scholarly journals Solar microflares: a case study on temperatures and the Fe XVIII emission

2019 ◽  
Vol 628 ◽  
pp. A134 ◽  
Author(s):  
U. Mitra-Kraev ◽  
G. Del Zanna
Keyword(s):  
Extreme Ultraviolet ◽  
Atomic Data ◽  
Solar Dynamics Observatory ◽  
Imaging Spectrometer ◽  
Heliospheric Observatory ◽  
X Ray ◽  
Solar Dynamics ◽  
Peak Emission ◽  
Good Agreement

In this paper, we discuss the temperature distribution and evolution of a microflare, simultaneously observed by Hinode’s X-Ray Telescope (XRT), its Extreme Ultraviolet Imaging Spectrometer (EIS), as well as the Atmospheric Imaging Assembly (AIA) on-board the Solar Dynamics Observatory (SDO). Using EIS lines, we find that during peak emission the distribution is nearly isothermal and peaked around 4.5 MK. This temperature is in good agreement with that obtained from the XRT filter ratio, validating the use of XRT to study these small events, invisible to full-Sun X-ray monitors such as the Geostationary Operational Environmental Satellite (GOES). The increase in the estimated Fe XVIII emission in the AIA 94 Å band can mostly be explained with the small temperature increase from the background temperatures. The presence of Fe XVIII emission does not guarantee that temperatures of 7 MK are reached, as is often assumed. With the help of new atomic data, we also revisit the temperatures measured by a Solar and Heliospheric Observatory (SoHO) Solar Ultraviolet Measurements of Emitted Radiation (SUMER) observation of an active region that produced microflares, also finding low temperatures (3–4 MK) from an Fe XVIII/Ca XIV ratio.

scholarly journals Fast degradation of the circular flare ribbon on 2014 August 24

2020 ◽  
Vol 636 ◽  
pp. L11
Author(s):  
Q. M. Zhang ◽  
S. H. Yang ◽  
T. Li ◽  
Y. J. Hou ◽  
Y. Li
Keyword(s):  
Extreme Ultraviolet ◽  
Null Point ◽  
Second Phase ◽  
Solar Dynamics Observatory ◽  
X Ray ◽  
Counterclockwise Direction ◽  
Solar Dynamics ◽  
Flare Ribbon ◽  
Two Phases ◽  
Two Jets

Context. The separation and elongation motions of solar flare ribbons have extensively been investigated. The degradation and disappearance of ribbons have rarely been explored. Aims. We report our multiwavelength observations of a C5.5 circular-ribbon flare associated with two jets (jet1 and jet2) on 2014 August 24, focusing on the fast degradation of the outer circular ribbon (CR). Methods. The flare was observed in ultraviolet (UV) and extreme-ultraviolet (EUV) wavelengths by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory spacecraft. Soft X-ray fluxes of the flare in 0.5−4 and 1−8 Å were recorded by the GOES spacecraft. Results. The flare, consisting of a short inner ribbon (IR) and outer CR, was triggered by the eruption of a minifilament. The brightness of IR and outer CR reached their maxima simultaneously at ∼04:58 UT in all AIA wavelengths. Subsequently, the short eastern part of the CR faded out quickly in 1600 Å but only gradually in EUV wavelengths. The long western part of the CR degraded in the counterclockwise direction and decelerated. The degradation was distinctly divided into two phases: phase I with faster apparent speeds (58−69 km s−1), and phase II with slower apparent speeds (29−35 km s−1). The second phase stopped at ∼05:10 UT when the western CR disappeared entirely. In addition to the outward propagation of jet1, the jet spire experienced untwisting motion in the counterclockwise direction during 04:55−05:00 UT. Conclusions. We conclude that the event can be explained by the breakout jet model. The coherent brightenings of the IR and CR at ∼04:58 UT may result from the impulsive interchange reconnection near the null point, whereas sub-Alfvénic slipping motion of the western CR in the counterclockwise direction indicates the occurrence of slipping magnetic reconnection. Another possible explanation of the quick disappearance of the hot loops that are connected to the western CR is that they are simply reconnected sequentially without the need for significant slippage after the null-point reconnection.

scholarly journals Formation and dynamics of transequatorial loops

2020 ◽  
Vol 640 ◽  
pp. A3
Author(s):  
Avyarthana Ghosh ◽  
Durgesh Tripathi
Keyword(s):  
Magnetic Reconnection ◽  
Extreme Ultraviolet ◽  
Imaging Techniques ◽  
Dynamical Evolution ◽  
Disk Center ◽  
Spectral Lines ◽  
Solar Dynamics Observatory ◽  
Plasma Parameters ◽  
Imaging Spectrometer ◽  
Solar Dynamics

