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View article: What does solar chromospheric activity look like under different inclination angles?
What does solar chromospheric activity look like under different inclination angles? Open
Context. Chromospheric observations in the Ca II lines are essential for studying the magnetic activity of stars. In the case of the Sun, the chromospheric plages, the main contributors to the Ca II K emission, are distributed between midl…
View article: Solar flare rates and probabilities based on the McIntosh classification: Impacts of GOES/XRS rescaling and revisited sunspot classifications
Solar flare rates and probabilities based on the McIntosh classification: Impacts of GOES/XRS rescaling and revisited sunspot classifications Open
In December 2019, the Space Weather Prediction Center (SWPC) started using the GOES-16 satellite as its primary input for solar X-ray flux monitoring. As such, it stopped applying a scaling factor that had been applied since the GOES-8 cam…
View article: How does the solar chromospheric activity look like under different inclination angles?
How does the solar chromospheric activity look like under different inclination angles? Open
Chromospheric plages are distributed between mid-latitude and the Equator and never close to the Poles. Therefore, we suspect that the inclination angle of the solar rotation axis has an impact on the observable chromospheric emission. We …
View article: Relationship between TIGRE solar S-index and USET Ca II K full disk images
Relationship between TIGRE solar S-index and USET Ca II K full disk images Open
Full disk observations of the solar chromosphere in the Ca II K line represent a valuable dataset for studies of solar magnetic activity. The S-index is widely used to investigate the magnetic activity of stars, however, its connection to …
View article: Relationship between TIGRE solar S-index and USET Ca II K full disk images
Relationship between TIGRE solar S-index and USET Ca II K full disk images Open
Context. Full disk observations of the solar chromosphere in the Ca II K line represent a valuable dataset for studies of solar magnetic activity. The well known S-index is widely used to investigate the magnetic activity of stars, however…
View article: The McNish and Lincoln Solar Activity Predictions: The Method and its Performance
The McNish and Lincoln Solar Activity Predictions: The Method and its Performance Open
The McNish and Lincoln (ML) method, introduced in 1949, was one of the first attempts to produce mid-term forecasts of solar activity, up to 12 months ahead. However, it has been poorly described and evaluated in the past literature, in pa…
View article: The McNish and Lincoln Solar-Activity Predictions: The Method and Its Performance
The McNish and Lincoln Solar-Activity Predictions: The Method and Its Performance Open
The McNish and Lincoln (ML) method, introduced in 1949, was one of the first attempts to produce midterm forecasts of solar activity, up to 12 months ahead. However, it has been poorly described and evaluated in the past literature, in par…
View article: The Extreme Space Weather Event of 1872 February: Sunspots, Magnetic Disturbance, and Auroral Displays
The Extreme Space Weather Event of 1872 February: Sunspots, Magnetic Disturbance, and Auroral Displays Open
We review observations of solar activity, geomagnetic variation, and auroral visibility for the extreme geomagnetic storm on 1872 February 4. The extreme storm (referred to here as the Chapman–Silverman storm) apparently originated from a …
View article: Katsue Misawa's sunspot observations in 1921–1934: a primary reference for the Wolfer–Brunner transition
Katsue Misawa's sunspot observations in 1921–1934: a primary reference for the Wolfer–Brunner transition Open
Our knowledge of the centennial solar variability is largely based on the time series of international sunspot number ($S_{N}$), a composite index based on multiple visual sunspot observers’ records from the 18th century onward and maintai…
View article: Magnitude Estimates for the Carrington Flare in 1859 September: As Seen from the Original Records
Magnitude Estimates for the Carrington Flare in 1859 September: As Seen from the Original Records Open
The Carrington flare in 1859 September is a benchmark, as the earliest reported solar flare and as an event with one of the greatest terrestrial impacts. To date, no rigorous estimate of the energy of this flare has been made on the basis …
View article: Recalibration of the Sunspot-Number: Status Report
Recalibration of the Sunspot-Number: Status Report Open
We report progress on the ongoing recalibration of the Wolf sunspot number ( $S_{\mathrm{N}}$ ) and group-sunspot number ( $G_{\mathrm{N}}$ ) following the release of version 2.0 of $S_{\mathrm{N}}$ in 2015. This report constitutes both…
View article: Scale Transfer in 1849 Heinrich Schwabe to Rudolf Wolf
Scale Transfer in 1849 Heinrich Schwabe to Rudolf Wolf Open
The focus of this study is to reveal the reason behind a scale problem detected around1849 in the historical version of the International Sunspot Number Series, i.e. version1 (Leussu et al, Astronomy and Astrophysics, 559, A28, 2013; Fried…
View article: Scale Transfer in 1849 : Heinrich Schwabe to Rudolf Wolf
Scale Transfer in 1849 : Heinrich Schwabe to Rudolf Wolf Open
