scholarly journals Origin of the Solar Rotation Harmonics Seen in the EUV and UV Irradiance

Solar Physics ◽  
2021 ◽  
Vol 296 (11) ◽  
Author(s):  
G. Giono ◽  
J. J. Zender ◽  
R. Kariyappa ◽  
L. Damé
Keyword(s):  
Time Series ◽  
Transition Region ◽  
Solar Irradiance ◽  
Solar Rotation ◽  
Coronal Holes ◽  
Active Regions ◽  
Higher Harmonics ◽  
Uv Irradiance ◽  
Possibilistic Clustering ◽  
Full Disk

AbstractLong-term periodicities in the solar irradiance are often observed with periods proportional to the solar rotational period of 27 days. These periods are linked either to some internal mechanism in the Sun or said to be higher harmonics of the rotation without further discussion of their origin. In this article, the origin of the peaks in periodicities seen in the solar extreme ultraviolet (EUV) and ultraviolet (UV) irradiance around the 7, 9, and 14 days periods is discussed. Maps of the active regions and coronal holes are produced from six images per day using the Spatial Possibilistic Clustering Algorithm (SPoCA), a segmentation algorithm. Spectral irradiance at coronal, transition-region/chromospheric, and photospheric levels are extracted for each feature as well as for the full disk by applying the maps to full-disk images (at 19.3, 30.4, and 170 nm sampling in the corona/hot flare plasma, the chromosphere/transition region, and the photosphere, respectively) from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) from January 2011 to December 2018. The peaks in periodicities at 7, 9, and 14 days as well as the solar rotation around 27 days can be seen in almost all of the solar irradiance time series. The segmentation also provided time series of the active regions and coronal holes visible area (i.e. in the area observed in the AIA images, not corrected for the line-of-sight effect with respect to the solar surface), which also show similar peaks in periodicities, indicating that the periodicities are due to the change in area of the features on the solar disk rather than to their absolute irradiance. A simple model was created to reproduce the power spectral density of the area covered by active regions also showing the same peaks in periodicities. Segmentation of solar images allows us to determine that the peaks in periodicities seen in solar EUV/UV irradiance from a few days to a month are due to the change in area of the solar features, in particular, active regions, as they are the main contributors to the total full-disk irradiance variability. The higher harmonics of the solar rotation are caused by the clipping of the area signal as the regions rotate behind the solar limb.

scholarly journals Variability of the Solar He I 10830 Å Triplet

1994 ◽  
Vol 154 ◽  
pp. 59-64 ◽  
Author(s):  
J. W. Harvey ◽  
W. C. Livingston
Keyword(s):  
Time Series ◽  
Water Vapor ◽  
Coronal Holes ◽  
Solar Chromosphere ◽  
Solar Cycles ◽  
Rotational Modulation ◽  
General Variation ◽  
Line Equivalent Width ◽  
Activity Indices ◽  
Full Disk

The He I 10830 Å triplet gives a unique view of the solar chromosphere. Digital spectroheliograms have been made regularly since early 1974 using this line and the NSO Vacuum Telescope on Kitt Peak. For many purposes (detection of coronal holes, giant two-ribbon flares, and dark point events) these images are sufficient. A Sun-as-a-star signal is also produced by averaging all the pixels in each daily image. To calibrate this ‘irradiance’ signal in terms of line equivalent width, a comparison is made with integrated sunlight spectrophotometric measurements obtained less frequently. After correction for the effects of water vapor blends, we find a linear relation between the two measurements. The daily averages have been assembled into a time series covering nearly two solar cycles. This time series shows cycle modulation of about ±30% and rotational modulation of about ±10%. The general variation is similar to that of other activity indices but with some interesting small differences. Since images are available, it has been possible to decompose the full disk index into components due to plages, filaments, coronal holes and background. At all times during the cycle, most of the signal comes from the background but most of the variability from plages.

A Discussion on the physics of the solar atmosphere - Physics of the solar atmosphere

1976 ◽  
Vol 281 (1304) ◽  
pp. 415-426
Keyword(s):  
Magnetic Field ◽  
Transition Region ◽  
Solar Atmosphere ◽  
Solar Rotation ◽  
Active Regions ◽  
Rotation Velocity ◽  
Coronal Magnetic Field ◽  
Velocity Fields ◽  
Field Structure ◽  
Magnetic Field Structure

A summary is given on recent results on the physics of the quiet solar atmosphere, and active regions. This includes: solar rotation, velocity fields and waves, magnetic field concentration, the transition region, coronal magnetic field structure, and prominences.

