The Experts below are selected from a list of 37542 Experts worldwide ranked by ideXlab platform
Sami K. Solanki - One of the best experts on this subject based on the ideXlab platform.
-
UV Solar Irradiance in observations and the NRLSSI and SATIRE-S models
Journal of Geophysical Research: Space Physics, 2015Co-Authors: Kok Leng Yeo, Sami K. Solanki, Yvonne C. Unruh, Natalie A. Krivova, William T. Ball, Jeff S. MorrillAbstract:Total Solar Irradiance and UV spectral Solar Irradiance have been monitored since 1978 through a succession of space missions. This is accompanied by the development of models aimed at replicating Solar Irradiance by relating the variability to Solar magnetic activity. The NRLSSI and SATIRE-S models provide the most comprehensive reconstructions of total and spectral Solar Irradiance over the period of satellite observation currently available. There is persistent controversy between the various measurements and models in terms of the wavelength dependence of the variation over the Solar cycle, with repercussions on our understanding of the influence of UV Solar Irradiance variability on the stratosphere. We review the measurement and modelling of UV Solar Irradiance variability over the period of satellite observation. The SATIRE-S reconstruction is consistent with spectral Solar Irradiance observations where they are reliable. It is also supported by an independent, empirical reconstruction of UV spectral Solar Irradiance based on UARS/SUSIM measurements from an earlier study. The weaker Solar cycle variability produced by NRLSSI between 300 and 400 nm is not evident in any available record. We show that although the method employed to construct NRLSSI is principally sound, reconstructed Solar cycle variability is detrimentally affected by the uncertainty in the SSI observations it draws upon in the derivation. Based on our findings, we recommend, when choosing between the two models, the use of SATIRE-S for climate studies.
-
Solar Cycle Variation in Solar Irradiance
Space Science Reviews, 2014Co-Authors: K. L. Yeo, Natalie A. Krivova, Sami K. SolankiAbstract:The correlation between Solar Irradiance and the 11-year Solar activity cycle is evident in the body of measurements made from space, which extend over the past four decades. Models relating variation in Solar Irradiance to photospheric magnetism have made significant progress in explaining most of the apparent trends in these observations. There are, however, persistent discrepancies between different measurements and models in terms of the absolute radiometry, secular variation and the spectral dependence of the Solar cycle variability. We present an overview of Solar Irradiance measurements and models, and discuss the key challenges in reconciling the divergence between the two.
-
Solar Irradiance Variability
Astronomische Nachrichten, 2013Co-Authors: Sami K. Solanki, Yvonne C. UnruhAbstract:The Sun has long been considered a constant star, to the extent that its total Irradiance was termed the Solar constant. It required radiometers in space to detect the small variations in Solar Irradiance on timescales of the Solar rotation and the Solar cycle. A part of the difficulty is that there are no other constant natural daytime sources to which the Sun's brightness can be compared. The discovery of Solar Irradiance variability rekindled a long-running discussion on how strongly the Sun affects our climate. A non-negligible influence is suggested by correlation studies between Solar variability and climate indicators. The mechanism for Solar Irradiance variations that fits the observations best is that magnetic features at the Solar surface, i.e. sunspots, faculae and the magnetic network, are responsible for almost all variations (although on short timescales convection and p-mode oscillations also contribute). In spite of significant progress important questions are still open. Thus there is a debate on how strongly Irradiance varies on timescales of centuries (i.e. how much darker the Sun was during the Maunder minimum than it is today). It is also not clear how the Solar spectrum changes over the Solar cycle. Both these questions are of fundamental importance for working out just how strongly the Sun influences our climate. Another interesting question is how Solar Irradiance variability compares with that of other cool dwarfs, particularly now that observations from space are available also for stars.
