scholarly journals On the variation of solar coronal rotation using SDO/AIA observations

2020 ◽  
Vol 492 (4) ◽  
pp. 5391-5398
Author(s):  
Jaidev Sharma ◽  
Brajesh Kumar ◽  
Anil K Malik ◽  
Hari Om Vats
Keyword(s):  
Extreme Ultraviolet ◽  
Rotation Period ◽  
Space Mission ◽  
Modulation Method ◽  
Solar Dynamics Observatory ◽  
Rotation Periods ◽  
Gaussian Fit ◽  
Solar Dynamics ◽  
Sidereal Rotation ◽  
Solar Coronal

ABSTRACT We report on the variability of the rotation periods of solar coronal layers with respect to temperature (or height). For this purpose, we have used observations from the Atmospheric Imaging Assembly (AIA) telescope on board the Solar Dynamics Observatory (SDO) space mission of National Aeronautics and Space Administration (NASA). The images used are at wavelengths of 94, 131, 171, 193, 211 and 335 Å during the period from 2012–2018. Analysis of solar full-disc images obtained at these wavelengths by AIA is carried out using the flux modulation method. 17 rectangular strips/bins at equal intervals of 10° (extending from 80°S to 80°N) are selected to extract a time series of extreme ultraviolet (EUV) intensity variations to obtain the autocorrelation coefficient. The peak of the Gaussian fit to the first secondary maximum in the autocorrelogram gives the synodic rotation period. Our analysis shows differential rotation with respect to latitude as well as temperature (or height). In the present study, we find that the sidereal rotation periods of different coronal layers decrease with increasing temperature (or height). The average sidereal rotation period at the lowest temperature (∼600 000 K) corresponding to AIA 171-Å, which originates from the upper transition region/quiet corona, is 27.03 days. The sidereal rotation period decreases with temperature (or height) to 25.47 days at a higher temperature (∼10 million K), corresponding to the flaring regions of the solar corona as seen in AIA 131-Å observations.

scholarly journals Reconstruction of asteroid spin states from Gaia DR2 photometry

2018 ◽  
Vol 620 ◽  
pp. A91 ◽  
Author(s):  
J. Ďurech ◽  
J. Hanuš
Keyword(s):  
Rotation Period ◽  
Inversion Method ◽  
Triaxial Ellipsoid ◽  
Independent Data ◽  
Rotation Periods ◽  
Shape Models ◽  
Pole Parameter ◽  
Data Points ◽  
Sidereal Rotation ◽  
Gaia Dr2

Context. In addition to stellar data, Gaia Data Release 2 (DR2) also contains accurate astrometry and photometry of about 14 000 asteroids covering 22 months of observations. Aims. We used Gaia asteroid photometry to reconstruct rotation periods, spin axis directions, and the coarse shapes of a subset of asteroids with enough observations. One of our aims was to test the reliability of the models with respect to the number of data points and to check the consistency of these models with independent data. Another aim was to produce new asteroid models to enlarge the sample of asteroids with known spin and shape. Methods. We used the lightcurve inversion method to scan the period and pole parameter space to create final shape models that best reproduce the observed data. To search for the sidereal rotation period, we also used a simpler model of a geometrically scattering triaxial ellipsoid. Results. By processing about 5400 asteroids with at least 10 observations in DR2, we derived models for 173 asteroids, 129 of which are new. Models of the remaining asteroids were already known from the inversion of independent data, and we used them for verification and error estimation. We also compared the formally best rotation periods based on Gaia data with those derived from dense lightcurves. Conclusions. We show that a correct rotation period can be determined even when the number of observations N is less than 20, but the rate of false solutions is high. For N > 30, the solution of the inverse problem is often successful and the parameters are likely to be correct in most cases. These results are very promising because the final Gaia catalogue should contain photometry for hundreds of thousands of asteroids, typically with several tens of data points per object, which should be sufficient for reliable spin reconstruction.

