Surface Incident Solar Radiation Research Articles

Century‐Long Variations in Surface Incident Solar Radiation Over Japan——Characterized by Observations and Reanalyses

ABSTRACTSurface incident solar radiation (Rs) is of great importance in determining the energy balance in the Earth system. In this study, we use century‐long homogenized observations over Japan to constrain five 20th century reanalyses to explore their performance in reproducing Rs variation on different time scales (high‐frequency components [HFCs], for signals with cycles less than 10 years; low‐frequency components [LFCs], for signals with cycles more than 10 years) by ensemble empirical mode decomposition (EEMD) method and to quantify the impact factors on the Rs estimations by the sum of tree (SOT) model. It is found that ERA20C, ERA20CM and CERA20C overestimated Rs by 0.48–1.49 W/m−2, while 20CRv2c and 20CRv3 underestimated Rs by −0.63 and −1.18 W/m−2, respectively for 1931–2010. Poor correlation coefficient (R) was found to be 0.10 for ERA20CM and 0.22 for 20CRv2c. 20CRv2c failed for 1931–1960 but improved considerably for 1961–2010. 20CRv3 uses an upgraded model and assimilates more observations compared with its predecessor 20CRv2c; however, only the original components and HFCs in Rs were improved, with nearly no improvement in the LFCs. In general, CERA20C Rs, with small biases and higher R of 0.73 for original signals, 0.83 for HFCs and LFCs, is superior to other reanalyses. No obvious trend in clear sky Rs demonstrated that reanalysed Rs are insensitive to the aerosol forcings. Therefore, cloud cover and water vapour maybe the main factors influenced reanalysed Rs. Most of time, Rs is more sensitive to cloud cover than vapour pressure for all reanalyses except original signals (with contribution ratio of 0.29 for cloud cover and 0.71 for vapour pressure) and LFCs (with contribution ratio of 0.41 for cloud cover and 0.59 for vapour pressure) in CERA20C, and original signals (with contribution ratio of 0.37 for cloud cover and 0.63 for vapour pressure) in ERA20C. This work pointed out that aerosol related processes such as aerosol forcings or aerosol radiative effect in reanalyses should be improved in the future, which will ultimately improve the interaction between aerosol and cloud in Rs simulations.

Impacts of Anthropogenic Emissions and Open Biomass Burning in South Asia and Southeast Asia on Air Quality and Meteorology Over Southern China

AbstractThe emissions from South Asia and Southeast Asia significantly impact air quality and meteorological conditions in China. However, the individual or joint contributions of anthropogenic emissions and/or biomass burning from outside China to surface particulate matter with aerodynamic diameters less than 2.5 μm (PM2.5) and aerosol optical depth (AOD) over southern China have not been fully investigated. Here, five experiments were designed to investigate the impacts of these emissions in January (winter), March (pre‐monsoon), and October (post‐monsoon) for 2017. Aerosols from South Asia and Southeast Asia contributed less to southern China during winter and post‐monsoon seasons, whereas the wind patterns and emission intensity during the pre‐monsoon season were conducive to the transport of aerosols. During pre‐monsoon season, the total emissions contributed approximately 5.0 μg m−3 to surface PM2.5 in Xizang Province. Biomass burning in Southeast Asia increased PM2.5 in Yunnan Province by 37.9 μg m−3, while anthropogenic emissions increased it by 8.9 μg m−3. Transboundary aerosols can be transported to Xizang Province and Yunnan Province, primarily influencing PM2.5 below 2 km height. It mainly affected PM2.5 levels above the planetary boundary layer over southeast China. Aerosols from outside China can account for 79.5% and 54.8% AOD in Yunnan Province and southeast China, respectively. These aerosols reduced surface incident solar radiation by approximately 6%, leading to decreases in air temperature, wind speed, and boundary layer height. The findings are only applicable to the pre‐monsoon season.

