Search

The Solar Resource estimate (SolaRes) tool based on the Speed-up Monte Carlo Advanced Radiative Transfer code using GPU (SMART-G) has the ambition to fulfil both research and industrial applications by providing accurate, precise, and high-time-resolution simulations of the solar resource. We investigate the capacity of SolaRes to reproduce the radiation field, relying on 2 years of ground-based measurements by pyrheliometers and pyranometers acquired in northern France (Lille and Palaiseau). Our main objective is to provide, as a first step in clear-sky conditions, a thorough regional validation of SolaRes, allowing us to investigate aerosol impacts on solar resource. We perform comparisons between SolaRes-simulated and clear-sky-measured global horizontal irradiance (GHI), direct normal irradiance (DNI), diffuse horizontal irradiance (DifHI), and global and diffuse irradiance on a tilted plane (GTI, DifTI), and we even consider the circumsolar contributions. Using spectral aerosol optical thickness (AOT) data sets as input, which are delivered by the AErosol RObotic NETwork (AERONET) and the Copernicus Atmosphere Monitoring Service (CAMS), we examine the influence of aerosol input data sets in SolaRes on the comparison scores. Two aerosol models are mixed to compute aerosol optical properties. We also perform a sensitivity study on the aerosol parametrisation and investigate the influence of applying more or less strict cloud-screening methods to derive ground-based proof data sets of clear-sky moments. SolaRes is validated with the (relative) root mean square difference (RMSD) in GHI as low as 1 % and a negligible mean bias difference (MBD). The impact of the cloud-screening method in GHI is 0.5 % of RMSD and 0.3 % of MBD. SolaRes also estimates the circumsolar contribution, which improves MBD in DNI and DifHI by 1 % and 4 %, respectively, and RMSD by ∼ 0.5 %. MBD in DNI is around - 1 % and RMSD around 2 %, and MBD in DifHI is 2 % and RMSD around 9 %. RMSD and MBD in both DNI and DifHI are larger than in GHI because they are more sensitive to the aerosol and surface properties. DifTI measured on a vertical plane facing south is simulated by SolaRes with an RMSD of 8 %, comparable to that obtained for DifHI. Our results suggest a strong influence of reflection by not only ground surface but also surrounding buildings. The sensitivity studies on the aerosol parameterisation show that the spectral AOT contains enough information for high performance in DNI simulations, with low influence of the choice of the aerosol models on the RMSD. However, choosing a model with smaller aerosol single scattering albedo significantly decreases SolaRes DifHI and GHI. The best combination in Lille and Palaiseau consists of continental clean mixed with desert dust. Also, complementary information on angular scattering and aerosol absorption provided by the AERONET-inverted model further improves simulated clear-sky GHI by reducing RMSD by ∼ 0.5 % and MBD by ∼ 0.8 %. Eventually, the choice of the data source has a significant influence. Indeed, using CAMS AOT instead of AERONET AOT increases the RMSD in GHI by ∼ 1 % and MBD by ∼ 0.4 % and RMSD in DNI by 5 %. The RMSD in GHI remains slightly smaller than state-of-the-art methods. [ABSTRACT FROM AUTHOR]

