107 citations · 619 across the 28 of their papers we have counts for
30 papers
Re-evaluating solar irradiance reconstructions: No evidence for large secular trends
Theodosios Chatzistergos, Natalie A. Krivova, Mathew J. Owens +1
Most current irradiance reconstructions suggest only a modest secular increase in TSI between the 1700 and 1986 activity minima ( Wm). However, 2 models, the CHRONOS and…
Quantifying the effect of passband on observations in the Ca II K line
Ajay Kumar Yadav, Theodosios Chatzistergos, Natalie Krivova +33
Full-disk observations of the Sun in the Ca II K line have been carried out since the late 19th century at various observatories worldwide. These long-term records of solar activit…
Solar Irradiance Reconstruction over the Telescopic Era Using a Revised Photospheric Magnetic Field Model
D. Temaj, N. A. Krivova, T. Chatzistergos +2
The Sun is the primary source of energy for Earth and one of the main external drivers of its climate. Solar irradiance -- the radiative power emitted by the Sun and received at 1-…
Structure and Dynamics of the Sun's Interior Revealed by Helioseismic and Magnetic Imager
Alexander Kosovichev, Sarbani Basu, Yuto Bekki +43
High-resolution helioseismology observations with the Helioseismic and Magnetic Imager (HMI) onboard Solar Dynamics Observatory (SDO) provide a unique three-dimensional view of the…
Revisiting the SATIRE-S irradiance reconstruction: Heritage of Mt Wilson magnetograms and Ca II K observations
Theodosios Chatzistergos, Natalie A. Krivova, Sami K. Solanki +1
Accurate information on long-term variations in solar irradiance, important for understanding the solar influence on Earth's climate, cannot be derived from direct irradiance measu…
Detectability of Solar Rotation Period Across Various Wavelengths
Valeriy Vasilyev, Timo Reinhold, Alexander I. Shapiro +3
The light curves of old G-dwarfs obtained in the visible and near-infrared wavelength ranges are highly irregular. This significantly complicates the detectability of the rotation…
Estimation of Polar Magnetic Fields using Ca II K Polar Network as a Proxy
Dibya Kirti Mishra, Bibhuti Kumar Jha, Theodosios Chatzistergos +3
The polar magnetic field plays a crucial role in the solar dynamo model and contributes to predicting future solar cycles. However, continuous and direct measurements of this polar…
Ca II K Polar Network Index of the Sun: A Proxy for Historical Polar Magnetic Field
Dibya Kirti Mishra, Bibhuti Kumar Jha, Theodosios Chatzistergos +4
The Sun's polar magnetic field is pivotal in understanding solar dynamo processes and forecasting future solar cycles. However, direct measurements of the polar field is only avail…
Solar variability in the Mg II h and k lines
K. Sowmya, M. Snow, A. I. Shapiro +3
Solar irradiance and its variations in the ultraviolet (UV) control the photochemistry in Earth's atmosphere and influence Earth's climate. The variability of Mg II h and k core-to…
The Extreme Space Weather Event of 1872 February: Sunspots, Magnetic Disturbance, and Auroral Displays
Hisashi Hayakawa, Edward W. Cliver, Frédéric Clette +19
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…
Butterfly Diagram and Other Properties of Plage Areas from Kodaikanal Ca II K Photographs Covering 1904-2007
Bibhuti Kumar Jha, Theodosios Chatzistergos, Dipankar Banerjee +4
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 Observator…
Differential Rotation of the Solar Chromosphere: A Century-long Perspective from Kodaikanal Solar Observatory Ca II K Data
Dibya Kirti Mishra, Srinjana Routh, Bibhuti Kumar Jha +5
Chromospheric differential rotation is a key component in comprehending the atmospheric coupling between the chromosphere and the photosphere at different phases of the solar cycle…
Analysis of full-disc H alpha observations: Carrington maps and filament properties in 1909-2022
Theodosios Chatzistergos, Ilaria Ermolli, Dipankar Banerjee +14
Full disc observations of the Sun in the H line provide information about the solar chromosphere and in particular about the filaments, which are dark and elongated features tha…
Investigating the effect of solar ambient and data characteristics on Ca II K observations and line profile measurements
M. Murabito, I. Ermolli, T. Chatzistergos +3
We analysed state-of-the-art observations of the solar atmosphere to investigate the dependence of the \ca brightness of several solar features on spectral bandwidth and spatial re…
Long-term changes in solar activity and irradiance
Theodosios Chatzistergos, Natalie A. Krivova, Kok Leng Yeo
The Sun is the main energy source to Earth, and understanding its variability is of direct relevance to climate studies. Measurements of total solar irradiance exist since 1978, bu…
Re-calibration of the Sunspot Number: Status Report
F. Clette, L. Lefèvre, T. Chatzistergos +18
We report progress on the ongoing recalibration of the Wolf sunspot number (SN) and Group sunspot number (GN) following the release of version 2.0 of SN in 2015. This report consti…
Rome Precision Solar Photometric Telescope: precision solar full-disk photometry during solar cycles 23-25
Ilaria Ermolli, Fabrizio Giorgi, Theodosios Chatzistergos
The Rome Precision Solar Photometric Telescope (Rome/PSPT) is a ground-based telescope engaged in precision solar photometry. It has a 27-year database of full-disk images of the p…
Full-disc Ca II K observations -- a window to past solar magnetism
Theodosios Chatzistergos, Natalie A. Krivova, Ilaria Ermolli
First such observations were made in 1892 and since then various sites around the world have carried out regular observations, with Kodaikanal, Meudon, Mt Wilson, and Coimbra being…
Scrutinizing the relationship between plage areas and sunspot areas and numbers
Theodosios Chatzistergos, Ilaria Ermolli, Natalie A. Krivova +3
Studies and reconstructions of past solar activity require data on sunspots as well as faculae/plage and network. Such data are also important for understanding the magnetic activi…
Reconstructing solar irradiance from historical Ca II K observations. I. Method and its validation
Theodosios Chatzistergos, Natalie A. Krivova, Ilaria Ermolli +5
Knowledge of solar irradiance variability is critical to Earth's climate models and understanding the solar influence on Earth's climate. Direct solar irradiance measurements are o…
Modelling solar irradiance from ground-based photometric observations
Theodosios Chatzistergos, Ilaria Ermolli, Fabrizio Giorgi +2
Total solar irradiance (TSI) has been monitored from space since 1978. The measurements show a prominent variability in phase with the solar cycle, as well as fluctuations on times…
Analysis of full disc Ca II K spectroheliograms III. Plage area composite series covering 1892-2019
Theodosios Chatzistergos, Ilaria Ermolli, Natalie A. Krivova +16
We derive the plage area evolution over the last 12 solar cycles employing data from all Ca II K archives available publicly in digital form known to us, including several as yet u…
Delving into the Historical Ca II K Archive from the Kodaikanal Observatory: the Potential of the Most Recent Digitised Series
Theodosios Chatzistergos, Ilaria Ermolli, Sami K. Solanki +4
Full-disc Ca II K photographic observations of the Sun carry direct information about the evolution of solar-plage regions for more than a century and are therefore a unique datase…
Recovering the unsigned photospheric magnetic field from Ca II K observations
Theodosios Chatzistergos, Ilaria Ermolli, Sami K. Solanki +3
We reassess the relationship between the photospheric magnetic field strength and the Ca II K intensity for a variety of surface features as a function of the position on the disc…