Diurnal Variation in Surface Incident Solar Radiation Retrieved by CERES and Himawari-8

The diurnal variation of surface incident solar radiation (Rs) has a significant impact on the Earth’s climate. Satellite-retrieved Rs datasets display good spatial and temporal continuity compared with ground-based observations and, more importantly, have higher accuracy than reanalysis datasets. Facilitated by these advantages, many scholars have evaluated satellite-retrieved Rs, especially based on monthly and annual data. However, there is a lack of evaluation on an hourly scale, which has a profound impact on sea–air interactions, climate change, agriculture, and prognostic models. This study evaluates Himawari-8 and Clouds and the Earth’s Radiant Energy System Synoptic (CERES)-retrieved hourly Rs data covering 60°S–60°N and 80°E–160°W based on ground-based observations from the Baseline Surface Radiation Network (BSRN). Hourly Rs were first standardized to remove the diurnal and seasonal cycles. Furthermore, the sensitivities of satellite-retrieved Rs products to clouds, aerosols, and land cover types were explored. It was found that Himawari-8-retrieved Rs was better than CERES-retrieved Rs at 8:00–16:00 and worse at 7:00 and 17:00. Both satellites performed better at continental sites than at island/coastal sites. The diurnal variations of statistical parameters of Himawari-8 satellite-retrieved Rs were stronger than those of CERES. Relatively larger MABs in the case of stratus and stratocumulus were exhibited for both hourly products. Smaller MAB values were found for CERES covered by deep convection and cumulus clouds and for Himawari-8 covered by deep convection and nimbostratus clouds. Larger MAB values at evergreen broadleaf forest sites and smaller MAB values at open shrubland sites were found for both products. In addition, Rs retrieved by Himawari-8 was more sensitive to AOD at 10:00–16:00, while that retrieved by CERES was more sensitive to COD at 9:00–15:00. The CERES product showed larger sensitivity to COD (at 9:00–15:00) and AOD (at 7:00–10:00) than Himawari-8. This work helps data producers know how to improve their future products and helps data users be aware of the uncertainties that exist in hourly satellite-retrieved Rs data.

Contributions of Local Land‒Atmosphere Coupling and Mesoscale Atmospheric Circulation to the 2013 Extreme Flash Drought and Heatwave Compound Event Over Southwest China

AbstractThe flash drought and heat wave compound event of the 2013 summer in Southwest China was exceptional, with profound socio‒economic impacts. Existing studies have captured the signal of this compound event; however, its causes are still poorly understood. In this study, we utilized a high‐resolution index to examine the life cycle of this compound event from 1980 to 2020 and quantified the relative contributions of land‒atmosphere coupling and mesoscale atmospheric circulation using the air parcel backward tracking method. It was found that the dry soil caused by the precipitation deficit further inhibited precipitation and caused the soil to become even drier, which then led to the development of the flash drought. The dry soil induced a substantial increase in the land‒atmosphere sensible heat flux and a rise in the near‐surface air temperature. During this process, the strength of land‒atmosphere coupling was 2.5 standard deviations higher than the mean value of the climate, playing an integral role in the near‐surface air temperature increase, accounting for 55.9% of the maximum temperature changes. The mesoscale atmospheric circulation contributed 44.1%, of which horizontal advection accounted for 41.1%, while vertical advection only accounted for 3.0%. The western Pacific subtropical high expanded westward, accompanied by the northward‐moving westerly jet stream, which prevented cold air from accessing the Southwest China, and abnormal subsidence interfered with precipitation formation. Furthermore, the control of an abnormally high‐pressure system over the region led to a decrease in cloud cover, allowing more surface incident solar radiation and contributing to the increase in the near‐surface air temperature.

Diurnal Cycle in Surface Incident Solar Radiation Characterized by CERES Satellite Retrieval

