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

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

Non-crossing Quantile Regression Neural Network as a Calibration Tool for Ensemble Weather Forecasts

Despite the maturity of ensemble numerical weather prediction(NWP),the resulting forecasts are still,more often than not,under-dispersed.As such,forecast calibration tools have become popular.Among those tools,quantile regression(QR)is highly competitive in terms of both flexibility and predictive performance.Nevertheless,a long-standing problem of QR is quantile crossing,which greatly limits the interpretability of QR-calibrated forecasts.On this point,this study proposes a non-crossing quantile regression neural network(NCQRNN),for calibrating ensemble NWP forecasts into a set of reliable quantile forecasts without crossing.The overarching design principle of NCQRNN is to add on top of the conventional QRNN structure another hidden layer,which imposes a non-decreasing mapping between the combined output from nodes of the last hidden layer to the nodes of the output layer,through a triangular weight matrix with positive entries.The empirical part of the work considers a solar irradiance case study,in which four years of ensemble irradiance forecasts at seven locations,issued by the European Centre for Medium-Range Weather Forecasts,are calibrated via NCQRNN,as well as via an eclectic mix of benchmarking models,ranging from the naïve climatology to the state-of-the-art deep-learning and other non-crossing models.Formal and stringent forecast verification suggests that the forecasts post-processed via NCQRNN attain the maximum sharpness subject to calibration,amongst all competitors.Furthermore,the proposed conception to resolve quantile crossing is remarkably simple yet general,and thus has broad applicability as it can be integrated with many shallow-and deep-learning-based neural networks.

A rapid assessment of MWRI-RM/FY3G brightness temperature

2023年4月发射的FY-3G上搭载17个频率的测雨微波成像仪(MWRI-RM),其业务定标的微波亮温(Tb)数据于2023年10月23日公开发布.本文比对了发布10天的MWRI-RM与全球降水测量(GPM)卫星上的微波成像仪(GMI)相匹配的Tb数据,并借助辐射传输模式进行双差分(DD)交叉定标分析,旨在快速评估新一代MWRI-RM观测数据质量.观测比较表明,MWR1-RM与GMI测量的Tb一致性很好,大多通道的平均偏差(MBE)和均方根误差(RMSE)均小于1K.两种传感器由于观测角度略有不同在水面产生约0.5 K差异.DD分析也展示出MWRI-RM的大多数通道性能与GMI相当接近,尤其是首次启用的高频166 GHz和183 GHz.

Dynamic and Thermodynamic Features of Low and Middle Clouds Derived from Atmospheric Radiation Measurement Program Mobile Facility Radiosonde Data at Shouxian, China

By using the radiosonde measurements collected at Shouxian,China,we examined the dynamics and thermodynamics of single- and two-layer clouds formed at low and middle levels.The analyses indicated that the horizontal wind speed above the cloud layers was higher than those within and below cloud layers.The maximum balloon ascent speed（5.3 m s^-1） was located in the vicinity of the layer with the maximum cloud occurrence frequency（24.4%）,indicating an upward motion（0.1-0.16 ms^-1）.The average thickness,magnitude and gradient of the temperature inversion layer above single-layer clouds were117±94 m,1.3±1.3℃ and 1.4±1.5℃（100 m）^-1,respectively.The average temperature inversion magnitude was the same（1.3℃） for single-low and single-middle clouds;however,a larger gradient[1.7±1.8℃（100 m）^-1]and smaller thickness（94±67 m） were detected above single-low clouds relative to those above single-middle clouds[0.9±0.7℃（100 m）^-1 and157±120 m].For the two-layer cloud,the temperature inversion parameters were 106±59 m,1.0±0.9℃ and 1.0±1.0℃（100 m）^-1 above the upper-layer cloud and 82 ± 60 m,0.6±0.9℃ and 0.7±0.6℃（100 m）^-1 above the low-layer cloud.Absolute differences between the cloud-base height（cloud-top height） and the lifting condensation level（equilibrium level）were less than 0.5 km for 66.4%（36.8%） of the cases analyzed in summer.

Data-driven Estimation of Cloud Effects on Surface Irradiance at Xianghe,a Suburban Site on the North China Plain

