scholarly journals SDO/HMI observations of the average supergranule are not compatible with separable flow models

2019 ◽  
Vol 623 ◽  
pp. A98 ◽  
Author(s):  
R. Z. Ferret
Keyword(s):  
Solar Physics ◽  
Integral Relation ◽  
Solar Dynamics Observatory ◽  
Common Assumption ◽  
Flow Models ◽  
Solar Dynamics ◽  
Open Question ◽  
Proportionality Relationship ◽  
Shed Light ◽  
Made In

Aims. Despite extensive studies carried out since its discovery half a century ago, the nature of supergranulation remains an open question in solar physics. Separability of flow models is a common assumption made in the literature to shed light on the properties of supergranules. This paper studies the ability of separable mass-conserving flow models to reproduce photospheric observations from the Helioseismic Magnetic Imager (HMI) on board of the Solar Dynamics Observatory (SDO) spacecraft corresponding to an average supergranule. Methods. For a steady mass-conserving separable flow model to be compatible with the observations, there is an integral relation between the horizontal and vertical components of the flow. We test this relation directly on observations and compare the results with the proportionality relationship for a separable model. Results. Observations of an average supergranule do not satisfy the condition for separability. Selecting a narrower range of horizontal scales of supergranules when performing the average does not change this result. Separable models are not consistent with observations of an average supergranule.

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 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 Fine-grained Solar Flare Forecasting Based on the Hybrid Convolutional Neural Networks*

2021 ◽  
Vol 922 (2) ◽  
pp. 232
Author(s):  
Zheng Deng ◽  
Feng Wang ◽  
Hui Deng ◽  
Lei. Tan ◽  
Linhua Deng ◽  
...  
Keyword(s):  
Solar Cycle ◽  
Solar Flare ◽  
Solar Physics ◽  
Forecast Model ◽  
Research Field ◽  
Generative Adversarial Networks ◽  
Solar Dynamics Observatory ◽  
Solar Dynamics ◽  
The Stability ◽  
Class Flare

Abstract Improving the performance of solar flare forecasting is a hot topic in the solar physics research field. Deep learning has been considered a promising approach to perform solar flare forecasting in recent years. We first used the generative adversarial networks (GAN) technique augmenting sample data to balance samples with different flare classes. We then proposed a hybrid convolutional neural network (CNN) model (M) for forecasting flare eruption in a solar cycle. Based on this model, we further investigated the effects of the rising and declining phases for flare forecasting. Two CNN models, i.e., M rp and M dp, were presented to forecast solar flare eruptions in the rising phase and declining phase of solar cycle 24, respectively. A series of testing results proved the following. (1) Sample balance is critical for the stability of the CNN model. The augmented data generated by GAN effectively improved the stability of the forecast model. (2) For C-class, M-class, and X-class flare forecasting using Solar Dynamics Observatory line-of-sight magnetograms, the means of the true skill statistics (TSS) scores of M are 0.646, 0.653, and 0.762, which improved by 20.1%, 22.3%, and 38.0% compared with previous studies. (3) It is valuable to separately model the flare forecasts in the rising and declining phases of a solar cycle. Compared with model M, the means of the TSS scores for No-flare, C-class, M-class, and X-class flare forecasting of the M rp improved by 5.9%, 9.4%, 17.9%, and 13.1%, and those of the M dp improved by 1.5%, 2.6%, 11.5%, and 12.2%.

scholarly journals How eruptions of a small filament feed materials to a nearby larger-scaled filament

2020 ◽  
Vol 498 (1) ◽  
pp. L104-L108 ◽  
Author(s):  
H Wei ◽  
Z Huang ◽  
Z Hou ◽  
Y Qi ◽  
H Fu ◽  
...  
Keyword(s):  
Magnetic Reconnection ◽  
Solar Physics ◽  
Solar Telescope ◽  
Solar Dynamics Observatory ◽  
Plasma Flows ◽  
Laboratory Plasma ◽  
Common Features ◽  
Multi Wavelength ◽  
Magnetic Channel ◽  
Solar Dynamics

ABSTRACT As one of the most common features in the solar atmosphere, filaments are significant not only in solar physics but also in stellar and laboratory plasma physics. With the New Vacuum Solar Telescope and the Solar Dynamics Observatory, here we report on multi-wavelength observations of eruptions of a small (30 arcsec) filament (SF) and its consequences while interacting with ambient magnetic features including a large (300 arcsec) filament (LF). The eruptions of the SF drive a two-side-loop jet that is a result of magnetic reconnection between the SF threads and an overlying magnetic channel. As a consequence of the eruption, the heating in the footpoints of the SF destabilizes the barbs of the LF rooted nearby. Supersonic chromospheric plasma flows along the barbs of the LF are then observed in the H α passband and they apparently feed materials to the LF. We suggest that they are shock-driven plasma flows or chromospheric evaporations, which can both be the consequences of heating in the chromosphere by non-thermal particles generated in the magnetic reconnection associated with the two-side-loop jet. Our observations demonstrate that the destabilization in the vicinity of the footpoints of a barb can drive chromospheric plasma feeding to the filament.