Surface incident solar radiation (Rs) plays an important role in climate change on Earth. Recently, the use of satellite-retrieved datasets to obtain global-scale Rs with high spatial and temporal resolutions has become an indispensable tool for research in related fields. Many studies were carried out for Rs evaluation based on the monthly satellite retrievals; however, few evaluations have been performed on their diurnal variation in Rs. This study used independently widely distributed ground-based data from the Baseline Surface Radiation Network (BSRN) to evaluate hourly Rs from the Clouds and the Earth’s Radiant Energy System Synoptic (CERES) SYN1deg–1Hour product through a detrended standardization process. Furthermore, we explored the influence of cloud cover and aerosols on the diurnal variation in Rs. We found that CERES-retrieved Rs performs better at midday than at 7:00–9:00 and 15:00–17:00. For spatial distribution, CERES-retrieved Rs performs better over the continent than over the island/coast and polar regions. The Bias, MAB and RMSE in CERES-retrieved Rs under clear-sky conditions are rather small, although the correlation coefficients are slightly lower than those under overcast-sky conditions from 9:00 to 15:00. In addition, the range in Rs bias caused by cloud cover is 1.97–5.38%, which is significantly larger than 0.31–2.52% by AOD.

Quantification of the urbanization impacts on solar dimming and brightening over China

Metropolis’ contribution (anthropogenic aerosols) to solar dimming and brightening remains a hot topic of special concern over the past several decades. However, urbanization effects on surface incident solar radiation (R s) have not been comprehensively investigated. In this study, the urbanization effects on solar dimming and brightening were addressed using the densely distributed reconstructed R s data at 375 stations and 92 urban–rural station pairs over the time period of 1960–2019 in China. The results indicate that the impacts of urbanization on the monthly mean R s is 0.86 ± 7.99 W m−2 during the study period, while the impact is 0.90 ± 8.30 W m−2 and 0.82 ± 8.26 W m−2 for the solar dimming (1960–1992) and brightening (1992–2019) phase, respectively. The urbanization effects on the trend of R s is −0.39 and 0.16 W m−2 per decade during dimming and brightening, respectively. It also found that urbanization effects on R s trend differs strikingly in magnitudes for specific regions in China. Generally, urbanization speeds up China’s dimming in the dimming phase and slows down China’s brightening in the brightening phase.

Homogenized century-long surface incident solar radiation over Japan

Abstract. Surface incident solar radiation (Rs) plays a key role in climate change on Earth. Rs can be directly measured, and it shows substantial variability on decadal scales, i.e. global dimming and brightening. Rs can also be derived from the observed sunshine duration (SunDu) with reliable accuracy. The SunDu-derived Rs has been used as a reference to detect and adjust inhomogeneity in the observed Rs. However, both the observed Rs and SunDu-derived Rs may have inhomogeneity. In Japan, SunDu has been measured since 1890, and Rs has been measured since 1961 at ∼100 stations. In this study, the observed Rs and SunDu-derived Rs were first checked for inhomogeneity independently using the statistical software RHtests. If confirmed by the metadata of these observations, the detected inhomogeneity was adjusted based on the RHtests quantile-matching method. Second, the two homogenized time series were compared to detect further possible inhomogeneity. If confirmed by the independent ground-based manual observations of cloud cover fraction, the detected inhomogeneity was adjusted based on the reference dataset. As a result, a sharp decrease of more than 20 W m−2 in the observed Rs from 1961 to 1975 caused by instrument displacement was detected and adjusted. Similarly, a decline of about 20 W m−2 in SunDu-derived Rs due to steady instrument replacement from 1985 to 1990 was detected and adjusted too. After homogenization, the two estimates of Rs agree well. The homogenized SunDu-derived Rs show an increased at a rate of 0.9 W m−2 per decade (p<0.01) from 1961 to 2014, which was caused by a positive aerosol-related radiative effect (2.2 W m−2 per decade) and a negative cloud cover radiative effect (−1.4 W m−2 per decade). The brightening over Japan was the strongest in spring, likely due to a significant decline in aerosol transported from Asian dust storms. The observed raw Rs data and their homogenized time series used in this study are available at https://doi.org/10.11888/Meteoro.tpdc.271524 (Ma et al., 2021).