Aims. We aim to study the dynamical evolution of transequatorial loops (TELs) using imaging techniques and spectroscopy. Methods. We used the images recorded by the Atmospheric Imaging Assembly and the Helioseismic Magnetic Imager on board the Solar Dynamics Observatory together with spectroscopic observations taken from the Extreme-Ultraviolet Imaging Spectrometer on board Hinode. Results. The data from the AIA 193 Å channel show that TELs are formed between AR 12230 and a newly emerging AR 12234, evolving between 10 and 14 December 2014. The xt-plots for 12 December 2014, obtained using AIA 193 Å data, reveal signatures of inflow and outflow towards an X-region. High-cadence AIA images also show recurrent intensity enhancements in close proximity to the X-region (P2), which is observed to have higher intensities for spectral lines that are formed at log T[K] = 6.20 and voids at other higher temperatures. The electron densities and temperatures in the X-region (and P2) are maintained steadily at log Ne= 8.5–8.7 cm−3 and log T[K] = 6.20, respectively. Doppler velocities in the X-region show predominant redshifts by about 5–8 km s−1 when they are closer to the disk center but blueshifts (along with some zero-velocity pixels) when away from the center. The full-width-half-maximum maps reveal non-thermal velocities of about 27–30 km s−1 for Fe XII, Fe XIII, and Fe XV lines. However, the brightest pixels have nonthermal velocities ∼62 km s−1 for Fe XII and Fe XIII lines. On the contrary, the dark X-region for Fe XV line have the highest non-thermal velocity (∼115 km s−1). Conclusions. We conclude that the TELs are formed due to magnetic reconnection. We further note that the TELs themselves undergo magnetic reconnection, which leads to the re-formation of loops among individual ARs. Moreover, this study, for the first time, provides measurements of plasma parameters in X-regions, thereby providing essential constraints for theoretical studies.

scholarly journals Using the ionospheric response to the solar eclipse on 20 March 2015 to detect spatial structure in the solar corona

2016 ◽  
Vol 374 (2077) ◽  
pp. 20150216 ◽  
Author(s):  
C. J. Scott ◽  
J. Bradford ◽  
S. A. Bell ◽  
J. Wilkinson ◽  
L. Barnard ◽  
...  
Keyword(s):  
Solar Eclipse ◽  
Extreme Ultraviolet ◽  
Arctic Region ◽  
The Arctic ◽  
High Time Resolution ◽  
Atmospheric Effects ◽  
Solar Dynamics Observatory ◽  
Ionospheric Response ◽  
X Ray ◽  
Solar Dynamics

The total solar eclipse that occurred over the Arctic region on 20 March 2015 was seen as a partial eclipse over much of Europe. Observations of this eclipse were used to investigate the high time resolution (1 min) decay and recovery of the Earth’s ionospheric E-region above the ionospheric monitoring station in Chilton, UK. At the altitude of this region (100 km), the maximum phase of the eclipse was 88.88% obscuration of the photosphere occurring at 9:29:41.5 UT. In comparison, the ionospheric response revealed a maximum obscuration of 66% (leaving a fraction, Φ , of uneclipsed radiation of 34±4%) occurring at 9:29 UT. The eclipse was re-created using data from the Solar Dynamics Observatory to estimate the fraction of radiation incident on the Earth’s atmosphere throughout the eclipse from nine different emission wavelengths in the extreme ultraviolet (EUV) and X-ray spectrum. These emissions, having varying spatial distributions, were each obscured differently during the eclipse. Those wavelengths associated with coronal emissions (94, 211 and 335 Å) most closely reproduced the time varying fraction of unobscured radiation observed in the ionosphere. These results could enable historic ionospheric eclipse measurements to be interpreted in terms of the distribution of EUV and X-ray emissions on the solar disc. This article is part of the themed issue ‘Atmospheric effects of solar eclipses stimulated by the 2015 UK eclipse’.

scholarly journals The EUV spectrum of the Sun: Quiet- and active-Sun irradiances and chemical composition

2019 ◽  
Vol 624 ◽  
pp. A36 ◽  
Author(s):  
G. Del Zanna
Keyword(s):  
Excellent Agreement ◽  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Active Regions ◽  
Atomic Data ◽  
Solar Dynamics Observatory ◽  
Chemical Abundances ◽  
Temperature Plasma ◽  
Medium Resolution ◽  
Solar Dynamics

