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Surface solar radiation is fundamental for terrestrial life. It provides warmth to make our planet habitable, drives atmospheric circulation, the hydrological cycle and photosynthesis. Europe has experienced an increase in surface solar radiation, termed "brightening," since the 1980s. This study investigates the causative factors behind this brightening. A novel algorithm from the EUMETSAT satellite application facility on climate monitoring (CM SAF) provides the unique opportunity to simulate surface solar radiation under various atmospheric conditions for clouds (clear‐sky or all‐sky), aerosol optical depth (time‐varying or climatological averages) and water vapor content (with or without its direct influence on surface solar radiation). Through a multiple linear regression approach, the study attributes brightening trends to changes in these atmospheric parameters. Analyzing 61 locations distributed across Europe from 1983 to 2020, aerosols emerge as key driver during 1983–2002, with Southern Europe and high elevations showing subdued effects (0%/decade–1%/decade) versus more pronounced impacts in Northern and Eastern Europe (2%/decade–6%/decade). Cloud effects exhibit spatial variability, inducing a negative effect on surface solar radiation (−3%/decade–−2%/decade) at most investigated locations in the same period. In the period 2001–2020, aerosol effects are much smaller, while cloud effects dominate the observed brightening (2%/decade–5%/decade). This study therefore finds a substantial decrease in the cloud radiative effect over Europe in the first two decades of the 21st century. Water vapor exerts negligible influence in both sub‐periods. Plain Language Summary: This study explores the recent increase in surface solar radiation in Europe, commonly referred to as "brightening," which began in the mid‐1980s. Surface solar radiation is crucial for life on Earth, fostering warmth, shaping wind patterns, and fueling the hydrological cycle and photosynthesis. Utilizing data derived from satellites, we simulated surface solar radiation under different atmospheric conditions regarding clouds, aerosols, and water vapor. This allowed us to separate the individual effects and analyze their contributions to the observed brightening across 61 locations in Europe from 1983 to 2020. We find that the decrease in aerosols was the dominant driver for the brightening during the initial period from 1983 to 2002. Southern Europe and high‐elevation areas showed modest aerosol effects, while Northern and Eastern Europe experienced higher values. Cloud effects were predominantly negative (decreasing surface solar radiation) at most locations. However, between 2001 and 2020 the aerosol effect resulted much smaller and the brightening was mostly attributed to a decrease in cloudiness during that sub‐period. Water vapor was found to have a negligible impact on surface solar radiation trends. Key Points: Satellite application facility on climate monitoring (CM SAF) Land Flux v1.0 surface solar radiation data agree well with station‐based measurements over Europe, also at high‐altitude locationsThe direct aerosol effect was the main driver of the European brightening from 1983 to 2002. Changes in cloudiness rather counteracted itFrom 2001 to 2020 the brightening in Europe was dominated by the cloud effect and the aerosol effect resulted much smaller [ABSTRACT FROM AUTHOR]

Numerous studies have investigated the long-term variability in surface solar radiation (SSR) around the world. However, the large disparity in the availability of observational data between developed and less developed/developing countries leads to an under-representation of studies on SSR changes in the latter. This is especially true for South America, where few observational studies have investigated the SSR trends and usually only at a local or regional scale. In this study we use data from 34 stations distributed throughout all of the regions of Brazil to present the SSR trends in the first 2 decades of the 21st century and investigate their associated causes. The stations were grouped into eight composites according to their proximity. Our results show that in north and northeast Brazil a strong dimming occurred, with significant contributions from increasing atmospheric absorption, most likely due to anthropogenic emissions, and increasing cloud cover. In the southeast and midwest regions of Brazil, near-zero trends resulted from competing effects of clear-sky processes (attenuation of solar radiation under cloudless conditions) and strong negative trends in cloud cover. In the southern part of the Amazon and in south Brazil a statistically insignificant brightening was observed, with significant contributions from decreasing biomass burning emissions in the former and competing minor contributions in the latter. These results can help deepen our knowledge and understanding of SSR long-term trends and their causes in South America, reducing the under-representation of this continent when compared with regions like Europe. [ABSTRACT FROM AUTHOR]

