Propagation Of Magnetoacoustic Waves Research Articles

The Coronal Power Spectrum from MHD Mode Conversion above Sunspots

Abstract Sunspots are intense regions of magnetic flux that are rooted deep below the photosphere. It is well established that sunspots host magnetohydrodynamic waves, with numerous observations showing a connection to the internal acoustic (or p-)modes of the Sun. The p-modes are fast waves below the equipartition layer and are thought to undergo a double mode conversion as they propagate upward into the atmosphere of sunspots, which can generate Alfvénic modes in the upper atmosphere. We employ 2.5D magnetohydrodynamic numerical simulations to investigate the adiabatic wave propagation and examine the resulting power spectra of coronal Alfvénic waves. A broadband wave source is used, which has a 1D power spectrum mimicking aspects of the observed p-mode power spectrum. We examine magnetoacoustic wave propagation and mode conversion from the photosphere to the corona. Frequency filtering of the upwardly propagating acoustic waves is a natural consequence of a gravitationally stratified atmosphere and plays a key role in shaping the power spectra of mode-converted waves. We demonstrate that the slow and fast magnetoacoustic waves and Alfvén waves above the equipartition layer have similarly shaped power spectra, which are modified versions of the driver spectrum. Notably, the results reveal that the coronal wave power spectra have a peak at a higher frequency than that of the underlying p-mode driver. This matches observations of coronal Alfvénic waves and further supports the role of the mode conversion process as a mechanism for Alfvénic wave generation in the Sun's atmosphere.

Resistivity effect in the vicinity of a coronal magnetic null point

Introduction: We aim to examine how magnetic resistivity impacts the movement of magnetoacoustic waves near a magnetic null-point in the solar corona.Method: The resistive, nonlinear MHD simulations are solved by the PLUTO code in 2.5D for different amount of the resistivity.Results and Discussion: Propagation of magnetoacoustic waves in the vicinity of a magnetic null point has the potential to create current sheets with high current density excitation and plasmoid generation. During the entire duration of the simulation, it is discovered that plasma density became significant due to the plasmoid and also current density is high for high resistivity. It is depicted that high resistivity also leads to bigger plasmoids or magnetic islands in comparison to small resistivity.

Effect of area divergence and frequency on damping of slow magnetoacoustic waves propagating along umbral fan loops

ABSTRACT Waves play an important role in the heating of solar atmosphere; however, observations of wave propagation and damping from the solar photosphere to corona through chromosphere and transition region are very rare. Recent observations have shown propagation of 3-min slow magnetoacoustic waves (SMAWs) along fan loops from the solar photosphere to corona. In this work, we investigate the role of area divergence and frequencies on the damping of SMAWs propagating from the photosphere to the corona along several fan loops rooted in the sunspot umbra. We study the Fourier power spectra of oscillations along fan loops at each atmospheric height which showed significant enhancements in 1–2, 2.3–3.6, and 4.2–6 min period bands. Amplitude of intensity oscillations in different period bands and heights are extracted after normalizing the filtered light curves with low-frequency background. We find damping of SMAW energy flux propagating along the fan loop 6 with damping lengths $\approx 170$ and $\approx 208$ km for 1.5- and 3-min period bands. We also show the decay of total wave energy content with height after incorporating area divergence effect, and present actual damping of SMAWs from photosphere to corona. Actual damping lengths in this case increases to $\approx 172$ and $\approx 303$ km for 1.5- and 3-min period bands. All the fan loops show such increase in actual damping lengths, and thus highlight the importance of area divergence effect. Results also show some frequency-dependent damping of SMAW energy fluxes with height where high-frequency waves are damped faster than low-frequency waves.

Modeling the Propagation of Slow Magnetoacoustic Waves in a Multistranded Coronal Loop

We study the propagation properties of slow magnetoacoustic waves in a multithermal coronal loop using a 3D MHD model, for the first time. A bundle of 33 vertical cylinders, each of 100 km radius, randomly distributed over a circular region of radius 1 Mm, is considered to represent the coronal loop. The slow waves are driven by perturbing the vertical velocity (v z ) at the base of the loop. We apply forward modeling to the simulation results to generate synthetic images in the coronal channels of the Solar Dynamics Observatory/Atmospheric Imaging Assembly. Furthermore, we add appropriate data noise to enable direct comparison with the real observations. It is found that the synthetic images at the instrument resolution show noncospatial features in different temperature channels in agreement with previous observations. Time–distance maps are constructed from the synthetic data to study the propagation properties. The results indicate that the oscillations are only visible in specific channels, depending on the temperature range of the plasma existing within the loop. Additionally, the propagation speed of slow waves is also found to be sensitive to the available temperature range. Overall, we propose that the cross-field thermal properties of coronal structures can be inferred using a combination of numerical simulations and observations of slow magnetoacoustic waves.

