Cloudless Sky Research Articles

A High-Precision Sub-Grid Parameterization Scheme for Clear-Sky Direct Solar Radiation in Complex Terrain—Part II: Considering Atmospheric Transparency Differences in Sub-Grid; Pre-Research for Application

Existing sub-grid parameterization schemes for clear-sky direct solar radiation (SPS-CSDSR) assume that the sub-grid cells have the same atmospheric transparency. This study shows that in undulating terrain, significant errors can occur when the sub-grid is in turbid weather or partly above the cloud top. A correction factor was proposed. It can effectively eliminate errors under a cloudless sky and can reduce some errors when part of the sub-grid is above the cloud or fog top. For atmospheric models with high horizontal resolution, example test verification shows that the cast shadowless coverage method can lead to large errors. It should no longer be used based on current computing power. These improvements and the high-precision fast terrain occlusion algorithm in Part I will allow SPS-CSDSR to achieve unprecedented high accuracy. Based on the proposed daily interpolation method, the high-precision SPS-CSDSR is also feasible for regional climate simulation. The analysis pointed out that the sub-grid terrain radiative effect (STRE) is distributed over inclined surfaces with larger areas and at different heights. Existing methods of coupling STRE on one flat surface have certain physical drawbacks. This paper suggests introducing parameterization of STRE at different altitudes and improving the coupling of land–air.

Reflection–Polarization Characteristics of Greenhouses Studied by Drone-Polarimetry Focusing on Polarized Light Pollution of Glass Surfaces

Drone-based imaging polarimetry is a valuable new tool for the remote sensing of the polarization characteristics of the Earth’s surface. After briefly reviewing two earlier drone-polarimetric studies, we present here the results of our drone-polarimetric campaigns, in which we measured the reflection–polarization patterns of greenhouses. From the measured patterns of the degree and angle of linear polarization of reflected light, we calculated the measure (plp) of polarized light pollution of glass surfaces. The knowledge of polarized light pollution is important for aquatic insect ecology, since polarotactic aquatic insects are the endangered victims of artificial horizontally polarized light sources. We found that the so-called Palm House of a botanical garden has only a low polarized light pollution, 3.6% ≤ plp ≤ 13.7%, while the greenhouses with tilted roofs are strongly polarized-light-polluting, with 24.8% ≤ plp ≤ 40.4%. Similarly, other tilted-roofed greenhouses contain very high polarized light pollution, plp ≤ 76.7%. Under overcast skies, the polarization patterns and plp values of greenhouses practically only depend on the direction of view relative to the glass surfaces, as the rotationally invariant diffuse cloud light is the only light source. However, under cloudless skies, the polarization patterns of glass surfaces significantly depend on the azimuth direction of view and its angle relative to the solar meridian because, in this case, sunlight is the dominant light source, rather than the sky. In the case of a given direction of view, those glass surfaces are the strongest polarized-light-polluting, from which sunlight and/or skylight is reflected at or near Brewster’s angle in a nearly vertical plane, i.e., with directions of polarization close to horizontal. Therefore, the plp value is usually greatest when the sun shines directly or from behind. The plp value of greenhouses is always the smallest in the green spectral range due to the green plants under the glass.

Wintertime Cooling of the Arctic TOA by Low‐Level Clouds

AbstractGlobally, clouds are known to warm the climate system in the thermal infrared because they typically emit thermal radiation to space at effective temperatures lower than the combined cloud‐free atmosphere and surface. However, here we show that ∼40% of low‐level clouds over sea ice tend to cool the Arctic system at TOA and contribute to a radiative cooling of the Arctic winter climate by −2.3 Wm−2, or a ∼16% reduction over the infrared warming effect of all clouds during winter. Based on satellite observations, low‐level clouds residing in surface‐based temperature inversions emit more longwave radiation to space than would occur in cloudless skies. While these clouds are known to significantly warm the surface, they cool the Arctic climate system overall. Our results imply that accurately representing the cloud radiative effects unique to the Arctic could help to constrain the regional energy budget.