The objective of the paper is to validate SolaRes (Solar Resource estimate) in clear-sky conditions, and to examine the aerosol influence on the differences between observation and estimate. SolaRes has the ambition to fulfil both research and industrial applications exploiting downwelling solar radiation at surface level. Consistently with solar resource applications, we show the capacity of SolaRes to reproduce the angular behaviour of the angular field, by validating not only global horizontal irradiance (GHI), but also direct normal irradiance (DNI), diffuse horizontal irradiance DifHI), global and diffuse irradiance in tilted plane (GTI, DifTI), and even the circumsolar contributions. Computations are made with the SMART-G radiative transfer code, taking spectral aerosol optical thickness (AOT) data sets as input, which are delivered by the Aerosol Robotic network (AERONET) and the Copernicus Atmospheric Monitoring Service (CAMS). A mixture of two aerosol models is required to compute aerosol optical properties. Measurements for validation are made at two sites in Northern France. Clear-sky is identified by two methods to show its influence: 1) a method reproducing the AOT variability conditions, and 2) a stricter method eliminating some residual cloud influence but also conditions with largest AOT. SolaRes is validated according to comparison scores found in the literature, with the (relative) root mean square difference (RMSD) in GHI as low as 1%, and the mean bias difference (MBD) which could be 0%. Angular behaviour is reproduced with satisfying scores. The circumsolar contribution improves MBD in DNI and DifHI, by 1% and 4% respectively, as well as RMSD by ~0.5%. MBD in DNI is around -1% and RMSD around 2%, and MBD in DifHI is 2% and RMSD around 9%. RMSD and MBD in both DNI and DifHI are larger than in GHI because they are more sensitive to the aerosol and surface properties. DifTI measured in a vertical plane facing South is reproduced with a RMSD of 8%, similar to DifHI. It is suggested a strong influence of reflection by not only ground surface but also surrounding buildings, increasing the albedo from 0.13 to 0.35. The sensitivity study on the aerosol parameterisation shows that the spectral AOT contains enough information for best quality in DNI retrieval. The choice of aerosol models in the parameterisation has an influence in RMSD smaller than 0.7%. Complementary information on angular scattering and aerosol absorption has a significant influence in GHI by reducing RMSD by ~0.5%, and MBD by ~0.8%. The uncertainty on the data source has a significant influence. The CAMS data set increases the RMSD in DNI by 5%, but has has less influence in GHI, by increasing RMSD by ~1% and MBD by ~0.4%. RMSD in GHI still remains slightly smaller than state-of-the-art methods. [ABSTRACT FROM AUTHOR]

• The ASoRA method estimates the atmospheric attenuation in a tower CSP. • The atmospheric attenuation occurs in the atmospehric column and in the slant path. • ASoRA is validated with data observed at Ouarzazate, Morocco. • The aerosols are assumed to lie in a surface layerwith a height varying with time. • A reanalysis data set is tested to show the efficiency of ASoRA in its global mode. • The estimated annual average of the solar resource parameters is given for Ouarzazate in 2014. The ASoRA method consists in estimating the solar resource in tower concentrated solar plants by exploiting global data sets. The solar resource parameters are not only the Direct Normal Irradiance (DNI) but also the slant path transmittance (T sp). The column to surface-level conversion process was validated by comparing the retrieved aerosol extinction coefficient (AEC) to independent measurements performed by a ground-based nephelometer. The Aerosol Robotic NETwork (AERONET) provided column-integrated aerosol extinction properties. The European Centre for Medium-Range Weather Forecasts Reanalysis Interim boundary layer height was used to reproduce the seasonal dependence of the aerosol vertical profile. At the daily resolution, ASoRA reproduced observed AEC with a relative root mean square difference (rRMSD) of 33% and a correlation coefficient of 0.90. The spectral extrapolation from monochromatic measurements to the solar broadband was validated by comparing computations and observations of DNI. ASoRA was also able to reproduce the hourly variability of DNI observed by a pyrheliometer with a RMSD of 38 W/m2, a rRMSD of 4.6%, and a correlation coefficient larger than 0.98. Despite larger uncertainties caused by using Modern-Era Retrospective analysis for Research and Applications (version 2) instead of AERONET, the annual average of T sp was underestimated by only 0.01, and the annual average of the irradiance loss in the slant path by only 4 W/m2. Largest impact on T sp comes from the parameterisation of the aerosol vertical profile, and the annual average of T sp was 0.945 at Ouarzazate (Morocco) in 2014, with an estimated uncertainty of 0.030. [ABSTRACT FROM AUTHOR]

Abstract: A data set acquired by eight particle-dedicated instruments set up on the SIRTA (Site Instrumental de Recherche par Télédétection Atmosphérique, which is French for Instrumented Site for Atmospheric Remote Sensing Research) during the ParisFog field campaign are exploited to document microphysical properties of particles contributing to extinction of visible radiation in variable situations. The study focuses on a 48-hour period when atmospheric conditions are highly variable: relative humidity changes between 50 and 100%, visibility ranges between 65 and 35000 m, the site is either downwind the Paris area either under maritime influence. A dense and homogeneous fog formed during the night by radiative cooling. In 6 h, visibility decreased down from 30000 m in the clear-sky regime to 65 m within the fog, because of advected urban pollution (factor 3 to 4 in visibility reduction), aerosol hydration (factor 20) and aerosol activation (factor 6). Computations of aerosol optical properties, based on Mie theory, show that extinction in clear-sky regime is due equally to the ultrafine modes and to the accumulation mode. Extinction by haze is due to hydrated aerosol particles distributed in the accumulation mode, defined by a geometric mean diameter of 0.6 μm and a geometric standard deviation of 1.4. These hydrated aerosol particles still contribute by 20±10% to extinction in the fog. The complementary extinction is due to fog droplets distributed around the geometric mean diameter of 3.2 μm with a geometric standard deviation of 1.5 during the first fog development stage. The study also shows that the experimental set-up could not count all fog droplets during the second and third fog development stages. [Copyright &y& Elsevier]