TRACE Emission Heights Estimated from TRACE Limb Observations

2001 ◽  
Vol 203 ◽  
pp. 431-433
Author(s):  
M. Zhang
Keyword(s):  
Transition Region ◽  
Coronal Holes ◽  
Active Regions ◽  
Height Variation ◽  
Quiet Sun ◽  
Trace Data ◽  
Coronal Structures

While TRACE data have provided us much information of transition region and coronal structures, many TRACE data users would like to have a knowledge of emission heights of TRACE bands. By analyzing TRACE limb observations, we give an average estimation of emission heights of TRACE 171, 195 and 1216 bands for different features like quiet Sun regions, active regions and coronal holes. Average emission heights over the limb are also discussed. Previous equator-to-pole height variation is further confirmed by TRACE data when averaging on quiet Sun regions. If averaging for all fluxes, a reverse equator-to-pole height variation is shown.

Spectroscopic Techniques for Determining Electron Densities in the Solar Atmosphere

1988 ◽  
Vol 102 ◽  
pp. 13-23
Author(s):  
H.E. Mason
Keyword(s):  
Transition Region ◽  
Solar Atmosphere ◽  
Coronal Holes ◽  
Active Regions ◽  
Impulsive Phase ◽  
Homogeneous Layer ◽  
Spectroscopic Techniques ◽  
Electron Densities ◽  
Coronal Emission

AbstractThe determination of electron density in the solar atmosphere using diagnostic line ratios has been a field of intense activity over the past ten years. These spectroscopic techniques have given us an insight into the physical conditions of such diverse phenomena as flares, active regions, sunspots, coronal holes and the quiet Sun. In this paper, an overview will be given of the methods used for determining electron densities in the solar atmosphere. This will include a discussion of the accuracy of the atomic parameters required in such analyses. Several different approximations are used to calculate electron scattering cross-sections. These will be outlined and their accuracy for individual ions will be assessed.The use of these techniques have led to some fundamental discoveries about the nature of the solar atmosphere. The transition region was conventionally envisaged as a homogeneous layer between the low temperature chromosphere and the high temperature corona. We now know that the transition region has unresolved filamentary structures with very small “filling factors” at low temperatures. In contrast, the coronal emission seems to be more homogeneously distributed. A lot of effort has gone into the determination of the electron densites in solar flares, particularily during the impulsive phase. Such studies are crucial to distinguish between various theoretical flare models. These problems will be discussed in relation to analyses of spectral data from SKYLAB, HRTS, SMM, SOLEX and XSST and with a view to future projects such as SOHO.

Segmentation of coronal features to understand the solar EIV and UV irradiance variability

2020 ◽  
Author(s):  
Joe Zender ◽  
Rens van der Zwaart ◽  
Rangaiah Kariyappa ◽  
Luc Damé ◽  
Gabriel Giono
Keyword(s):  
Linear Model ◽  
Solar Irradiance ◽  
Feature Detection ◽  
Clustering Algorithm ◽  
Coronal Holes ◽  
Principal Component ◽  
Detection Algorithm ◽  
Solar Dynamics Observatory ◽  
The Earth ◽  
Possibilistic Clustering

<p>The study of solar irradiance variability is of great importance in heliophysics, the Earth’s climate, and space weather applications. These studies require careful identifying, tracking and monitoring of features in the solar magnetosphere, chromosphere, and corona.  We studied the variability of solar irradiance for a period of 10 years (May 2010–January 2020) using the Large Yield Radiometer (LYRA), the Sun Watcher using APS and image Processing (SWAP) on board PROBA2, the Atmospheric Imaging Assembly (AIA), and the Helioseismic and Magnetic Imager (HMI) of on board the Solar Dynamics Observatory (SDO), and applied a linear model between the identified features and the measured solar irradiance by LYRA.</p><p>We used the spatial possibilistic clustering algorithm (SPoCA) to identify coronal holes, and a morphological feature detection algorithm to identify active regions (AR), coronal bright points (BPS), and the quite sun (QS) and segment coronal features from the EUV observations of AIA. The AIA segmentation maps were then applied on SWAP images, images of all AIA wavelengths, HMI line-of-sight (LOS) magnetograms, and parameters such as the intensity, fractional area, and contribution of ARs/CHs/BPs/QS features were computed and compared with LYRA irradiance measurements as a proxy for ultraviolet irradiation incident to the Earth atmosphere.</p><p>We modelled the relation between the solar disk features (ARs, CHs, BPs, and QS) applied to magnetrogram and EUV images against the solar irradiance as measured by LYRA and the F10.7 radio flux. To avoid correlation between different the segmented features, a principal component analysis (PCM) was done. Using the independent component, a straightforward linear model was used and corresponding coefficients computed using the Bayesian framework. The model selected is stable and coefficients converge well.</p><p>The application of the model to data from 2010 to 2020 indicates that both at solar cycle timeframes as well as shorter timeframes, the active region influence the EUV irradiance as measured at Earth. Our model replicates the LYRA measured irradiance well.</p>