Clouds are a dominant modulator of the energy budget.The cloud shortwave radiative effect at the surface(CRE)is closely related to the cloud macro-and micro-physical properties.Systematic observation of surface irradiance and cloud properties are needed to narrow uncertainties in CRE.In this study,1-min irradiance and Total Sky Imager measurements from 2005 to 2009 at Xianghe in North China Plain are used to estimate cloud types,evaluate cloud fraction(CF),and quantify the sensitivities of surface irradiance with respect to changes in CF whether clouds obscure the sun or not.The annual mean CF is 0.50,further noting that CF exhibits a distinct seasonal variation,with a minimum in winter(0.37)and maximum in summer(0.68).Cumulus occurs more frequently in summer(32%),which is close to the sum of the occurrence of stratus and cirrus.The annual CRE is–54.4 W m^(–2),with seasonal values ranging from^(–2)9.5 W m^(–2)in winter and–78.2 W m^(–2)in summer.When clouds do not obscure the sun,CF is a dominant factor affecting diffuse irradiance,which in turn affects global irradiance.There is a positive linear relationship between CF and CRE under sun-unobscured conditions,the mean sensitivity of CRE for each CF 0.1 increase is about 1.2 W m^(–2)[79.5°<SZA(Solar Zenith Angle)<80.5°]to 7.0 W m^(–2)(29.5°<SZA<30.5°).When clouds obscure the sun,CF affects both direct and diffuse irradiance,resulting in a non-linear relationship between CF and CRE,and the slope decreases with increasing CF.It should be noted that,although only data at Xianghe is used in this study,our results are representative of neighboring areas,including most parts of the North China Plain.

A Concise Overview on Solar Resource Assessment and Forecasting

China’s recently announced directive on tackling climate change,namely,to reach carbon peak by 2030 and to achieve carbon neutrality by 2060,has led to an unprecedented nationwide response among the academia and industry.Under such a directive,a rapid increase in the grid penetration rate of solar in the near future can be fully anticipated.Although solar radiation is an atmospheric process,its utilization,as to produce electricity,has hitherto been handled by engineers.In that,it is thought important to bridge the two fields,atmospheric sciences and solar engineering,for the common good of carbon neutrality.In thisüberreview,all major aspects pertaining to solar resource assessment and forecasting are discussed in brief.Given the size of the topic at hand,instead of presenting technical details,which would be overly lengthy and repetitive,the overarching goal of this review is to comprehensively compile a catalog of some recent,and some not so recent,review papers,so that the interested readers can explore the details on their own.

Intensive Radiosonde Measurements of Summertime Convection over the Inner Mongolia Grassland in 2014:Difference between Shallow Cumulus and Other Conditions

Using radiosonde measurements from 26 July to 30 July 2014 at Baiqi over the Inner Mongolia grassland of China, the vertical structure of shallow cumulus （SCu） clouds and associated environmental conditions were investigated. The cloud base height and the cloud top height of SCu was 3.4 km and 5 km, respectively. The temperature of the SCu layer was less than 0℃. The horizontal advection of specific humidity was smaller than the vertical transport in the atmosphere below 5 km. Above 5 km, the thermodynamic structure of the atmosphere remained stable. At the interface of the cloud layer and free air atmosphere, there was obvious wind shear and a temperature inversion （-2.9~C）. Comparisons of environmental parameters associated with cumulus congestus, rain and clear days, showed that the formation of SCu was characterized by a higher Bowen ratio （high sensible heat flux and low latent heat flux）, which indicated intensive turbulence in the boundary layer. The formation of SCu was associated with the boundary layer height exceeding the lifting condensation level. The maintenance of SCu was likely associated with the lower convective available potential energy, weak wind shear, and weak subsidence of the synoptic system, which did not favor the dramatic vertical development of SCu and thereby the transformation of SCu to cumulus congestus.

A Comparison of Cloud Layers from Ground and Satellite Active Remote Sensing at the Southern Great Plains ARM Site

Using the data collected over the Southern Great Plains ARM site from 2006 to 2010, the surface Active Remote Sensing of Cloud （ARSCL） and CloudSat-CALIPSO satellite （CC） retrievals of total cloud and six specified cloud types [low, midlow （ML）, high-mid-low （HML）, mid, high-mid （HM） and high] were compared in terms of cloud fraction （CF）, cloud-base height （CBH）, cloud-top height （CTH） and cloud thickness （CT）, on different temporal scales, to identify their respective advantages and limitations. Good agreement between the two methods was exhibited in the total CF. However, large discrepancies were found between the cloud distributions of the two methods at a high （240-m） vertical grid spacing. Compared to the satellites, ARSCL retrievals detected more boundary layer clouds, while they underestimated high clouds. In terms of the six specific cloud types, more low- and mid-level clouds but less HML- and high-level clouds were detected by ARSCL than by CC. In contrast, the ARSCL retrievals of ML- and HM-level clouds agreed more closely with the estimations from the CC product. Lower CBHs tended to be reported by the surface data for low-, ML- and HML-level clouds; however, higher CTHs were often recorded by the satellite product for HML-, HM- and high-level clouds. The mean CTs for low- and ML-level cloud were similar between the two products; however, the mean CTs for HML-, mid-, HM- and high-level clouds from ARSCL were smaller than those from CC.