-
evolution of the Solar Irradiance during the holocene
Astronomy and Astrophysics, 2011Co-Authors: L E A Vieria, Sami K. Solanki, Natalie A. Krivova, Ilya UsoskinAbstract:Context. Long-term records of Solar radiative output are vital for understanding Solar variability and past climate change. Measurements of Solar Irradiance are available for only the last three decades, which calls for reconstructions of this quantity over longer time scales using suitable models. Aims. We present a physically consistent reconstruction of the total Solar Irradiance for the Holocene. Methods. We extend the SATIRE (Spectral And Total Irradiance REconstruction) models to estimate the evolution of the total (and partly spectral) Solar Irradiance over the Holocene. The basic assumption is that the variations of the Solar Irradiance are due to the evolution of the dark and bright magnetic features on the Solar surface. The evolution of the decadally averaged magnetic flux is computed from decadal values of cosmogenic isotope concentrations recorded in natural archives employing a series of physics-based models connecting the processes from the modulation of the cosmic ray flux in the heliosphere to their record in natural archives. We then compute the total Solar Irradiance (TSI) as a linear combination of the jth and jth + 1 decadal values of the open magnetic flux. In order to evaluate the uncertainties due to the evolution of the Earth’s magnetic dipole moment, we employ four reconstructions of the open flux which are based on conceptually different paleomagnetic models. Results. Reconstructions of the TSI over the Holocene, each valid for a different paleomagnetic time series, are presented. Our analysis suggests that major sources of uncertainty in the TSI in this model are the heritage of the uncertainty of the TSI since 1610 reconstructed from sunspot data and the uncertainty of the evolution of the Earth’s magnetic dipole moment. The analysis of the distribution functions of the reconstructed Irradiance for the last 3000 years, which is the period that the reconstructions overlap, indicates that the estimates based on the virtual axial dipole moment are significantly lower at earlier times than the reconstructions based on the virtual dipole moment. We also present a combined reconstruction, which represents our best estimate of total Solar Irradiance for any given time during the Holocene. Conclusions. We present the first physics-based reconstruction of the total Solar Irradiance over the Holocene, which will be of interest for studies of climate change over the last 11 500 years. The reconstruction indicates that the decadally averaged total Solar Irradiance ranges over approximately 1.5 W/m 2 from grand maxima to grand minima.
-
evolution of the Solar Irradiance during the holocene
arXiv: Solar and Stellar Astrophysics, 2011Co-Authors: L E A Vieira, Sami K. Solanki, Natalie A. Krivova, Ilya UsoskinAbstract:Aims. We present a physically consistent reconstruction of the total Solar Irradiance for the Holocene. Methods. We extend the SATIRE models to estimate the evolution of the total (and partly spectral) Solar Irradiance over the Holocene. The basic assumption is that the variations of the Solar Irradiance are due to the evolution of the dark and bright magnetic features on the Solar surface. The evolution of the decadally averaged magnetic flux is computed from decadal values of cosmogenic isotope concentrations recorded in natural archives employing a series of physics-based models connecting the processes from the modulation of the cosmic ray flux in the heliosphere to their record in natural archives. We then compute the total Solar Irradiance (TSI) as a linear combination of the jth and jth + 1 decadal values of the open magnetic flux. Results. Reconstructions of the TSI over the Holocene, each valid for a di_erent paleomagnetic time series, are presented. Our analysis suggests that major sources of uncertainty in the TSI in this model are the heritage of the uncertainty of the TSI since 1610 reconstructed from sunspot data and the uncertainty of the evolution of the Earth's magnetic dipole moment. The analysis of the distribution functions of the reconstructed Irradiance for the last 3000 years indicates that the estimates based on the virtual axial dipole moment are significantly lower at earlier times than the reconstructions based on the virtual dipole moment. Conclusions. We present the first physics-based reconstruction of the total Solar Irradiance over the Holocene, which will be of interest for studies of climate change over the last 11500 years. The reconstruction indicates that the decadally averaged total Solar Irradiance ranges over approximately 1.5 W/m2 from grand maxima to grand minima.
Robert Arnone - One of the best experts on this subject based on the ideXlab platform.
