Magnetic Kelvin-Helmholtz Instability at the Sun (original) (raw)
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Drift instabilities in the solar corona within the multi-fluid description
Astronomy and Astrophysics, 2009
Context. Recent observations have revealed that the solar atmosphere is highly structured in density, temperature, and magnetic field. The presence of these gradients may lead to the appearance of currents in the plasma, which in the weakly collisional corona can constitute sources of free energy for driving micro-instabilities. Such instabilities are very important since they represent a possible source of ion-cyclotron waves that have been conjectured as playing a prominent role in coronal heating, but whose solar origin remains unclear. Aims. Considering a density stratification transverse to the magnetic field, this paper aims at studying the possible occurrence of gradient-induced plasma micro-instabilities under the conditions typical of coronal holes. Methods. Taking the WKB (Wentzel-Kramers-Brillouin) approximation into account, we performed the Fourier plane wave analysis using the collisionless multi-fluid model. By neglecting the electron inertia, this model allowed us to take into account ion-cyclotron wave effects that are absent from the one-fluid model of magnetohydrodynamics (MHD). Realistic models of density and temperature, as well as a 2D analytical magnetic-field model, have been used to define the background plasma in the open-field funnel in a polar coronal hole. The ray-tracing theory has been used to compute the ray path of the unstable waves, as well as the evolution of their growth rates during the propagation. Results. We demonstrate that in typical coronal hole conditions, and when assuming typical transverse density length scales taken from radio observations, the current generated by a relative electron-ion drift provides enough free energy for driving the mode unstable. This instability results from coupling between slow-mode waves propagating in opposite directions. However, the ray-tracing computation shows that the unstable waves propagate upward to only a short distance but then are reflected backward. The corresponding growth rate increases and decreases intermittently in the upward propagating phase, and the instability ceases while the wave is propagating downward. Conclusions. Drift currents caused by fine structures in the density distribution in the magnetically-open coronal funnels can provide enough energy to drive plasma micro-instabilities, which constitute a possible source of the ion-cyclotron waves that have been invoked for coronal heating.
The Astrophysical Journal, 2018
We analyze the observations from Solar TErrestrial RElations Observatory (STEREO)-A&B/COR-1 of an eruptive prominence in the intermediate corona on 7 June 2011 at 08:45 UT, which consists of magnetic Rayleigh-Taylor (MRT) unstable plasma segments. Its upper northward segment shows spatio-temporal evolution of MRT instability in form of finger structures upto the outer corona and low inter-planetary space. Using method of Dolei et al.(2014), It is estimated that the density in each bright finger is greater than corresponding dark region lying below of it in the surrounding intermediate corona. The instability is evolved due to wave perturbations that are parallel to the magnetic field at the density interface. We conjecture that the prominence plasma is supported by tension component of the magnetic field against gravity. Using linear stability theory, magnetic field is estimated as 21-40 mG to suppress growth of MRT in the observed finger structures. In the southward plasma segment, a horn-like structure is observed at 11:55 UT in the intermediate corona that also indicates MRT instability. Falling blobs are also observed in both the plasma segments. In the outer corona upto 6-13 solar radii, the mushroom-like plasma structures have been identified in the upper northward MRT unstable plasma segment using STEREO-A/COR-2. These structures most likely grew due to the breaking and twisting of fingers at large spatial scales in weaker magnetic fields. In the lower inter-planetary space upto 20 solar radii, these structures are fragmented into various small-scale localized plasma spikes most likely due to turbulent mixing.
Kinetic Signatures and Intermittent Turbulence in the Solar Wind Plasma
Physical Review Letters, 2012
A connection between kinetic processes and intermittent turbulence is observed in the solar wind plasma using measurements from the Wind spacecraft at 1 A.U. In particular, kinetic effects such as temperature anisotropy and plasma heating are concentrated near coherent structures, such as current sheets, which are nonuniformly distributed in space. Furthermore, these coherent structures are preferentially found in plasma unstable to the mirror and firehose instabilities. The inhomogeneous heating in these regions, which is present in both the magnetic field parallel and perpendicular temperature components, results in protons at least 3-4 times hotter than under typical stable plasma conditions. These results offer a new understanding of kinetic processes in a turbulent regime, where linear Vlasov theory is not sufficient to explain the inhomogeneous plasma dynamics operating near non-Gaussian structures.