scholarly journals Single and Multiwavelength Detection of Coronal Dimming and Coronal Wave Using Faster R-CNN

2019 ◽  
Vol 2019 ◽  
pp. 1-9 ◽  
Author(s):  
Zongxia Xie ◽  
Chunyang Ji
Keyword(s):  
Deep Learning ◽  
Space Weather ◽  
Coronal Mass Ejections ◽  
Solar Physics ◽  
Automatic Detection ◽  
Solar Dynamics Observatory ◽  
Solar Events ◽  
Solar Dynamics ◽  
Coronal Dimming ◽  
Coronal Wave

Automatic detection of solar events, especially uncommon events such as coronal dimming (CD) and coronal wave (CW), is very important in solar physics research. The CD and CW are not only related to the detection of coronal mass ejections (CMEs) but also affect space weather. In this paper, we have studied methods for automatically detecting them. In addition, we have collected and processed a dataset that includes the solar images and event records, where the solar images come from the Atmospheric Imaging Assembly (AIA) of Solar Dynamics Observatory (SDO) and the event records come from Heliophysics Event Knowledgebase (HEK). Different from the methods used before, we introduce the idea of deep learning. We train single-wavelength and multiwavelength models based on Faster R-CNN. In terms of accuracy, the single-wavelength model performs better. The multiwavelength model has a better detection performance on multiple solar events than the single-wavelength model.

scholarly journals Asymmetric expansion of coronal mass ejections in the low corona

2020 ◽  
Vol 635 ◽  
pp. A100 ◽  
Author(s):  
H. Cremades ◽  
F. A. Iglesias ◽  
L. A. Merenda
Keyword(s):  
Coronal Mass Ejections ◽  
Weather Forecasting ◽  
Extreme Ultraviolet ◽  
Solar Physics ◽  
Flux Rope ◽  
Field Configuration ◽  
Solar Dynamics Observatory ◽  
Orthogonal Direction ◽  
Solar Dynamics ◽  
Vantage Points

Aims. Understanding how magnetic fields are structured within coronal mass ejections (CMEs), and how they evolve from the low corona into the heliosphere, is a major challenge for space weather forecasting and for solar physics. The study of CME morphology is a particularly auspicious approach to this problem, given that it holds a close relationship with the CME magnetic field configuration. Although earlier studies have suggested an asymmetry in the width of CMEs in orthogonal directions, this has not been inspected using multi-viewpoint observations. Methods. The improved spatial, temporal, and spectral resolution, added to the multiple vantage points offered by missions of the Heliophysics System Observatory, constitute a unique opportunity to gain insight into this regard. We inspect the early evolution (below ten solar radii) of the morphology of a dozen CMEs occurring under specific conditions of observing spacecraft location and CME trajectory, favorable to reduce uncertainties typically involved in the 3D reconstruction used here. These events are carefully reconstructed by means of a forward modeling tool using simultaneous observations of the Solar-Terrestrial Relations Observatory (STEREO) Extreme Ultraviolet Imager and the Solar Dynamics Observatory Atmospheric Imaging Assembly as input when originating low in the corona, and followed up in the outer fields of view of the STEREO and the Solar and Heliospheric Observatory coronagraphs. We then examine the height evolution of the morphological parameters arising from the reconstructions. Results. The multi-viewpoint analysis of this set of CMEs revealed that their initial expansion – below three solar radii – is considerably asymmetric and non-self-similar. Both angular widths, namely along the main axes of CMEs (AWL) and in the orthogonal direction (AWD, representative of the flux rope diameter), exhibit much steeper change rates below this height, with the growth rate of AWL found to be larger than that of AWD, also below that height. Angular widths along the main axes of CMEs are on average ≈1.8 times larger than widths in the orthogonal direction AWD. The ratios of the two expansion speeds, namely in the directions of CMEs main axes and in their orthogonal, are nearly constant in time after ∼4 solar radii, with an average ratio ≈1.6. Heights at which the width change rate is defined to stabilize are greater for AWL than for AWD.

scholarly journals Extreme-ultraviolet bursts and nanoflares in the quiet-Sun transition region and corona

2021 ◽  
Vol 647 ◽  
pp. A159
Author(s):  
L. P. Chitta ◽  
H. Peter ◽  
P. R. Young
Keyword(s):  
High Resolution ◽  
Solar Atmosphere ◽  
Significant Role ◽  
Extreme Ultraviolet ◽  
Coronal Heating ◽  
Solar Dynamics Observatory ◽  
Quiet Sun ◽  
Solar Dynamics ◽  
Event Based ◽  
Open Question