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 The 3D solar corona Cycle 24 rising phase from SDO/AIA tomography

2011 ◽  
Vol 7 (S286) ◽  
pp. 238-241
Author(s):  
Federico A. Nuevo ◽  
Alberto M. Vásquez ◽  
Richard A. Frazin ◽  
Zhenguang Huang ◽  
Ward B. Manchester
Keyword(s):  
Solar Corona ◽  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Source Surface ◽  
Solar Dynamics Observatory ◽  
Differential Emission Measure ◽  
Height Range ◽  
Field Source ◽  
Solar Dynamics ◽  
Cycle 24

AbstractWe recently extended the differential emission measure tomography (DEMT) technique to be applied to the six iron bands of the Atmospheric Imaging Assembly (AIA) instrument aboard the Solar Dynamics Observatory (SDO). DEMT products are the 3D reconstruction of the coronal emissivity in the instrument's bands, and the 3D distribution of the local differential emission measure, in the height range 1.0 to 1.25 R⊙. We show here derived maps of the electron density and temperature of the inner solar corona during the rising phase of solar Cycle 24. We discuss the distribution of our results in the context of open/closed magnetic regions, as derived from a global potential field source surface (PFSS) model of the same period. We also compare the results derived with SDO/AIA to those derived with the Extreme UltraViolet Imager (EUVI) instrument aboard the Solar TErrestrial RElations Observatory (STEREO).

scholarly journals Transverse coronal loop oscillations excited by homologous circular-ribbon flares

2020 ◽  
Vol 638 ◽  
pp. A32 ◽  
Author(s):  
Q. M. Zhang ◽  
J. Dai ◽  
Z. Xu ◽  
D. Li ◽  
L. Lu ◽  
...  
Keyword(s):  
Extreme Ultraviolet ◽  
Resonant Absorption ◽  
Line Center ◽  
Inhomogeneous Layer ◽  
Solar Dynamics Observatory ◽  
Second Stage ◽  
Kink Mode ◽  
Gradual Expansion ◽  
Solar Dynamics ◽  
Transverse Oscillations

Aims. We report our multiwavelength observations of two homologous circular-ribbon flares in active region 11991 on 2014 March 5, focusing on the transverse oscillations of an extreme-ultraviolet (EUV) loop excited by the flares. Methods. The flares were observed in ultraviolet and EUV wavelengths by the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory spacecraft. These flares were also observed in Hα line center by the 1 m New Vacuum Solar Telescope. Soft X-ray fluxes of the flares in 0.5–4 and 1–8 Å were recorded by the GOES spacecraft. Results. The transverse oscillations are of fast standing kink mode. The first-stage oscillation triggered by the C2.8 flare is decayless with lower amplitudes (310–510 km). The periods (115–118 s) in different wavelengths are nearly the same, indicating coherent oscillations. The magnetic field of the loop is estimated to be 65–78 G. The second-stage oscillation triggered by the M1.0 flare is decaying with larger amplitudes (1250–1280 km). The periods decrease from 117 s in 211 Å to 70 s in 171 Å, implying a decrease of loop length or an implosion after a gradual expansion. The damping time, which is 147–315 s, increases with the period, so that the values of τ/P are close to each other in different wavelengths. The thickness of the inhomogeneous layer is estimated to be ∼0″​​​.45 under the assumption of resonant absorption. Conclusions. This is the first observation of the excitation of two kink-mode loop oscillations by two sympathetic flares. The results are important to understand the excitation of kink oscillations of coronal loops and hence the energy balance in the solar corona. Our findings also validate the prevalence of significantly amplified amplitudes of oscillations by successive drivers.

scholarly journals Statistical Analysis and Catalog of Non-polar Coronal Holes Covering the SDO-Era Using CATCH

Solar Physics ◽  
2019 ◽  
Vol 294 (10) ◽  
Author(s):  
Stephan G. Heinemann ◽  
Manuela Temmer ◽  
Niko Heinemann ◽  
Karin Dissauer ◽  
Evangelia Samara ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Coronal Hole ◽  
High Speed ◽  
Extreme Ultraviolet ◽  
Coronal Holes ◽  
Central Meridian ◽  
Solar Dynamics Observatory ◽  
Speed Solar Wind ◽  
Solar Dynamics ◽  
Hole Boundary

