Changes In Surface Solar Radiation Research Articles

How strong are the links between global warming and surface solar radiation changes?

How strong are the links between global warming and surface solar radiation changes?

Impact of renewed solar dimming on streamflow generation in monsoon dominated tropical river basins

From 1950s to 1980s, various observational studies around the globe found a significant decrease in surface solar radiation (SSR), which reversed in late 1980s for most of the countries including India. SSR observations at 12 stations located across India revealed that a much stronger dimming has reappeared during the last decade (2006–2015) after a brightening during 1996–2005. In the present study, effects of renewed solar dimming on actual evapotranspiration and runoff were analyzed using a semi-distributed hydrological model, Soil and Water Assessment Tool (SWAT) in 24 river basins (ranging from 1260 to 40000 km2) located in peninsular India. For these river basins, calibration (2003–2009) and validation (2010–2014) were performed using the observed daily discharge data, obtained from water resources information system (WRIS) of India, with a 3 year warm up period (2000–2002). The sequential uncertainty domain parameter fitting algorithm (SUFI-2) of SWAT-CUP (calibration and uncertainty program) was used with modified Nash–Sutcliffe efficiency (MNS) as the objective function to calibrate 13 model parameters, which can potentially affect streamflow. In nearly all the river basins, the p- and r-factor of 95 percentage prediction uncertainty (PPU) were more than 0.7 and less than 1, respectively. At daily timescale, MNS values were more than 0.5 in most of the river basins, reaching up to 0.66 and 0.71 during calibration and validation periods, respectively. Calibrated model was used to analyze the water balance of these river basins and different sets of experiments (with observed SSR trends) were performed to find SSR impacts on it. The model was simulated with and without the observed declines in SSR trends. The average change in SSR (in terms of evaporation equivalent) was −267.93 ± 100.92 mm/day/year (−5.62 ± 2.12%) with maximum reaching up to −417.12 mm/day/year (−8.99%). Due to this SSR change, actual evaporation was reduced resulting in 18.97 ± 9.78 mm/day/year (4.13 ± 2.50%) change in percolation. The percolation changes were higher for river basins having areas covered by forests and cropland/woodland, and having loam and sandy-clay soils. The increase in runoff generated was 6.90 ± 3.42 mm/day/year (2.14 ± 1.58%) with a maximum of 15.25 mm/day/year (7.56%) whereas corresponding increase in streamflow was found to be 9.93 ± 5.27 mm/day/year(4.21 ± 2.38%) with a maximum of 26.71 mm/day/year (11.86 %). The study reveals that the recent observed SSR changes are significant enough to have resulted in increased streamflow in the monsoon dominated tropical river basins of India.

Hourly Surface Observations Suggest Stronger Solar Dimming and Brightening at Sunrise and Sunset Over China

AbstractExploration of the diurnal pattern of global dimming and brightening has been limited by the paucity of high‐temporal resolution observations. Based on 22 years’ continuous observations of hourly surface solar radiation (SSR) over 96 stations across China for 1993–2014, this study evidences higher relative changes in diurnal SSR in terms of both frequency and magnitude at sunrise and sunset, with a longer pathway for the sun passing through the atmosphere, than the hours in between. This, in general, leads to a further shortening of the days between sunrise and sunset in the cold seasons and the polluted region of north China with low radiation levels but a further extension in the other seasons and regions with sufficient sunlight. Pollution reduction by 39.4%–69.7% during the 2014 Asia‐Pacific Economic Cooperation summit at Beijing are accompanied with a 10.4–80.0% rebound of diurnal SSR in the forenoon and late afternoon.