This article presents a realistic and novel method to estimate the solar radiant flux collected by the receiver of a solar power tower (SPT) system, taking into account the detailed atmospheric radiative transfer. It describes how an atmospheric radiative transfer Monte Carlo code is modified to solve the radiative transfer both in the atmosphere and within the concentrating system consisting of the heliostat field and the receiver. To validate the geometric modeling of a complete SPT (624 heliostats with 24 facets) as well as the estimation of its optical efficiency (both independent of the atmosphere), a comparison with the reference ray-tracing code "Solstice" is presented for two times of the day, two solar disk half-angles, and two heliostat surface slope errors. This new model allows the estimation of not only the optical losses but also, as in Moulana (2019), the gains due to atmospheric and environmental contributions i.e., radiant flux from circumsolar, aerosol scattering, ground reflection, etc. Annual average results (with a numerical uncertainty less than 0.01%) under clear sky conditions (without clouds) show that the gains are not negligible and could reach up to 0.414 MW (1.08% of the radiant flux collected by the receiver) for a relatively small SPT located in a desert area. • The method to consider 3D objects in a scattering atmosphere is described. • Two tracking modes to account for atmospheric and environmental gains are presented. • Comparisons with a reference ray-tracing code without the atmosphere are shown. • First results with the atmosphere show that the annual gains can exceed 1%. [ABSTRACT FROM AUTHOR]

In the companion (Part I) paper, we have described and evaluated a new versatile optical particle counter/sizer named LOAC (Light Optical Aerosol Counter), based on scattering measurements at angles of 12 and 60°. That allows for some typology identification of particles (droplets, carbonaceous, salts, and mineral dust) in addition to sizesegregated counting in a large diameter range from 0.2 µm up to possibly more than 100 µm depending on sampling conditions (Renard et al., 2016). Its capabilities overpass those of preceding optical particle counters (OPCs) allowing the characterization of all kind of aerosols from submicronicsized absorbing carbonaceous particles in polluted air to very coarse particles (>10-20 µm in diameter) in desert dust plumes or fog and clouds. LOAC's light and compact design allows measurements under all kinds of balloons, on-board unmanned aerial vehicles (UAVs) and at ground level. We illustrate here the first LOAC airborne results obtained from a UAV and a variety of scientific balloons. The UAV was deployed in a peri-urban environment near Bordeaux in France. Balloon operations include (i) tethered balloons deployed in urban environments in Vienna (Austria) and Paris (France), (ii) pressurized balloons drifting in the lower troposphere over the western Mediterranean (during the Chemistry-Aerosol Mediterranean Experiment - ChArMEx campaigns), (iii) meteorological sounding balloons launched in the western Mediterranean region (ChArMEx) and from Aire-sur-l'Adour in south-western France (VOLTAIRE-LOAC campaign). More focus is put on measurements performed in the Mediterranean during (ChArMEx) and especially during African dust transport events to illustrate the original capability of balloon-borne LOAC to monitor in situ coarse mineral dust particles. In particular, LOAC has detected unexpected large particles in desert sand plumes. [ABSTRACT FROM AUTHOR]