The quiet solar corona consists of myriads of loop-like features, with magnetic fields originating from network and internetwork regions on the solar surface. The continuous interaction between these different magnetic patches leads to transient brightenings or bursts that might contribute to the heating of the solar atmosphere. The literature on a variety of such burst phenomena in the solar atmosphere is rich. However, it remains unclear whether such transients, which are mostly observed in the extreme ultraviolet (EUV), play a significant role in atmospheric heating. We revisit the open question of these bursts as a prelude to the new high-resolution EUV imagery expected from the recently launched Solar Orbiter. We use EUV image sequences recorded by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) to investigate statistical properties of the bursts. We detect the bursts in the 171 Å filter images of AIA in an automated way through a pixel-wise analysis by imposing different intensity thresholds. By exploiting the high cadence (12 s) of the AIA observations, we find that the distribution of lifetimes of these events peaks at about 120 s. However, a significant number of events also have lifetimes shorter than 60 s. The sizes of the detected bursts are limited by the spatial resolution, which indicates that a larger number of events might be hidden in the AIA data. We estimate that about 100 new bursts appear per second on the whole Sun. The detected bursts have nanoflare-like energies of 1024 erg per event. Based on this, we estimate that at least 100 times more events of a similar nature would be required to account for the energy that is required to heat the corona. When AIA observations are considered alone, the EUV bursts discussed here therefore play no significant role in the coronal heating of the quiet Sun. If the coronal heating of the quiet Sun is mainly bursty, then the high-resolution EUV observations from Solar Orbiter may be able to reduce the deficit in the number of EUV bursts seen with SDO/AIA at least partly by detecting more such events.

Observations for the Role of Flux rope Eruption in a Geoeffective Solar Flare

2014 ◽  
Vol 4 (2) ◽  
pp. 555-564
Author(s):  
A.M Aslam
Keyword(s):  
Solar Flare ◽  
Flux Rope ◽  
Magnetic Configuration ◽  
Solar Dynamics Observatory ◽  
Multi Wavelength ◽  
Solar Dynamics ◽  
Halo Coronal Mass Ejection ◽  
Mass Ejection ◽  
The Waves

On September 24, 2011 a solar flare of M 7.1 class was released from the Sun. The flare was observed by most of the space and ground based observatories in various wavebands. We have carried out a study of this flare to understand its causes on Sun and impact on earth. The flare was released from NOAA active region AR 11302 at 12:33 UT. Although the region had already produced many M class flares and one X- class flare before this flare, the magnetic configuration was not relaxed and still continued to evolve as seen from HMI observations. From the Solar Dynamics Observatory (SDO) multi-wavelength (131 Ã…, 171 Ã…, 304 Ã… and 1600Ã…) observations we identified that a rapidly rising flux rope triggered the flare although HMI observations revealed that magnetic configuration did not undergo a much pronounced change. The flare was associated with a halo Coronal Mass Ejection (CME) as recorded by LASCO/SOHO Observations. The flare associated CME was effective in causing an intense geomagnetic storm with minimum Dst index -103 nT. A radio burst of type II was also recorded by the WAVES/WIND. In the present study attempt is made to study the nature of coupling between solar transients and geospace.

scholarly journals Coronavirus and Soft Law in Germany: Business as Usual?

2021 ◽  
pp. 1-17
Author(s):  
Matthias Knauff
Keyword(s):  
Legal Order ◽  
Soft Law ◽  
Constitutional Order ◽  
Binding Forms ◽  
Almost All ◽  
Business As Usual ◽  
Shed Light ◽  
Made In

In combating the coronavirus pandemic in Germany, soft law has played an important, albeit not a central, role. Its use basically corresponds to that of under “normal circumstances”. In accordance with the German constitutional order, almost all substantial decisions are made in a legally binding form. However, these are often prepared through or supplemented by soft law. This article shows that soft law has played an important role in fighting the pandemic and its effects in Germany, although there cannot be any doubt that legally binding forms of regulation have prevailed. At the same time, the current pandemic has shed light on the advantages and effects of soft law in the context of the German legal order.

scholarly journals Multi-Stranded Coronal Loops: Quantifying Strand Number and Heating Frequency from Simulated Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) Observations

Solar Physics ◽  
2021 ◽  
Vol 296 (6) ◽  
Author(s):  
Thomas Williams ◽  
Robert W. Walsh ◽  
Stephane Regnier ◽  
Craig D. Johnston
Keyword(s):  
Energy Content ◽  
Time Lag ◽  
Low Frequency ◽  
Building Blocks ◽  
Coronal Loops ◽  
Loop Model ◽  
Solar Dynamics Observatory ◽  
Heat Deposition ◽  
Total Energy Content ◽  
Solar Dynamics

AbstractCoronal loops form the basic building blocks of the magnetically closed solar corona yet much is still to be determined concerning their possible fine-scale structuring and the rate of heat deposition within them. Using an improved multi-stranded loop model to better approximate the numerically challenging transition region, this article examines synthetic NASA Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) emission simulated in response to a series of prescribed spatially and temporally random, impulsive and localised heating events across numerous sub-loop elements with a strong weighting towards the base of the structure: the nanoflare heating scenario. The total number of strands and nanoflare repetition times is varied systematically in such a way that the total energy content remains approximately constant across all the cases analysed. Repeated time-lag detection during an emission time series provides a good approximation for the nanoflare repetition time for low-frequency heating. Furthermore, using a combination of AIA 171/193 and 193/211 channel ratios in combination with spectroscopic determination of the standard deviation of the loop-apex temperature over several hours alongside simulations from the outlined multi-stranded loop model, it is demonstrated that both the imposed heating rate and number of strands can be realised.

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