How Rotating Solar Atmospheric Jets Become Kelvin–Helmholtz Unstable
Frontiers in Astronomy and Space Sciences, 2019
Recent observations support the propagation of a number of magnetohydrodynamic (MHD) modes which, under some conditions, can become unstable and the developing instability is the Kelvin-Helmholtz instability (KHI). In its nonlinear stage the KHI can trigger the occurrence of wave turbulence which is considered as a candidate mechanism for coronal heating. We review the modeling of tornado-like phenomena in the solar chromosphere and corona as moving weakly twisted and spinning cylindrical flux tubes, showing that the KHI rises at the excitation of high-mode MHD waves. The instability occurs within a wavenumber range whose width depends on the MHD mode number m, the plasma density contrast between the rotating jet and its environment, and also on the twists of the internal magnetic field and the jet velocity. We have studied KHI in two twisted spinning solar polar coronal hole jets, in a twisted rotating jet emerging from a filament eruption, and in a rotating macrospicule. The theoretically calculated KHI development times of a few minutes for wavelengths comparable to the half-widths of the jets are in good agreement with the observationally determined growth times only for high order (10 m 65) MHD modes. Therefore, we expect that the observed KHI in these cases is due to unstable high-order MHD modes.
Astronomy and Astrophysics, 2010
Vortex-type motions have been measured by tracking bright points in high-resolution observations of the solar photosphere. These small-scale motions are thought to be determinant in the evolution of magnetic footpoints and their interaction with plasma and therefore likely to play a role in heating the upper solar atmosphere by twisting magnetic flux tubes. We report the observation of magnetic concentrations being dragged towards the center of a convective vortex motion in the solar photosphere from high-resolution ground-based and space-borne data. We describe this event by analyzing a series of images at different solar atmospheric layers. By computing horizontal proper motions, we detect a vortex whose center appears to be the draining point for the magnetic concentrations detected in magnetograms and well-correlated with the locations of bright points seen in G-band and CN images.
Kelvin-Helmholtz instability driven by coronal mass ejections in the turbulent corona
Recent high resolution AIA/SDO images show evidence of the development of the Kelvin-Helmholtz instability, as coronal mass ejections (CMEs) expand in the ambient corona. A large-scale magnetic field mostly tangential to the interface is observed, both on the CME and on the background sides. However, this magnetic field is not intense enough to quench the instability. There is also observational evidence that the ambient corona is in a turbulent regime, and therefore the development of the instability can differ significantly from the laminar case.
The Astrophysical Journal, 2022
Previous studies have suggested that the Kelvin–Helmholtz instability (KHI) and magnetohydrodynamic (MHD) wave emissions via the KHI along various shear flow boundaries in a solar–terrestrial environment may be possible. We expand upon these previous studies to investigate the linear and nonlinear evolution of the KHI and emission of MHD waves along the boundaries of coronal mass ejections (CMEs). Our results demonstrate that the KHI and MHD wave emission due to the KHI are possible along the CME boundaries during the KHI development. We found that magnetic field orientation in the region outside of the CME has strong effects on the strength of MHD wave emission. While a smaller parallel component of the magnetic field resulted in larger growth rates in the KHI development, a larger parallel component of the magnetic field resulted in stronger MHD wave emissions. For all cases we investigated, we identified emitted waves to be fast MHD waves. We suggest that these emitted MHD waves ...
