Estimation and Long-term Trend Analysis of Surface Solar Radiation in Antarctica: A Case Study of Zhongshan Station

Long-term,ground-based daily global solar radiation (DGSR) at Zhongshan Station in Antarctica can quantitatively reveal the basic characteristics of Earth’s surface radiation balance and validate satellite data for the Antarctic region.The fixed station was established in 1989,and conventional radiation observations started much later in 2008.In this study,a random forest (RF) model for estimating DGSR is developed using ground meteorological observation data,and a highprecision,long-term DGSR dataset is constructed.Then,the trend of DGSR from 1990 to 2019 at Zhongshan Station,Antarctica is analyzed.The RF model,which performs better than other models,shows a desirable performance of DGSR hindcast estimation with an R~2 of 0.984,root-mean-square error of 1.377 MJ m~(-2),and mean absolute error of 0.828 MJ m~(-2).The trend of DGSR annual anomalies increases during 1990–2004 and then begins to decrease after 2004.Note that the maximum value of annual anomalies occurs during approximately 2004/05 and is mainly related to the days with precipitation (especially those related to good weather during the polar day period) at this station.In addition to clouds and water vapor,bad weather conditions (such as snowfall,which can result in low visibility and then decreased sunshine duration and solar radiation) are the other major factors affecting solar radiation at this station.The high-precision,longterm estimated DGSR dataset enables further study and understanding of the role of Antarctica in global climate change and the interactions between snow,ice,and atmosphere.     

Interdecadal Variability in Surface Solar Radiation over Northwest China and Its Possible Cause

The present study investigates the interdecadal variability of seasonal mean surface solar radiation over Northwest China using station observations from 1961-2003. Spring and summer surface solar radiation over Northwest China was lower in the late 1970s through 1990s than in the 1960s through the mid-1970s, and fall and winter surface solar radiation displayed similar patterns. These results indicate that the decrease in spring and summer surface solar radiation may be associated with increased low-cloud cover over Northwest China. Rainfall anomalies were closely related to the low-cloud cover over Northwest China and with the Northern Hemisphere circumglobal teleconnection in spring, summer, and winter.     

Sensitivity of the Grid-point Atmospheric Model of IAP LASG （GAMILI.I.0） Climate Simulations to Cloud Droplet Effective Radius and Liquid Water Path

This paper documents a study to examine the sensitivity to cloud droplet effective radius and liquid water path and the alleviation the energy imbalance at the top of the atmosphere and at the surface in the latest version of the Grid-point Atmospheric Model of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics （LASG）, Institute of Atmospheric Physics （IAP） （GAMIL1.1.0）. Considerable negative biases in all flux components, and thus an energy imbalance, are found in GAMIL1.1.0. In order to alleviate the energy imbalance, two modifications, namely an increase in cloud droplet effective radius and a decrease in cloud liquid water path, have been made to the cloud properties used in GAMIL. With the increased cloud droplet effective radius, the single scattering albedo of clouds is reduced, and thus the reflection of solar radiation into space by clouds is reduced and the net solar radiation flux at the top of the atmosphere is increased. With the reduced cloud optical depth, the net surface shortwave radiation flux is increased, causing a net warming over the land surface. This results in an increase in both sensible and latent heat fluxes over the land regions, which is largely balanced by the increased terrestrial radiation fluxes. Consequently, the energy balance at the top of atmosphere and at the surface is achieved with energy flux components consistent with available satellite observations.     

THE LIGHT EQUIVALENT OF TOTAL SOLAR RADIATION AND ITS APPLICATION IN THE CALCULATION OF ILLUMINATION CLIMATOLOGY

From 1983 to 1984,14 solar radiation observation stations which are located in different climate zoneswere chosen for the simultaneous observation of natural illumination with the hourly observation of insola-tion every day.In this paper,according to the data the light equivalent of total solar radiation (LEOTSR)has been given.A multivariate regression equation is employed to calculate the annual and monthly meanvalues of the LEOTSR at 14 observation stations.The variables of the equation include latitude,elevation,surface mean absolute humidity and sunshine duration.The results show that the relative errors are lessthan 10%.The LEOTSR for 464 observation stations was calculated by means of the multivariate regression equationswhich were obtained by the data of 14 observation stations.The total illumination is given by the LEOTSRmultiplying the total radiation.The climatological values of total illumination for each station are alsocalculated according to its LEOTSR and solar radiation.Finally,the climatological charts of total illuminationin China have been drawn.     

