scholarly journals Clouds over Hyytiälä, Finland: an algorithm to classify clouds based on solar radiation and cloud base height measurements

2020 ◽  
Author(s):  
Ilona Ylivinkka ◽  
Santeri Kaupinmäki ◽  
Meri Virman ◽  
Maija Peltola ◽  
Ditte Taipale ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Global Radiation ◽  
Simple Algorithm ◽  
Cloud Base ◽  
Aerosol Formation ◽  
Detection Range ◽  
Clear Sky ◽  
Overall Performance ◽  
Sky Conditions ◽  
Cloud Base Height

Abstract. We developed a simple algorithm to classify clouds based on global radiation and cloud base height measured by pyranometer and ceilometer, respectively. We separated clouds into seven different classes (stratus, stratocumulus, cumulus, nimbostratus, altocumulus+altostratus, cirrus+cirrocumulus+cirrostratus and clear sky+cirrus). We also included classes for cumulus and cirrus clouds causing global radiation enhancement, and classified multilayered clouds, when captured by the ceilometer, based on their height and characteristics (transparency, patchiness and uniformity). The overall performance of the algorithm was nearly 70 % when compared with classification by an observer using total sky images. The performance was best for clouds having well-distinguishable effects on solar radiation: nimbostratus clouds were classified correctly in 100 % of the cases. The worst performance corresponds to cirriform clouds (50 %). Although the overall performance of the algorithm was good, it is likely to miss the occurrence of high and multilayered clouds. This is due to the technical limits of the instrumentation: the vertical detection range of the ceilometer and occultation of the laser pulse by the lowest cloud layer. We examined the use of brightness parameter, which is defined as a ratio between measured global radiation and modeled radiation at the top of the atmosphere, as an indicator of clear sky conditions. Our results show that cumulus, altocumulus, altostratus and cirriform clouds can be present when the parameter indicates clear sky conditions. Those conditions have previously been associated with enhanced aerosol formation under clear sky. This is an important finding especially in case of low clouds coupled to the surface which can influence aerosol population via aerosol-cloud interactions. Overall, caution is required when the parameter is used in the analysis of processes affected by partitioning of radiation by clouds.

scholarly journals Clouds over Hyytiälä, Finland: an algorithm to classify clouds based on solar radiation and cloud base height measurements

2020 ◽  
Vol 13 (10) ◽  
pp. 5595-5619
Author(s):  
Ilona Ylivinkka ◽  
Santeri Kaupinmäki ◽  
Meri Virman ◽  
Maija Peltola ◽  
Ditte Taipale ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Global Radiation ◽  
Cloud Base ◽  
Aerosol Formation ◽  
Clearness Index ◽  
Detection Range ◽  
Clear Sky ◽  
Overall Performance ◽  
Sky Conditions ◽  
Cloud Base Height

Abstract. We developed a simple algorithm to classify clouds based on global radiation and cloud base height measured by pyranometer and ceilometer, respectively. We separated clouds into seven different classes (stratus, stratocumulus, cumulus, nimbostratus, altocumulus + altostratus, cirrus + cirrocumulus + cirrostratus and clear sky + cirrus). We also included classes for cumulus and cirrus clouds causing global radiation enhancement, and we classified multilayered clouds, when captured by the ceilometer, based on their height and characteristics (transmittance, patchiness and uniformity). The overall performance of the algorithm was nearly 70 % when compared with classification by an observer using total-sky images. The performance was best for clouds having well-distinguishable effects on solar radiation: nimbostratus clouds were classified correctly in 100 % of the cases. The worst performance corresponds to cirriform clouds (50 %). Although the overall performance of the algorithm was good, it is likely to miss the occurrences of high and multilayered clouds. This is due to the technical limits of the instrumentation: the vertical detection range of the ceilometer and occultation of the laser pulse by the lowest cloud layer. We examined the use of clearness index, which is defined as a ratio between measured global radiation and modeled radiation at the top of the atmosphere, as an indicator of clear-sky conditions. Our results show that cumulus, altocumulus, altostratus and cirriform clouds can be present when the index indicates clear-sky conditions. Those conditions have previously been associated with enhanced aerosol formation under clear skies. This is an important finding especially in the case of low clouds coupled to the surface, which can influence aerosol population via aerosol–cloud interactions. Overall, caution is required when the clearness index is used in the analysis of processes affected by partitioning of radiation by clouds.

