Clear-sky Radiation Research Articles

Worldwide variations in artificial skyglow.

Despite constituting a widespread and significant environmental change, understanding of artificial nighttime skyglow is extremely limited. Until now, published monitoring studies have been local or regional in scope, and typically of short duration. In this first major international compilation of monitoring data we answer several key questions about skyglow properties. Skyglow is observed to vary over four orders of magnitude, a range hundreds of times larger than was the case before artificial light. Nearly all of the study sites were polluted by artificial light. A non-linear relationship is observed between the sky brightness on clear and overcast nights, with a change in behavior near the rural to urban landuse transition. Overcast skies ranged from a third darker to almost 18 times brighter than clear. Clear sky radiances estimated by the World Atlas of Artificial Night Sky Brightness were found to be overestimated by ~25%; our dataset will play an important role in the calibration and ground truthing of future skyglow models. Most of the brightly lit sites darkened as the night progressed, typically by ~5% per hour. The great variation in skyglow radiance observed from site-to-site and with changing meteorological conditions underlines the need for a long-term international monitoring program.

Forecasting solar radiation using an optimized hybrid model by Cuckoo Search algorithm

Due to energy crisis and environmental problems, it is very urgent to find alternative energy sources nowadays. Solar energy, as one of the great potential clean energies, has widely attracted the attention of researchers. In this paper, an optimized hybrid method by CS (Cuckoo Search) on the basis of the OP-ELM (Optimally Pruned Extreme Learning Machine), called CS-OP-ELM, is developed to forecast clear sky and real sky global horizontal radiation. First, MRSR (Multiresponse Sparse Regression) and LOO-CV (leave-one-out cross-validation) can be applied to rank neurons and prune the possibly meaningless neurons of the FFNN (Feed Forward Neural Network), respectively. Then, Direct strategy and Direct-Recursive strategy based on OP-ELM are introduced to build a hybrid model. Furthermore, CS (Cuckoo Search) optimized algorithm is employed to determine the proper weight coefficients. In order to verify the effectiveness of the developed method, hourly solar radiation data from six sites of the United States has been collected, and methods like ARMA (Autoregression moving average), BP (Back Propagation) neural network and OP-ELM can be compared with CS-OP-ELM. Experimental results show the optimized hybrid method CS-OP-ELM has the best forecasting performance.

Brief Accuracy Assessment of Aerosol Climatologies for the Retrieval of Solar Surface Radiation

Solar surface irradiance is an important variable in many different fields, e.g., climate monitoring and solar energy. Remote sensing data are nowadays well established and the only observational data source in many regions of the world. Aerosols significantly affect the clear sky radiation and hence also the all sky radiation. In order to achieve the optimal accuracy for surface radiation, information of aerosols with low uncertainty is needed. In this study, the effect of four different aerosol climatologies on the solar surface radiation have been evaluated for the period 2006–2009 at nine BSRN stations. The use of the aerosol climatology from the European Center of Medium Weather Forecast (MACC) leads to the highest accuracy of solar radiation. The mean absolute bias is 6.8 Watt per square meter for global irradiance and 11.3 for direct irradiance. With the Max-Planck climatology (MAC-v1) 9.4 and 14.8 Watt per square meter and with GADS/OPAC (Global Aerosol Data Set/Optical Properties of Aerosols and Clouds) 10.0 and 14.6 Watt per square meter have been achieved, respectively. The improvement in the accuracy of solar radiation by using the MACC climatology is relatively large. Also remarkable is that the new MAC-v1 climatology and the older GADS/OPAC climatology performs on the same level with respect to the achieved accuracy in radiation. The effect of interannual variations of Aerosol Optical Depth (AOD) on the global irradiance is rather low for the investigated sites and period.

A hybrid modelling approach for assessing solar radiation

A hybrid technique for solar radiation estimation, a core part of hydrological cycle, is presented in this study which parameterises the cloud cover effect (cloud cover index) not just from the geostationary satellites but also the PSU/NCAR’s Mesoscale Modelling system (MM5) model. This, together with output from a global clear sky radiation model and observed datasets of temperature and precipitation are used as inputs within the Gamma test (GT) environment for the development of nonlinear models for global solar radiation estimation. The study also explores the ability of Gamma test to determine the optimum input combination and data length selection. Artificial neural network- and local linear regression-based nonlinear techniques are used to test the proposed methodology, and the results have shown a high degree of correlation between the observed and estimated values. It is believed that this study will initiate further exploration of GT for improving informed data and model selection.

