Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userScience Objective: Understanding Energy Transport by Alfvenic Waves in Solar Flares
81
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
Solar flares are driven by the release of magnetic energy from reconnection events in the solar corona, whereafter energy is transported to the chromosphere, heating the plasma and causing the characteristic radiative losses. In the collisional thick-target model, electrons accelerated to energies exceeding 10 keV traverse the corona and impact the chromosphere, where they deposit their energy through collisions with the much denser plasma in the lower atmosphere. While there are undoubtedly high energy non-thermal electrons accelerated in flares, it is unclear whether these electron beams are the sole mechanism of energy transport, or whether they only dominate in certain phases of the flares evolution. Alfvenic waves are generated during the post-reconnection relaxation of magnetic field lines, so it is important to examine their role in energy transport.
rate research
Read More
We report the discovery of torsional Alfvenic oscillations in solar flares, which modulate the time evolution of the magnetic free energy $E_f(t)$, while the magnetic potential energy $E_p(t)$ is uncorrelated, and the nonpotential energy varies as $E_{np}(t) = E_p + E_f(t)$. The mean observed time period of the torsional oscillations is $P_{obs}=15.1 pm 3.9$ min, the mean field line length is $L=135pm35$ Mm, and the mean phase speed is $v_{phase} =315 pm 120$ km s$^{-1}$, which we interpret as torsional Alfvenic waves in flare loops with enhanced electron densities. Most of the torsional oscillations are found to be decay-less, but exhibit a positive or negative trend in the evolution of the free energy, indicating new emerging flux (if positive), magnetic cancellation, or flare energy dissipation (if negative). The time evolution of the free energy has been calculated in this study with the {sl Vertical-Current Approximation (Version 4) Nonlinear Force-Free Field (VCA4-NLFFF)} code, which incorporates automatically detected coronal loops in the solution and bypasses the non-forcefreeness of the photospheric boundary condition, in contrast to traditional NLFFF codes.
How do magnetohydrodynamic waves travel from the fully ionized corona, into and through the underlying partially ionized chromosphere, and what are the consequences for solar flares? To address these questions, we have developed a 2-fluid model (of plasma and neutrals) and used it to perform 1D simulations of Alfven waves in a solar atmosphere with realistic density and temperature structure. Studies of a range of solar features (faculae, plage, penumbra and umbra) show that energy transmission from corona to chromosphere can exceed 20% of incident energy for wave periods of one second or less. Damping of waves in the chromosphere depends strongly on wave frequency: waves with periods 10 seconds or longer pass through the chromosphere with relatively little damping, however, for periods of 1 second or less, a substantial fraction (37%-100%) of wave energy entering the chromosphere is damped by ion-neutral friction in the mid and upper chromosphere, with electron resistivity playing some role in the lower chromosphere and in umbras. We therefore conclude that Alfvenic waves with periods of a few seconds or less are capable of heating the chromosphere during solar flares, and speculate that they could also contribute to electron acceleration or exciting sunquakes.
This paper presents an overview of some recent observational and theoretical results on solar flares, with an emphasis on flare impulsive-phase chromospheric properties, including: electron diagnostics, optical and UV emission, and discoveries made by the Hinode mission, especially in the EUV. A brief perspective on future observations and theoretical requirements is also given
Determining the energy transport mechanisms in flares remains a central goal in solar flares physics that is still not adequately answered by the standard flare model. In particular, the relative roles of particles and/or waves as transport mechanisms, the contributions of low energy protons and ions to the overall flare budget, and the limits of low energy non-thermal electron distribution are questions that still cannot be adequately reconciled with current instrumentation. In this White Paper submitted in response to the call for inputs to the Next Generation Solar Physics Mission review process initiated by JAXA, NASA and ESA in 2016, we outline the open questions in this area and possible instrumentation that could provide the required observations to help answer these and other flare-related questions.
We analyse observations of the X9.3 solar flare (SOL2017-09-06T11:53) observed by SDO/HMI and Hinode/SOT. Our aim is to learn about the nature of the HMI pseudocontinuum Ic used as a proxy for the white-light continuum. From model atmospheres retrieved by an inversion code applied to the Stokes profiles observed by the Hinode satellite we synthesise profiles of the FeI 617.3 nm line and compare them to HMI observations. Based on a pixel-by-pixel comparison we show that the value of Ic represents the continuum level well in quiet-Sun regions only. In magnetised regions it suffers from a simplistic algorithm that is applied to a complex line shape. During this flare both instruments also registered emission profiles in the flare ribbons. Such emission profiles are poorly represented by the six spectral points of HMI, the used algorithm does not account for emission profiles in general, and thus the derived pseudocontinuum intensity does not approximate the continuum value properly.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