scholarly journals Skill of Direct Solar Radiation Predicted by the ECMWF Global Atmospheric Model over Australia

2014 ◽  
Vol 53 (11) ◽  
pp. 2571-2588 ◽  
Author(s):  
Alberto Troccoli ◽  
Jean-Jacques Morcrette
Keyword(s):  
Solar Radiation ◽  
Power Plants ◽  
Solar Power ◽  
Weather Prediction ◽  
Global Radiation ◽  
Atmospheric Model ◽  
Direct Solar Radiation ◽  
Efficient Production ◽  
Clear Sky ◽  
Sky Conditions

AbstractPrediction of direct solar radiation is key in sectors such as solar power and agriculture; for instance, it can enable more efficient production of energy from concentrating solar power plants. An assessment of the quality of the direct solar radiation forecast by two versions of the European Centre for Medium-Range Weather Forecasts (ECMWF) global numerical weather prediction model up to 5 days ahead is carried out here. The performance of the model is measured against observations from four solar monitoring stations over Australia, characterized by diverse geographic and climatic features, for the year 2006. As a reference, the performance of global radiation forecast is carried out as well. In terms of direct solar radiation, while the skill of the two model versions is very similar, and with relative mean absolute errors (rMAEs) ranging from 18% to 45% and correlations between 0.85 and 0.25 at around midday, their performance is substantially enhanced via a simple postprocessing bias-correction procedure. There is a marked dependency on cloudy conditions, with rMAEs 2–4 times as large for very cloudy-to-overcast conditions relative to clear-sky conditions. There is also a distinct dependency on the background climatic clear-sky conditions of the location considered. Tests made on a simulated operational setup targeting three quantiles show that direct radiation forecasts achieve potentially high scores. Overall, these analyses provide an indication of the potential practical use of direct irradiance forecast for applications such as solar power operations.

scholarly journals Assessment and Day-Ahead Forecasting of Hourly Solar Radiation in Medellín, Colombia

Energies ◽  
2019 ◽  
Vol 12 (22) ◽  
pp. 4402
Author(s):  
Julián Urrego-Ortiz ◽  
J. Alejandro Martínez ◽  
Paola A. Arias ◽  
Álvaro Jaramillo-Duque
Keyword(s):  
Solar Radiation ◽  
Markov Model ◽  
Power Plants ◽  
Wrf Model ◽  
Tropical Andes ◽  
Clear Sky ◽  
Proposed Model ◽  
Solar Power Plants ◽  
Solar Resource ◽  
Sky Conditions

The description and forecasting of hourly solar resource is fundamental for the operation of solar energy systems in the electric grid. In this work, we provide insights regarding the hourly variation of the global horizontal irradiance in Medellín, Colombia, a large urban area within the tropical Andes. We propose a model based on Markov chains for forecasting the hourly solar irradiance for one day ahead. The Markov model was compared against estimates produced by different configurations of the weather research forecasting model (WRF). Our assessment showed that for the period considered, the average availability of the solar resource was of 5 PSH (peak sun hours), corresponding to an average daily radiation of ~5 kWh/m2. This shows that Medellín, Colombia, has a substantial availability of the solar resource that can be a complementary source of energy during the dry season periods. In the case of the Markov model, the estimates exhibited typical root mean squared errors between ~80 W/m2 and ~170 W/m2 (~50%–~110%) under overcast conditions, and ~57 W/m2 to ~171 W/m2 (~16%–~38%) for clear sky conditions. In general, the proposed model had a performance comparable with the WRF model, while presenting a computationally inexpensive alternative to forecast hourly solar radiation one day in advance. The Markov model is presented as an alternative to estimate time series that can be used in energy markets by agents and power-system operators to deal with the uncertainty of solar power plants.