Retrieval of Atmospheric and Cloud Property Anomalies and Their Trend from Temporally and Spatially Averaged Infrared Spectra Observed from Space

Abstract A surface, atmospheric, and cloud (fraction, height, optical thickness, and particle size) property anomaly retrieval from highly averaged longwave spectral radiances is simulated using 28 years of reanalysis. Instantaneous nadir-view spectral radiances observed from an instrument on a 90° inclination polar orbit are computed. Spectral radiance changes caused by surface, atmospheric, and cloud property perturbations are also computed and used for the retrieval. This study’s objectives are 1) to investigate whether or not separating clear sky from cloudy sky reduces the retrieval error and 2) to estimate the error in a trend of retrieved properties. This simulation differs from earlier studies in that annual 10° latitude zonal cloud and atmospheric property anomalies defined as the deviation from 28-yr climatological means are retrieved instead of the difference of these properties from two time periods. The root-mean-square (RMS) difference of temperature and humidity anomalies retrieved from all-sky radiance anomalies is similar to the RMS difference derived from clear-sky radiance anomalies computed by removing clouds. This indicates that the cloud property anomaly retrieval error does not affect the retrieved temperature and humidity anomalies. When retrieval errors are nearly random, the error in the trend of retrieved properties is small. Approximately 30% of 10° latitude zones meet conditions that the true temperature and water vapor amount trends are within a 95% confidence interval of retrieved trends, and that the standard deviation of retrieved anomalies σret is within 20% of the standard deviation of true anomalies σn. If σret/σn − 1 is within ±0.2, 91% of the true trends fall within the 95% confidence interval of the corresponding retrieved trend.

KPV: A clear-sky index for photovoltaics

The rapidly growing installed base of distributed solar photovoltaic (PV) systems is causing increased interest in forecasting their power output. A key step towards this is accurately estimating the output from a PV system based on the known output from a nearby PV system. However, each PV system is unique with its own hardware configuration, orientation, shading, etc. Thus, the process of using the power output from one system to estimate the power output of another nearby system is not necessarily straightforward. In order to address these challenges, a modified clear-sky index for photovoltaics is proposed. This index is the ratio of the instantaneous PV power output to the instantaneous theoretical clear-sky power output derived from a clear-sky radiation model and PV system simulation routine. This definition performs better than previous clear-sky indices when both PV systems’ characteristics are known and the two PV systems have similar orientations. Through this index, the performance of a nearby PV system can be predicted quite accurately. This is demonstrated through the analysis of power output data from five residential PV systems in Canberra, Australia.

Application and evaluation of a new radiation code under McICA scheme in BCC_AGCM2.0.1

Abstract. This research incorporates the correlated k distribution BCC-RAD radiation model into the climate model BCC_AGCM2.0.1 and examines the change in climate simulation by implementation of the new radiation algorithm. It is shown that both clear-sky radiation fluxes and cloud radiative forcings (CRFs) are improved. The modeled atmospheric temperature and specific humidity are also improved due to changes in radiative heating rates, which most likely stem from the revised treatment of gaseous absorption. Subgrid cloud variability, including vertical overlap of fractional clouds and horizontal inhomogeneity in cloud condensate, is addressed by using the Monte Carlo Independent Column Approximation (McICA) method. In McICA, a cloud-type-dependent function for cloud fraction decorrelation length, which gives zonal mean results very close to the observations of CloudSat/CALIPSO, is developed. Compared to utilizing a globally constant decorrelation length, the maximum changes in seasonal CRFs by the new scheme can be as large as 10 and 20 W m−2 for longwave (LW) and shortwave (SW) CRFs, respectively, mostly located in the tropics. The inclusion of an observation-based horizontal inhomogeneity of cloud condensate has also a significant impact on CRFs, with global means of ~ 1.5 W m−2 and ~ 3.7 Wm−2 for LW and SW CRFs at the top of atmosphere (TOA), respectively. Generally, incorporating McICA and horizontal inhomogeneity of cloud condensate in the BCC-RAD model reduces global mean TOA and surface SW and LW flux biases in BCC_AGCM2.0.1. These results demonstrate the feasibility of the new model configuration to be used in BCC_AGCM2.0.1 for climate simulations, and also indicate that more detailed real-world information on cloud structures should be obtained to constrain cloud settings in McICA in the future.