Improvement of ERA5 over ERA-Interim in Simulating Surface Incident Solar Radiation throughout China

AbstractSurface incident solar radiation (Rs) is important for providing essential information on climate change. Existing studies have shown that the Rs values from current reanalyses are significantly overestimated throughout China. The European Centre for Medium-Range Weather Forecasts (ECMWF) recently released the fifth generation of atmospheric reanalysis (i.e., ERA5) with a much higher spatiotemporal resolution and a major upgrade compared to its predecessor, ERA-Interim. This study is to verify whether ERA5 can improve the Rs simulation using sunshine duration–derived Rs values at ~2200 stations over China from 1979 to 2014 as reference data. Compared with the observed multiyear national mean, the Rs overestimation is reduced from 15.88 W m−2 in ERA-Interim to 10.07 W m−2 in ERA5. From 1979 to 1993, ERA-Interim (−1.99 W m−2 decade−1; p < 0.05) and ERA5 (−2.42 W m−2 decade−1; p < 0.05) estimates of Rs in China continued to decrease and the decline of the latter is closer to the observed. After 1993, they both show a strong brightening (i.e., 2.26 W m−2 decade−1 in ERA-Interim and 1.49 W m−2 decade−1 in ERA5) but observations show a nonsignificant increase by 0.30 W m−2 decade−1. Due to the improvement of total cloud cover (TCC) simulation by ERA5, its Rs trend bias induced by the TCC trend bias is smaller than that in ERA-Interim. In addition, the reason why the simulation trend in ERA5 remains biased might be that ERA5 still ignores aerosol changes on interannual or decadal time scales. Therefore, subsequent reanalysis products still need to improve their simulation of clouds, water vapor, and aerosol, especially in aerosol direct and indirect effects on Rs.

Contrast patterns and trends of lapse rates calculated from near-surface air and land surface temperatures in China from 1961 to 2014

The near-surface lapse rate reflects the atmospheric stability above the surface. Lapse rates calculated from land surface temperature (γTs) and near-surface air temperature (γTa) have been widely used. However, γTs and γTa have different sensitivity to local surface energy balance and large-scale energy transport and therefore they may have diverse spatial and temporal variability, which has not been clearly illustrated in existing studies. In this study, we calculated and compared γTa and γTs at ~ 2200 stations over China from 1961 to 2014. This study finds that γTa and γTs have a similar multiyear national average (0.53 °C/100 m) and seasonal cycle. Nevertheless, γTs shows steeper multiyear average than γTa at high latitudes, and γTs in summer is steeper than γTa, especially in Northwest China. The North China shows the shallowest γTa and γTs, then inhibiting the vertical diffusion of air pollutants and further reducing the lapse rates due to accumulation of pollutants. Moreover, the long-term trend signs for γTa and γTs are opposite in northern China. However, the trends in γTa and γTs are both negative in Southwest China and positive in Southeast China. Surface incident solar radiation, surface downward longwave radiation and precipitant frequency jointly can account for 80% and 75% of the long-term trends in γTa and γTs in China, respectively, which provides an explanation of trends of γTa and γTs from perspective of surface energy balance.

Evaluation of Reanalysis Surface Incident Solar Radiation Data in China

Surface incident solar radiation (Rs) of reanalysis products is widely used in ecological conservation, agricultural production, civil engineering and various solar energy applications. It is of great importance to have a good knowledge of the uncertainty of reanalysis Rs products. In this study, we evaluated the Rs estimates from two representative global reanalysis (ERA-Interim and MERRA-2) using quality- controlled surface measurements from China Meteorological Administration (CMA) and Multi-layer Simulation and Data Assimilation Center of the Tibetan Plateau (DAM) from 2000 to 2009. Error causes are further analyzed in combination radiation products from the Earth’s Radiant Energy System (CERES) EBAF through time series estimation, hotspot selection and Geodetector methods. Both the ERA-Interim and MERRA-2 products overestimate the Rs in China, and the MERRA-2 overestimation is more pronounced. The errors of the ERA-Interim are greater in spring and winter, while that of the MERRA-2 are almost the same in all seasons. As more quality-controlled measurements were used for validation, the conclusions seem more reliable, thereby providing scientific reference for rational use of these datasets. It was also found that the main causes of errors are the cloud coverage in the southeast coastal area, aerosol optical depth (AOD) and water vapor content in the Sichuan Basin, and cloud coverage and AOD in the northeast and middle east of China.