We benchmark new atomic data against a selection of irradiances obtained from medium-resolution quiet-Sun spectra in the extreme ultraviolet (EUV), from 60 to 1040 Å. We used as a baseline the irradiances measured during solar minimum on 2008 April 14 by the prototype (PEVE) of the Solar Dynamics Observatory Extreme ultraviolet Variability Experiment (EVE). We took into account some inconsistencies in the PEVE data, using flight EVE data and irradiances we obtained from Solar and Heliospheric Observatory (SoHO) Coronal Diagnostics Spectrometer (CDS) data. We performed a differential emission measure and find overall excellent agreement (to within the accuracy of the observations, about 20%) between predicted and measured irradiances in most cases, although we point out several problems with the currently available ion charge-state distributions. We used the photospheric chemical abundances of Asplund et al. (2009, ARA&A, 47, 481). The new atomic data are nearly complete in this spectral range for medium-resolution irradiance spectra. Finally, we used observations of the active Sun in 1969 to show that the composition of the solar corona up to 1 MK is nearly photospheric in this case as well. Variations of a factor of 2 are present for higher-temperature plasma, which is emitted within active regions. These results are in excellent agreement with our previous findings.

scholarly journals New Homogeneous Dataset of Solar EUV Synoptic Maps from SOHO/EIT and SDO/AIA

Solar Physics ◽  
2019 ◽  
Vol 295 (1) ◽  
Author(s):  
A. Hamada ◽  
T. Asikainen ◽  
K. Mursula
Keyword(s):  
Extreme Ultraviolet ◽  
Solar Surface ◽  
Intensity Scale ◽  
Solar Dynamics Observatory ◽  
Heliospheric Observatory ◽  
Imaging Telescope ◽  
Solar Dynamics ◽  
Sensor Degradation ◽  
Full Disk

AbstractSynoptic maps of solar EUV intensities have been constructed for many decades in order to display the distribution of the different EUV emissions across the solar surface, with each map representing one Carrington rotation (i.e. one rotation of the Sun). This article presents a new solar EUV synoptic map dataset based on full-disk images from the Solar and Heliospheric Observatory/Extreme Ultraviolet Imaging Telescope (SOHO/EIT) and Solar Dynamics Observatory/Atmospheric Imaging Assembly (SDO/AIA). In order to remove the significant and complicated drift of EIT and AIA EUV intensities due to sensor degradation, we construct the synoptic maps in standardized intensity scale. We describe a method of homogenizing the SOHO/EIT maps with SDO/AIA maps by transforming the EIT intensity histograms to AIA levels. The new maps cover the years from 1996 to 2018 with 307 SOHO/EIT and 116 SDO/AIA synoptic maps, respectively. These maps provide a systematic and homogeneous view of the entire solar surface in four EUV wavelengths, and are well suited, e.g., for studying long-term coronal hole evolution.

scholarly journals Solar extreme ultraviolet (EUV) flare observations and findings from the Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE)

2015 ◽  
Vol 11 (S320) ◽  
pp. 27-40
Author(s):  
Thomas N. Woods ◽  
Francis G. Eparvier ◽  
James P. Mason
Keyword(s):  
Extreme Ultraviolet ◽  
Late Phase ◽  
Impulsive Phase ◽  
The Sun ◽  
Solar Dynamics Observatory ◽  
X Ray ◽  
Gradual Phase ◽  
Stellar Flares ◽  
Solar Dynamics ◽  
Coronal Dimming

AbstractNew solar soft X-ray (SXR) and extreme ultraviolet (EUV) irradiance observations from NASA Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE) provide full coverage from 0.1 to 106 nm and continuously at a cadence of 10 seconds for spectra at 0.1 nm resolution. These observations during flares can usually be decomposed into four distinct characteristics: impulsive phase, gradual phase, coronal dimming, and EUV late phase. Over 6000 flares have been observed during the SDO mission; some flares show all four phases, and some only show the gradual phase. The focus is on the newer results about the EUV late phase and coronal dimming and its relationship to coronal mass ejections (CMEs). These EVE flare measurements are based on observing the sun-as-a-star, so these results could exemplify stellar flares. Of particular interest is that new coronal dimming measurements of stars could be used to estimate mass and velocity of stellar CMEs.

scholarly journals The Solar and Heliospheric Observatory

1984 ◽  
Vol 86 ◽  
pp. 155-158 ◽  
Author(s):  
Giancarlo Noci
Keyword(s):  
Solar Physics ◽  
Grazing Incidence ◽  
Spectral Irradiance ◽  
The Sun ◽  
Solar Dynamics Observatory ◽  
Solar Constant ◽  
Heliospheric Observatory ◽  
Explorer Mission ◽  
Solar Dynamics ◽  
Euv Spectrum