Abstract Coronal holes are usually defined as dark structures seen in the extreme ultraviolet and X-ray spectrum which are generally associated with open magnetic fields. Deriving reliably the coronal hole boundary is of high interest, as its area, underlying magnetic field, and other properties give important hints as regards high speed solar wind acceleration processes and compression regions arriving at Earth. In this study we present a new threshold-based extraction method, which incorporates the intensity gradient along the coronal hole boundary, which is implemented as a user-friendly SSW-IDL GUI. The Collection of Analysis Tools for Coronal Holes (CATCH) enables the user to download data, perform guided coronal hole extraction and analyze the underlying photospheric magnetic field. We use CATCH to analyze non-polar coronal holes during the SDO-era, based on 193 Å filtergrams taken by the Atmospheric Imaging Assembly (AIA) and magnetograms taken by the Heliospheric and Magnetic Imager (HMI), both on board the Solar Dynamics Observatory (SDO). Between 2010 and 2019 we investigate 707 coronal holes that are located close to the central meridian. We find coronal holes distributed across latitudes of about ${\pm}\, 60^{\circ}$±60∘, for which we derive sizes between $1.6 \times 10^{9}$1.6×109 and $1.8 \times 10^{11}\mbox{ km}^{2}$1.8×1011 km2. The absolute value of the mean signed magnetic field strength tends towards an average of $2.9\pm 1.9$2.9±1.9 G. As far as the abundance and size of coronal holes is concerned, we find no distinct trend towards the northern or southern hemisphere. We find that variations in local and global conditions may significantly change the threshold needed for reliable coronal hole extraction and thus, we can highlight the importance of individually assessing and extracting coronal holes.

scholarly journals Nature of the energy source powering solar coronal loops driven by nanoflares

2018 ◽  
Vol 615 ◽  
pp. L9 ◽  
Author(s):  
L. P. Chitta ◽  
H. Peter ◽  
S. K. Solanki
Keyword(s):  
Magnetic Field ◽  
Energy Source ◽  
Extreme Ultraviolet ◽  
Magnetic Energy ◽  
Plasma Heating ◽  
Active Regions ◽  
Coronal Loops ◽  
Solar Dynamics Observatory ◽  
Mixed Polarity ◽  
Solar Dynamics

Context. Magnetic energy is required to heat the corona, the outer atmosphere of the Sun, to millions of degrees. Aims. We study the nature of the magnetic energy source that is probably responsible for the brightening of coronal loops driven by nanoflares in the cores of solar active regions. Methods. We consider observations of two active regions (ARs), 11890 and 12234, in which nanoflares have been detected. To this end, we use ultraviolet (UV) and extreme ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) for coronal loop diagnostics. These images are combined with the co-temporal line-of-sight magnetic field maps from the Helioseismic and Magnetic Imager (HMI) onboard SDO to investigate the connection between coronal loops and their magnetic roots in the photosphere. Results. The core of these ARs exhibit loop brightening in multiple EUV channels of AIA, particularly in its 9.4 nm filter. The HMI magnetic field maps reveal the presence of a complex mixed polarity magnetic field distribution at the base of these loops. We detect the cancellation of photospheric magnetic flux at these locations at a rate of about 1015 Mx s−1. The associated compact coronal brightenings directly above the cancelling magnetic features are indicative of plasma heating due to chromospheric magnetic reconnection. Conclusions. We suggest that the complex magnetic topology and the evolution of magnetic field, such as flux cancellation in the photosphere and the resulting chromospheric reconnection, can play an important role in energizing active region coronal loops driven by nanoflares. Our estimate of magnetic energy release during flux cancellation in the quiet Sun suggests that chromospheric reconnection can also power the quiet corona.

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.

Sign in / Sign up

Export Citation Format

Share Document