Magnetoacoustic waves in a partially ionized astrophysical plasma with the thermal misbalance: A two-fluid approach

We consider the propagation of magnetoacoustic (MA) and acoustic waves of various frequency ranges in a partially ionized plasma at an arbitrary angle to the magnetic field, taking into account the influence of heating, radiative, and thermo-conductive cooling, as well as ion-neutral collisions. A dispersion equation that describes the evolution of nine modes was obtained in a compact mathematical form using the two-fluid model. The number and type of propagating waves (modified fast and slow MA waves, MA waves in the ion component, acoustic waves in the neutral component, as well as isothermal MA and isothermal acoustic waves) vary in different frequency ranges depending on the parameters of the medium. Analytical expressions are found for the speed and damping rates of all these propagating waves, and it is shown how dispersion and damping are formed by three processes: thermal misbalance, ion-neutral collisions, and thermal conductivity. Comparison of analytical calculations of the velocity and damping rates of MA waves with the numerical solution of the dispersion relation under conditions characteristic of the low solar atmosphere and prominences showed high accuracy of the obtained analytical expressions. The strong influence of thermal misbalance caused by gasdynamic perturbations on the speed and damping rate of modified magnetoacoustic waves in a strongly coupled region is shown as well.

Magnetic field fluctuations in the shocked umbral chromosphere

Context.Umbral chromospheric observations show the presence of magnetoacoustic shocks. Several recent studies have reported magnetic field fluctuations associated with these shock waves. The mechanism behind these periodic magnetic field changes is still an unresolved question.Aims.We aim to study the properties and origin of magnetic field fluctuations in the umbral chromosphere.Methods.Temporal series of spectropolarimetric observations were acquired with the GREGOR telescope on 2017 June 18. The chromospheric and photospheric conditions, including the temporal evolution of the magnetic field, were derived from simultaneous inversions of the He I10 830 Å triplet and the Si I10 827 Å line using the HAZEL2 code. The oscillations were interpreted using wavelet analysis and context information from ultraviolet observations acquired with the Atmospheric Imaging Assembly on board the Solar Dynamics Observatory (SDO/AIA) and the Interface Region Imaging Spectrograph (IRIS).Results.The chromospheric magnetic field shows strong fluctuations in the sunspot umbra, with peak field strengths of up to 2900 G. This inferred field strength is comparable to the magnetic field strength in the upper photosphere. Magnetic field and velocity umbral oscillations exhibit a strong coherence, with the magnetic field lagging the shock fronts detected in the velocity fluctuations. This points to a common origin of the fluctuations in both parameters, and the analysis of the phase shift between photospheric and chromospheric velocity is consistent with upward wave propagation. These results suggest that the strong inferred magnetic field fluctuations are caused by changes in the response height of the He I10 830 Å line to the magnetic field, which is sensitive to the high photosphere during and right after the shock. The analysis of extreme ultraviolet data shows a weak brightening in a coronal loop rooted in the umbra around the time of the measured magnetic field fluctuations. This coronal activity could possibly have some impact on the inferred fluctuations, but it is not the main driver of the magnetic field oscillations since they are found before the extreme ultraviolet event takes place.Conclusions.Chromospheric magnetic field fluctuations measured with the He I10 830 Å triplet arise due to variations in the opacity of the line. After strong shocks are produced by the propagation of slow magnetoacoustic waves, the response of the line to the magnetic field can be shifted down to the upper photosphere. This is seen as remarkably large fluctuations in the line-of-sight magnetic field strength.

A study of the propagation of magnetoacoustic waves in small-scale magnetic fields using solar photospheric and chromospheric Dopplergrams: HMI/SDO and MAST observations

In this work, we present a study of the propagation of low-frequency magneto-acoustic waves into the solar chromosphere within small-scale inclined magnetic fields over a quiet-magnetic network region utilizing near-simultaneous photospheric and chromospheric Dopplergrams obtained from the HMI instrument onboard SDO spacecraft and the Multi-Application Solar Telescope (MAST) operational at the Udaipur Solar Observatory, respectively. Acoustic waves are stochastically excited inside the convection zone of the Sun and intermittently interact with the background magnetic fields resulting into episodic signals. In order to detect these episodic signals, we apply the wavelet transform technique to the photospheric and chromospheric velocity oscillations in magnetic network regions. The wavelet power spectrum over photospheric and chromospheric velocity signals show a one-to-one correspondence between the presence of power in the 2.5–4 mHz band. Further, we notice that power in the 2.5–4 mHz band is not consistently present in the chromospheric wavelet power spectrum despite its presence in the photospheric wavelet power spectrum. This indicates that leakage of photospheric oscillations (2.5–4 mHz band) into the higher atmosphere is not a continuous process. The average phase and coherence spectra estimated from these photospheric and chromospheric velocity oscillations illustrate the propagation of photospheric oscillations (2.5–4 mHz) into the solar chromosphere along the inclined magnetic fields. Additionally, chromospheric power maps estimated from the MAST Dopplergrams also show the presence of high-frequency acoustic halos around relatively high magnetic concentrations, depicting the refraction of high-frequency fast mode waves around vA≈vs layer in the solar atmosphere.