IMPLEMENTASI DIGITAL IMAGE PROCESSING SEBAGAI PENDETEKSI POSISI MATAHARI PADA PERANCANGAN DUAL AXIS SOLAR TRACKER

One of the uses of new renewable energy (EBT) in Indonesia which has great potential is solar panels. Solar panels are electrical devices that are used to convert solar energy into electrical energy. The limited surface area of the panels requires users to be able to pay attention to the work efficiency of solar panels. The aspect that has the most influence on optimizing the efficiency of solar panel performance is the placement of the surface of the solar panel against incoming solar radiation. Therefore, it is necessary to have a method to detect the position of the sun to provide input to the actuator so that the surface of the solar panel is positioned in the direction of the sun's rays. This study describes the accuracy of detecting the position of the sun using digital image processing methods. This process needs to be done as a reference in designing a dual axis solar tracker. Detection of the sun's position using this method gets 100% accurate results in cloudless sky conditions and gets 80% success results in cloudy sky conditions.

The Use of Evolutionary Algorithms in the Modelling of Diffuse Radiation in Terms of Simulating the Energy Efficiency of Photovoltaic Systems

In light of the rapidly growing number of photovoltaic micro-grids, the modelling of their short-term power yields based on meteorological measurements is increasing in significance. This requires the knowledge of total and diffuse instantaneous solar radiation; however, most meteorological stations conduct actinometric measurements only with regard to total solar radiation, especially on a minute scale. This paper contains an analysis of the currently used PV cell mathematical model and suggests its modification aimed at calculating PV cell power with satisfactory accuracy, without the knowledge of diffuse solar radiation. Three function families were proposed to approximate the relationship between diffuse irradiance and the total and theoretical total irradiance variance for a cloudless sky. A program has been implemented to identify functions from the aforementioned function families. It leverages an evolution strategy algorithm and a fitness function based on the least-squares point method. It was employed to calculate the desired functions based on actual measurement data. The outcome was the sought-after dependence that enables predicting diffuse irradiance based on more frequently available measurement data.

Impact of atmospheric extinction coefficient on the solar spectrum at selective wavelengths at Helwan in Egypt

Solar irradiance alterations due to the various atmospheric conditions have received great scientific concern. These alternations can be investigated by both monochromatic extinction coefficient and atmospheric transparency. In this work, continuous measurements of solar spectral irradiation using the Spectroradiometer for six selective wavelengths (350, 368, 500, 615, 780, and 870 nm) are carried out at the Helwan station, (NRIAG) in Egypt. Twelve clear-sky days of continuous observations have been monitored under different atmospheric conditions. The results have shown that using Langley method under cloudless sky for the total atmospheric extinction at the selective wavelengths was correlated. The extinction coefficient at the selected wavelengths shows obvious diurnal variations in each season. The perceptible effect of local climate has been obtained from the comparison of seasonal extinctions. The highest value of extinction coefficient was 0.59 km−1 at 615 nm in summer while the lowest one at 350 nm was 0.07 km−1 in winter. Moreover, it has been found that the afternoon values of transparency have a shift toward the longer wavelengths.

Whither the Working-Class Journalist over Thirty?

Whither the Working-Class Journalist over Thirty?

Moman's Secret Agenda

Moman's Secret Agenda

Comparison of Cloud Amounts Retrieved with Three Automatic Methods and Visual Observations

Four methods have been used for the estimation of the total cloud amount and cloud amount for low clouds: visual observations, the Long method applied on pyranometer measurements, the Automatic Partial Cloud Amount Detection Algorithm (APCADA) method applied on pyrgeometers measurements, and ceilometer measurements of the cloud base height. Records from meteorological observers indicate that clear days (0–1 octa) represent the most frequent cloud amount for low clouds. In contrast, the total cloud amount is more aleatory. Results obtained from the Long method show maximum frequency in the extreme cloud amount values. The APCADA method also indicates the predominance of cloudless skies. The ceilometer method shows a predominance of completely clear skies, but the completely cloudy (8 octas) is the second most frequent case. Automatic methods report more cloudless and overcast skies than the observer. Automatic methods agree with the visual method or differ in ±1 octa for 60–76% cases for low cloud amount and for 56–63% cases for total cloud amount. In general, low cloud amount agrees more with observer measurements than total cloud amount and the automatic methods underestimated total cloud amount observer values possibly due to the difficulty in monitoring high clouds.