scholarly journals An automated method for the evaluation of the pointing accuracy of sun-tracking devices

2016 ◽  
Author(s):  
Dietmar J. Baumgartner ◽  
Werner Pötzi ◽  
Heinrich Freislich ◽  
Heinz Strutzmann ◽  
Astrid M. Veronig ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Monitoring System ◽  
Automated System ◽  
Accuracy Evaluation ◽  
Tracking Accuracy ◽  
Clear Sky ◽  
Automated Method ◽  
Pointing Accuracy ◽  
Sky Conditions ◽  
Tracking Devices

Abstract. The accuracy of solar radiation measurements (for direct and diffuse radiation) depends significantly on the precision of the operational sun-tracking device. Thus rigid targets for instrument performance and operation have been specified for international monitoring networks, such as e.g., the Baseline Surface Radiation Network (BSRN) operating under the auspices of the World Climate Research Program (WCRP). Sun-tracking devices fulfilling these accuracy requirements are available from various instrument manufacturers, however none of the commercially available systems comprises an automatic accuracy control system, allowing platform operators to independently validate the pointing accuracy of sun-tracking sensors during operation. Here we present KSO-STREAMS (KSO-SunTRackEr Accuracy Monitoring System), a fully automated, system independent and cost-effective method for evaluating the pointing accuracy of sun-tracking devices. We detail the monitoring system setup, its design and specifications and results from its application to the sun-tracking system operated at the Austrian RADiation network (ARAD) site Kanzelhöhe Observatory (KSO). Results from an evaluation campaign from March to June 2015 show that the tracking accuracy of the device operated at KSO lies for the vast majority of observations (99.8 %) within BSRN specifications (i.e., 0.1° tracking accuracy). Evaluation of manufacturer specified active tracking accuracies (0.02°), during periods with direct solar radiation exceeding 300 W m−2, shows that these are satisfied for 72.9 % of observations. Tracking accuracies are highest during clear-sky conditions and on days where prevailing clear-sky conditions are interrupted by frontal movement: in these cases we obtain complete fulfillment of BSRN requirements and 76.4 % of observations within manufacturer specified active tracking accuracies. Limitations to tracking surveillance arise during overcast conditions and periods of partial solar limb coverage by clouds. On days with variable cloud-cover 78.1 % (99.9 %) of observations meet active tracking (BSRN) accuracy requirements while for days with prevailing overcast conditions these numbers reduce to 64.3 % (99.5 %), respectively.

Terrestrial Solar Radiation

2017 ◽  
pp. 191-293
Keyword(s):  
Solar Radiation ◽  
Horizontal Plane ◽  
Cloud Cover ◽  
Weather Conditions ◽  
Clear Sky ◽  
Solar Tracking ◽  
Sky Conditions ◽  
The Impact ◽  
Estimation Models

After shading a light on the extraterrestrial solar radiation in the chapter 3 it is important to evaluate the global terrestrial solar radiation and its components. The information on terrestrial solar radiation is required in several different forms depending on the kinds of calculations and kind of application that are to be done. Of course, terrestrial solar radiation on the horizontal plane depends on the different weather conditions such as cloud cover, relative humidity, and ambient temperature. Therefore, the impact of the atmosphere on solar radiation should be considered. One of the most important points of terrestrial solar radiation evaluation is its determination during clear sky conditions. Therefore, in this chapter, the equations that determine the air mass basing on available theories are given and the clear sky conditions are introduced with shading a light on the previous work in identifying clear sky conditions. Taking into consideration that, clear sky solar radiation estimation is of great importance for solar tracking, a detailed review of main available models is given in this chapter. As daily, monthly, seasonally, biannually and yearly mean daily solar radiations are required information for designing and installing long term tracking systems, different available methods are commented regarding their applicability for the estimation of solar radiation information in the desired format from the data that are available. An important accent is paid also on the assessment and comparison of monthly mean daily solar radiation estimation models.

scholarly journals Analysis on the impact of aerosol optical depth on surface solar radiation in the Shanghai megacity, China

