Solar flares as proxy for the young Sun: satellite observed thermosphere response to an X17.2 flare of Earth's upper atmosphere

Abstract. We analyzed the measured thermospheric response of an extreme solar X17.2 flare that irradiated the Earth's upper atmosphere during the so-called Halloween events in late October/early November 2003. We suggest that such events can serve as proxies for the intense electromagnetic and corpuscular radiation environment of the Sun or other stars during their early phases of evolution. We applied and compared empirical thermosphere models with satellite drag measurements from the GRACE satellites and found that the Jacchia-Bowman 2008 model can reproduce the drag measurements very well during undisturbed solar conditions but gets worse during extreme solar events. By analyzing the peak of the X17.2 flare spectra and comparing it with spectra of young solar proxies, our results indicate that the peak flare radiation flux corresponds to a hypothetical Sun-like star or the Sun at the age of approximately 2.3 Gyr. This implies that the peak extreme ultraviolet (EUV) radiation is enhanced by a factor of about 2.5 times compared to today's Sun. On the assumption that the Sun emitted an EUV flux of that magnitude and by modifying the activity indices in the Jacchia-Bowman 2008 model, we obtain an average exobase temperature of 1950 K, which corresponds with previous theoretical studies related to thermospheric heating and expansion caused by the solar EUV flux.

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Ultraviolet Observations of Stellar Coronae: Early Results from HST

Highlights of Astronomy ◽

10.1017/s1539299600009965 ◽

1992 ◽

Vol 9 ◽

pp. 657-658

Author(s):

J.L. Linsky

Keyword(s):

High Resolution ◽

Spectral Resolution ◽

Solar Flares ◽

Extreme Ultraviolet ◽

The Sun ◽

X Ray ◽

Spectroscopic Diagnostics ◽

Early Results ◽

Active Stars ◽

Ultraviolet Observations

Although coronae for stars other than the Sun have previously been detected only in the X-ray and radio portions of the spectrum, the HST and future spacecraft sensitive to ultraviolet (UV) and extreme ultraviolet (ETIV) light will have the spectral resolution to study the dynamics and spectroscopic diagnostics of hot coronal plasmas. In the UV region accessible to HST, forbidden lines of FeXII at 1242 and 1349Å, of FeXXI at 1354Å, and other species seen in solar flares, are predicted to be present in the spectra of active stars. Upcoming observations with the Goddard High Resolution Spectrograph (GHRS) by S. Maran will search for these lines in the dM2e star AU Mic and other stars.

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What can large-scale magnetohydrodynamic numerical experiments tell us about coronal heating?

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2015.0055 ◽

2015 ◽

Vol 373 (2042) ◽

pp. 20150055 ◽

Cited By ~ 18

Author(s):

H. Peter

Keyword(s):

Magnetic Field ◽

Numerical Experiments ◽

Large Scale ◽

Extreme Ultraviolet ◽

Complex Structure ◽

Three Dimensional ◽

Upper Atmosphere ◽

Good Representation ◽

The Sun ◽

Coronal Emission

The upper atmosphere of the Sun is governed by the complex structure of the magnetic field. This controls the heating of the coronal plasma to over a million kelvin. Numerical experiments in the form of three-dimensional magnetohydrodynamic simulations are used to investigate the intimate interaction between magnetic field and plasma. These models allow one to synthesize the coronal emission just as it would be observed by real solar instrumentation. Large-scale models encompassing a whole active region form evolving coronal loops with properties similar to those seen in extreme ultraviolet light from the Sun, and reproduce a number of average observed quantities. This suggests that the spatial and temporal distributions of the heating as well as the energy distribution of individual heat deposition events in the model are a good representation of the real Sun. This provides evidence that the braiding of fieldlines through magneto-convective motions in the photosphere is a good concept to heat the upper atmosphere of the Sun.

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The Solar Orbiter EUI instrument: The Extreme Ultraviolet Imager

Astronomy and Astrophysics ◽

10.1051/0004-6361/201936663 ◽

2020 ◽

Vol 642 ◽

pp. A8 ◽

Cited By ~ 10

Author(s):

P. Rochus ◽

F. Auchère ◽

D. Berghmans ◽

L. Harra ◽

W. Schmutz ◽

...

