scholarly journals Power-law energy distributions of small-scale impulsive events on the active Sun: results from IRIS

2020 ◽  
Vol 499 (1) ◽  
pp. 1385-1394
Author(s):  
Nived Vilangot Nhalil ◽  
Chris J Nelson ◽  
Mihalis Mathioudakis ◽  
J Gerry Doyle ◽  
Gavin Ramsay
Keyword(s):  
Energy Range ◽  
Power Law ◽  
Coronal Heating ◽  
Radiative Energy ◽  
Small Scale ◽  
Data Sets ◽  
Imaging Data ◽  
Power Law Distribution ◽  
Energy Distributions ◽  
Power Law Index

ABSTRACT Numerous studies have analysed inferred power-law distributions between frequency and energy of impulsive events in the outer solar atmosphere in an attempt to understand the predominant energy supply mechanism in the corona. Here, we apply a burst detection algorithm to high-resolution imaging data obtained by the Interface Region Imaging Spectrograph to further investigate the derived power-law index, γ, of bright impulsive events in the transition region. Applying the algorithm with a constant minimum event lifetime (of either 60 s or 110 s) indicated that the target under investigation, such as Plage and Sunspot, has an influence on the observed power-law index. For regions dominated by sunspots, we always find γ < 2; however, for data sets where the target is a plage region, we often find that γ > 2 in the energy range (∼1023, ∼1026) erg. Applying the algorithm with a minimum event lifetime of three time-steps indicated that cadence was another important factor, with the highest cadence data sets returning γ > 2 values. The estimated total radiative power obtained for the observed energy distributions is typically 10–25 per cent of what would be required to sustain the corona indicating that impulsive events in this energy range are not sufficient to solve coronal heating. If we were to extend the power-law distribution down to an energy of 1021 erg, and assume parity between radiative energy release and the deposition of thermal energy, then such bursts could provide 25–50 per cent of the required energy to account for the coronal heating problem.

scholarly journals Predicting observational signatures of coronal heating by Alfvén waves and nanoflares

2007 ◽  
Vol 3 (S247) ◽  
pp. 279-287
Author(s):  
Patrick Antolin ◽  
Kazunari Shibata ◽  
Takahiro Kudoh ◽  
Daiko Shiota ◽  
David Brooks
Keyword(s):  
Power Law ◽  
Alfven Waves ◽  
Alfvén Waves ◽  
Power Law Distribution ◽  
Longitudinal Modes ◽  
Heating Mechanism ◽  
Set Up ◽  
Power Law Index ◽  
Power Law Distributions ◽  
Release Processes

AbstractAlfvén waves can dissipate their energy by means of nonlinear mechanisms, and constitute good candidates to heat and maintain the solar corona to the observed few million degrees. Another appealing candidate is the nanoflare-reconnection heating, in which energy is released through many small magnetic reconnection events. Distinguishing the observational features of each mechanism is an extremely difficult task. On the other hand, observations have shown that energy release processes in the corona follow a power law distribution in frequency whose index may tell us whether small heating events contribute substantially to the heating or not. In this work we show a link between the power law index and the operating heating mechanism in a loop. We set up two coronal loop models: in the first model Alfvén waves created by footpoint shuffling nonlinearly convert to longitudinal modes which dissipate their energy through shocks; in the second model numerous heating events with nanoflare-like energies are input randomly along the loop, either distributed uniformly or concentrated at the footpoints. Both models are based on a 1.5-D MHD code. The obtained coronae differ in many aspects, for instance, in the simulated intensity profile that Hinode/XRT would observe. The intensity histograms display power law distributions whose indexes differ considerably. This number is found to be related to the distribution of the shocks along the loop. We thus test the observational signatures of the power law index as a diagnostic tool for the above heating mechanisms and the influence of the location of nanoflares.

scholarly journals On the partial eruption of a bifurcated solar filament structure

2020 ◽  
Vol 500 (1) ◽  
pp. 684-695
Author(s):  
Aabha Monga ◽  
Rahul Sharma ◽  
Jiajia Liu ◽  
Consuelo Cid ◽  
Wahab Uddin ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Extreme Ultraviolet ◽  
Free Field ◽  
Small Scale ◽  
Data Sets ◽  
Imaging Data ◽  
Filament Structure ◽  
Filament Channel ◽  
Solar Filament ◽  
Using Data