-
Solar Irradiance short wave radiation users guide
1995Co-Authors: Paul Martinolich, Robert ArnoneAbstract:Abstract : Solar Irradiance for short wave radiation (400-700 nm) at the sea surface can be calculated using inputs obtained from satellite systems and model estimates. The short wave Solar Irradiance is important for estimating the surface heating that occurs in the near surface and estimating the available Irradiance for biological growth in the upper ocean. The variability of the Solar Irradiance is believed to have significant influence on the global carbon cycle. This users guide provides an understanding of the models and operational procedures for using the software and understanding the results. (AN)
-
Solar Irradiance short wave radiation users guide. Final report
1995Co-Authors: Paul Martinolich, Robert ArnoneAbstract:Solar Irradiance for short wave radiation (400-700 nm) at the sea surface can be calculated using inputs obtained from satellite systems and model estimates. The short wave Solar Irradiance is important for estimating the surface heating that occurs in the near surface and estimating the available Irradiance for biological growth in the upper ocean. The variability of the Solar Irradiance is believed to have significant influence on the global carbon cycle. This users guide provides an understanding of the models and operational procedures for using the software and understanding the results.
Stefan Winkler - One of the best experts on this subject based on the ideXlab platform.
-
Estimating Solar Irradiance Using Sky Imagers
arXiv: Image and Video Processing, 2019Co-Authors: Soumyabrata Dev, Yee Hui Lee, Florian M. Savoy, Stefan WinklerAbstract:Ground-based whole sky cameras are extensively used for localized monitoring of clouds nowadays. They capture hemispherical images of the sky at regular intervals using a fisheye lens. In this paper, we propose a framework for estimating Solar Irradiance from pictures taken by those imagers. Unlike pyranometers, such sky images contain information about cloud coverage and can be used to derive cloud movement. An accurate estimation of Solar Irradiance using solely those images is thus a first step towards short-term forecasting of Solar energy generation based on cloud movement. We derive and validate our model using pyranometers co-located with our whole sky imagers. We achieve a better performance in estimating Solar Irradiance and in particular its short-term variations as compared to other related methods using ground-based observations.
-
Estimating Solar Irradiance using sky imagers
Atmospheric Measurement Techniques, 2019Co-Authors: Soumyabrata Dev, Yee Hui Lee, Florian M. Savoy, Stefan WinklerAbstract:Abstract. Ground-based whole-sky cameras are now extensively used for the localized monitoring of clouds. They capture hemispherical images of the sky at regular intervals using a fish-eye lens. In this paper, we propose a framework for estimating Solar Irradiance from pictures taken by those imagers. Unlike pyranometers, such sky images contain information about cloud coverage and can be used to derive cloud movement. An accurate estimation of Solar Irradiance using solely those images is thus a first step towards the short-term forecasting of Solar energy generation based on cloud movement. We derive and validate our model using pyranometers colocated with our whole-sky imagers. We achieve a better performance in estimating Solar Irradiance and in particular its short-term variations compared to other related methods using ground-based observations.
-
Predicting Solar Irradiance in Singapore
2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall), 2019Co-Authors: T. A. Fathima, Vasudevan Nedumpozhimana, Yee Hui Lee, Stefan Winkler, Soumyabrata DevAbstract:Solar Irradiance is the primary input for all Solar energy generation systems. The amount of available Solar radiation over time under the local weather conditions helps to decide the optimal location, technology and size of a Solar energy project. We study the behaviour of incident Solar Irradiance on the earth's surface using weather sensors. In this paper, we propose a time-series based technique to forecast the Solar Irradiance values for shorter lead times of upto 15 minutes. Our experiments are conducted in the tropical region viz. Singapore, which receives a large amount of Solar Irradiance throughout the year. We benchmark our method with two common forecasting techniques, namely persistence model and average model, and we obtain good prediction performance. We report a root mean square of 147 W/m2 for a lead time of 15 minutes.
-
A Chaotic Approach on Solar Irradiance Forecasting
2019 Photonics & Electromagnetics Research Symposium - Fall (PIERS - Fall), 2019Co-Authors: T. A. Fathima, Vasudevan Nedumpozhimana, Stefan WinklerAbstract:We analyse the time series of Solar Irradiance measurements using chaos theory. The False Nearest Neighbour method (FNN), one of the most common methods of chaotic analysis is used for the analysis. One year data from the weather station located at Nanyang Technological University (NTU) Singapore with a temporal resolution of 1 minute is employed for the study. The data is sampled at 60 minutes interval and 30 minutes interval for the analysis using the FNN method. Our experiments revealed that the optimum dimension required for Solar Irradiance is 4 for both samplings. This indicates that a minimum of 4 dimensions is required for embedding the data for the best representation of input. This study on obtaining the embedding dimension of Solar Irradiance measurement will greatly assist in fixing the number of previous data required for Solar Irradiance forecasting.