Reconstructing Six Decades of Surface Temperatures at a Shallow Lake

Lake surface water temperature (LSWT) plays a fundamental role in the lake energy budget. However, direct observations of LSWT require considerable effort for acquisition and hence are rare relative to a large number of lakes. In lakes where LSWT has not been covered sufficiently by in situ measurements, remote sensing and lake modeling can be used to produce a fine spatio-temporal record of LSWTs. In our study, the Moderate-Resolution Imaging Spectroradiometer (MODIS) LSWT was used to compare with in situ data at the overpass times over the six sites in Lake Chaohu, a large shallow lake in China. MODIS-derived LSWT reflected the variation of lake surface temperature well, with a correlation coefficient of 0.96 and a cool bias of 1.25 °C. The bias was modified by an “Upper Envelop” smoothing method and then employed to evaluate the general lake model (GLM) performance, a one-dimensional hydrodynamic model. The GLM simulations showed good performance compared with MODIS LSWT data at an interannual time scale. A 57-year record of simulated LSWT was hindcast by the well-calibrated GLM for Lake Chaohu. The results showed that LSWT decreased by 0.08 °C/year from 1960 to 1981 and then increased by 0.05 °C/year. These trends were most likely caused by a cooling effect of decreased surface incident solar radiation and a warming effect of reduced wind speed. Our study promoted the use of MODIS-derived LSWT as an alternative data source, and then combined with a numerical model for inland water surface temperature, and also further provided an understanding of climate warming effect on such a shallow eutrophic lake. Key points: (1) Moderate-Resolution Imaging Spectroradiometer (MODIS) lake water surface temperature (LSWT) was validated with real-time in situ data collected at Lake Chaohu with high accuracy; (2) MODIS LSWT was modified by the bias correction and employed to evaluate a one-dimensional lake model at interannual and intraannual scale; The LSWT hindcast by a well-calibrated model at Lake Chaohu decreased by 0.08 °C/year from 1960 to 1981 and increased by 0.05 °C/year from 1982 to 2016.

Determining Factors of Monthly to Decadal Variability in Surface Solar Radiation in China: Evidences From Current Reanalyses

AbstractClouds and aerosols play essential roles in regulating surface incident solar radiation (Rs). It has been suggested that the increased aerosol loading over China is a key factor for the decadal variability in Rs and can explain the bias in its trend from reanalyses because the reanalyses do not include the interannual variability of aerosols. In this study, we compare the Rs derived from sunshine duration at 2,400 weather stations in China and that from five reanalyses from 1980 to 2014. The determining factors for the biases in the mean values and trends of Rs from the reanalyses are examined, with the help of Rs and the cloud fraction (CF), from satellite and 2,400 weather stations. Our results show that all reanalyses overestimate the multiyear Rs by 24.10–40.00 W/m2 due to their underestimations of CF, which is more obvious in southern China. The biases in the simulated CF in the reanalyses can explain the biases in Rs by 55–41%, and the bias in clear‐sky surface solar radiation (Rc), which is primarily due to biases in aerosol loading, can explain 32–9% of the bias in Rs. The errors in the trend of the simulated CF can explain the errors in the Rs trends in the reanalyses by 73–12%, and the trend errors in the Rc can explain 43–30% of the trend error in Rs. Our study suggests that more work is needed to improve the simulation of aerosols, clouds, and aerosol‐cloud‐radiation interactions in the reanalyses.

Evaluation of the Himawari-8 Shortwave Downward Radiation (SWDR) Product and its Comparison With the CERES-SYN, MERRA-2, and ERA-Interim Datasets

The land surface shortwave downward radiation (SWDR), also known as surface incident solar radiation, is usually defined as the total solar spectral energy between 300 nm and 3000 nm that arrives at the earth's surface. The SWDR is an essential variable for numerous land models and thus need to be accurately mapped using various approaches. Although numerous efforts have been made to assess the applicability and accuracy of the SWDR datasets produced by satellite and numeric models, few studies have evaluated the performance of the SWDR products from Himawari-8. In this paper, the Himawari-8 SWDR products with both 1 km and 5 km spatial scales were evaluated using ground measurements. The validation results indicate that both of the Himawari-8 SWDR products are in close agreement with ground measurements, even though obvious biases are found. Also, an in-depth intercomparison between the Himawari-8 SWDR product at a 5 km resolution and three other SWDR radiation datasets (CERES-SYN, MERRA-2, and ERA-Interim) was conducted. Here, the Himawari-8 showed the highest levels of accuracy among the four SWDR datasets. Considering its higher temporal and spatial resolutions, the Himawari-8 SWDR products are more detailed and provide the unprecedented potential to improve land surface modeling and reveal the cloud-radiation interactions, even at a 10-min temporal scale.