Keyword(s):

High Resolution ◽

Extreme Ultraviolet ◽

Optical Element ◽

Radiation Environment ◽

The Sun ◽

Systematic Effort ◽

Resolution Imaging ◽

Outer Corona ◽

Vantage Points ◽

Orbiter Mission

Context. The Extreme Ultraviolet Imager (EUI) is part of the remote sensing instrument package of the ESA/NASA Solar Orbiter mission that will explore the inner heliosphere and observe the Sun from vantage points close to the Sun and out of the ecliptic. Solar Orbiter will advance the “connection science” between solar activity and the heliosphere. Aims. With EUI we aim to improve our understanding of the structure and dynamics of the solar atmosphere, globally as well as at high resolution, and from high solar latitude perspectives. Methods. The EUI consists of three telescopes, the Full Sun Imager and two High Resolution Imagers, which are optimised to image in Lyman-α and EUV (17.4 nm, 30.4 nm) to provide a coverage from chromosphere up to corona. The EUI is designed to cope with the strong constraints imposed by the Solar Orbiter mission characteristics. Limited telemetry availability is compensated by state-of-the-art image compression, onboard image processing, and event selection. The imposed power limitations and potentially harsh radiation environment necessitate the use of novel CMOS sensors. As the unobstructed field of view of the telescopes needs to protrude through the spacecraft’s heat shield, the apertures have been kept as small as possible, without compromising optical performance. This led to a systematic effort to optimise the throughput of every optical element and the reduction of noise levels in the sensor. Results. In this paper we review the design of the two elements of the EUI instrument: the Optical Bench System and the Common Electronic Box. Particular attention is also given to the onboard software, the intended operations, the ground software, and the foreseen data products. Conclusions. The EUI will bring unique science opportunities thanks to its specific design, its viewpoint, and to the planned synergies with the other Solar Orbiter instruments. In particular, we highlight science opportunities brought by the out-of-ecliptic vantage point of the solar poles, the high-resolution imaging of the high chromosphere and corona, and the connection to the outer corona as observed by coronagraphs.

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Hard Solar X-Ray Bursts

Highlights of Astronomy ◽

10.1017/s1539299600001738 ◽

1968 ◽

Vol 1 ◽

pp. 541-543

Author(s):

C. de Jager

Keyword(s):

Solar Radiation ◽

Solar Flares ◽

Spectral Region ◽

Radiation Flux ◽

Point Of View ◽

The Sun ◽

X Ray ◽

Quiet Sun ◽

Observational Techniques

A tentative spectrum of the Sun in the X-ray region is shown in Figure 1 (De Jager, 1967). The quiet Sun emits a measurable spectrum at photon energies below about 3 keV. During the occurrence of solar flares an enhancement of the emitted energy, and a hardening of the spectrum is clearly visible. The soft X-ray bursts apparently show a maximum radiation flux at wavelengths of about 10 Å.In the spectral region above about 10 keV hardly any quiet solar radiation is observable. During the occurrence of solar flares hard X-ray bursts are occasionally observed. From the point of view of observational techniques these bursts may be divided in the so-called deka-keV bursts, covering the range 10-200 keV, and the deci-MeV bursts in the range between 0·2 and 1 MeV. Many deka-keV bursts have been observed during the years 1966-67 by Winckler et al., by means of the OGO-I and OGO-III satellites (see Arnoldy et al., 1967). The existence of deci-MeV bursts has been doubted various times (see e.g. Chubb et al., 1966). Its reality seems now to be proved (see also De Jager, 1967). However, they may be much rarer than the deka-keV bursts, although it is not yet completely sure that the selection is not observational.

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Energetics of magnetic transients in a solar active region plage

Astronomy and Astrophysics ◽

10.1051/0004-6361/201834548 ◽

2019 ◽

Vol 623 ◽

pp. A176 ◽

Cited By ~ 3

Author(s):

L. P. Chitta ◽

A. R. C. Sukarmadji ◽

L. Rouppe van der Voort ◽

H. Peter

Keyword(s):