2011 ◽  
Vol 11 (7) ◽  
pp. 3281-3289 ◽  
Author(s):  
J. Xu ◽  
C. Li ◽  
H. Shi ◽  
Q. He ◽  
L. Pan
Keyword(s):  
Solar Radiation ◽  
Aerosol Optical Depth ◽  
Optical Depth ◽  
Decadal Variation ◽  
Surface Solar Radiation ◽  
Atmospheric Transparency ◽  
Clear Sky ◽  
Term Variation ◽  
Sky Conditions

Abstract. This study investigated the decadal variation of the direct surface solar radiation (DiSR) and the diffuse surface solar radiation (DfSR) during 1961–2008 in the Shanghai megacity as well as their relationships to Aerosol Optical Depth (AOD) under clear-sky conditions. Three successive periods with unique features of long term variation of DiSR were identified for both clear-sky and all-sky conditions: a "dimming" period from the late 1960s to the mid 1980s, a "stabilization"/"slight brightening" period from the mid 1980s to the mid 1990s, and a "renewed dimming" period thereafter. During the two dimming periods of DiSR, DfSR brightened significantly under clear-sky conditions, indicating that change in atmospheric transparency resulting from aerosol emission has an important role on decadal variation of surface solar radiation (SSR) over this area. The analysis on the relationship between the Moderate-resolution Imaging Spectroradiometer (MODIS) retrieved AOD and the corresponding hourly measurements of DiSR and DfSR under clear-sky conditions clearly revealed that AOD is significantly correlated and anti-correlated with DfSR and DiSR, respectively, both above 99% confidence in all seasons, indicating the great impact of aerosols on SSR through absorption and/or scattering in the atmosphere. In addition, both AOD and the corresponding DiSR and DfSR measured during the satellite passage over Shanghai show obvious weekly cycles. On weekends, AOD is lower than the weekly average, corresponding to higher DiSR and lower DfSR, while the opposite pattern was true for weekdays. Less AOD on weekends due to the reduction of transportation and industrial activities results in enhancement of atmospheric transparency under cloud free conditions so as to increase DiSR and decrease DfSR simultaneously. Results show that aerosol loading from the anthropogenic emissions is an important modulator for the long term variation of SSR in Shanghai.

scholarly journals Cloud Base Height Estimation from ISCCP Cloud-Type Classification Applied to A-Train Data

2017 ◽  
Vol 2017 ◽  
pp. 1-14 ◽  
Author(s):  
Yao Liang ◽  
Xuejin Sun ◽  
Steven D. Miller ◽  
Haoran Li ◽  
Yongbo Zhou ◽  
...  
Keyword(s):  
Global Radiation ◽  
Estimation Method ◽  
Separation Distance ◽  
Cloud Base ◽  
Radiation Balance ◽  
Cloud Type ◽  
Active Sensors ◽  
Combined Algorithm ◽  
Type Classification ◽  
Cloud Base Height

Cloud base height (CBH) is an important cloud macro parameter that plays a key role in global radiation balance and aviation flight. Building on a previous algorithm, CBH is estimated by combining measurements from CloudSat/CALIPSO and MODIS based on the International Satellite Cloud Climatology Project (ISCCP) cloud-type classification and a weighted distance algorithm. Additional constraints on cloud water path (CWP) and cloud top height (CTH) are introduced. The combined algorithm takes advantage of active and passive remote sensing to effectively estimate CBH in a wide-swath imagery where the cloud vertical structure details are known only along the curtain slice of the nonscanning active sensors. Comparisons between the estimated and observed CBHs show high correlation. The coefficient of association (R2) is 0.8602 with separation distance between donor and recipient points in the range of 0 to 100 km and falls off to 0.5856 when the separation distance increases to the range of 401 to 600 km. Also, differences are mainly within 1 km when separation distance ranges from 0 km to 600 km. The CBH estimation method was applied to the 3D cloud structure of Tropical CycloneBill, and the method is further assessed by comparing CTH estimated by the algorithm with the MODIS CTH product.

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