Marius Paulescu - One of the best experts on this subject based on the ideXlab platform.
-
Quantifiers for the Solar Irradiance variability: A new perspective
Solar Energy, 2018Co-Authors: Robert Blaga, Marius PaulescuAbstract:Abstract This paper focuses on variability in Solar Irradiance time series. Six quantifiers for the Solar Irradiance variability, very different in their nature, are analyzed. One of them, based on the cumulative distribution function of the increments of clearness index time series, is developed in this study. The new quantifier is obtained by integrating the complementary cumulative distribution function over all values of the increments. The same level of variability is expressed by different quantifiers of different magnitudes. In order to surpass this obstacle a normalizing procedure is applied. This is a key task in comparing the output of different quantifiers toward a unique standard in the evaluation of the Solar Irradiance variability. As application, a new multi-parameter ranking procedure for classifying the days according to the Solar Irradiance variability is introduced.
-
Parametric modeling: A simple and versatile route to Solar Irradiance
Energy Conversion and Management, 2018Co-Authors: Delia Calinoiu, Robert Blaga, Eugenia Paulescu, Nicoleta Stefu, Nicolina Pop, Remus Boata, Andreea Sabadus, Marius PaulescuAbstract:Abstract A clear-sky Solar Irradiance model is certainly a basic tool in the estimation of Solar resources. With all the abundance of such models, there is plenty of room for searching a clear-sky Solar Irradiance model with general applicability, i.e. to be able to provide high-accurate estimates in most places around the world. This paper reports an upgraded version (further referred to as SIMv.2) of our parametric clear-sky Solar Irradiance model SIMv.1, aiming to improve the accuracy of estimates in arid environment. The new elements of SIMv.2, such as new equations for aerosol absorption and downward fraction, have been introduced targeting a better capture of the peculiarities of the Solar radiation extinction by aerosols. Overall, the results of testing SIMv.2 at twelve stations located in regions with temperate, arid and tropical climate show that SIMv.2 performs much better than SIMv.1, an improvement in nRMSE of 37.1% for global Solar Irradiance and of 24.7% for the diffuse component being noticed. The comparison with other fourteen clear-sky Solar Irradiance models at five stations located in arid climate places SIMv.2 in the class of the best performing models. The limitation of the SIMv.2 performance in extreme weather conditions is discussed in two cases.
-
the assessment of beam Solar Irradiance using parametric modeling
International Journal of Green Energy, 2014Co-Authors: Nicolina Pop, Paul Mircea Gravila, Angel Pacurar, Remus Boata, Marius PaulescuAbstract:The performance of a Solar thermal power converter is closely related to the occurrence of beam Solar Irradiance on the collector surface. In this thought, the present study deals with modeling the beam Solar Irradiance component, studying the influence of different atmospheric parameters (ozone column content, Angstrom turbidity coefficient, water vapor column content) on its magnitude. The occurrence of beam Solar Irradiance at a given moment is indicated by the sunshine number, a Boolean parameter stating whether the sun is shining or not. The tests show that the estimation accuracy is strongly influenced by the stability of the radiative regime.
-
Nowcasting Solar Irradiance using the sunshine number
Energy Conversion and Management, 2014Co-Authors: Marius Paulescu, Oana Mares, Eugenia Paulescu, Nicoleta Stefu, Angel Pacurar, Delia Calinoiu, Paul Mircea Gravila, Nicolina Pop, Remus BoataAbstract:This paper focuses on short-term forecasting of Solar Irradiance. An innovative two-state model is proposed: if the sun is shining, the Solar Irradiance is estimated with an empirical model fitted on historical data; if the sun is covered, the clear sky Solar Irradiance is adjusted according to the cloud transmittance. The distinction between these two states is made by the sunshine number, a binary indicator of whether the Sun is covered by clouds or not, previously introduced by Badescu (2002). Sunshine number is the sole quantity effectively forecasted in the model. The general structure of the model and its advantages are discussed. Its performance on real data is demonstrated, and comparison of the model results against classical ARIMA approach applied to clearness index time series, as main competitor, is made. We conclude with an outlook to future developments oriented to improve the model accuracy.