ABSTRACT The partial eruption of a filament channel with bifurcated substructures is investigated using data sets obtained from both ground-based and space-borne facilities. Small-scale flux reconnection/cancellation events in the region triggered the pile-up of ambient magnetic field, observed as bright extreme ultraviolet (EUV) loops in close proximity to the filament channel. This led to the formation of a V-shaped cusp structure at the site of interaction between the coalesced EUV loops and the filament channel, with the presence of distinct plasmoid structures and associated bidirectional flows. Analysis of imaging data from SDO/AIA further suggests vertical splitting of the filament structure into two substructures. The perturbed upper branch of the filament structure rose up and erupted with the onset of an energetic GOES M1.4 flare at 04:30 ut on 2015 January 28. The estimated twist number and squashing factor obtained from non-linear force free-field extrapolation of the magnetic field data support the vertical split in the filament structure with high twist in the upper substructure. The loss in equilibrium of the upper branch due to torus instability implies that this is a potential triggering mechanism for the observed partial eruption.

scholarly journals Ultra-small scale-free geometric networks

2006 ◽  
Vol 43 (3) ◽  
pp. 665-677 ◽  
Author(s):  
J. E. Yukich
Keyword(s):  
Long Range ◽  
Power Law ◽  
Degree Distribution ◽  
Small Scale ◽  
Graph Distance ◽  
Power Law Distribution ◽  
Scale Free

We consider a family of long-range percolation models (Gp)p>0on ℤdthat allow dependence between edges and have the following connectivity properties forp∈ (1/d, ∞): (i) the degree distribution of vertices inGphas a power-law distribution; (ii) the graph distance between pointsxandyis bounded by a multiple of logpdlogpd|x-y| with probability 1 -o(1); and (iii) an adversary can delete a relatively small number of nodes fromGp(ℤd∩ [0,n]d), resulting in two large, disconnected subgraphs.

scholarly journals Starspot Activity and Superflares on Solar-type Stars

2016 ◽  
Vol 12 (S328) ◽  
pp. 22-29
Author(s):  
Hiroyuki Maehara
Keyword(s):  
Solar Flare ◽  
Power Law ◽  
Magnetic Energy ◽  
Rotation Period ◽  
Occurrence Frequency ◽  
Clear Correlation ◽  
Rotating Stars ◽  
Power Law Distribution ◽  
Solar Type ◽  
Power Law Index

AbstractRecent high-precision photometry from space (e.g., Kepler) enables us to investigate the nature of “superflares” on solar-type stars. The bolometric energy of superflares detected by Kepler ranges from 1033 erg to 1036 erg which is 10-10,000 times larger than that released by a typical X10 class solar flare. The occurrence frequency (dN/dE) of superflares as a function of flare energy (E) shows the power-law distribution with the power-law index of ~−1.8 for 1034 < E < 1036 erg. Most of superflare stars show quasi-periodic light variations which suggest the presence of large starspots. The bolometric energy released by flares is consistent with the magnetic energy stored near the starspots. The occurrence frequency of superflares increases as the rotation period decreases. However, the energy of the largest flares observed in a given period bin does not show any clear correlation with the rotation period. These results suggest that superflares would occur on the slowly-rotating stars.

Penalized KS method to fit data sets with power law distribution over a bounded subinterval

2021 ◽  
pp. 1-40
Author(s):  
Fatih Olmez ◽  
Peter R. Kramer ◽  
John Fricks ◽  
Deena R. Schmidt ◽  
Janet Best
Keyword(s):  
Power Law ◽  
Data Sets ◽  
Power Law Distribution

scholarly journals Ultra-small scale-free geometric networks

2006 ◽  
Vol 43 (03) ◽  
pp. 665-677
Author(s):  
J. E. Yukich
Keyword(s):  
Long Range ◽  
Power Law ◽  
Degree Distribution ◽  
Small Scale ◽  
Graph Distance ◽  
Power Law Distribution ◽  
Scale Free

We consider a family of long-range percolation models (G p ) p&gt;0 on ℤ d that allow dependence between edges and have the following connectivity properties for p ∈ (1/d, ∞): (i) the degree distribution of vertices in G p has a power-law distribution; (ii) the graph distance between points x and y is bounded by a multiple of log pd log pd | x - y | with probability 1 - o(1); and (iii) an adversary can delete a relatively small number of nodes from G p (ℤ d ∩ [0, n] d ), resulting in two large, disconnected subgraphs.

scholarly journals Probabilistic approach to rock fall hazard assessment: potential of historical data analysis

2002 ◽  
Vol 2 (1/2) ◽  
pp. 15-26 ◽  
Author(s):  
C. Dussauge-Peisser ◽  
A. Helmstetter ◽  
J.-R. Grasso ◽  
D. Hantz ◽  
P. Desvarreux ◽  
...  
Keyword(s):  
Power Law ◽  
Historical Data ◽  
Volcanic Eruptions ◽  
Rock Fall ◽  
Hazard Evaluation ◽  
Data Sets ◽  
Volume Distribution ◽  
Power Law Distribution ◽  
Large Variability ◽  
French Alps