Magnetic Field ◽

Active Region ◽

Magnetic Flux ◽

Numerical Simulations ◽

Extreme Ultraviolet ◽

Spatial Scales ◽

Coronal Loops ◽

The Sun ◽

Flux Emergence ◽

Transient Events

Context. Densely packed coronal loops are rooted in photospheric plages in the vicinity of active regions on the Sun. The photospheric magnetic features underlying these plage areas are patches of mostly unidirectional magnetic field extending several arcsec on the solar surface. Aims. We aim to explore the transient nature of the magnetic field, its mixed-polarity characteristics, and the associated energetics in the active region plage using high spatial resolution observations and numerical simulations. Methods. We used photospheric Fe I 6173 Å spectropolarimetric observations of a decaying active region obtained from the Swedish 1-m Solar Telescope (SST). These data were inverted to retrieve the photospheric magnetic field underlying the plage as identified in the extreme-ultraviolet emission maps obtained from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). To obtain better insight into the evolution of extended unidirectional magnetic field patches on the Sun, we performed 3D radiation magnetohydrodynamic simulations of magnetoconvection using the MURaM code. Results. The observations show transient magnetic flux emergence and cancellation events within the extended predominantly unipolar patch on timescales of a few 100 s and on spatial scales comparable to granules. These transient events occur at the footpoints of active region plage loops. In one case the coronal response at the footpoints of these loops is clearly associated with the underlying transient. The numerical simulations also reveal similar magnetic flux emergence and cancellation events that extend to even smaller spatial and temporal scales. Individual simulated transient events transfer an energy flux in excess of 1 MW m−2 through the photosphere. Conclusions. We suggest that the magnetic transients could play an important role in the energetics of active region plage. Both in observations and simulations, the opposite-polarity magnetic field brought up by transient flux emergence cancels with the surrounding plage field. Magnetic reconnection associated with such transient events likely conduits magnetic energy to power the overlying chromosphere and coronal loops.

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Observation of the Radio Radiation Flux of the Sun and Flares at a Wavelength of 5 cm

Geomagnetism and Aeronomy ◽

10.1134/s0016793220080241 ◽

2020 ◽

Vol 60 (8) ◽

pp. 1087-1092

Author(s):

A. G. Tlatov ◽

V. M. Bogod ◽

O. Pons ◽

M. Rodriges ◽

R. Estrada ◽

...

Keyword(s):

Radiation Flux ◽

The Sun ◽

Radio Radiation

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Hydrodynamic Models of Solar and Stellar Flares

International Astronomical Union Colloquium ◽

10.1017/s0252921100031948 ◽

1989 ◽

Vol 104 (1) ◽

pp. 289-298

Author(s):

Giovanni Peres

Keyword(s):

High Resolution ◽

Light Curve ◽

Solar Flares ◽

Impulsive Phase ◽

Light Curves ◽

Physical Parameters ◽

The Sun ◽

Hydrodynamic Models ◽

X Ray ◽

Stellar Flares

AbstractThis paper discusses the hydrodynamic modeling of flaring plasma confined in magnetic loops and its objectives within the broader scope of flare physics. In particular, the Palermo-Harvard model is discussed along with its applications to the detailed fitting of X-ray light curves of solar flares and to the simulation of high-resolution Caxix spectra in the impulsive phase. These two approaches provide complementary constraints on the relevant features of solar flares. The extension to the stellar case, with the fitting of the light curve of an X-ray flare which occurred on Proxima Centauri, demonstrates the feasibility of using this kind of model for stars too. Although the stellar observations do not provide the wealth of details available for the Sun, and, therefore, constrain the model more loosely, there are strong motivations to pursue this line of research: the wider range of physical parameters in stellar flares and the possibility of studying further the solar-stellar connection.

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Radio imaging-spectroscopy observations of the Sun in decimetric and centimetric wavelengths

Proceedings of the International Astronomical Union ◽

10.1017/s1743921313003001 ◽

2012 ◽

Vol 8 (S294) ◽

pp. 489-494 ◽

Cited By ~ 9

Author(s):

Yihua Yan ◽

Wei Wang ◽

Fei Liu ◽

Lihong Geng ◽

Zhijun Chen ◽

...

Keyword(s):

Radio Emission ◽

Solar Flares ◽

Inner Mongolia ◽

Imaging Spectroscopy ◽

Current Status ◽

The Sun ◽

Radio Imaging ◽

Time Space ◽

Decimetric Wave ◽

Wave Range

AbstractTo address fundamental processes in the solar eruptive phenomena it is important to have imaging-spectroscopy over centimetric-decimetric wave range. The Chinese Spectral Radioheliograph (CSRH) in 0.4-15 GHz range with high time, space and frequency resolutions is being constructed to achieve this goal. The perspectives to open new observational windows on solar flares and CMEs will be achieved by mapping the radio emission from unstable electron populations during the basic processes of energy release. CSRH is located in a radio quiet region in Inner Mongolia of China. The array of CSRH-I in 0.4-2.0 GHz with 40 4.5m antennas has been established and starts test observations. The 60 2m antennas for array of CSRH-II in 2-15 GHz have been mounted and assembled. The progress and current status of CSRH are introduced.

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