Stalled high-pressure weather systems

Stalled High Pressure Weather Systems (SHPWS) are associated with abnormally high temperatures, low wind velocities (except at their peripheries, where they can be quite high), cloudless skies, and a consequent lack of precipitation. Analysis shows that the high temperatures and clear skies associated with their formation are caused by the settling out of reflective (dimming) atmospheric Sulfur Dioxide (SO2) aerosols within the area of a “High”. This cleansing of the atmosphere allows sunshine to strike the Earth’s surface with greater intensity, resulting in substantially increased warming.

Predicting Daylight Illuminance for 15 CIE Standard Skies Using a Simple Software Tool

Estimation of internal daylight availability is the key step in evaluating various daylighting schemes. Interior daylight is often expressed as daylight factor under the traditional International Commission on Illumination (CIE) overcast sky. Nonetheless, such approach may be inflexible to estimate the kinetic situations as the solar locations vary under cloudless skies. Recently, the CIE adopted 15 standard skies covering the usual skies found in the world. The interior daylight illuminance is influenced by the sky conditions in terms of luminance levels and distributions with respect to the window-facing orientation at any given period. The daylight coefficient concept considering the variations of the sky luminance patterns can be employed to accurately compute the indoor daylight level. A full-scale computer simulation can be costly in modeling the building geometry with a long simulation time. Moreover, additional times and advanced skills are required for preparation and post-processing. Simple design programs would be convenient and helpful in preliminary design phase when various designs and schemes are being studied and analyzed. This paper adopts a simple computer program for computing the interior daylight under the 15 CIE standard skies. The capability of the suggested software was assessed against the simulated results using a computer program, namely, RADIANCE, and the field measurement readings. The running time based on the simple program was far less than that using RADIANCE. The findings showed that the internal daylight simulated by the proposed simple software were in good agreement with the simulated results by RADIANCE and measured readings. The peak daylight factor discrepancy was <2%, and the RMSE was 14.5% of the corresponding measured average values.

Effect of Aerosol Vertical Distribution on the Modeling of Solar Radiation

Default aerosol extinction coefficient profiles are commonly used instead of measured profiles in radiative transfer modeling, increasing the uncertainties in the simulations. The present study aimed to determine the magnitude of these uncertainties and contribute towards the understanding of the complex interactions between aerosols and solar radiation. Default, artificial and measured profiles of the aerosol extinction coefficient were used to simulate the profiles of different radiometric quantities in the atmosphere for different surface, atmospheric, and aerosol properties and for four spectral bands: ultraviolet-B, ultraviolet-A, visible, and near-infrared. Case studies were performed over different areas in Europe and North Africa. Analysis of the results showed that under cloudless skies, changing the altitude of an artificial aerosol layer has minor impact on the levels of shortwave radiation at the top and bottom of the atmosphere, even for high aerosol loads. Differences of up to 30% were, however, detected for individual spectral bands. Using measured instead of default profiles for the simulations led to more significant differences in the atmosphere, which became very large during dust episodes (10–60% for actinic flux at altitudes between 1 and 2 km, and up to 15 K/day for heating rates depending on the site and solar elevation).

The deep blue day is decreasing in China.

The deep blue sky is an indicator of a lower concentration of aerosols and a cloudless sky. With increasing human emissions, a trend towards days with fewer deep blue skies might indicate a decline in a good living environment for humans. This study investigates the long-term changes of the deep blue sky in China from 1980 to 2018. Due to a lack of direct measurements, we use atmospheric visibility and low cloud cover to classify blue sky days into three grades: light blue day, medium blue day, and deep blue day. Climatologically, annual deep blue days increase from southeast China to northwest China, with the maximum number in Xinjiang and eastern Inner Mongolia and the minimum number in western Qinghai and southern Hebei. From 1980 to 2018, annual deep blue days show a prominent decreasing trend in most of China, with area-mean annual deep blue days decreasing by −0.48 days per year (d/y) in China, and the variation becomes more obvious after 2013. The maximum decreasing trend is observed in eastern China. The most prominent decreases of deep blue days are seen in winter. Both air pollution and the change in meteorological conditions contribute to the decrease of wintertime deep blue days in China. Specifically, the decrease in surface wind speed hinders the cleaning of air by winds, the increase in surface air temperature, and decrease in relative humidity is favorable for low cloud increase, and the increasing emission of pollution reduces atmospheric visibility.Supplementary InformationThe online version contains supplementary material available at 10.1007/s00704-021-03898-1.