The focus of this study is to reveal the reason behind a scale problem detected around 1849 in the historical version of the International Sunspot Number Series, i.e. version 1 (Leussu et al, Astronomy and Astrophysics, 559, A28, 2013; Fri…
View article: Reconstructing the Sunspot Number : challenges and impact
Reconstructing the Sunspot Number : challenges and impact Open
<p>We will present the international effort that led to the first-ever revision of the Sunspot and Group Numbers (let us call them "the Sunspot Series"), a well-known series that had never been put into question since its c…
View article: Diagnosing and calibrating the multi-century Sunspot Number Series
Diagnosing and calibrating the multi-century Sunspot Number Series Open
<p>Visual sunspot observations form the longest scientific record of solar activity, spanning over four centuries. Long term solar studies&#160; are crucial to predict the future evolution of the solar cycles and at improving our…
View article: Maximal growth rate of the ascending phase of a sunspot cycle for predicting its amplitude
Maximal growth rate of the ascending phase of a sunspot cycle for predicting its amplitude Open
Forecasting the solar cycle amplitude is important for a better understanding of the solar dynamo as well as for many space weather applications. We demonstrated a steady relationship between the maximal growth rate of sunspot activity in …
View article: Maximal growth rate of the ascending phase of a sunspot cycle for predicting its amplitude
Maximal growth rate of the ascending phase of a sunspot cycle for predicting its amplitude Open
Context. Forecasting the solar cycle amplitude is important for a better understanding of the solar dynamo as well as for many space weather applications. Different empirical relations of solar cycle parameters with the peak amplitude of t…
View article: Nonparametric monitoring of sunspot number observations
Nonparametric monitoring of sunspot number observations Open
Solar activity is an important driver of long-term climate trends and must be accounted for in climate models. Unfortunately, direct measurements of this quantity over long periods do not exist. The only observation related to solar activi…
View article: Predicting the solar cycle amplitude with the new catalogue of hemispheric sunspot numbers
Predicting the solar cycle amplitude with the new catalogue of hemispheric sunspot numbers Open
<p>The sun&#8217;s magnetic field drives the 11-year solar cycle, and predicting its strength has practical importance for many space weather applications. Previous studies have shown that analysing the solar activity of the two …
View article: Nonparametric monitoring of sunspot number observations: a case study
Nonparametric monitoring of sunspot number observations: a case study Open
Solar activity is an important driver of long-term climate trends and must be accounted for in climate models. Unfortunately, direct measurements of this quantity over long periods do not exist. The only observation related to solar activi…
View article: Is the <i>F</i><sub>10.7cm</sub> – Sunspot Number relation linear and stable?
Is the <i>F</i><sub>10.7cm</sub> – Sunspot Number relation linear and stable? Open
The F 10.7cm radio flux and the Sunspot Number are the most widely used long-term indices of solar activity. They are strongly correlated, which led to the publication of many proxy relations allowing to convert one index onto the other. H…
View article: Sunspot observations by Hisako Koyama: 1945–1996
Sunspot observations by Hisako Koyama: 1945–1996 Open
Sunspot records are the only observational tracer of solar activity that provides a fundamental, multicentury reference. Its homogeneity has been largely maintained with a succession of long-duration visual observers. In this article, we e…
View article: Historical astronomical data: urgent need for preservation, digitization enabling scientific exploration
Historical astronomical data: urgent need for preservation, digitization enabling scientific exploration Open
Over the past decades and even centuries, the astronomical community has accumulated a signif-icant heritage of recorded observations of a great many astronomical objects. Those records con-tain irreplaceable information about long-term ev…
View article: Historical astronomical data:urgent need for preservation, digitization enabling scientific exploration
Historical astronomical data:urgent need for preservation, digitization enabling scientific exploration Open
Over the past decades and even centuries, the astronomical community has\naccumulated a signif-icant heritage of recorded observations of a great many\nastronomical objects. Those records con-tain irreplaceable information about\nlong-term…
View article: To Understand Future Solar Activity, One Has to Know the Past
To Understand Future Solar Activity, One Has to Know the Past Open
Short-term funding strategies present serious problems for programs like solar activity studies, where observations and analysis span decades or longer.
View article: Multi-instrument observations of the solar eclipse on 20 March 2015 and its effects on the ionosphere over Belgium and Europe
Multi-instrument observations of the solar eclipse on 20 March 2015 and its effects on the ionosphere over Belgium and Europe Open
A total solar eclipse occurred on 20 March 2015, with a totality path passing mostly above the North Atlantic Ocean, which resulted in a partial solar eclipse over Belgium and large parts of Europe. In anticipation of this event, a dedicat…