Effect of The Atmosphere on UVB Radiation Reaching The Earth’s Surface:Dependence on Solar Zenith Angle

The atmosphere protects humans,plants,animals,and microorganisms from damaging doses of ultraviolet-B(UVB) solar radiation(280-320 nm) because it modifies the UVB reaching the Earth’s surface.This modification is a function of the solar radiation’s path length through the atmosphere and the amount of each attenuator along the path length.The path length is determined by solar zenith angle(SZA).The present work explains the dependence of hemispherical transmittance of UVB on SZA.The database used consists of five years of hourly UVB and global solar radiation measurements.From 2001 to 2005,the South Valley University(SVU) meteorological research station(26.20°N,32.75°E) carried out these measurements on a horizontal surface.In addition,the corresponding extraterrestrial UVB(UVBext) and broadband solar radiation(Gext) were estimated.Consequently,the hemispherical transmittance of UVB(KtUVB) and the hemispherical transmittance of global solar radiation(Kt) were estimated.Furthermore,the UVB redaction due to the atmosphere was evaluated.An analysis of the dependence between KtUVB and SZA at different ranges of Kt was performed.A functional dependence between KtUVB and SZA(KtUVB=-a(SZA)+b) for very narrow Kt-ranges(width of ranges was 0.01) was developed.The results are discussed,and the sensitivity of △KtUVB to △SZA for very narrow Kt-ranges was studied.It was found that the sensitivity of △KtUVB to △SZA slightly increases with increased Kt,which means KtUVB is sensitive to SZA as Kt increases.The maximum correlation(R) between KtUVB and SZA was equal to-0.83 for Kt= 0.76.     

Variation Characteristics of Ultraviolet Radiation over the North China Plain简

In situ measured data of broadband solar radiation （Rs） and ultraviolet （Uv） radiation were used to investigate the spa- tiotemporal variation properties of Uv radiation and the ratio of Uv radiation to Rs over the North China Plain （NCP）. Based on the analysis, an empirical model for estimating Uv radiation under all weather conditions in this region was developed. The results showed that the annual Uv radiation over the NCP ranges from 0.38-0.52 MJ m^-2 d^-1. The highest value during the study period was recorded at the Changwu site, which is located near the margin of the Loess Plateau, while the lowest value appeared at the station in Beijing. The seasonal variation pattern of the ratio of Uv radiation to Rs is similar to that of Uv radiation; namely, the highest value appears in August and then decreases gradually until the lowest value appears in November. A small increasing trend in the Uv radiation levels and the ratio of Uv radiation to Rs was observed over the NCP. The evaluation results showed that the empirical estimation model can be widely used to estimate Uv radiation under all atmospheric conditions. The relative error between the modeled and measured daily values were within ± 15%.     

Estimation of Hourly Solar Radiation at the Surface under Cloudless Conditions on the Tibetan Plateau Using a Simple Radiation Model

In this study,the clear sky hourly global and net solar irradiances at the surface determined using SUNFLUX,a simple parameterization scheme,for three stations(Gaize,Naqu,and Lhasa) on the Tibetan Plateau were evaluated against observation data.Our modeled results agree well with observations.The correlation coefficients between modeled and observed values were > 0.99 for all three stations.The relative error of modeled results,in average was < 7%,and the root-mean-square variance was < 27 W m 2.The solar irradiances in the radiation model were slightly overestimated compared with observation data;there were at least two likely causes.First,the radiative effects of aerosols were not included in the radiation model.Second,solar irradiances determined by thermopile pyranometers include a thermal offset error that causes solar radiation to be slightly underestimated.The solar radiation absorbed by the ozone and water vapor was estimated.The results show that monthly mean solar radiation absorbed by the ozone is < 2% of the global solar radiation(< 14 W m 2).Solar radiation absorbed by water vapor is stronger in summer than in winter.The maximum amount of monthly mean solar radiation absorbed by water vapor can be up to 13% of the global solar radiation(95 W m 2).This indicates that water vapor measurements with high precision are very important for precise determination of solar radiation.     

Testing and Improving the Performance of the Common Land Model:A Case Study for the Gobi Landscape

Land surface processes take place on the interface between the earth and atmosphere, exerting significant influences on the weather and climate. Correct modeling of these processes is important to numerical weather forecast and climate prediction. In order to obtain a more thorough understanding of the land surface processes over the Gobi landscape, we evaluated the performance of the Common Land Model(Co LM) at Dunhuang station in Gansu Province of China to determine whether the model formulation, driven by observational data, is capable of simulating surface fluxes over the underlying desert surface. In comparison with the enhanced observation data collected at Dunhuang station over the period 22–28 August 2008, the results showed that the surface albedo simulated by Co LM was larger than that in the observation, and the simulated surface temperature was lower than the observed. After the measured values were used to correct the surface albedo, the solar radiation absorbed by the ground surface was more consistent with the measurements. A new empirical relationship of the surface thermal exchange coefficient rah was used to modify the thermal aerodynamic impedance. The simulated soil surface temperature became significantly closer to the observed value, and the simulated surface sensible heat as well as net radiative fluxes were also improved.     