Earth’s Stratospheric Aerosol Parameters Reconstruction from Polarimetric Measurements of the Sky

Earth’s climate changes are the result of natural changes in the energy balance of Sun irradiation and influence of anthropogenic factors on the variations of ozone layer thickness and stratospheric aerosol abundance. It is developed a miniature polarimeter for satellite polarimetric experiments in the ultraviolet region of the sunlight spectrum. The main task of this device is to the obtain an information on the stratospheric aerosol physical properties. We tested this polarimeter on a bench specially designed and manufactured as well. It is possible to measure by it the phase dependences of the degree of linear polarization (DLP) of solar radiation scattered by the Earth’s atmosphere. A set of special computer programs was developed for comparing the spectral polarimetric measurements DLP data of cloudless sky with model calculations of DLP for the artificial gas-aerosol medium. Thus, the prototype of satellite polarimeter as well as special computer programs make it possible to study the Earth’s atmosphere aerosol physical characteristics.

Microclimatic features of landscapes in the territory with a sparse network of meteorological observations

Automatic monitoring of air temperature and humidity in the mountain-depression landscapes of the Tunka depression has been organized. The results of the analysis of observation data for 10 years showed significant differences in the temperature regime in different landscapes. The sites can be divided into three groups – the slopes of the depression, pine- herbaceous landscapes, and the lacustrine-bog complex of the central part. The average annual air temperature at all sites is negative and vary in range -0.7 … -2.1°C. Vegetation has the greatest influence on microclimatic characteristics. The maximum contrasts in the temperature regime of the air throughout the year are observed in open areas with cloudless skies. In winter, this is explained by radiation cooling, and in summer – by the heating of the open surface in the daytime. In this case, not only the daily amplitude of air temperature in the open areas increases, but also the largest contrasts between the open and closed areas are observed.

Field Quality Control of Spectral Solar Irradiance Measurements by Comparison with Broadband Measurements

Measurement of solar spectral irradiance is required in an increasingly wide variety of technical applications, such as atmospheric studies, health, and solar energy, among others. The solar spectral irradiance at ground level has a strong dependence on many atmospheric parameters. In addition, spectroradiometer optics and detectors have high sensitivity. Because of this, it is necessary to compare with a reference instrumentation or light source to verify the quality of measurements. A simple and realistic test for validating solar spectral irradiance measurements is presented in this study. This methodology is applicable for a specific spectral range inside the broadband range from 280 to 4000 nm under cloudless sky conditions. The method compares solar spectral irradiance measurements with both predictions of clear-sky solar spectral irradiance and measurements of broadband instruments such as pyrheliometers. For the spectral estimation, a free atmospheric transmittance simulation code with the air mass calculation as the mean parameter was used. The spectral direct normal irradiance (Gbλ) measurements of two different spectroradiometers were tested at Plataforma Solar de Almería, Spain. The results are presented in this article. Although only Gbλ measurements were considered in this study, the same methodology can be applied to the other solar irradiance components.

Study of solar radiation on an all-movable radio telescope

To grasp the effect of nonuniform temperature field, the effects of a nonuniform sunshine temperature field on a large, all-movable radio telescope were analyzed in this study. Based on the overall parameters of a radio telescope model, first, several specific steps of the ray-casting algorithm were introduced for calculating sunlight shadows on radio telescopes, and then a special program was developed for simulating sunlight and shadows on radio telescopes. Second, the periodic air temperature, heat radiation, and heat conduction were computed every half hour under a cloudless sky on a summer day, i.e., the worst-case climate conditions. The transient structural temperatures were then analyzed over a period of several days of sunshine with a rational initial structural-temperature distribution until the whole set of structural temperatures converged to the results obtained the day before. As a result, the temporal and spatial characteristics of the temperature distribution for the radio telescope were statistically investigated. Furthermore, the phenomenon called the solar cooker effect was found to exist in such a Cassegrain reflector system. The variations in the solar cooker effect over time and its spatial distributions in the secondary reflector were observed to elucidate the mechanism of the effect. The results presented here provide some references for the future operation, sensor distribution, and local temperature control of radio telescopes.