PROJECTION OF INCIDENT SURFACE SOLAR RADIATION IN CHINA UNDER A CLIMATE CHANGE SCENARIO

Abstract. We projected incident surface solar radiation (SSR) over China in the middle (2040–2059) and end (2080–2099) of the 21st century in the Representative Concentration Pathway (RCP) 8.5 scenario using a multi-model ensemble derived from the weighted average of seven global climate models (GCMs). The multi-model ensemble captured the contemporary (1979–2005) spatial and temporal characteristics of SSR and reproduced the long-term temporal evolution of the mean annual SSR in China. However, it tended to overestimate values compared to observations due to the absence of aerosol effects in the simulations. The future changes in SSR showed increases over eastern and southern China, and decreases over the Tibetan Plateau (TP) and northwest China relative to the present day. At the end of the 21st century, there were SSR increases of 9–21 W m−2 over northwest, central, and south China, and decreases of 18–30 W m−2 over the TP in June–July–August (JJA). In northeast China, SSR showed seasonal variation with increases in JJA and decreases in December–January–February. The time series of annual SSR had a decreased linear trend for the TP, and a slightly increased trend for China during 2006–2099. The results of our study suggest that solar energy resources will likely decrease in the TP under future climate change scenarios.

Causes of Dimming and Brightening in China Inferred from Homogenized Daily Clear-Sky and All-Sky in situ Surface Solar Radiation Records (1958–2016)

AbstractThis paper presents a study on long-term surface solar radiation (SSR) changes over China under clear- and all-sky conditions and analyzes the causes of the “dimming” and “brightening.” To eliminate the nonclimatic signals in the historical records, the daily SSR dataset was first homogenized using quantile-matching (QM) adjustment. The results reveal rapid dimming before 2000 not only under all-sky conditions, but also under clear-sky conditions, at a decline rate of −9.7 ± 0.4 W m−2 decade−1 (1958–99). This is slightly stronger than that under all-sky conditions at −7.4 ± 0.4 W m−2 decade−1, since the clear-sky dimming stopped 15 years later. A rapid “wettening” of about 40-Pa surface water vapor pressure (SWVP) from 1985 to 2000 was found over China. It contributed 2.2% to the SSR decline under clear-sky conditions during the whole dimming period (1958–99). Therefore, water vapor cannot be the main cause of the long-term dimming in China. After a stable decade (1999–2008), an intensive brightening appeared under the clear-sky conditions at a rate of 10.6 ± 2.0 W m−2 decade−1, whereas a much weaker brightening (−0.8 ± 3.1 W m−2 decade−1) has been observed under all-sky conditions between 2008 and 2016. The remarkable divergence between clear- and all-sky trends in recent decades indicates that the clouds played two opposite roles in the SSR changes during the past 30 years, by compensating for the declining SSR under the cloud-free conditions in 1985–99 and by counteracting the increasing SSR under cloud-free conditions in 2008–16. Aerosols remain as the main cause of dimming and brightening over China in the last 60 years, although the clouds counteract the effects of aerosols after 2000.

Projections of future changes in solar radiation in China based on CMIP5 climate models

Surface solar radiation research is important for understanding future climate change and the application of large-scale photovoltaic systems. We used the coupled model intercomparison project phase 5 (CMIP5) under the RCP8.5 scenario to project potential changes in surface solar radiation, surface temperatures, and cloud fractions between 2006 and 2049 in China, as well as how these changes may affect photovoltaic power generation. The results show that the following. (1) For surface temperatures, the median trends of all considered models show warming in China of 0.05 K/year. The maximum positive trends for all-sky radiation appear in the southeast of China, reaching 0.4 W/m2/year. Cloud cover exhibits a mainly decreasing trend in the overall region of China. (2) The all-sky radiation of most selected regions shows a decreasing trend. The maximum negative value (−0.08 W/m2/year) appears in Qinghai. (3) Compared with the average photovoltaic power output from 2006 to 2015, the photovoltaic power output in western China will decrease by −0.04 %/ year, while photovoltaic power output in southeastern China will increase by 0.06–0.1%/year.

