simulations point out that the decreases in low-cloud-cover (LCC) over the North China Plain are the largest positive contributor of all cloud types to the marked annual and seasonal ACC-induced SSR increases, and the positive contributions from both high-cloud-cover (HCC) and LCC declines in summer and winter greatly contribute to the ACC-induced SSR increases over East China. The contributions from medium-low-cloud-cover (mid-LCC) and LCC variations dominate the ACC-caused SSR trends over southwestern and South China all year round, except for the larger HCC contribution in summer.

From dimming to brightening during 1961 to 2014 in the maize growing season of China

AbstractClimate patterns, cropping systems, and agricultural technologies have greater diversity among various regions in China. Knowledge of the spatial–temporal patterns of solar radiation during the maize growing season is essential for farmers and extension technicians in their optimization of cropping choices and development of adaptation strategies for climate change. In this study, based on the observed solar radiation in six subregions of China, we analyzed the spatial distributions and temporal trends of incident solar radiation (SRi), beam solar radiation (SRb), and diffuse solar radiation (SRd) during 1961–2014. From 1961 to 1984, the annual SRi in most areas showed a downward trend, with a median value of −27.8 MJ m−2 year−1, which is primarily due to a decrease in SRb. However, after 1985, 76% of locations had reversed to brightening. This finding is primarily due to an increase in SRd. The trends in SRi during the whole growing season (WGS) of maize changed by −12.4% to 18.3% during the past 30 years, and 74% of the selected locations showed an increasing trend. At most of the stations, SRb showed a decreasing trend during the WGS, and SRd showed an increasing trend. The trends of SRi, SRb, and SRd during the vegetative period and reproductive period of maize have generally followed a trend similar to the WGSs. Therefore, we conclude that annual solar radiation changed from dimming to brightening from 1961 to 2014 in China. Solar brightening occurred during the maize growing season, which was mainly caused by an increase in diffuse radiation.

Impact of Urbanization on Sunshine Duration from 1987 to 2016 in Hangzhou City, China

Worldwide solar dimming from the 1960s to the 1980s has been widely recognized, but the occurrence of solar brightening since the late 1980s is still under debate—particularly in China. This study aims to properly examine the biases of urbanization in the observed sunshine duration series from 1987 to 2016 and explore the related driving factors based on five meteorological stations around Hangzhou City, China. The results inferred a weak and insignificant decreasing trend in annual mean sunshine duration (−0.09 h/d decade−1) from 1987 to 2016 in the Hangzhou region, indicating a solar dimming tendency. However, large differences in sunshine duration changes between rural, suburban, and urban stations were observed on the annual, seasonal, and monthly scales, which can be attributed to the varied urbanization effects. Using rural stations as a baseline, we found evident urbanization effects on the annual mean sunshine duration series at urban and suburban stations—particularly in the period of 2002–2016. The effects of urbanization on the annual mean sunshine duration trends during 1987−2016 were estimated to be −0.16 and −0.35 h/d decade−1 at suburban and urban stations, respectively. For urban stations, the strongest urbanization effect was observed in summer (−0.46 h/d decade−1) on the seasonal scale and in June (−0.63 h/d decade−1) on the monthly scale. The notable negative impact of urbanization on local solar radiation changes was closely related to the changes in anthropogenic pollutions, which largely reduced the estimations of solar radiation trends in the Hangzhou region. This result highlights the necessity to carefully consider urbanization impacts when analyzing the trend in regional solar radiation and designing cities for sustainable development.

Impact of global dimming/brightening on estimating Angström-Prescott parameters based on geographically weighted regression in China

Variations of solar radiation is related to energy planning and architectural designing. It is important to estimate solar radiation from other climate factors because of the limited measurement solar radiation data. In this study, temporospatial changes of solar radiation and sunshine hour are analysed for global dimming/brightening periods based on meteorological data in China. Results show that the trends of solar radiation and sunshine hour are both decreasing dramatically for 1961–1990 (the global dimming period) but levelling off for 1991–2010 (the global brightening period), which indicates that sunshine hour can be used the reliable indicator of solar radiation. Spatially, the change trends of solar radiation are consistent with sunshine hour in 36 stations during the period of 1961–1990, but they are consistent in just 27 stations during the period of 1991–2010. To assess the impact of changing solar radiation on Angstrom-Prescott parameters (a and b) in the equation of solar radiation estimation from sunshine hour, geographically weighted regression is developed to calculate a and b. There is not dramatic difference in the spatial patterns of a and b for the period of 1961–2010 and 1961–1990. However, there is significantly inconsistent changes in a and b during the global brightening period compared with the global dimming period, which suggests that global dimming/brightening has important impact on estimating solar radiation from sunshine hour, with dramatic variability among different regions.

Surface Brightening in Eastern and Central China Since the Implementation of the Clean Air Action in 2013: Causes and Implications

AbstractSurface brightening has been observed in China since 2005. However, it remains unclear whether the brightening has accelerated recently in response to the strictest ever air pollution control policies since 2013. By combining intensive surface and satellite observations, we find an unprecedented rapid increasing trend in surface solar radiation (SSR) of 0.70–1.16 W m−2 yr−1 over the eastern and central China for 2014–2019. Using a novel method to identify the relative contributions of aerosol and cloud radiative effects to the SSR trends, we find that the strongly declining aerosol radiative effect due to the strict air pollution controls is the main cause of the upward SSR trends; cloud variations should not be the main reason. Distinction exists in seasonal trends of SSR, with decreasing trends in winter and increasing trends in other seasons. Air pollution controls play an important role in regulating SSR, which has valuable implications for photovoltaic power generation.