Super fast plasma streams as drivers of transient and anomalous magnetospheric dynamics
Annales Geophysicae, 2012
We present multi spacecraft measurements in the magnetosheath (MSH) and in the solar wind (SW) by Interball, Cluster and Polar, demonstrating that coherent structures with magnetosonic Mach number up to 3-Supermagnetosonic Plasma Streams (SPS)-generate transient and anomalous boundary dynamics, which may cause substantial displacements of the magnetospheric boundaries and the riddling of peripheral boundary layers. In this regard, for the first time, we describe a direct plasma penetration into the flank boundary layers, which is a candidate for being the dominant transport mechanism for disturbed MSH periods. Typically SPS's have a ram pressure exceeding by several times that of the SW and lead to long-range correlations between processes at the bow shock (BS) and at the magnetopause (MP) on one side and between MSH and MP boundary layers on the other side. We demonstrate that SPS's can be observed both near the BS and near the MP and argue that they are often triggered by hot flow anomalies (HFA), which represent local obstacles to the SW flow and can induce the SPS generation as a means for achieving a local flow balance. Finally, we also discuss other causes of SPS's, both SW-induced and intrinsic to the MSH. SPS's appear to be universal means for establishing a new equilibrium between flowing plasmas and may also prove to be important for astrophysical and fusion applications.
MHD turbulence and heating of the open field-line solar corona
Nonlinear Processes in Geophysics, 2003
This paper discusses the possibility that heating of the solar corona in open field-line regions emanating from coronal holes is due to a nonlinear cascade, driven by low-frequency or quasi-static magnetohydrodynamic fluctuations. Reflection from coronal inhomogeneities plays an important role in sustaining the cascade. Physical and observational constraints are discussed. Kinetic processes that convert cascaded energy into heat must occur in regions of turbulent small-scale reconnection, and may be similar in some respects to ion heating due to intense electron beams observed in the aurora.
The Astrophysical Journal, 2014
State-of-the-art solar instrumentation is now revealing magnetic activity of the Sun with unprecedented temporal and spatial resolutions. Observations with the 1.6m aperture New Solar Telescope (NST) of the Big Bear Solar Observatory (BBSO) are making next steps in our understanding of the solar surface structure. Granular-scale magnetic flux emergence and the response of the solar atmosphere are among the key research topics of high-resolution solar physics. As part of a joint observing program with NASA's Interface Region Imaging Spectrograph (IRIS) mission, on August 7, 2013, the NST observed active region NOAA 11810 in the photospheric TiO 7057Å band with a resolution of 0.034 /pix, and chromospheric Hei 10830Å and Hα 6563Å wavelengths. Complimentary data are provided by Solar Dynamics Observatory (SDO) and Hinode space-based telescopes. The region displayed a group of solar pores, in the vicinity of which we detect a small-scale buoyant horizontal magnetic flux tube causing abnormal granulation and interacting with the pre-existing ambient field in upper atmospheric layers. Following the expansion of distorted granules at the the emergence site, we observed a sudden appearance of an extended surge in the HeI 10830Å data (bandpass of 0.05Å). The IRIS transition region imaging catched ejection of a hot plasma jet associated with the HeI-surge. The SDO/HMI data used to study the evolution of the magnetic and Doppler velocity fields reveal emerging magnetic looplike structures. Hinode/Caii H and IRIS filtergrams detail the connectivities of the newly emerged magnetic field in the lower solar chromosphere. From these data we find that the orientation of the emerging flux tube was almost perpendicular to the overlying ambient field. Nevertheless the interaction of emerging magnetic field lines with the pre-existing overlying arXiv:1405.3550v1 [astro-ph.SR] 10 May 2014 -2field generates high-temperature emission regions and boosts the surge/jet production. The localized heating is detected before and after the first signs of the surge/jet ejection. We compare the results with previous observations and theoretical models, and propose a scenario for the activation of plasma jet/surges and confined heating triggered by buoyant magnetic flux tubes rising up into a magnetized upper environment. Such process may play a significant role in the mass and energy flow from the interior to the corona.