Solar “brightening” impact on summer surface ozone between 1990 and 2010 in Europe – a model sensitivity study of the influence of the aerosol–radiation interactions

Abstract. Surface solar radiation (SSR) observations have indicated an increasing trend in Europe since the mid-1980s, referred to as solar “brightening”. In this study, we used the regional air quality model, CAMx (Comprehensive Air Quality Model with Extensions) to simulate and quantify, with various sensitivity runs (where the year 2010 served as the base case), the effects of increased radiation between 1990 and 2010 on photolysis rates (with the PHOT1, PHOT2 and PHOT3 scenarios, which represented the radiation in 1990) and biogenic volatile organic compound (BVOC) emissions (with the BIO scenario, which represented the biogenic emissions in 1990), and their consequent impacts on summer surface ozone concentrations over Europe between 1990 and 2010. The PHOT1 and PHOT2 scenarios examined the effect of doubling and tripling the anthropogenic PM2.5 concentrations, respectively, while the PHOT3 investigated the impact of an increase in just the sulfate concentrations by a factor of 3.4 (as in 1990), applied only to the calculation of photolysis rates. In the BIO scenario, we reduced the 2010 SSR by 3 % (keeping plant cover and temperature the same), recalculated the biogenic emissions and repeated the base case simulations with the new biogenic emissions. The impact on photolysis rates for all three scenarios was an increase (in 2010 compared to 1990) of 3–6 % which resulted in daytime (10:00–18:00 Local Mean Time – LMT) mean surface ozone differences of 0.2–0.7 ppb (0.5–1.5 %), with the largest hourly difference rising as high as 4–8 ppb (10–16 %). The effect of changes in BVOC emissions on daytime mean surface ozone was much smaller (up to 0.08 ppb, ∼ 0.2 %), as isoprene and terpene (monoterpene and sesquiterpene) emissions increased only by 2.5–3 and 0.7 %, respectively. Overall, the impact of the SSR changes on surface ozone was greater via the effects on photolysis rates compared to the effects on BVOC emissions, and the sensitivity test of their combined impact (the combination of PHOT3 and BIO is denoted as the COMBO scenario) showed nearly additive effects. In addition, all the sensitivity runs were repeated on a second base case with increased NOx emissions to account for any potential underestimation of modeled ozone production; the results did not change significantly in magnitude, but the spatial coverage of the effects was profoundly extended. Finally, the role of the aerosol–radiation interaction (ARI) changes in the European summer surface ozone trends was suggested to be more important when comparing to the order of magnitude of the ozone trends instead of the total ozone concentrations, indicating a potential partial damping of the effects of ozone precursor emissions' reduction.

Impacts of 3D Aerosol, Cloud, and Water Vapor Variations on the Recent Brightening during the South Asian Monsoon Season

South Asia is experiencing a levelling-off trend in solar radiation and even a transition from dimming to brightening. Any change in incident solar radiation, which is the only significant energy source of the global ecosystem, profoundly affects our habitats. Here, we use multiple observations of the A-Train constellation to evaluate the impacts of three-dimensional (3D) aerosol, cloud, and water vapor variations on the changes in surface solar radiation during the monsoon season (June–September) in South Asia from 2006 to 2015. Results show that surface shortwave radiation (SSR) has possibly increased by 16.2 W m−2 during this period. However, an increase in aerosol loading is inconsistent with the SSR variations. Instead, clouds are generally reduced and thinned by approximately 8.8% and 280 m, respectively, with a decrease in both cloud water path (by 34.7 g m−2) and particle number concentration under cloudy conditions. Consequently, the shortwave cloud radiative effect decreases by approximately 45.5 W m−2 at the surface. Moreover, precipitable water in clear-sky conditions decreases by 2.8 mm (mainly below 2 km), and related solar brightening increases by 2.5 W m−2. Overall, the decreases in 3D water vapor and clouds distinctly result in increased absorption of SSR and subsequent surface brightening.

Numerical simulation of surface solar radiation over Southern Africa. Part 1: Evaluation of regional and global climate models