ELEMENTARY VIEW OF GREENHOUSE EFFECT OF THE ATMOSPHERES OF VARIOUS PLANETS

The global mean temperatures of the atmosphere and the surface of various planets of the solar system are deter-mined by taking the system as in radiative equilibrium,with the atmosphere taken as transparent to solar radiation butwith an albedo α,and composed of N layers each of which absorbs all infrared radiation that falls on it,and a top layerof partial absorptivity a,while the surface is taken as black.It is found that,for the earth's atmosphere with α=0.33,N=0,a=0.83,it gives the current observed mean surface temperature T_s=15℃ and the effective mean radiative temper-ature of the atmosphere T_a=242.6K.On the other hand;the atmosphere of Venus is characterized by α=0.70 andN=70,which yields a surface temperature of about 700K.It is also found that surface evaporation and absorption of solar radiation by the atmosphere tend to lower the sur-face temperature.     

Influence of Changes in Solar Radiation on Changes of Surface Temperature in China

The long-term trends of total surface solar radiation(SSR),surface diffuse radiation,and surface air temperature were analyzed in this study based on updated 48-yr data from 55 observational stations in China,and then the correlation between SSR and the diurnal temperature range(DTR) was studied.The effect of total solar radiation on surface air temperature in China was investigated on the basis of the above analyses.A strong correlation between SSR and DTR was found for the period 1961-2008 in China.The highest correlation and steepest regression line slope occurred in winter,indicating that the solar radiation effect on DTR was the largest in this season.Clouds and water vapor have strong influences on both SSR and DTR,and hence on their relationship.The largest correlations between SSR and DTR occurred in wintertime in northern China,regardless of all-day(including clear days and cloudy days) or clear-day cases.Our results also showed that radiation arriving at the surface in China decreased significantly during 1961-1989(dimming period),but began to increase during 1990-2008(brightening period),in agreement with previous global studies.The reduction of total SSR offset partially the greenhouse warming during 1961-1989.However,with the increase of SSR after 1990,this offsetting effect vanished;on the contrary,it even made a contribution to the accelerated warming.Nonetheless,the greenhouse warming still played a controlling role because of the increasing of minimum and mean surface temperatures in the whole study period of 1961-2008.We estimated that the greenhouse gases alone may have caused surface temperatures to rise by 0.31-0.46℃(10 yr) 1 during 1961-2008,which is higher than previously estimated.Analysis of the corresponding changes in total solar radiation,diffuse radiation,and total cloud cover indicated that the dimming and brightening phenomena in China were likely attributable to increases in absorptive and scattering aerosols in the atmosphere,respectively.     

A Case Study of the Impacts of Dust Aerosols on Surface Atmospheric Variables and Energy Budgets in a Semi-Arid Region of China

The authors present a case study investigating the impacts of dust aerosols on surface atmospheric variables and energy budgets in a semi-arid region of China. Enhanced observational meteorological data, radiative fluxes, near-surface heat fluxes, and concentrations of dust aerosols were collected from Tongyu station, one of the reference sites of the International Coordinated Energy and Water Cycle Observations Project (CEOP), during a typical dust storm event in June 2006. A comprehensive analysis of these data show that in this semi-arid area, higher wind velocities and a continuously reduced air pressure were identified during the dust storm period. Dust storm events are usually associated with low relative humidity weather conditions, which result in low latent heat flux values. Dust aerosols suspended in the air decrease the net radiation, mainly by reducing the direct solar radiation reaching the land surface. This reduction in net radiation results in a decrease in soil temperatures at a depth of 2 cm. The combination of increased air temperature and decreased soil temperature strengthens the energy exchange of the atmosphere-earth system, increasing the surface sensible heat flux. After the dust storm event, the atmosphere was dominated by higher pressures and was relatively wet and cold. Net radiation and latent heat flux show an evident increase, while the surface sensible heat flux shows a clear decrease.     