In the past years several space missions have been proposed for the study of the Sun and of the Heliosphere. These missions were intended to clarify various different aspects of solar physics. For example, the GRIST (Grazing Incidence Solar Telescope) mission was intended as a means to improve our knowledge of the upper transition region and low corona through the detection of the solar EUV spectrum with a spatial resolution larger than in previous missions; the DISCO (Dual Spectral Irradiance and Solar Constant Orbiter) and SDO (Solar Dynamics Observatory) missions were proposed to gat observational data about the solar oscillations better than those obtained from ground based instruments; the SOHO (Solar and Heliospheric Observatory) mission was initially proposed to combine the properties of GRIST with the study of the extended corona (up to several radii of heliocentric distance) by observing the scattered Ly-alpha and OVI radiation, which was also the basis of the SCE (Solar Corona Explorer) mission proposal; the development of the interest about the variability of the Sun, both in itself and for its consequences in the history of the Earth, led to propose observations of the solar constant (included in DISCO).

scholarly journals Energetics of Hi-C EUV brightenings

2018 ◽  
Vol 615 ◽  
pp. A47 ◽  
Author(s):  
Srividya Subramanian ◽  
Vinay L. Kashyap ◽  
Durgesh Tripathi ◽  
Maria S. Madjarska ◽  
John G. Doyle
Keyword(s):  
High Resolution ◽  
Energy Loss ◽  
Extreme Ultraviolet ◽  
Thermal Structure ◽  
Emission Measure ◽  
Light Curves ◽  
Solar Dynamics Observatory ◽  
Differential Emission Measure ◽  
Dominant Mechanism ◽  
Solar Dynamics

We study the thermal structure and energetics of the point-like extreme ultraviolet (EUV) brightenings within a system of fan loops observed in the active region AR 11520. These brightenings were simultaneously observed on 2012 July 11 by the High-resolution Coronal (Hi-C) imager and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO). We identified 27 brightenings by automatically determining intensity enhancements in both Hi-C and AIA 193 Å light curves. The energetics of these brightenings were studied using the Differential Emission Measure (DEM) diagnostics. The DEM weighted temperatures of these transients are in the range log T(K) = 6.2−6.6 with radiative energies ≈1024−25 ergs and densities approximately equal to a few times 109 cm−3. To the best of our knowledge, these are the smallest brightenings in EUV ever detected. We used these results to determine the mechanism of energy loss in these brightenings. Our analysis reveals that the dominant mechanism of energy loss for all the identified brightenings is conduction rather than radiation.

scholarly journals Hot prominence spicules launched from turbulent cool solar prominences

2019 ◽  
Vol 627 ◽  
pp. L5 ◽  
Author(s):  
L. P. Chitta ◽  
H. Peter ◽  
L. Li
Keyword(s):  
Transition Region ◽  
Extreme Ultraviolet ◽  
The Sun ◽  
Solar Dynamics Observatory ◽  
Solar Prominences ◽  
Solar Filament ◽  
Solar Dynamics ◽  
Ultraviolet Observations ◽  
Hot Corona ◽  
Shed Light

A solar filament is a dense cool condensation that is supported and thermally insulated by magnetic fields in the rarefied hot corona. Its evolution and stability, leading to either an eruption or disappearance, depend on its coupling with the surrounding hot corona through a thin transition region, where the temperature steeply rises. However, the heating and dynamics of this transition region remain elusive. We report extreme-ultraviolet observations of quiescent filaments from the Solar Dynamics Observatory that reveal prominence spicules propagating through the transition region of the filament-corona system. These thin needle-like jet features are generated and heated to at least 0.7 MK by turbulent motions of the material in the filament. We suggest that the prominence spicules continuously channel the heated mass into the corona and aid in the filament evaporation and decay. Our results shed light on the turbulence-driven heating in magnetized condensations that are commonly observed on the Sun and in the interstellar medium.

scholarly journals Observation and simulation of a filament eruption associated with the contraction of the overlying coronal loops and the filament rotation

2013 ◽  
Vol 8 (S300) ◽  
pp. 504-506
Author(s):  
X. L. Yan ◽  
Z. K. Xue ◽  
Z. X. Mei
Keyword(s):  
Coronal Loop ◽  
Coronal Loops ◽  
Solar Dynamics Observatory ◽  
Filament Eruption ◽  
Solar Dynamics ◽  
Rotation Motion

AbstractBy using the data of Solar Dynamics Observatory (SDO), we present a case study of the contraction of the overlying coronal loop and the rotation motion of a sigmoid filament on 2012 May 22. At the beginning of the filament eruption, the overlying coronal loop experienced a significant contraction. In the following, the filament started to rotate counterclockwise. We also carried the simulation to investigate the process of the filament eruption.

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