In the second part of this study, possible impacts of climate change on Surface Solar Radiation (SSR) in Southern Africa (SA) are evaluated. We use outputs from 20 regional climate simulations from five Regional Climate Models (RCM) that participate in the Coordinated Regional Downscaling Experiment program over the African domain (CORDEX-Africa) along with their 10 driving Global Climate Models (GCM) from the Coupled Model Intercomparison Project Phase 5 (CMIP5). Multi-model mean projections of SSR trends are consistent between the GCMs and their nested RCMs. However, this consistency is not found for each GCM/RCM setup. Over the centre of SA, GCMs and RCMs project a statistically significant increase in SSR by 2099 of about + 1 W/m2 per decade in RCP4.5 (+ 1.5 W/m2 per decade in RCP8.5) during the DJF season in their multi-model means. Over Eastern Equatorial Africa (EA-E) a statistically significant decrease in SSR of about − 1.5 W/m2 per decade in RCP4.5 (− 2 W/m2 per decade in RCP8.5) is found in the ensemble means in DJF, whereas in JJA SSR is predicted to increase by about + 0.5 W/m2 per decade under RCP4.5 (+ 1 W/m2 per decade in RCP8.5). SSR projections are fairly similar between RCP8.5 and RCP4.5 before 2050 and then the differences between those two scenarios increase up to about 1 W/m2 per decade with larger changes in RCP8.5 than in RCP4.5 scenario. These SSR evolutions are generally consistent with projected changes in Cloud Cover Fraction over SA and may also related to the changes in atmosphere water vapor content. SSR change signals emerge earlier out of internal variability estimated from reanalyses (European Centre for Medium-Range Weather Forecasts Reanalysis ERA-Interim, ERAIN) in DJF in RCMs than in GCMs, which suggests a higher sensitivity of RCMs to the forcing RCP scenarios than their driving GCMs in simulating SSR changes. Uncertainty in SSR change projections over SA is dominated by the internal climate variability before 2050, and after that model and scenario uncertainties become as important as internal variability until the end of the 21st century.

Long-term series and trends in surface solar radiation in Athens, Greece

Abstract. We present a long-term series of surface solar radiation (SSR) from the city of Athens, Greece. SSR measurements were performed from 1954 to 2012, and before that (1900–1953) sunshine duration (SD) records were used in order to reconstruct monthly SSR. Analysis of the whole data set (1900–2012) mainly showed very small (0.02 %) changes in SSR from 1900 to 1953, including a maximum decrease of −2.9 % decade−1 in SSR during the 1910 to 1940 period, assuming a linear change. For the dimming period 1955–1980, −2 % decade−1 was observed that matches various European long-term SSR-measurement-related studies. This percentage in Athens is in the lower limit, compared to other studies in the Mediterranean area. For the brightening period 1980–2012 we calculated +1.5 % decade−1, which is also in the lower limit of the reported positive changes in SSR around Europe. Comparing the 30-year periods 1954–1983 and 1983–2012, we found a difference of 4.5 %. However, measurements of the first 30-year period are associated with higher uncertainties than those of the second period, especially when looking at year-to-year changes. The difference between the two periods was observed for all seasons except winter. Analyzing SSR calculations of all-sky and clear-sky (cloudless) conditions/days, we report that most of the observed changes in SSR after 1954 can be attributed partly to cloudiness and mostly to aerosol load changes.

Projected changes in surface solar radiation in CMIP5 global climate models and in EURO-CORDEX regional climate models for Europe

The objective of the present work is to compare the projections of surface solar radiation (SSR) simulated by four regional climate models (CCLM, RCA4, WRF, ALADIN) with the respective fields of their ten driving CMIP5 global climate models. First the annual and seasonal SSR changes are examined in the regional and in the global climate models based on the RCP8.5 emission scenarios. The results show significant discrepancies between the projected SSR, the multi-model mean of RCMs indicates a decrease in SSR of −0.60 W/m2 per decade over Europe, while the multi-model mean of the associated GCMs used to drive the RCMs gives an increase in SSR of +0.39 W/m2 per decade for the period of 2006–2100 over Europe. At seasonal scale the largest differences appear in spring and summer. The different signs of SSR projected changes can be interpreted as the consequence of the different behavior of cloud cover in global and regional climate models. Cloudiness shows a significant decline in GCMs with −0.24% per decade which explains the extra income in SSR, while in case of the regional models no significant changes in cloudiness can be detected. The reduction of SSR in RCMs can be attributed to increasing atmospheric absorption in line with the increase of water vapor content. Both global and regional models overestimate SSR in absolute terms as compared to surface observations, in line with an underestimation of cloud cover. Regional models further have difficulties to adequately reproduce the observed trends in SSR over the past decades.