All-Sky Direct Radiative Effects of Urban Aerosols in Beijing and Shanghai,China

Aerosol particles can directly alter the radiation balance by scattering and absorbing incident solar radiation, thus decreasing the amount of light reaching the surface and increasing the fraction of diffuse radiation—the so-called ‘aerosol direct radiative effect'. Using the Moderate Resolution Imaging Spectroradiometer aerosol products, the aerosol direct radiative effects under all-sky conditions in Beijing and Shanghai in 2007 were explored in this study. The total shortwave radiation was calculated using the Fu-Liou radiative transfer model, with the influence of clouds taken into account through sunshine-duration data, and the diffuse radiation was calculated with radiation decomposition models. Good correlation between measured and calculated total radiation was obtained at both cities, with an R greater than 0.9, and thus this calculation method was adopted to derive aerosol direct radiative effects. The presence of aerosols caused the mean total and diffuse solar radiation reaching the surface to change by-19.9% and +27.4% in Beijing, respectively, and by-18.4% and +6.5% in Shanghai. It was also found that, despite the strong negative correlation between aerosol optical depth and total radiation change, the diffuse radiation changes were determined predominantly by clouds. The effects of such changes induced by aerosols on plant productivity should be further studied.     

Characteristics of Solar Radiation and the Impact of Clouds at Yangbajing, Tibet

Yangbajing (YBJ) is located in the Tibetan Plateau, China. The characteristics of solar radiation and its relationship with clouds at YBJ from April 2009 to April 2010 were analyzed in this paper. The annual mean solar radiation was 478.4 W m 2 , and the annual mean transmittance was 0.713. The atmospheric mean trans- mittance of clear skies reaches 0.828 when the solar elevation angle (SEA) is greater than 10 degrees. Comparisons with numerical simulations show that the atmosphere of YBJ is clean. Impacts from atmospheric conditions on solar radiation are similar for clear skies during the year because the standard deviation of transmittance in clear skies was less than 0.05 when the SEA was greater than 10 degrees. It is important to understand the impact of clouds on solar radiation without considering other impact factors. In the last part of this article, the authors analyzed and established a statistical quantitative relationship between surface solar radiation and cloud fraction.     

Study of distinctive regional features of surface solar radiation in North and East China

Solar radiation is an important energy source for plants on the earth and also a major component of the global energy balance. Variations in solar radiation incident at the earth’s surface profoundly affect the human and terrestrial environment, including the climate change. To provide useful information for predicting the future climate change in China, distinctive regional features in spatial and temporal variations of the surface solar radiation (SSR) and corresponding attributions (such as cloud and aer...     

Four-stream Radiative Transfer Parameterization Scheme in a Land Surface Process Model

Accurate estimates of albedos are required in climate modeling. Accurate and simple schemes for radiative transfer within canopy are required for these estimates, but severe limitations exist. This paper developed a four-stream solar radiative transfer model and coupled it with a land surface process model. The radiative model uses a four-stream approximation method as in the atmosphere to obtain analytic solutions of the basic equation of canopy radiative transfer. As an analytical model, the four-stream radiative transfer model can be easily applied efficiently to improve the parameterization of land surface radiation in climate models. Our four-stream solar radiative transfer model is based on a two-stream short wave radiative transfer model. It can simulate short wave solar radiative transfer within canopy according to the relevant theory in the atmosphere. Each parameter of the basic radiative transfer equation of canopy has special geometry and optical characters of leaves or canopy. The upward or downward radiative fluxes are related to the diffuse phase function, the G-function, leaf reflectivity and transmission, leaf area index, and the solar angle of the incident beam. The four-stream simulation is compared with that of the two-stream model. The four-stream model is proved successful through its consistent modeling of canopy albedo at any solar incident angle. In order to compare and find differences between the results predicted by the four- and two-stream models, a number of numerical experiments are performed through examining the effects of different leaf area indices, leaf angle distributions, optical properties of leaves, and ground surface conditions on the canopy albedo. Parallel experiments show that the canopy albedos predicted by the two models differ significantly when the leaf angle distribution is spherical and vertical. The results also show that the difference is particularly great for different incident solar beams. One additional experiment is carried out to evaluate the simulations of the BATS land surface model coupled with the two- and four-stream radiative transfer models. Station observations in 1998 are used for comparison. The results indicate that the simulation of BATS coupled with the four-stream model is the best because the surface absorbed solar radiation from the four-stream model is the closest to the observation.     