Assessment of the effect of air pollution controls on trends in shortwave radiation over the United States from 1995 through 2010 from multiple observation networks

Abstract. Long-term data sets of all-sky and clear-sky downwelling shortwave (SW) radiation, cloud cover fraction, and aerosol optical depth (AOD) were analyzed together with surface concentrations from several networks (e.g., Surface Radiation Budget Network (SURFRAD), Clean Air Status and Trend Network (CASTNET), Interagency Monitoring of Protection Visual Environments (IMPROVE) and Atmospheric Radiation Measurement (ARM)) in the United States (US). Seven states with varying climatology were selected to better understand the effects of aerosols and clouds on SW radiation. This analysis aims to assess the effects of reductions in anthropogenic aerosol burden resulting from substantial reductions in emissions of sulfur dioxide (SO2) and nitrogen oxides (NOx) over the past 16 yr across the US, based on trends in SW radiation. The SO2 and NOx emission data show decreasing trends from 1995 to 2010, which indirectly validates the effects of the Clean Air Act (CAA) in the US. Meanwhile, the total column AOD and surface total PM2.5 observations also show decreasing trends in the eastern US but slightly increasing trends in the western US. Moreover, measured surface concentrations of several other pollutants (i.e., SO2, SO4 and NOx) have similar behavior to AOD and total PM2.5. Analysis of the observed data shows strong increasing trends in all-sky downwelling SW radiation with decreasing trends in cloud cover. However, since observations of both all-sky direct and diffuse SW radiation show increasing trends, there may be other factors contributing to the radiation trends in addition to the decreasing trends in overall cloud cover. To investigate the role of direct radiative effects of aerosols, clear-sky downwelling radiation is analyzed so that cloud effects are eliminated. However, similar increasing trends in clear-sky total and diffuse SW radiation are observed. While significantly decreasing trends in AOD and surface PM2.5 concentrations along with increasing SW radiation (both all-sky and clear-sky) in the eastern US during 1995–2010 imply the occurrence of direct aerosol mediated "brightening", the increasing trends of both all-sky and clear-sky diffuse SW radiation contradicts this conclusion since diffuse radiation would be expected to decrease as aerosols direct effects decrease and cloud cover decreases. After investigating several confounding factors, the increasing trend in clear-sky diffuse SW may be due to more high-level cirrus from increasing air traffic over the US. The clear-sky radiation observations in the western US also show indications of "brightening" even though the AOD, PM2.5 and surface concentration do not vary drastically. This outcome was not unexpected because the CAA controls were mainly aimed at reducing air pollutant emissions in the eastern US and air pollutant levels in the western US were much lower at the onset. This suggests other factors affect the "brightening" especially in the western US.

A surface radiation climatology across two Meteosat satellite generations

Long-term observations of the surface radiation budget are essential for climate monitoring, climate model evaluation and solar energy applications. The Satellite Application Facility on Climate Monitoring (CM SAF) released a climate data record (CDR) of global and direct surface irradiance as well as effective cloud albedo derived from observations of the Meteosat First Generation satellites (MFG, 1983–2005). This study presents an extension of this CDR using measurements from the Meteosat Second Generation satellites (MSG, 2004–present). This extended surface radiation dataset spans nearly 30years of data and, therefore, is in its uniquely high temporal and spatial resolution a valuable contribution to the climate community.In order to enable climatological consistency and homogeneity, the retrieval algorithm had to be modified for MSG: 1. The two narrowband visible channels of the MSG satellites are combined to simulate the MFG broadband visible channel; 2. The maximum cloud reflectance is empirically adjusted to account for the differences in the dynamic range of MSG compared to MFG.The extended dataset is tested for homogeneity and no significant breaks are detected during the overlap period of 2004–2005. Validation of the extended global radiation dataset against ground based observations from the Baseline Surface Radiation Network yields a mean monthly absolute bias of 8.15Wm−2. This complies with the target accuracy threshold of 15Wm−2 defined by the Global Climate Observing System.Global radiation has an overall positive, and significant, trend over the Meteosat disk which is mainly due to a negative trend in the effective cloud albedo, i.e., a decrease in cloudiness. Trends due to changes in the clear sky radiation are small and only induced by trends in the water vapor fields. Trends caused by changes in the direct effects of atmospheric aerosol are not represented because an aerosol climatology is used.