scholarly journals Segmentation of Coronal Features to Understand the Solar EUV and UV Irradiance Variability III. Inclusion and Analysis of Bright Points

Solar Physics ◽  
2021 ◽  
Vol 296 (9) ◽  
Author(s):  
Rens van der Zwaard ◽  
Matthias Bergmann ◽  
Joe Zender ◽  
Rangaiah Kariyappa ◽  
Gabriel Giono ◽  
...  
Keyword(s):  
Linear Model ◽  
Solar Irradiance ◽  
Active Regions ◽  
Solar Photosphere ◽  
Earth Atmosphere ◽  
Earth’S Atmosphere ◽  
The Earth ◽  
Coronal Bright Points ◽  
Possibilistic Clustering ◽  
Earth's Atmosphere

AbstractThe study of solar irradiance variability is of great importance in heliophysics, Earth’s climate, and space weather applications. These studies require careful identifying, tracking and monitoring of features in the solar photosphere, chromosphere, and corona. Do coronal bright points contribute to the solar irradiance or its variability as input to the Earth atmosphere? We studied the variability of solar irradiance for a period of 10 years (May 2010 – June 2020) using the Large Yield Radiometer (LYRA), the Sun Watcher using APS and image Processing (SWAP) on board PROBA2, and the Atmospheric Imaging Assembly (AIA), and applied a linear model between the segmented features identified in the EUV images and the solar irradiance measured by LYRA. Based on EUV images from AIA, a spatial possibilistic clustering algorithm (SPoCA) is applied to identify coronal holes (CHs), and a morphological feature detection algorithm is applied to identify active regions (ARs), coronal bright points (BPs), and the quiet Sun (QS). The resulting segmentation maps were then applied on SWAP images, images of all AIA wavelengths, and parameters such as the intensity, fractional area, and contribution of ARs/CHs/BPs/QS features were computed and compared with LYRA irradiance measurements as a proxy for ultraviolet irradiation incident to the Earth atmosphere. We modeled the relation between the solar disk features (ARs, CHs, BPs, and QS) applied to EUV images against the solar irradiance as measured by LYRA and the F10.7 radio flux. A straightforward linear model was used and corresponding coefficients computed using a Bayesian method, indicating a strong influence of active regions to the EUV irradiance as measured at Earth’s atmosphere. It is concluded that the long- and short-term fluctuations of the active regions drive the EUV signal as measured at Earth’s atmosphere. A significant contribution from the bright points to the LYRA irradiance could not be found.

scholarly journals An Analysis of the Solar Rotation Velocity by Tracing Coronal Features

2001 ◽  
Vol 203 ◽  
pp. 377-380 ◽  
Author(s):  
R. Brajša ◽  
B. Vršnak ◽  
V. Ruždjak ◽  
D. Roša ◽  
D. Hržina ◽  
...  
Keyword(s):  
Solar Rotation ◽  
Coronal Holes ◽  
Active Regions ◽  
Rotation Velocity ◽  
Coronal Loops ◽  
X Ray

The solar rotation is determined tracing coronal EUV and soft X-ray bright points, active regions, parts of coronal holes and foot points of coronal loops. Full-disc solar images in the EUV part of the spectrum from the SOHO spacecraft (EIT, Fe XV, 28.4 nm) and from the Yohkoh satellite (SXT, 2 nm) are used.