Correlative Analysis of the Relationship between Changes in Surface Solar Radiation and Haze pollution (Atmospheric Turbidity Index) in Beijing from 1961 to 2011*

<div> <p>Increased aerosol or haze is the reason that solar radiation decreases, but there is no evidence to support this theory. This research aims to quantitatively analyze the contribution of air pollution to surface solar radiation (SSR) reduction in Beijing. Because there is no long-term serial ground observational aerosol data, in order to reflect the atmospheric pollution and aerosol levels, we developed an atmospheric turbidity index (ATI).Monthly and annual variations in the ATI are significantly correlated with aerosol optical depth (AOD), and ATI could well reflect the change of air pollution. The ATI and SSR are significantly negatively correlated. The changes in the Beijing SSR presented a clear decreasing trend. From the inter-annual variability, the SSR exhibited a rapidly declining trend from 1960 to approximately1990 and a gradual increasing trend after 1990. The atmosphere turbidity index in the Beijing area was the main factor which indicated the change in SSR.</p> </div> <p> </p>

Mixed‐layer ocean responses to anthropogenic aerosol dimming from 1870 to 2000

AbstractIt is debated to what extent surface solar radiation (SSR) changes through varying anthropogenic aerosol emissions since industrialization affected surface temperatures (tsurf). We use mixed‐layer ocean experiments with the general circulation model ECHAM6.1 and explicit aerosols (HAM2.2) to identify regions where this effect is discernible. For each decade from 1870 to 2000 we derive three equilibria: anthropogenic aerosol emissions and greenhouse gas concentrations at the respective decade's levels (ALL), either aerosols or greenhouse gases fixed at year 1850 levels (GHG and AERO). We duplicated parts of the experiments with different prescribed divergence of ocean heat transport (Q_ALL, Q_AERO, and Q_GHG). Comparing year 2000 with year 1870 equilibria, we find global average cooling of −1.4 K for AERO and warming of 1.4 K for GHG. ALL and Q_ALL warm by 0.6 K and 0.4 K, respectively. The way divergence of ocean heat transport is prescribed thus matters. Pattern correlations of year 2000 tsurf responses in ALL with the sum of AERO and GHG are higher (0.88) than with Q_ALL (0.71) confirming additivity of global patterns, but not of global means. The imprint of anthropogenic aerosols on tsurf response patterns in ALL is distinct, thus potentially detectable. Over the decades, ocean fractions affected by either changing aerosol optical depth or all‐sky SSR vary in concert, supporting linkage between anthropogenic aerosols and all‐sky SSR. SSR changes and tsurf responses are marginally collocated. Oceanic regions with strongest tsurf response to aerosol‐induced SSR changes are the northern midlatitudes and North Pacific with tsurf sensitivities up to −0.7 K W m−2 SSR change.

Changes in surface solar radiation in Northeastern Spain over the past six centuries recorded by tree-ring δ13C

Although solar radiation at the surface plays a determinant role in carbon discrimination in tree rings, stable carbon isotope chronologies (δ13C) have often been interpreted as a temperature proxy due to the co-variability of temperature and surface solar radiation. Furthermore, even when surface solar radiation is assumed to be the main driver of 13C discrimination in tree rings, δ13C records have been calibrated against sunshine duration or cloud cover series for which longer observational records exists. In this study, we use different instrumental and satellite data over northeast Spain (southern Europe) to identify the main driver of tree-ring 13C discrimination in this region. Special attention is paid to periods in which the co-variability of those climate variables may have been weaker, such as years after large volcanic eruptions. The analysis identified surface solar radiation as the main driver of tree-ring δ13C changes in this region, although the influence of other climatic factors may not be negligible. Accordingly, we suggest that a reconstruction of SSR over the last 600 years is possible. The relation between multidecadal variations of an independent temperature reconstruction and surface solar radiation in this region shows no clear sign, and warmer (colder) periods may be accompanied by both higher and lower surface solar radiation. However, our reconstructed records of surface solar radiation reveals a sunnier Little Ice Age in agreement with other δ13C tree-ring series used to reconstruct sunshine duration in central and northern Europe.

