1,720,979 research outputs found
Assessment of sunspot number cross-calibration approaches
Get PDFContext. Group sunspot number data form the longest record of direct observations of solar activity and variability. However, the observations were conducted by many observers using different telescopes and at diverse locations, which necessitates their proper cross-calibration. Historically, such a cross-calibration was performed with a simple linear scaling. More recently some non-linear approaches have also been developed, as well as modifications of the classical linear scaling. This resulted in a number of new composite sunspot series, which diverge before the 20th century, thus also leading to an uncertainty in the past solar activity and variability. Aims. Our aim was to understand the causes of divergence between different sunspot series. To this end, we scrutinised the existing cross-calibration methods to identify the sources of their biases and uncertainties. Methods. We used synthetic data imitating observers with different observing capabilities to test the performance of different cross-calibration approaches, including both simple linear scaling and non-linear non-parametric techniques. Some of these methods require a direct overlap between the records of two observers, while others rely on statistical properties of sunspot groups. Results. We found that linear approaches generally overestimated and underestimated the maxima of strong and weak activity cycles, respectively, thus introducing a bias in the secular variability. In contrast, for typical characteristics of existing records of observers, non-parametric approaches returned more consistent results and lower errors. Out of these latter, methods relying on statistical properties of the records return worse results. Conclusions. Our analysis revealed limitations of the various approaches and identified the best approaches. For future recalibrations of sunspot number, we recommend using a direct non-linear calibration when the data coverage is sufficient. However, the errors returned by such daisy-chain methods accumulate when going further back in time, if a multi-step daisy-chain (backbone) calibration is needed. To bridge extensive data gaps, we therefore recommend using a statistical method (e.g. active-day fraction)
Butterfly Diagram and Other Properties of Plage Areas from Kodaikanal Ca ii K Photographs Covering 1904 – 2007
No full textAbstract Ca ii K observations of the Sun have a great potential for probing the Sun’s magnetism and activity, as well as for reconstructing solar irradiance. The Kodaikanal Solar Observatory (KoSO) in India, houses one of the most prominent Ca ii K archives, spanning from 1904 to 2007, obtained under the same experimental conditions over a century, a feat very few other sites have achieved. However, the KoSO Ca ii K archive suffers from several inconsistencies (e.g., missing/incorrect timestamps of observations and orientation of some images) which have limited the use of the archive. This study is a step towards bringing the KoSO archive to its full potential. We did this by developing an automatic method to orient the images more accurately than in previous studies. Furthermore, we included more data than in earlier studies (considering images that could not previously be analyzed by other techniques, as well as 2845 newly digitized images), while also accounting for mistakes in the observational date/time. These images were accurately processed to identify plage regions along with their locations, enabling us to construct the butterfly diagram of plage areas from the entire KoSO Ca ii K archive covering 1904 – 2007. Our butterfly diagram shows significantly fewer data gaps compared to earlier versions due to the larger set of data used in this study. Moreover, our butterfly diagram is consistent with Spörer’s law for sunspots, validating our automatic image orientation method. Additionally, we found that the mean latitude of plage areas calculated over the entire period is 20.5 % ± 2.0 higher than that of sunspots, irrespective of the phase or the strength of the solar cycle. We also studied the north–south asymmetry showing that the northern hemisphere dominated plage areas during solar cycles 19 and 20, while the southern hemisphere dominated during Solar Cycles 21 – 23.H2020 European Research Council http://dx.doi.org/10.13039/100010663Max Planck Institute for Solar System Researc
Analysis of historical solar observations and long-term changes in solar irradiance
Get PDFThe Sun is the main external driver of Earth's climate.
Various mechanisms of the solar influence on climate have been proposed. The debate is ongoing, but variation in the radiative flux of the Sun is among the main candidates. Direct measurements of the solar irradiance exist for merely 40 years, which is a rather short period to derive conclusions about any possible long term changes in solar irradiance and their possible influence on climate.
The main driver of the irradiance variations on time-scales of days to decades, and possibly longer, is believed to be the solar surface magnetism. Models have been developed that reconstruct the irradiance by using appropriate proxies of the magnetic activity of the Sun.
Irradiance models require input data representing both dark and bright magnetic features emerging at the solar surface. The most widely ever used proxies are the sunspot areas (available since 1874), the sunspot number (available since 1700), and the sunspot group number (available since 1610). However, these records do not provide direct information on bright features. Their evolution has to be inferred from the sunspot data via certain assumptions whose justification is still very unclear.
Therefore, there is a strong need for a more direct facular proxy. %in order to resolve the ambiguities of the models.
Ca II K full-disc spectroheliograms are uniquely suited for that purpose. Observations in the Ca II K line started as early as in 1892 at various sites, providing a good temporal coverage of the whole 20th century.
However, these data suffer from a variety of problems hindering their immediate applicability.
The historical Ca II K observations are stored in photographic plates or films, which have a non-linear response to the incident radiation. Information on this relation has not been recorded for the majority of the historical observations. Furthermore, a plethora of artefacts have been introduced on these images during their various life stages. These artefacts need to be accurately accounted for in order to provide meaningful results from such data.
We have developed a method to recover the relation for the response of the plates to the incident radiation by using information that is stored on the solar disc of the image. This method is based on the assumption that the darker parts of the quiet Sun regions remain unchanged in time. We have also developed a method of calculating the quiet Sun background of the images, which includes the centre-to-limb variation and takes into account
various large-scale artefacts. We have shown that the accuracy of this method is greater than that of previously proposed techniques.
We have also reassessed the relation between the magnetic field strength and the Ca II K contrast, by using a larger number of Ca II images than was done in earlier such studies.
We find that this relation can be well described with a power law function, and the best fit parameters are unaffected by the activity level or the position on the disc. Hence this relation potentially allows a reconstruction of pseudo-magnetograms from the available Ca II K observations covering almost the whole 20th century, that can be used by irradiance models.
The sunspot data (i.e. records of sunspot number), despite their extensive use, are not free of problems either. The process of cross-calibrating different records by individual observers has recently become a matter of debate. This debate brought to light that the majority of the methods used so far fail to take into consideration the non-linearity that arises due to different observing capabilities of the observers. We addressed the issue of the shape of the relation for the inter-calibration between different group sunspot number series.
We have shown, with the aid of synthetic observations derived from the royal Greenwich observatory sunspot area records, that it is strongly non-linear, contrary to what is commonly assumed.
We have developed a method to recalibrate the sunspot group number series with a non-linear non-parametric method based on daily statistics between the observers. Using Monte Carlo simulations we have accounted for the error propagation, which has not been done by any previous reconstruction.
Our reconstruction of the group sunspot number favours moderate activity levels for the 18th and 19th century and supports the existence of the modern grand maximum of solar activity
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Get PDFWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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