Application of Tropospheric Sulfate Aerosol Emissions to Mitigate Meteorological Phenomena with Extremely High Daily Temperatures

Abstract This research examined whether tropospheric sulfate ion aerosols (SO4 2−) might be applied at a regional scale to mitigate meteorological phenomena with extremely high daily temperatures. The specific objectives of this work were: 1) to model the behaviour of SO4 2−aerosols in the troposphere and their influence on surface temperature and incident solar radiation, at a regional scale, using an appropriate online coupled mesoscale meteorology and chemistry model; 2) to determine the main engineering design parameters using tropospheric SO4 2−aerosols in order to artificially reduce the temperature and incoming radiation at surface during events of extremely high daily temperatures, and 3) to evaluate a preliminary technical proposal for the injection of regionally engineered tropospheric SO4 2−aerosols based on the integral anti-hail system of the Province of Mendoza. In order to accomplish these objectives, we used the Weather Research & Forecasting Model coupled with Chemistry (WRF/Chem) to model and evaluate the behaviour of tropospheric SO4 2−over the Province of Mendoza (Argentina) (PMA) on a clear sky day during a heat wave event occurred in January 2012. In addition, using WRF/Chem, we evaluated the potential reductions on surface temperature and incident shortwave radiation around the metropolitan area of Great Mendoza, PMA, based on an artificially designed aerosol layer and on observed meteorological parameters. The results demonstrated the ability of WRF/Chem to represent the behaviour of tropospheric SO4 2− aerosols at a regional scale and suggested that the inclusion of these aerosols in the atmosphere causes changes in the surface energy balance and, therefore, in the surface temperature and the regional atmospheric circulation. However, it became evident that, given the high rate of injection and the large amount of mass required for its practical implementation by means of the technology currently used by the anti-hail program, it is inefficient and energetically costly.

Does the modern‐era retrospective analysis for research and applications‐2 aerosol reanalysis introduce an improvement in the simulation of surface solar radiation over China?

Surface incident solar radiation (Rs) is a key parameter of energy and water cycles of the Earth. Reanalyses represent important sources of information on Rs. However, reanalyses Rs may have important bias due to their imperfect parameterizations and input errors of cloud and aerosol. NASA's Global Modelling and Assimilation Office has recently released Version 2 of the Modern‐Era Retrospective Analysis for Research and Applications (MERRA2), which incorporates a reanalysis of atmospheric optical depth for the first time. In this study, we evaluate Rs from MERRA2 and its predecessor (MERRA) in China from 1980 to 2014. We first compare three possible reference data sources: (a) observed Rs at 122 stations, (b) satellite retrievals of Rs and (c) Rs values derived from sunshine durations measured at 2,400 weather stations. We find sunshine duration derived Rs is a reliable reference and use it to evaluate MERRA and MERRA2. Our results show that both MERRA and MERRA2 have a high mean bias of 38.63 and 43.86 W/m2 over China due to their underestimation of cloud fraction, which is greater in southern China. MERRA2 displays improved capability in reproducing monthly and annual variability, and national mean trend of Rs. MERRA overestimates the trend of Rs by 3.23 W/m2 in eastern China. MERRA2 reduced this trend bias over the North China Plain likely due to its aerosol assimilation. However, MERRA2 show a negative bias in trend of Rs (−3.44 W/m2) in the south China likely due to its overestimation of atmospheric aerosols loading and aerosol‐cloud interaction. The results provide guidance for future development of reanalysis and its scientific applications for ecological and hydrological models.