Projections of long-term changes in solar radiation based on CMIP5 climate models and their influence on energy yields of photovoltaic systems

Traditionally, for the planning and assessment of solar energy systems, the amount of solar radiation (sunlight) incident on the Earth’s surface is assumed to be constant over the years. However, with changing climate and air pollution levels, solar resources may no longer be stable over time and undergo substantial decadal changes. Observational records covering the past decades confirm long-term changes in this quantity. Here we examine how the latest generation of climate models used for the 5th IPCC report projects potential changes in surface solar radiation over the coming decades, and how this may affect, in combination with the expected greenhouse warming, solar power output from photovoltaic (PV) systems. For this purpose, projections up to the mid 21st century from 39 state of the art climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) are analysed globally and for selected key regions with major solar power production capacity. The large model ensemble allows to assess the degree of consistency of their projections. Models are largely consistent in the sign of the projected changes in solar radiation under cloud-free conditions as well as surface temperatures over most of the globe, while still reasonably consistent over a considerable part of the globe in the sign of changes in cloudiness and associated changes in solar radiation. A first order estimate of the impact of solar radiation and temperature changes on energy yields of PV systems under the RPC8.5 scenario indicates statistically significant decreases in PV outputs in large parts of the world, but notable exceptions with positive trends in large parts of Europe, South-East of North America and the South-East of China. Projected changes between 2006 and 2049 under the RCP8.5 scenario overall are on the order of 1%/decade for horizontal planes, but may be larger for tilted or tracked planes as well as on shorter (decadal) timescales.

The effect of aerosols and sea surface temperature on China's climate in the late twentieth century from ensembles of global climate simulations

AbstractOver the late twentieth century, China has seen a strong increase in aerosol emissions, whose quantitative role for observed changes in surface solar radiation (SSR), surface air temperature (SAT), and precipitation remains debated. We use ensembles of transient sensitivity experiments with the global climate model ECHAM5 from the Max Planck Institute for Meteorology, Hamburg, Germany, combined with the Hamburg Aerosol Module to examine the effect of aerosols and prescribed, observation‐based sea surface temperatures (SSTs) on the above variables. Observations and control experiments agree reasonably well in eastern China in terms of SSR dimming (−6 ± 2 W/m2/decade, 1960–2000; stronger than in models of the Coupled Model Intercomparison Project Phase 5, CMIP5), statistically nonsignificant summer SAT trend (1950–2005), and drying in summer from 1950 to 1990 (−2.5% to −3.5% per decade, essentially via reduction of convective precipitation). Other observed features are not reproduced by the model, e.g., precipitation increase in the 1990s in the Yangtze River valley or, from the 1960s onward, the strong winter warming in northern China and Mongolia and SSR dimming in western China. Aerosol effects are stronger for sulfur dioxide than for black and organic carbon and are more pronounced at lower model resolution. Transient SSTs are crucial for decadal‐scale SAT variability over land, especially the strong warming in the 1990s, and, via SST forced reduction of cloud cover, for the ceasing of SSR dimming around the year 2000. Unforced cloud variability leads to relevant scatter (up to ±2 W/m2/decade) of modeled SSR trends at individual observation sites.

Yearly changes in surface solar radiation in New Caledonia

Abstract. New Caledonia experiences a decrease in surface solar irradiation since 2004. It is of order of 4% of the mean yearly irradiation over the 10 years period: 2004–2013, and amounts to −9 W m−2. The preeminent roles of the changes in cloud cover and to a lesser extent, those in aerosol optical depth on the decrease in yearly irradiation are evidenced. The study highlights the role of data sets offering a worldwide coverage in understanding changes in solar radiation and planning large solar energy plants such as the ICOADS (International Comprehensive Ocean-Atmosphere Data Set) of the NOAA and MACC (Monitoring Atmosphere Composition and Climate) data sets combined with the McClear model.