Can Top-of-Atmosphere Radiation Measurements Constrain Climate Predictions? Part I: Tuning

Perturbed physics configurations of version 3 of the Hadley Centre Atmosphere Model (HadAM3) driven with observed sea surface temperatures (SST) and sea ice were tuned to outgoing radiation observations using a Gauss–Newton line search optimization algorithm to adjust the model parameters. Four key parameters that previous research found affected climate sensitivity were adjusted to several different target values including two sets of observations. The observations used were the global average reflected shortwave radiation (RSR) and outgoing longwave radiation (OLR) from the Clouds and the Earth's Radiant Energy System instruments combined with observations of ocean heat content. Using the same method, configurations were also generated that were consistent with the earlier Earth Radiation Budget Experiment results. Many, though not all, tuning experiments were successful, with about 2500 configurations being generated and the changes in simulated outgoing radiation largely due to changes in clouds. Clear-sky radiation changes were small, largely due to a cancellation between changes in upper-tropospheric relative humidity and temperature. Changes in other climate variables are strongly related to changes in OLR and RSR particularly on large scales. There appears to be some equifinality with different parameter configurations producing OLR and RSR values close to observed values. These models have small differences in their climatology with the one group being similar to the standard configuration and the other group drier in the tropics and warmer everywhere.

Evaluation of clear-sky conditions in high altitude sites

The correct assessment of cloud conditions in any site is important for determining the characteristics of solar resource availability. The criterion proposed by Iqbal has been widely used for this purpose, through the classification of the daily clearness index Kt. However, evidence was found to suggest that this criterion may not be applicable to data measured in high altitude sites, because partially cloudy days are incorrectly classified as clear-sky days. This paper analyzes the cloudiness state of the sky by observing the values of the clearness index Kt and the clear-sky index Kc. These indices were obtained from reliable global solar irradiance data measured over a year in three places of Argentina located at different altitudes (25, 1200 and 3700 m.a.s.l). ESRA and ARG-P models were used to estimate daily clear-sky global solar irradiation values Hc. They also reveal that the most probable value of Kc which corresponds to an actual clear-sky day of a particular location and time depends on the model used to estimate the clear-sky global solar radiation values. Thus, it was confirmed that, unlike the index Kc, the Iqbal's criterion does not correctly classify the cloud cover status from data measured in high altitude sites (>1000 m.a.s.l.).

Low simulated radiation limit for runaway greenhouse climates

Terrestrial planet atmospheres must be in long-term radiation balance, with solar radiation absorbed matched by thermal radiation emitted. For hot moist atmospheres, however, there is an upper limit on the thermal emission which is decoupled from the surface temperature. If net absorbed solar radiation exceeds this limit the planet will heat uncontrollably, the so-called \runaway greenhouse. Here we show that a runaway greenhouse induced steam atmosphere may be a stable state for a planet with the same amount of incident solar radiation as Earth has today, contrary to previous results. We have calculated the clear-sky radiation limits at line-by-line spectral resolution for the first time. The thermal radiation limit is lower than previously reported (282 W/sq m rather than 310W/sq m) and much more solar radiation would be absorbed (294W/sq m rather than 222W/sq m). Avoiding a runaway greenhouse under the present solar constant requires that the atmosphere is subsaturated with water, and that cloud albedo forcing exceeds cloud greenhouse forcing. Greenhouse warming could in theory trigger a runaway greenhouse but palaeoclimate comparisons suggest that foreseeable increases in greenhouse gases will be insufficient to do this.

Sensor-based clear and cloud radiance calculations in the community radiative transfer model

The community radiative transfer model (CRTM) has been implemented for clear and cloudy satellite radiance simulations in the National Oceanic and Atmospheric Administration (NOAA) National Centers for Environmental Prediction (NCEP) Gridpoint Statistical Interpolation data assimilation system for global and regional forecasting as well as reanalysis for climate studies. Clear-sky satellite radiances are successfully assimilated, while cloudy radiances need to be assimilated for improving precipitation and severe weather forecasting. However, cloud radiance calculations are much slower than the calculations for clear-sky radiance, and exceed our computational capacity for weather forecasting. In order to make cloud radiance assimilation affordable, cloud optical parameters at the band central wavelength are used in the CRTM (OPTRAN-CRTM) where the optical transmittance (OPTRAN) band model is applied. The approximation implies that only one radiative transfer solution for each band (i.e., channel) is needed, instead of typically more than 10,000 solutions that are required for a detailed line-by-line radiative transfer model (LBLRTM). This paper investigated the accuracy of the approximation and helps us to understand the error source. Two NOAA operational sensors, High Resolution Infrared Radiation Sounder/3 (HIRS/3) and Advanced Microwave Sounding Unit (AMSU), have been chosen for this investigation with both clear and cloudy cases. By comparing the CRTM cloud radiance calculations with the LBLRTM simulations, we found that the CRTM cloud radiance model can achieve accuracy better than 0.4 K for the IR sensor and 0.1 K for the microwave sensor. The results suggest that the CRTM cloud radiance calculations may be adequate to the operational satellite radiance assimilation for numerical forecast model. The accuracy using OPTRAN is much better than using the scaling method (SCALING-CRTM). In clear-sky applications, the scaling of the optical depth derived at nadir for brightness temperature calculation at the other direction may result in an error up to about 7 K for some HIRS/3 channels. Under cloudy conditions, SCALING-CRTM may result in an error of about 3.5 K.