Downward long-wave irradiance (DnLWI) is a variable that directly influences the surface net radiation, which in turn affects weather and climate. Due to the lack of abundant DnLWI observations, numerical weather prediction (NWP) models provide a very effective way to yield the DnLWI. Nevertheless, the reliability of the DnLWI predicted by the NWP models needs the evaluation based on the observations or accurate radiative transfer models. In this study, the DnLWI product of the China Meteorological Administration mesoscale model (CMA-MESO) was extensively validated using long-term high time-resolution (1 min) DnLWI measurements carried out at 42 sites in China. The results showed that the DnLWIs predicted by the CMA-MESO model generally agreed well with the observations, i.e., with a relative mean bias error (rMBE) of –2.0 %, but overestimated them under overcast (3.1 %) and underestimated them under dry (–5.3 %) and cloudless (–5.2 %) conditions. It is also found that the discrepancies in the DnLWI predicted by the CMA-MESO model exhibited spatial and diurnal variations, e.g., the discrepancies were significantly smaller at night than those during the day due to the stable nocturnal boundary layer. According to the results of the partial least squares analysis, the high cloud cover, medium cloud cover, planetary boundary layer height, and integrated cloud ice were the most important factors affecting the accuracy of the DnLWIs predicted by the CMA-MESO model under all sky conditions. By comparing the outputs of the CMA-MESO model and the MODerate resolution atmospheric TRANsmission (MODTRAN) model, it was found that the uncertainties in the DnLWI predicted by the CMA-MESO model mainly arose from an inappropriate consideration of the high and medium clouds under all sky conditions as well as shortcomings in the radiation scheme under cold dry cloudless conditions. [ABSTRACT FROM AUTHOR]

The downward surface longwave flux (DSLF) plays a relevant role in the Earth's surface radiative budget, which is crucial to monitor, understand and model the impact of changes at local and global scales on surface temperature and surface conditions. This study focuses on the evaluation and intercomparison of four DSLF products: (a) a recently developed all‐weather DSLF product based on the multivariate adaptive regression splines (MARS) algorithm driven by satellite cloud information from the Meteosat Second Generation (MSG) and ERA5 reanalysis screen variables; (b) the Satellite Application Facility on Land Surface Analysis (LSA SAF); (c) CERES Synoptic top‐of‐atmosphere and surface fluxes and clouds (CERES‐SYN1deg) and (d) ERA5 reanalysis. The study covers the period 2005–2021 and the MSG region focusing on monthly means. The evaluation performed against 48 ground stations from the Baseline Surface Radiation Network (BSRN) and FLUXNET2015 networks showed that the MARS product outperforms the remaining products, particularly the LSA SAF, while ERA5 and CERES show similar performance metrics. The fours products are intercompared in terms of their mean spatial variability and temporal mean annual cycles and inter‐annual variability in four selected regions, showing a high level of agreement, particularly between MARS, ERA5 and CERES. Our results highlight the clear added value of MARS with respect to LSA SAF, while providing higher spatial resolution (0.05°), constrained by satellite cloud information, when compared with ERA5 (0.25°) or CERES (1°). Plain Language Summary: Radiation that reaches the Earth's surface is fundamental for our understanding of the Earth's energy balance. In this work, we use a complex mathematical method together with data from weather satellites and ground‐based instruments to estimate the heat radiation component. To evaluate our results, we perform a comparison with those from various existing methods, including the one used by the Portuguese meteorological service. Our method generally outperforms the already existing techniques, with small errors as compared to surface measurements, demonstrating the added value of this new approach in improving our understanding of Earth's energy budget. Key Points: Evaluation of a new high spatial (0.05°) and temporal (30 min) resolution DSLF product constrained by MSG satellite cloud informationThe new DSLF MARS product outperforms the current LSA SAF when evaluated against 48 ground stationsHigh level of spatial and temporal variability consistency between four DSLF products MARS, LSA SAF, ERA5, CERES [ABSTRACT FROM AUTHOR]

Numerous studies have investigated the long term variability of surface solar radiation (SSR) around the world. However, the large disparity in the availability of observational data between developed and least developed/developing countries leads to an underrepresentation of studies on SSR changes in the latter. This is especially true for South America, where few observational studies have investigated the SSR decadal trends, and usually only at a local or regional scale. In this study we use data from 34 stations distributed throughout all the regions of Brazil to present the decadal SSR decadal trends in the first two decades of the 21st century and investigate their associated causes. The stations were grouped into 8 composites according to their proximity. Our results show that in the North and Northeast Brazil a strong dimming occurred, with significant contributions from increasing atmospheric absorption, most likely due to anthropogenic emissions, and increasing cloud cover. In the Southeast and Midwest regions of Brazil near-zero trends resulted from competing effects of clear-sky processes and strong negative trends in cloud cover. In the South part of the Amazon and in Southern Brazil a statistically insignificant brightening was observed, with significant contribution from decreasing biomass burning emissions in the former and competing minor contributions in the latter. These results can contribute to deepen the knowledge and understanding of SSR decadal trends and their causes in South America, reducing the underrepresentation of this continent when compared to regions like Europe. [ABSTRACT FROM AUTHOR]