Impact of land use/land cover change on changes in surface solar radiation in eastern China since the reform and opening up

Observational evidence of the impacts of land use/land cover change (LULCC) on changes in surface solar radiation (SSR) in eastern China (EC) during 1979–2008 are identified by using diurnal temperature range as a proxy of SSR and by using observation minus reanalysis approach to disentangle these effects. For the period 1979–2008, the impact of LULCC is shown as a reduction in SSR in most stations in EC, whereas SSR in the reanalysis data has increased at nearly every location. The competition of the dimming effect of LULCC with the brightening effect in the reanalysis results in an observed dipole pattern of SSR with slightly decreasing (increasing) trends in most stations north (south) of the Yangtze River and statistically significant decreasing trends in central EC. In terms of EC area mean, this competition has resulted in a slightly dimming trend in the observed SSR during 1979–2008, although a transition from an apparent dimming to a general leveling off near 1990 is identified. For the period 1990–2008, LULCC has significantly reduced SSR in central EC and southern China. This dimming effect of LULCC competes with the apparent brightening effect in the reanalysis to result in the general leveling off in the observed SSR in terms of EC area mean and a sandwich spatial pattern in the observed SSR in EC where parts of central EC show significant dimming. The impact of LULCC on the changes in SSR may be through both biogeophysical and biogeochemical processes.

Long-term changes in surface solar radiation and their effects on air temperature in the Shanghai region

Various studies that analyze long-term records of surface radiation measurements have noted a widespread decrease in the downward surface solar radiation (SSR) between the 1950s and 1980s and a more recent partial recovery at many locations. However, few studies have assessed the relative contribution of diffuse and direct radiation to the variations in air temperature. To examine the phenomenon in which varying direct/diffuse radiation contributes to the warming trend in Shanghai, the daily radiation and air temperature data for Shanghai region were collected and analyzed. Our results indicated that the variation in SSR in the Shanghai region was mainly induced by the variation in direct radiation during 1961–2013. Global dimming occurred in the Shanghai region in all four seasons before the 1980s; however, brightening only occurred in the Shanghai region during spring after the 1990s due to the decreasing cloud coverage. Direct radiation was negatively correlated to cloud coverage in all four seasons and was significantly negatively correlated to human activities (air pollution), while diffuse radiation was strongly positively correlated to human activities and only related to cloud coverage in spring. These results suggest that moderate air pollution might lead to maximized diffuse radiation in the Shanghai region. Direct radiation was the major contributor to the air temperature in spring, summer and autumn before the 1980s. However, since the 1980s, the contribution of diffuse radiation to air temperature has exceeded that of direct radiation. In addition, direct radiation has only slightly mediated the minimum air temperature at night, particularly in spring and autumn. We infer that the contribution of diffuse radiation to the air temperature in the Shanghai region might occur through the warming effects of aerosols (e.g., black carbon), a type of air pollution caused by human activities, such as traffic, wood-based cooking and biomass burning.

The near future availability of photovoltaic energy in Europe and Africa in climate-aerosol modeling experiments

Abstract The near future change in productivity of photovoltaic energy (PVE) in Europe and Africa is assessed by using the climate variables simulated by the ECHAM5-HAM aerosol-climate model, and a model for the performance of photovoltaic systems. The climate simulations are forced by green-house gases emissions from the IPCC SRES B2 scenario. In addition, different scenarios for future anthropogenic aerosols emissions are applied. Thus, the sensitivity of the future PVE productivity to changes in aerosol atmospheric burdens between 2000 and 2030 is analyzed. The analysis indicates that reductions in aerosols emissions in the near future result in an increase of global warming, and a significant response in surface solar radiation and associated PVE productivity. A statistically significant reduction in PVE productivity up to 7% is observed in eastern Europe and northern Africa, while a significant increase up to 10% is observed in western Europe and eastern Mediterranean. The changes in surface solar radiation and PVE productivity are related to global effects of aerosols reduction on the large scale circulation and associated cloud cover pattern, rather than to local effects on the atmospheric optical properties. PVE assessment is then discussed in the frame of the present situation and next decades evolution of the photovoltaic market, highlighting that the effects on productivity induced by industrial and public policies, and technological development are comparable to climate related effects. The presented results encourage the improvement and further use of climate models in assessment of future renewable energies availability.