A clear sky irradiation assessment using the European Solar Radiation Atlas model and Shuttle Radar Topography Mission database: A case study for Romanian territory

The objectives of this paper are to develop a software application that allows to establish the clear-sky solar radiation on horizontal surface considering the shading effect of complex topography of terrain and to employ it in order to assess the amount of clear-sky irradiation over Romanian territory. In order to achieve the first objective, a clear sky solar radiation model developed in accordance with the latest mathematical equations published in European Solar Radiation Atlas has been adopted and implemented together with a digital elevation model developed based on the Shuttle Radar Topography Mission database. In order to achieve the second objective, based on a digital elevation model of the Romanian territory, the monthly average daily clear-sky irradiation over whole territory has been established. The estimates have been validated using the solar radiation values from other two well known databases, the relative errors shown that the irradiance values have a good accuracy. The software application has been involved in order to build and analyze the maps of monthly average of daily irradiation, in the assumption of the clear-sky conditions and in horizontal surface, over whole Romanian territory.

Constraints on the partitioning of Kīlauea’s lavas between surface and tube flows, estimated from infrared satellite data, sulfur dioxide emission rates, and field observations

This paper describes how observations of sulfur dioxide (SO2) degassing rates (obtained in situ), thermal emission rates (obtained from infrared satellite data), and semiquantitative flow field observations can be used to elucidate the partitioning of lava between the surface and tube systems at Kīlauea volcano, Hawai’i, over a decadal timescale. For most of our study period, 2000 to 2009, we found that the infrared spectral radiance measured by Moderate Resolution Imaging Spectroradiometer from the flow field under clear-sky conditions is controlled by the lava effusion rate and the amount of flow accommodated by the subsurface tube system. At Kīlauea, the degree of tubing is estimated qualitatively using field observations, and we show that the satellite data and in situ gas data can be used to estimate the percentage of lava on the surface relative to the total amount erupted. This empirical relationship works to describe many cases in the past decade at Kīlauea but breaks down when there is a lack of concurrent clear-sky radiance and SO2 data or when magma is being stored and degassed prior to eruption. Our observations provide a simple way to estimate the partitioning of Kīlauea’s total lava supply between surface and tube-fed flows using a long-term dataset. This is important because the transition between periods when lava is distributed primarily by surface flows to periods where tubes dominate has been suggested to indicate significant changes in the character of decadal-scale eruptions at Kīlauea (Heliker et al., Bull Volcanol 59:381–393, 1998). In addition, it is during those times when surface flows predominate that the flow field does most of its lateral expansion and the hazards associated with the lava effusion become more pronounced.

Relationship between sunshine duration and solar radiation

This paper examines the relationship between sunshine duration and solar radiation received on the earth’s surface. Sixty-nine thousand pairs of sunshine–radiation readings from 670 sites were analyzed. A generalization of the Ångström–Prescott equation of the form K¯=K¯clear[β+(1-β)Sγ] was found to most efficiently fit the data and suggests the relationship between the average daily atmospheric transmittance K¯ and the sunshine fraction S is non-linear. The suggested reason for this non-linearity is that a reduced sunshine fraction not only decreases the clear sky radiation duration, but also the radiation transmitted through clouds, i.e. clouds get optically thicker with decreasing S. This finding is supported on theoretical grounds and by analyzing instantaneous solar radiation measurements from Australia and Germany.Representing the sunshine fraction in terms of the proportion of beam radiation reaching the earth’s surface S=H¯b/H¯b,clear leads to a fundamental connection between the monthly average diffuse fraction and the sunshine–radiation relationship. Moreover, it confirms the non-linearity of the latter relationship, which was previously questioned because of limited data and/or poor quality sunshine measurements.