Influence of Magnetic Fields on Solar Hydrodynamics: Experimental Results

1977 ◽  
Vol 36 ◽  
pp. 143-180 ◽  
Author(s):  
J.O. Stenflo
Keyword(s):  
Solar Activity ◽  
Energy Balance ◽  
Magnetic Fields ◽  
Solar Atmosphere ◽  
General Problem ◽  
Solar Rotation ◽  
Active Regions ◽  
Physical Conditions ◽  
Dynamic Phenomena

It is well-known that solar activity is basically caused by the Interaction of magnetic fields with convection and solar rotation, resulting in a great variety of dynamic phenomena, like flares, surges, sunspots, prominences, etc. Many conferences have been devoted to solar activity, including the role of magnetic fields. Similar attention has not been paid to the role of magnetic fields for the overall dynamics and energy balance of the solar atmosphere, related to the general problem of chromospheric and coronal heating. To penetrate this problem we have to focus our attention more on the physical conditions in the ‘quiet’ regions than on the conspicuous phenomena in active regions.

scholarly journals The influence of solar wind on extratropical cyclones – Part 1: Wilcox effect revisited

2009 ◽  
Vol 27 (1) ◽  
pp. 1-30 ◽  
Author(s):  
P. Prikryl ◽  
V. Rušin ◽  
M. Rybanský
Keyword(s):  
Time Series ◽  
Solar Wind ◽  
Northern Hemisphere ◽  
High Speed ◽  
Coronal Holes ◽  
Extratropical Cyclones ◽  
Sector Boundary ◽  
Speed Solar Wind ◽  
The Mean ◽  
High Speed Solar Wind

Abstract. A sun-weather correlation, namely the link between solar magnetic sector boundary passage (SBP) by the Earth and upper-level tropospheric vorticity area index (VAI), that was found by Wilcox et al. (1974) and shown to be statistically significant by Hines and Halevy (1977) is revisited. A minimum in the VAI one day after SBP followed by an increase a few days later was observed. Using the ECMWF ERA-40 re-analysis dataset for the original period from 1963 to 1973 and extending it to 2002, we have verified what has become known as the "Wilcox effect" for the Northern as well as the Southern Hemisphere winters. The effect persists through years of high and low volcanic aerosol loading except for the Northern Hemisphere at 500 mb, when the VAI minimum is weak during the low aerosol years after 1973, particularly for sector boundaries associated with south-to-north reversals of the interplanetary magnetic field (IMF) BZ component. The "disappearance" of the Wilcox effect was found previously by Tinsley et al. (1994) who suggested that enhanced stratospheric volcanic aerosols and changes in air-earth current density are necessary conditions for the effect. The present results indicate that the Wilcox effect does not require high aerosol loading to be detected. The results are corroborated by a correlation with coronal holes where the fast solar wind originates. Ground-based measurements of the green coronal emission line (Fe XIV, 530.3 nm) are used in the superposed epoch analysis keyed by the times of sector boundary passage to show a one-to-one correspondence between the mean VAI variations and coronal holes. The VAI is modulated by high-speed solar wind streams with a delay of 1–2 days. The Fourier spectra of VAI time series show peaks at periods similar to those found in the solar corona and solar wind time series. In the modulation of VAI by solar wind the IMF BZ seems to control the phase of the Wilcox effect and the depth of the VAI minimum. The mean VAI response to SBP associated with the north-to-south reversal of BZ is leading by up to 2 days the mean VAI response to SBP associated with the south-to-north reversal of BZ. For the latter, less geoeffective events, the VAI minimum deepens (with the above exception of the Northern Hemisphere low-aerosol 500-mb VAI) and the VAI maximum is delayed. The phase shift between the mean VAI responses obtained for these two subsets of SBP events may explain the reduced amplitude of the overall Wilcox effect. In a companion paper, Prikryl et al. (2009) propose a new mechanism to explain the Wilcox effect, namely that solar-wind-generated auroral atmospheric gravity waves (AGWs) influence the growth of extratropical cyclones. It is also observed that severe extratropical storms, explosive cyclogenesis and significant sea level pressure deepenings of extratropical storms tend to occur within a few days of the arrival of high-speed solar wind. These observations are discussed in the context of the proposed AGW mechanism as well as the previously suggested atmospheric electrical current (AEC) model (Tinsley et al., 1994), which requires the presence of stratospheric aerosols for a significant (Wilcox) effect.

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