Aerosol Optical Properties and Radiative Impacts in the Pearl River Delta Region of China during the Dry Season

Aerosol optical properties and direct radiative effects on surface irradiance were examined using seven years （2006-2012） of Cimel sunphotometer data collected at Panyu--the main atmospheric composition monitoring station in the Pearl River Delta （PRD） region of China. During the dry season （October to February）, mean values of the aerosol optical depth （AOD） at 550 nm, the Angstrom exponent, and the single scattering albedo at 440 nm （SSA） were 0.54, 1.33 and 0.87, respectively. About 90% of aerosols were dominated by fine-mode strongly absorbing particles. The size distribution was bimodal, with fine-mode particles dominating. The fine mode showed a peak at a radius of 0.12 μm in February and October （- 0.10 μm3 μm-2）. The mean diurnal shortwave direct radiative forcing at the surface, inside the atmosphere （FATM）, and at the top of the atmosphere, was -33.4± 7.0, 26.1 ± 5.6 and -7.3 ±2.7 W m-2, respectively. The corresponding mean values of aerosol direct shortwave radiative forcing per AOD were -60.0 ±7.8, 47.3 ± 8.3 and -12.8 ±3.1 W m-2, respectively. Moreover, during the study period, FATM showed a significant decreasing trend （p 〈 0.01） and SSA increased from 0.87 in 2006 to 0.91 in 2012, suggesting a decreasing trend of absorbing particles being released into the atmosphere. Optical properties and radiative impacts of the absorbing particles can be used to improve the accuracy of inversion algorithms for satellite-based aerosol retrievals in the PRD region and to better constrain the climate effect of aerosols in climate models.

Can MODIS Detect Trends in Aerosol Optical Depth over Land?

The Moderate Resolution Imaging Spectroradiometer （MODIS） sensor onboard NASA＇s Aqua satellite has been collect- ing valuable data about the Earth system for more than 14 years, and one of the benefits of this is that it has made it possible to detect the long-term variation in aerosol loading across the globe. However, the long-term aerosol optical depth （AOD） trends derived from MODIS need careful validation and assessment, especially over land. Using AOD products with at least 70 months＇ worth of measurements collected during 2002-15 at 53 Aerosol Robotic Network （AERONET） sites over land, Mann-Kendall （MK） trends in AOD were derived and taken as the ground truth data for evaluating the corresponding results from MOD｜S onboard Aqua. The results showed that the AERONET AOD trends over all sites in Europe and North Amer- ica, as well as most sites in Africa and Asia, can be reproduced by MODIS/Aqua. However, disagreement in AOD trends between MODIS and AERONET was found at a few sites in Australia and South America. The AOD trends calculated from AERONET instantaneous data at the MODIS overpass times were consistent with those from AERONET daily data, which suggests that the AOD trends derived from satellite measurements of 1-2 overpasses may be representative of those from daily measurements.

ANALYSIS OF COLUMN-INTEGRATED AEROSOL OPTICAL THICKNESS IN BEIJING FROM AERONET OBSERVATIONS

Aerosol Optical Thickness （AOT）, water vapor content and derived Angstrom exponent acquired by a CIMEL sun photometer in Beijing are analyzed. Monthly means computed from quality-assured daily means, seasonal trends and inter-annual variations are presented and discussed. Summer has the highest seasonal average AOT at 440 nm （τa440）, Angstrom exponent （α440-870） and water vapor content with the values 0.93, 1.34 and 3.0 cm, respectively. The second highest seasonal average τa440 appears in spring with the largest variation of α440-870 and minimum α440-870 0.99 due to the impact of coarse particles. The minimum seasonal average τa440 （0.44） and water vapor content （0.4 cm） appear in winter. The annual average τa440 , α440-870 and water vapor content for about 4-year observation period are 0.70, 1.19 and 1.4 cm, respectively. All monthly average Angstrom exponents are within 0.8-1.4. which indicates aerosol in Beijing is a very complex mixture of both fine- and coarse-mode particles （from anthropogenic influence and natural mineral dust）.

Spatial and temporal distribution of the cloud optical depth over China based on MODIS satellite data during 2003–2016

The cloud optical depth(COD) is one of the important parameters used to characterize atmospheric clouds. We analyzed the seasonal variations in the COD over East Asia in 2011 using cloud mode data from the AERONET(Aerosol Robotic Network) ground-based observational network. The applicability of the MODIS(Moderate Resolution Imaging Spectroradiometer) COD product was verified and compared with the AERONET cloud mode dataset. There was a good correlation between the AERONET and the MODIS. The spatial and temporal distribution and trends in the COD over China were then analyzed using MODIS satellite data from 2003 to 2016. The seasonal changes in the AERONET data and the time sequence variation of the satellite data suggest that the seasonal variations in the COD are significant. The result shows that the COD first decreases and then increases with the season in northern China, and reaches the maximum in summer and minimum in winter.However, the spatial distribution change is just the opposite in southern China. The spatial variation trend shows the COD in China decreases first with time and gradually increases after 2014. And the trend of COD in the western and central China is consistent with that in China. While the trend of COD shows a continuously increasing over time in northeast China and the Pearl River Delta.