On the suitability of current atmospheric reanalyses for regional warming studies over China

Abstract. Reanalyses are widely used because they add value to routine observations by generating physically or dynamically consistent and spatiotemporally complete atmospheric fields. Existing studies include extensive discussions of the temporal suitability of reanalyses in studies of global change. This study adds to this existing work by investigating the suitability of reanalyses in studies of regional climate change, in which land–atmosphere interactions play a comparatively important role. In this study, surface air temperatures (Ta) from 12 current reanalysis products are investigated; in particular, the spatial patterns of trends in Ta are examined using homogenized measurements of Ta made at ∼ 2200 meteorological stations in China from 1979 to 2010. The results show that ∼ 80 % of the mean differences in Ta between the reanalyses and the in situ observations can be attributed to the differences in elevation between the stations and the model grids. Thus, the Ta climatologies display good skill, and these findings rebut previous reports of biases in Ta. However, the biases in theTa trends in the reanalyses diverge spatially (standard deviation = 0.15–0.30 °C decade−1 using 1° × 1° grid cells). The simulated biases in the trends in Ta correlate well with those of precipitation frequency, surface incident solar radiation (Rs) and atmospheric downward longwave radiation (Ld) among the reanalyses (r = −0.83, 0.80 and 0.77; p < 0.1) when the spatial patterns of these variables are considered. The biases in the trends in Ta over southern China (on the order of −0.07 °C decade−1) are caused by biases in the trends in Rs, Ld and precipitation frequency on the order of 0.10, −0.08 and −0.06 °C decade−1, respectively. The biases in the trends in Ta over northern China (on the order of −0.12 °C decade−1) result jointly from those in Ld and precipitation frequency. Therefore, improving the simulation of precipitation frequency and Rs helps to maximize the signal component corresponding to regional climate. In addition, the analysis of Ta observations helps represent regional warming in ERA-Interim and JRA-55. Incorporating vegetation dynamics in reanalyses and the use of accurate aerosol information, as in the Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), would lead to improvements in the modelling of regional warming. The use of the ensemble technique adopted in the twentieth-century atmospheric model ensemble ERA-20CM significantly narrows the uncertainties associated with regional warming in reanalyses (standard deviation = 0.15 °C decade−1).

A Revisit of Global Dimming and Brightening Based on the Sunshine Duration

AbstractObservations show that the surface incident solar radiation (Rs) decreased over land from the 1950s to the 1980s and increased thereafter, known as global dimming and brightening. This claim has been questioned due to the inhomogeneity and low spatial‐temporal coverage of Rs observations. Based on direct comparisons of ~200 observed and sunshine duration (SunDu) derived Rs station pairs, meeting data record lengths exceeding 60 months and spatial distances less than 110 km, we show that meteorological observations of SunDu can be used as a proxy for measured Rs. Our revised results from ~2,600 stations show global dimming from the 1950s to the 1980s over China (−1.90 W/m2 per decade), Europe (−1.36 W/m2 per decade), and the United States (−1.10 W/m2 per decade), brightening from 1980 to 2009 in Europe (1.66 W/m2 per decade) and a decline from 1994 to 2010 in China (−1.06 W/m2 per decade). Even if 1994–2010 is well known as a period of global brightening, the observed and SunDu‐derived Rs over China still exhibit declining trends. Trends in Rs from 1923 to 1950 are also found over Europe (1.91 W/m2 per decade) and the United States (−1.31 W/m2 per decade), but the results in Europe may not well represent the actual trend for the European continent due to poor spatial sampling.

Merging Satellite Retrievals and Reanalyses to Produce Global Long-Term and Consistent Surface Incident Solar Radiation Datasets