Use of a clear-day solar radiation model to homogenize solar radiation measurements in Hawai‘i

The reliability of solar irradiance measurements is dependent on the calibration of the pyranometer used to make them. Internationally recognized standards for pyranometer calibrations require resources that may not be available to all observers. To fill this gap, we propose a method of homogenizing hourly solar radiation time series based on comparison of clear-sky radiation observations against estimates derived from a clear-sky radiation model. Inhomogeneities in the record are identified based on shifts in pyranometer response in relation to the model estimates, and corrected to produce a homogeneous time series. This method was applied to the ∼23year record of hourly solar irradiance measurements recorded at three climate stations along a 870m elevation gradient (2120–2990m) on the slopes of Haleakalā Volcano, Maui, Hawai‘i. Corrections resulted in changes in monthly solar radiation of as much as 6.8–7.4% among the three stations.

Scales of spatial and temporal variation of solar irradiance on Reunion tropical island

Tropical islands, such as Reunion Island (21°S, 55.5°E) in the southwestern Indian Ocean, have significant solar resource that is highly variable in both spatial and temporal scales because of heterogeneous and rapidly changing cloudiness. The characterization of this variability is essential to enhance penetration of solar energy systems, such as photovoltaic or thermal farms. This work focuses on the large-scale, meso-scale and local-scale variability in cloudiness and surface solar irradiance at different temporal scales. Vertical velocity at 500hPa from ERA-Interim reanalyses are used to study large-scale subsidence. CALIPSO, MODIS and Meteosat-7 satellite observations are used to study cloud properties and associated irradiances at the meso-scale. Solar irradiance measurements at seven Meteo-France stations around Reunion Island are used to investigate three meteorologically-distinct regions, namely the windward and leeward coasts, and the coasts parallel to the general trade wind direction. Day-to-day variations in daily irradiation values and diurnal-scale variability of solar irradiances are seasonally dependent. Winter seasons are characterized by large-scale atmospheric subsidence and broken low-level cloudiness, while in summer, clouds are found both at low and high altitudes. Three parameters are introduced to characterize solar irradiance diurnal cycle regimes. Five physically-sensible regimes are found, identified as clear, morning clear, overcast, afternoon clear, and random cloudiness. Regime occurrences have marked seasonal dependencies and vary significantly between the windward, leeward and lateral coasts. In winter and early summer, when cloudiness is driven predominantly by local (thermal, orographic) processes, the aggregated solar daily irradiation (average of the seven ground stations) remains near 80% of the clear-sky irradiation. In late summer, this values drops below 65% as large-scale overcast systems regularly affect the entire island. The station-to-station dis-correlation distance in terms of daily clear-sky index, defined as the distance for which the correlation coefficient drops to 0.5, is 62km in summer and 29km in winter. For hourly clear-sky indexes, the station-to-station dis-correlation distances is 4 and 3km, for summer and winter, respectively. Accordingly, aggregate analyses show that compensation effects are more important at hourly than daily time scales. The measurements also reveal that the atmosphere over the island tends to be clearer in the morning than in the afternoon while over the ocean surrounding the island, the opposite is true. These results provide insights and tools to help develop improved diurnal-scale solar irradiance forecast systems for tropical islands.

Estimation of global solar radiation using clear sky radiation in Yemen

In this communication, the usability of clear sky radiation for predicting the average global solar radiation has been investigated. For this aim, the various regression analyses were applied by using S/S o and S/S nh parameters. Also, equations which represent the two periods of the year, winter and summer, were developed by using these parameters. The equations developed by using S/S o and S/S nh have approximately the same results. Having the better values of the equations developed by using the change of summer and winter is another result. In addition, the use of the RMSE and MBE in isolation is not an adequate indicator of model performance. Using the t-statistic method and the harmony of results obtained with each method prove that the results are reliable.

The Analysis of Measurement and Model of Solar Radiation in Hohhot

The data of four sets of the sun radiation testing system in Hohhot was processed by the method of standard deviation to get the highest relative accuracy as a model with data. By comparing the measuring value with the calculating value of clear-sky solar radiation model established, it is found the model is only fit for the sunny day, moreover the lager percentage of sunshine is, the model is more appropriate. This model can meet the practical needs of general engineering and also can be used in the analysis of building energy efficiency