Deriving Ocean Surface Currents: A method using Geostationary Ocean Color Imager hourly data

Tracking the movement of natural surface features across the time intervals between successive images has gained widespread acceptance for mapping ocean surface currents (OSCs). The 500-m and 1-h spatiotemporal resolutions of the Geostationary Ocean Color Imager (GOCI), launched in 2010, are ideal for observing the dynamics of mesoscale eddies and the diurnal changes dominated by tides. All reported works to date, however, are limited to a few occasions when there were cloudless skies and pixel-level accuracy. As a result, the abundant GOCI hourly data have not been put into an operational service to derive OSCs. This article revisits ocean feature detection and tracking techniques to discuss the development of a satellite image-matching system (SIMS). The results show that a SIMS can detect and track features from two consecutive GOCI images to approximately a 0.25-pixel level of accuracy in the presence of variable gaps due to land and clouds. Suspicious vectors can be ruled out by initially using size-irrelevant filtering and majority filtering methods with minimum preset thresholds. The products of pathlines and streamlines derived from GOCI hourly data make it possible to gain a better understanding of OSCs, both qualitatively and quantitatively.

A Method to Estimation of Global Solar Radiation with Meteorological Parameters under Cloudless Sky Condition using Artificial Neural Network

In this work, variation of global radiation hourly basis and model developed to estimate the radiation under cloudless sky condition were purposed at Lopburi province (14.83°N, 100.62°E). Data of global radiation and meteorological parameters from 2012 to 2017 were investigated. For the variation of global radiation, the maximum and minimum of radiation are 3.46 MJ/m2 in April and 2.40 MJ/m2 in December, and there are some meteorological parameters influencing on the radiation. Therefore, a model for estimation of hourly global solar radiation under cloudless sky condition at this site was proposed based on the artificial neural network (ANN). This ANN has one input layer, two hidden layers and one output layer. The input layer consists of some meteorological parameters that are solar zenith angle, visibility, air temperature, relative humidity, wind speed and air pressure, and the output layer is global solar radiation under clear sky condition. The ANN was trained using the input and output data collected at Lopburi meteorological station during the year: 2012-2014. It was then validated against an independent data at the site for the period of three years (2015-2017). The validation result indicates that the estimated solar radiation under clear sky condition obtained from ANN are in good agreement with that from the measurement, with root mean square difference (RMSD) of 8.52% and mean bias difference (MBD) of 1.22%. Therefore, the model can be applied for estimation of global radiation under cloudless sky condition at other meteorological stations with similar climate. The estimated solar radiation data are useful for management in solar power plant, solar thermal energy system and also for the studies in the atmospheric field. Keywords: solar radiation, meteorological parameter, artificial neural network

Effect of Street Lighting on the Urban and Rural Night-Time Radiance and the Brightness of the Night Sky

In April 2020, due to the coronavirus pandemic and the tourism decrease in Cracow (Poland), the Road Authority of the City of Cracow, followed by the authorities of several neighbouring municipalities, decided to turn off street lighting at night. It is worth noting that this is the first time that street lighting has been turned off in such a large area on a longer time frame at this scale, including one of the most populated cities in Poland, which made it possible to make unique observations. During this period, with the help of small night-sky radiance meters (Sky Quality Meters (SQM)), many ground-based measurements were made, both within the city and in its vicinity. For this purpose, the existing light pollution monitoring stations in Cracow and neighbouring cities were used. It was found that after switching off street lighting, the zenith surface brightness of the cloudless sky decreased by 15–39%, and this value was proportional to the city’s population. The night-time light satellite data (VIIRS/DNB) on radiance from Cracow and neighbouring communes were also analysed, both their daily values as well as monthly and annual averages. It was found that in the case of a large city such as Cracow, turning off all street lighting reduces the amount of light energy radiated into the sky by about 50%, which is a relatively small decrease in radiance, while reducing the surface brightness of the night sky by about 40%, regardless of the state of the atmosphere. The effect of a significant decrease in radiance as a result of switching off street lighting was found in each of the analysed communes, especially the urbanised ones.