The study of aerosols in the troposphere and in the stratosphere is of major importance both for climate and air quality studies. Among the numerous instruments available, optical aerosol particles counters (OPCs) provide the size distribution in diameter range from about 100 nm to a few tens of μm. Most of them are very sensitive to the nature of aerosols, and this can result in significant biases in the retrieved size distribution. We describe here a new versatile optical particle/sizer counter named LOAC (Light Optical Aerosol Counter), which is light and compact enough to perform measurements not only at the surface but under all kinds of balloons in the troposphere and in the stratosphere. LOAC is an original OPC performing observations at two scattering angles. The first one is around 12°, and is almost insensitive to the refractive index of the particles; the second one is around 60° and is strongly sensitive to the refractive index of the particles. By combining measurement at the two angles, it is possible to retrieve the size distribution between 0.2 and 100 μm and to estimate the nature of the dominant particles (droplets, carbonaceous, salts and mineral particles) when the aerosol is relatively homogeneous. This typology is based on calibration charts obtained in the laboratory. The uncertainty for total concentrations measurements is ±20% when concentrations are higher than 1 particle cm-3 (for a 10 min integration time). For lower concentrations, the uncertainty is up to about ±60% for concentrations smaller than 10-2 particle cm-3. Also, the uncertainties in size calibration are ±0.025 μm for particles smaller than 0.6 μm, 5% for particles in the 0.7-2 μm range, and 10% for particles greater than 2 μm. The measurement accuracy of submicronic particles could be reduced in a strongly turbid case when concentration of particles > 3 μm exceeds a few particles cm-3. Several campaigns of cross-comparison of LOAC with other particle counting instruments and remote sensing photometers have been conducted to validate both the size distribution derived by LOAC and the retrieved particle number density. The typology of the aerosols has been validated in well-defined conditions including urban pollution, desert dust episodes, sea spray, fog, and cloud. Comparison with reference aerosol mass monitoring instruments also shows that the LOAC measurements can be successfully converted to mass concentrations. [ABSTRACT FROM AUTHOR]

The study of aerosols in the troposphere and in the stratosphere is of major importance both for climate and air quality studies. Among the numerous instruments available, optical aerosol particles counters (OPCs) provide the size distribution in diameter range from about 100 nm to a few tens of µm. Most of them are very sensitive to the nature of aerosols, and this can result in significant biases in the retrieved size distribution. We describe here a new versatile optical particle/sizer counter named LOAC (Light Optical Aerosol Counter), which is light and compact enough to perform measurements not only at the surface but under all kinds of balloons in the troposphere and in the stratosphere. LOAC is an original OPC performing observations at two scattering angles. The first one is around 12°, and is almost insensitive to the refractive index of the particles; the second one is around 60° and is strongly sensitive to the refractive index of the particles. By combining measurement at the two angles, it is possible to retrieve the size distribution between 0.2 and 100 µm and to estimate the nature of the dominant particles (droplets, carbonaceous, salts and mineral particles) when the aerosol is relatively homogeneous. This typology is based on calibration charts obtained in the laboratory. The uncertainty for total concentrations measurements is ±20% when concentrations are higher than 1 particle cm-3 (for a 10 min integration time). For lower concentrations, the uncertainty is up to about ±60% for concentrations smaller than 10-2 particle cm-3. Also, the uncertainties in size calibration are ±0.025 μm for particles smaller than 0.6 μm, 5% for particles in the 0.7-2 μm range, and 10% for particles greater than 2 μm. The measurement accuracy of submicronic particles could be reduced in a strongly turbid case when concentration of particles > 3 µm exceeds a few particles cm-3. Several campaigns of cross-comparison of LOAC with other particle counting instruments and remote sensing photometers have been conducted to validate both the size distribution derived by LOAC and the retrieved particle number density. The typology of the aerosols has been validated in well-defined conditions including urban pollution, desert dust episodes, sea spray, fog, and cloud. Comparison with reference aerosol mass monitoring instruments also shows that the LOAC measurements can be successfully converted to mass concentrations. [ABSTRACT FROM AUTHOR]

Radiative fog formation is a complex phenomenon involving local physical and microphysical processes that take place when particular meteorological conditions occur. This study aims at quantifying the ability of a regional numerical weather model to analyze and forecast the conditions favourable to radiative fog formation at an instrumental site in the Paris area. Data from the ParisFog campaign have been used in order to quantify the meteorological conditions favorable to radiative fog formation (pre-fog conditions) by setting threshold values on the key meteorological variables driving this process: 2-m temperature tendency, 10-m wind speed, 2-m relative humidity and net infrared flux. Data from the ParisFog observation periods of November 2011 indicate that use of these thresholds leads to the detection of 87 % of cases in which radiative fog formation was observed. In order to evaluate the ability of a regional weather model to reproduce adequately these conditions, the same thresholds are applied to meteorological model fields in both analysis and forecast mode. It is shown that, with this simple methodology, the model detects 74 % of the meteorological conditions finally leading to observed radiative fog, and 48 % 2 days in advance. Finally, sensitivity tests are conducted in order to evaluate the impact of using larger time or space windows on the forecasting skills. [ABSTRACT FROM AUTHOR]