Surface incident solar radiation (Rs) is a key parameter in many climatic and ecological processes. The data from satellites and reanalysis have been widely used. However, for reanalysis, Rs data has been shown to have substantial spatial bias, and the time span of reliable satellite Rs is too short for climatic and ecological studies. Combining reanalysis and satellite data would be an effective method for generating long-term and consistent Rs datasets. Here, we apply a cumulative probability density function-based (CPDF) method to merge eight reanalyses with the latest available satellite Rs data from Clouds and Earth’s Radiant Energy System Energy Balanced and Filled (CERES EBAF) surface retrievals. The CPDF method not only reduces the spatial bias of the reanalysis Rs data, but also makes the Rs datasets in a global, long-term and consistent way. The observed Rs data collected at 54 Baseline Surface Radiation Network (BSRN) stations from 1992 to 2016 are used to evaluate the method. Results show that the CPDF method could reduce the mean absolute biases (MAB) of the reanalysis Rs effectively by 21.24–64.36%. The European Centre for Medium-Range Weather Forecasts Re-Analysis interim (ERA-interim) reanalysis Rs data, which are available for 1979 onward, perform the best before MAB = 13.20 W·m−2 and after MAB = 10.40 W·m−2 merging. This small post-merging MAB of the ERA-interim reanalysis is caused by the MAB of 9.90 W·m−2 in the satellite Rs retrievals. The Japanese 55-year reanalysis provides Rs values back to 1958, and CPDF can reduce its MAB by 32.87%, to 11.17 W·m−2. The National Oceanic and Atmospheric Administration (NOAA)-CIRES twentieth-century reanalysis (CIRES) and the ECMWF twentieth-century reanalysis (ERA20CM) provide century-long Rs estimates. CIRES performs better after merging. The MAB of CIRES can be reduced by 32.10%, to 12.99 W·m−2, while ERA20CM’s can be reduced by 12.51%, to 16.40 W·m−2.

Evaluation of Eight Current Reanalyses in Simulating Land Surface Temperature from 1979 to 2003 in China

Abstract Land surface temperature Ts provides essential supplementary information to surface air temperature, the most widely used metric in global warming studies. A lack of reliable observational Ts data makes assessing model simulations difficult. Here, the authors first examined the simulated Ts of eight current reanalyses based on homogenized Ts data collected at ~2200 weather stations from 1979 to 2003 in China. The results show that the reanalyses are skillful in simulating the interannual variance of Ts in China (r = 0.95) except over the Tibetan Plateau. ERA-Interim and MERRA land versions perform better in this respect than ERA-Interim and MERRA. Observations show that the interannual variance of Ts over the north China plain and south China is mostly influenced by surface incident solar radiation Rs, followed by precipitation frequency, whereas the opposite is true over the northwest China, northeast China, and the Tibetan Plateau. This variable relationship is well captured by ERA-Interim, ERA-Interim land, MERRA, and JRA-55. The homogenized Ts data show a warming of 0.34°C decade−1 from 1979 to 2003 in China, varying between 0.25° and 0.42°C decade−1 for the eight reanalyses. However, the reanalyses substantially underestimate the warming trend of Ts over northwest China, northeast China, and the Tibetan Plateau and significantly overestimate the warming trend of Ts over the north China plain and south China owing to their biases in simulating the Rs and precipitation frequency trends. This study provides a diagnostic method for examining the capability of current atmospheric/land reanalysis data in regional climate change studies.

Water storage in reservoirs built from 1997 to 2014 significantly altered the calculated evapotranspiration trends over China

Global or regional mean evapotranspiration (ET), calculated as the difference between observed precipitation (P) and runoff (R), has been widely used as the standard method to investigate the long-term variability of ET and evaluate hydrological and climate models. The increasing number of reservoirs built in China has led to a considerable amount of water storage, which could significantly alter regional water budgets. This change in terrestrial water storage (ΔS) because of the newly built reservoirs reduces the observed R but does not directly translate into ET. The present study is the first to quantify this reservoir effect on the estimated ET at the national and basin scale from 1997 to 2014 in China. The results show that the reservoir total storage capacity in China increased by 0.38 × 1012 m3 from 1997 to 2014. If this change in ΔS is not considered, a significant increase in the calculated ET of 4.2% per decade is derived. However, after this change in ΔS is taken into account, the calculated trend of ET decreases to almost zero for the period 1997 to 2014, which is consistent with the negligible changes in the determining factors for ET, including precipitation, surface incident solar radiation, and air temperature. The impact of reservoirs and the determining factors of ET are further explored in six major river basins of China, which confirmed our conclusions at the national scale. This study indicates that the impact of ΔS due to reservoir construction on calculated ET trends must be considered.