The Distribution of Time Delays Between Nanoflares in Magnetohydrodynamic Simulations

Knizhnik, K. J.; Reep, Jeffrey W.

doi:10.1007/s11207-020-1588-2

Cited by 11 publications

(22 citation statements)

References 71 publications

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“…Studies have predicted a range of periodicities for nanoflares (Viall & Klimchuk 2011;Bradshaw et al 2012;Klimchuk 2015) depending on parameters, such cooling rates. Utilizing MHD simulations of the time intervals between nanoflare reconnection events, Knizhnik & Reep (2020) found a power law distribution, similar to the conclusion of Eastwood et al (2009) for Type III storms. The time intervals we observed between acceleration events are very consistent over intervals of many days, and thus not explainable by a process resulting in a power law distribution.…”

Section: Discussionsupporting

confidence: 83%

Periodicities in an active region correlated with Type III radio bursts observed by Parker Solar Probe

Cattell

Glesener

Leiran

et al. 2021

A&A

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Context. Periodicities have frequently been reported across many wavelengths in the solar corona. Correlated periods of ~5 min, comparable to solar p-modes, are suggestive of coupling between the photosphere and the corona. Aims. Our study investigates whether there are correlations in the periodic behavior of Type III radio bursts which are indicative of nonthermal electron acceleration processes, and coronal extreme ultraviolet (EUV) emission used to assess heating and cooling in an active region when there are no large flares. Methods. We used coordinated observations of Type III radio bursts from the FIELDS instrument on Parker Solar Probe (PSP), of EUV emissions by the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and white light observations by SDO Helioseismic and Magnetic Image (HMI), and of solar flare X-rays by Nuclear Spectroscopic Telescope Array (NuSTAR) on April 12, 2019. Several methods for assessing periodicities are utilized and compared to validate periods obtained. Results. Periodicities of ~5 min in the EUV in several areas of an active region are well correlated with the repetition rate of the Type III radio bursts observed on both PSP and Wind. Detrended 211 and 171 Å light curves show periodic profiles in multiple locations, with 171 Å peaks sometimes lagging those seen in 211 Å. This is suggestive of impulsive events that result in heating and then cooling in the lower corona. NuSTAR X-rays provide evidence for at least one microflare during the interval of Type III bursts, but there is not a one-to-one correspondence between the X-rays and the Type III bursts. Our study provides evidence for periodic acceleration of nonthermal electrons (required to generate Type III radio bursts) when there were no observable flares either in the X-ray data or the EUV. The acceleration process, therefore, must be associated with small impulsive events, perhaps nanoflares.

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Section: Discussionsupporting

confidence: 83%

Periodicities in an active region correlated with Type III radio bursts observed by Parker Solar Probe

Cattell

Glesener

Leiran

et al. 2021

A&A

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“…These models and observational considerations typically find nanoflare energy distributions with power laws of −2.5 α −1.5. However, recent MHD simulations tracking discontinuities in field line tracing by Knizhnik & Reep (2020) suggest nanoflares with time delay and energy powerlaws with α ≈ −1. Consequently, our models test heating event power laws with α = −1 and α = −2.5.…”

Section: Power Law Slopes Of Event Delaysmentioning

confidence: 98%

Transition region contribution to AIA observations in the context of coronal heating

Schonfeld,

Klimchuk

2020

Preprint

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We investigate the relative contributions from the transition region and corona of coronal loops observed by the Atmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). Using EBTEL (Enthalpy-Based Thermal Evolution of Loops) hydrodynamic simulations, we model loops with multiple lengths and energy fluxes heated randomly by events drawn from power-law distributions with different slopes and minimum delays between events to investigate how each of these parameters influences observable loop properties. We generate AIA intensities from the corona and transition region for each realization. The variations within and between models generated with these different parameters illustrate the sensitivity of narrowband imaging to the details of coronal heating.We then analyze the transition region and coronal emission from a number of observed active regions and find broad agreement with the trends in the models. In both models and observations, the transition region brightness is significant, often greater than the coronal brightness in all six "coronal" AIA channels. We also identify an inverse relationship, consistent with heating theories, between the slope of the differential emission measure (DEM) coolward of the peak temperature and the observed ratio of coronal to transition region intensity. These results highlight the use of narrowband observations and the importance of properly considering the transition region in investigations of coronal heating.

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“…One suggested energy source for coronal heating is photospheric motions, which add stress and energy into the coronal magnetic field. The magnetic field then reconnects and converts its stored magnetic energy into heat as a series of localized, rapid heating events, termed 'nanoflares' (Parker 1983(Parker , 1988Klimchuk 2006Klimchuk , 2015Knizhnik et al 2018Knizhnik et al , 2019Knizhnik & Reep 2020).…”

Section: Introductionmentioning

confidence: 99%

“…To this end, Knizhnik & Reep (2020) studied the question of nanoflare frequencies using MHD simulations of a driven Parker (1972) plane-parallel magnetic field between two plates. Their coronal magnetic field was driven by twisting motions on one plate, and held fixed and unmoving on the other plate.…”

Section: Introductionmentioning

confidence: 99%

Nanoflare Diagnostics from Magnetohydrodynamic Heating Profiles

Knizhnik,

Barnes,

Reep

et al. 2020

Preprint

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The nanoflare paradigm of coronal heating has proven extremely promising for explaining the presence of hot, multi-million degree loops in the solar corona. In this paradigm, localized heating events supply enough energy to heat the solar atmosphere to its observed temperatures. Rigorously modeling this process, however, has proven difficult, since it requires an accurate treatment of both the magnetic field dynamics and reconnection as well as the plasma's response to magnetic perturbations. In this paper, we combine fully 3D magnetohydrodynamic (MHD) simulations of coronal active region plasma driven by photospheric motions with spatially-averaged, time-dependent hydrodynamic (HD) modeling of coronal loops to obtain physically motivated observables that can be quantitatively compared with observational measurements of active region cores. We take the behavior of reconnected field lines from the MHD simulation and use them to populate the HD model to obtain the thermodynamic evolution of the plasma and subsequently the emission measure distribution. We find the that the photospheric driving of the MHD model produces only very low-frequency nanoflare heating which cannot account for the full range of active region core observations as measured by the low-temperature emission measure slope. Additionally, we calculate the spatial and temporal distributions of field lines exhibiting collective behavior, and argue that loops occur due to random energization occurring on clusters of adjacent field lines.

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The Distribution of Time Delays Between Nanoflares in Magnetohydrodynamic Simulations

Cited by 11 publications

References 71 publications

Periodicities in an active region correlated with Type III radio bursts observed by Parker Solar Probe

Periodicities in an active region correlated with Type III radio bursts observed by Parker Solar Probe

Transition region contribution to AIA observations in the context of coronal heating

Nanoflare Diagnostics from Magnetohydrodynamic Heating Profiles

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