C. Fröhlich - One of the best experts on this subject based on the ideXlab platform.
-
total Solar Irradiance during the holocene
Geophysical Research Letters, 2009Co-Authors: F Steinhilber, J Beer, C. FröhlichAbstract:[1] For the first time a record of total Solar Irradiance covering 9300 years is presented, which covers almost the entire Holocene. This reconstruction is based on a recently observationally derived relationship between total Solar Irradiance and the open Solar magnetic field. Here we show that the open Solar magnetic field can be obtained from the cosmogenic radionuclide 10Be measured in ice cores. Thus, 10Be allows to reconstruct total Solar Irradiance much further back than the existing record of the sunspot number which is usually used to reconstruct total Solar Irradiance. The resulting increase in Solar-cycle averaged TSI from the Maunder Minimum to the present amounts to (0.9 ± 0.4) Wm−2. In combination with climate models, our reconstruction offers the possibility to test the claimed links between climate and TSI forcing.
-
Solar Irradiance Variability
Solar Variability and Its Effects on Climate, 2004Co-Authors: C. FröhlichAbstract:Since November 1978 a set of total Solar Irradiance (TSI) measurements from space is available, yielding a time series of more than 23 years. From measurements made by different space radiometers (HF on NIMBUS 7, ACRIM I on SMM, ACRIM II on UARS and VIRGO on SOHO) a composite record of TSI can be compiled. This leads to a reliable record of TSI with an overall precision of the order of 0.05 Wm -2 . This time series is compared to an empirical model based on sunspot darkening and brightening due to faculae and network. Since early 1996 spectral measurements by filter-radiometers of VIRGO provide continuous time series of spectral Solar Irradiance (SSI) at 402, 500 and 862 nm. These time series are analyzed and compared to TSI yielding information about the redistribution of energy within the spectrum during changes of TSI.
-
Total Solar Irradiance variations
Journal of Atmospheric and Solar-Terrestrial Physics, 1999Co-Authors: J. M. Pap, C. FröhlichAbstract:Abstract Total Solar Irradiance has been monitored from space for nearly two decades. These space-borne observations have established conclusively that total Solar Irradiance changes over a wide range of periodicities—from minutes to the 11-year Solar cycle. Since the total energy flux of the Sun is the principal driver for all Earths atmospheric phenomena, the accurate knowledge of the Solar radiation received by the Earth and its variations is an extremely important issue. In this paper we review the long-term variations of total Solar Irradiance during Solar cycles 21 and 22. We conclude that, within the current accuracy and precision of the measurements, the minimum level of total Solar Irradiance is about the same for both Solar cycles 21 and 22.
-
Long-Term Variations in Total Solar Irradiance
Solar Physics, 1994Co-Authors: J. M. Pap, C. Fröhlich, R. C. Willson, Richard F. Donnelly, Larry PugaAbstract:For more than a decade total Solar Irradiance has been monitored simultaneously from space by different satellites. The detection of total Solar Irradiance variations by satellite-based experiments during the past decade and a half has stimulated modeling efforts to help identify their causes and to provide estimates of Irradiance data, using ‘proxy’ indicators of Solar activity, for time intervals when no satellite observations exist. In this paper total Solar Irradiance observed by the Nimbus-7/ERB, SMM/ACRIM I, and UARS/ACRIM II radiometers is modeled with the Photometric Sunspot Index and the Mg II core-to-wing ratio. Since the formation of the Mg II line is very similar to that of the Ca II K line, the Mg core-to-wing ratio, derived from the Irradiance observations of the Nimbus-7 and NOAA9 satellites, is used as a proxy for the bright magnetic elements. It is shown that the observed changes in total Solar Irradiance are underestimated by the proxy models at the time of maximum and during the beginning of the declining portion of Solar cycle 22 similar to behavior just before the maximum of Solar cycle 21. This disagreement between total Irradiance observations and their model estimates is indicative of the fact that the underlying physical mechanism of the changes observed in the Solar radiative output is not well-understood. Furthermore, the uncertainties in the proxy data used for Irradiance modeling and the resulting limitation of the models should be taken into account, especially when the Irradiance models are used for climatic studies.