NUMERICAL SIMULATIONS OF THE EFFECTS OF AEROSOLS IN THE ATMOSPHERIC BOUNDARY LAYER ON THE CLIMATE

The climatic effects of the atmospheric boundary aerosols are studied by the use of a three-dimensional climatemodel.Simulated results show that the climate states both at the surface and in the atmosphere change remarkably whenthe aerosols with different optical thicknesses and properties are introduced into the atmospheric boundary layer of themodel.The aerosols absorb and scatter the solar shortwave radiation,therefore,they reduce the solar energy reachingthe ground surface and decrease the surface and the soil temperatures.The temperature in the boundary layer increasesbecause of the supplementary absorption of radiation by the boundary aerosols.In the atmosphere,the temperatures atall isobaric surfaces rise up except for the 100 hPa level.The atmospheric temperatures below the 500 hPa level aredirectly influenced by the boundary aerosols,while the atmospheric temperatures above the 500 hPa level are influencedby the heating due to convective condensation and the changes in the vertical motion field.Cyclonic differential circula-tions appear over the desert areas at the low levels,and anticyclonic differential circulations exist at the upper levels inthe horizontal flow fields.The vertical motions change in correspondence with the differential circulations.The changesin precipitation are directly related to that of vertical motions.The mechanisms of climate effects of the boundaryaerosols are also discussed in this paper.     

SATELLITE OBSERVATION OF SURFACE ALBEDO OVER THE QINGHAI-XIZANG PLATEAU REGION

A method has been developed to determine the surface albedo over the Qinghai-Xizang Plateau region from NOAA polar orbiter AVHRR (Advanced Very High Resolution Radiometer) data. The empirical relationship between clear-sky planetary and surface albedos is established the basis of surface global radiation measurements and the specified ratio between atmospheric reflection and absoption of solar radiation. The method is applied to the Qinghai-Xizang region with several measurements during the period of Sep. to Nov., 1985. A comparison is presented between the estimated surface albedos and that of surface observation. The results show that the presented method is suitable to detecting the spatial and temporal variation of surface albedo and is relevant for climatological studies. The possible error sources and improvements are discussed as well.     

INFLUENCES OF DIURNAL CHANGE OF SOLAR RADIATION ON SIMULATED PROPERTIES OF SUMMER MONSOON

Comparative experiments with and without the diurnal change of solar radiation are made inthis paper by use of an air-sea coupled 7-layer primitive equation modeling system in a zonal domainbetween 60°S and 60°N.The results show that the quasi-stationary patterns of the mean monsooncirculations are not evidently affected by the diurnal change of solar radiation.The main influencesmay come from the land-sea distribution and the orography.However,the inclusion of the diurnalchange of solar radiation into the model system may improve the intensities of the simulatedmonsoon circulations both at the high and the low levels.It can influence the distributive patternof precipitation to a larger extent.Without the diurnal change,precipitation in the interior of landwould decrease and in the coastal regions it would increase.The changes of the soil temperatureand the soil moisture are fairly correspondent to that of precipitation.The areas with increasingprecipitation and the areas with decreasing precipitation are distributed in the wave form.As to theinfluences on the monsoon development,the results indicate that the diurnal change of solarradiation can speed up the development of the monsoon in the early stage.Therefore,the inclusionof the diurnal change of solar radiation can make the model equilibrium state to reach earlier.     

Atmospheric Corrections Using MODTRAN for TOA and Surface BRDF Characteristics from High Resolution Spectroradiometric/Angular Measurements from a Helicopter Platform

High-resolution spectral radiance measurements were taken by a spectral radiometer on board a heli copter over the US Oklahoma Southern Great Plain near the Atmospheric Radiation Measurements (ARM) site during August 1998. The radiometer has a spectral range from 350 nm to 2500 nm at 1 nm resolution. The measurements covered several grass and cropland scene types at multiple solar zenith angles. Detailed atmospheric corrections using the Moderate Resolution Transmittance (MODTRAN) radiation model and in-situ sounding and aerosol measurements have been applied to the helicopter measurements in order to re trieve the surface and top of atmosphere (TOA) Bidirectional Reflectance Distribution Function (BRDF) characteristics. The atmospheric corrections are most significant in the visible wavelengths and in the strong water vapor absorption wavelengths in the near infrared region. Adjusting the BRDF to TOA requires a larger correction in the visible channels since Rayleigh scattering contributes significantly to the TOA reflectance. The opposite corrections to the visible and near infrarred wavelengths can alter the radiance dif ference and ratio that many remote sensing techniques are based on, such as the normalized difference vege tation index (NDVI). The data show that surface BRDFs and spectral albedos are highly sensitive to the veg etation type and solar zenith angle while BRDF at TOA depends more on atmospheric conditions and the vi ewing geometry. Comparison with the Clouds and the Earth＇s Radiant Energy System (CERES) derived clear sky Angular Distribution Model (ADM) for crop and grass scene type shows a standard deviation of 0.08 in broadband anisotropic function at 25° solar zenith angle and 0.15 at 50° solar zenith angle, respectively.     

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 va...