Abstract. We study the rock fall volume distribution for three rock fall inventories and we fit the observed data by a power-law distribution, which has recently been proposed to describe landslide and rock fall volume distributions, and is also observed for many other natural phenomena, such as volcanic eruptions or earthquakes. We use these statistical distributions of past events to estimate rock fall occurrence rates on the studied areas. It is an alternative to deterministic approaches, which have not proved successful in predicting individual rock falls. The first one concerns calcareous cliffs around Grenoble, French Alps, from 1935 to 1995. The second data set is gathered during the 1912–1992 time window in Yosemite Valley, USA, in granite cliffs. The third one covers the 1954–1976 period in the Arly gorges, French Alps, with metamorphic and sedimentary rocks. For the three data sets, we find a good agreement between the observed volume distributions and a fit by a power-law distribution for volumes larger than 50 m3 , or 20 m3 for the Arly gorges. We obtain similar values of the b exponent close to 0.45 for the 3 data sets. In agreement with previous studies, this suggests, that the b value is not dependant on the geological settings. Regarding the rate of rock fall activity, determined as the number of rock fall events with volume larger than 1 m3 per year, we find a large variability from one site to the other. The rock fall activity, as part of a local erosion rate, is thus spatially dependent. We discuss the implications of these observations for the rock fall hazard evaluation. First, assuming that the volume distributions are temporally stable, a complete rock fall inventory allows for the prediction of recurrence rates for future events of a given volume in the range of the observed historical data. Second, assuming that the observed volume distribution follows a power-law distribution without cutoff at small or large scales, we can extrapolate these predictions to events smaller or larger than those reported in the data sets. Finally, we discuss the possible biases induced by the poor quality of the rock fall inventories, and the sensibility of the extrapolated predictions to variations in the parameters of the power law.

Statistical properties of starspots on solar-type stars and their correlation with flare activity

2018 ◽  
Vol 14 (A30) ◽  
pp. 369-372
Author(s):  
Hiroyuki Maehara
Keyword(s):  
Power Law ◽  
Solar Flares ◽  
Magnetic Activity ◽  
Statistical Properties ◽  
Flare Activity ◽  
The Sun ◽  
Power Law Distribution ◽  
Physical Processes ◽  
Energy Distributions ◽  
Solar Type

AbstractWe analyzed the statistical properties of starspots on solar-type stars and the correlation between properties of starspots and flare activity using observations from the Kepler mission. We found the size distribution of starspots on solar-type stars shows the power-law distribution and both size distributions of starspots on slowly-rotating solar-type stars and of relatively large sunspots are roughly lie on the same power-law line. We also found that the frequency-energy distributions for superflares and solar flares from spots with different sizes are the same for solar-type stars and the Sun. These results suggest that the magnetic activity on solar-type stars and that on the Sun are caused by the same physical processes

scholarly journals Characterizing EoR foregrounds: a study of the Lockman Hole region at 325 MHz

2020 ◽  
Vol 495 (4) ◽  
pp. 4071-4084
Author(s):  
Aishrila Mazumder ◽  
Arnab Chakraborty ◽  
Abhirup Datta ◽  
Samir Choudhuri ◽  
Nirupam Roy ◽  
...  
Keyword(s):  
Power Law ◽  
Galactic Plane ◽  
Low Frequency ◽  
Detailed Comparison ◽  
Data Sets ◽  
Diffuse Emission ◽  
Angular Power Spectrum ◽  
Power Law Index ◽  
First Time ◽  
Lockman Hole

ABSTRACT One of the key science goals for the most sensitive telescopes, both current and upcoming, is the detection of the redshifted 21-cm signal from the Cosmic Dawn and Epoch of Reionization. The success of detection relies on accurate foreground modelling for their removal from data sets. This paper presents the characterization of astrophysical sources in the Lockman Hole region. Using 325-MHz data obtained from the Giant Metrewave Radio Telescope, a 6° × 6° mosaiced map is produced with an rms reaching 50 μJy per beam. A source catalogue containing 6186 sources is created, and the Euclidean normalized differential source counts have been derived from it, consistent with previous observations as well as simulations. A detailed comparison of the source catalogue is also made with previous findings – at both lower and higher frequencies. The angular power spectrum (APS) of the diffuse Galactic synchrotron emission is determined for three different Galactic latitudes using the tapered gridded estimator. The values of the APS lie between ∼1 and ∼100 mK2. Fitting a power law of the form Aℓ−β gives values of A and β varying across the latitudes considered. This paper demonstrates, for the first time, the variation of the power-law index for diffuse emission at very high Galactic locations. It follows the same trend that is seen at locations near the Galactic plane, thus emphasizing the need for low-frequency observations for developing better models of the diffuse emission.

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