Применение к радиационной акустике метода Уитхэма для анализа волновых явлений в намагниченной плазме

The exact governing equation of radiative acoustics in radiating grey gas is derived in this work, taking into account the influence of the transverse magnetic field. The radiative MHD is described by three equations of hydrodynamics and two equations of radiation momentum with extensive use of the formalism of radiative thermodynamics. In order to describe the propagation of linear radiative magneto-acoustic perturbation waves with scattering and attenuation, radiation-thermal dissipation conditions, radiation drag force, and magnetic force and Joule heat are introduced into these equations. The Eddington approximation is used, which allows us to study the modes of radiative magneto-hydrodynamic waves in two asymptotic cases - optically thin and thick gas. The exact governing equation derived in this paper allows, using the heuristic Whitham method, to obtain a set of approximate governing equations of lower order, each of which is part of a reliable approximation to the exact equation in a certain region of the independent time variable. The relatively simple form of such equations allows, without formally solving the full problem, to investigate the physical processes occurring in each radiative magneto-hydrodynamic linear travelling wave.

From a magnetoacoustic system to a J-T black hole: A little trip down memory lane

<abstract><p>We assign a Riemannian metric to a system of nonlinear equations that describe the one-dimensional propagation of long magnetoacoustic waves (also called magnetosonic waves) in a cold plasma under the inference of a transverse magnetic field. The metric, which in general is expressed in terms of the density of the plasma and its speed across the magnetic field, when specialized to a particular solution of the nonlinear system (the Gurevich-Krylov (G-K) solution) is mapped explicitly to a Jackiw-Teitelboim (J-T) black hole metric, which is the main result. Dilaton fields, constructed from data involved in the G-K solution, are presented - which with the plasma metric provide for elliptic function solutions of the J-T equations of motion in 2d dilaton gravity. A correspondence between solutions of the nonlinear plasma system (whose Galilean invariance is also established) and certain solutions of a resonant nonlinear Schrödinger equation is set up, along with some other general background material to render an expository tone in the presentation.</p></abstract>

Magnetoacoustic Waves in a Dissipative Quantum Plasma With Spin-1/2 and Exchange-Correlation Effects

Using quantum magneto-hydrodynamic theory, the nonlinear propagation of magnetoacoustic waves have been investigated in a quantum magneto-plasma having dissipative ions fluid as well as quantum electrons and positrons, including exchange-correlation and electrons/positrons spin effects. The Korteweg-devris-Burger equation is derived employing the reductive perturbation method. It has been found that the quantum magneto-plasma system under consideration supports buth magnetoacoustic solitary and shock waves depending on the values of the plasma parameters. The effects of quantum plasma parameters (such as exchange-correlation coefficients, magnetic field strength, kinematic viscosity and the concentrations of electrons and positrons) on the magnetoacoustic shock waves (both monotonic shock waves and oscillatory shock waves) are examined. The profiles of both monotonic and oscillatory shock waves are found to be significantly affected by these parameters.The results of the current study may be useful to understand the properties of magnetoacoustic waves propagating in dense space plasma environments where the quantum mechanical effects of electrons and positrons are included.

Plasma Heating and Nanoflare Caused by Slow-mode Wave in a Coronal Loop

We present a detailed analysis of a reflecting intensity perturbation in a large coronal loop that appeared as a sloshing oscillation and lasted for at least one and a half periods. The perturbation is initiated by a microflare at one footpoint of the loop, propagates along the loop, and is eventually reflected at the remote footpoint where significant brightenings are observed in all of the Atmospheric Imaging Assembly extreme-ultraviolet channels. This unique observation provides us with the opportunity to better understand not only the thermal properties and damping mechanisms of the sloshing oscillation but also the energy transfer at the remote footpoint. Based on differential emission measures analysis and the technique of coronal seismology, we find that (1) the calculated local sound speed is consistent with the observed propagation speed of the perturbation during the oscillation, which is suggestive of a slow magnetoacoustic wave; (2) thermal conduction is the major damping mechanism of the wave but an additional damping mechanism such as anomalous enhancement of compressive viscosity or wave leakage is also required to account for the rapid decay of the observed waves; (3) the wave produced a nanoflare at the remote footpoint, with a peak thermal energy of ∼1024–1025 erg. This work provides a consistent picture of the magnetoacoustic wave propagation and reflection in a coronal loop, and reports the first solid evidence of a wave-induced nanoflare. The results reveal new clues for further simulation studies and may help with solving the coronal heating problem.

Multi-threaded prominence oscillations triggered by a coronal shock wave

Context. Understanding the interplay between ubiquitous coronal shock waves and the resulting prominence oscillations is a key factor in improving our knowledge of prominences and the solar corona overall. In particular, prominences are a key element of the solar corona and represent a window into an as yet unexplained processes in the Sun’s atmosphere. Aims. To date, most studies on oscillations of prominences have ignored their finer structure and analyzed them strictly as monolithic bodies. In this work, we study the causal relations between a localised energy release and a remote prominence oscillation, where the prominence has a realistic thread-like structure. Methods. In our work, we used an open source magnetohydrodynamic code known as MPI-AMRVAC to create a multi-threaded prominence body. In this domain, we introduced an additional energy source from which a shock wave originates, thereby inducing prominence oscillation. We studied two cases with different source amplitudes to analyze its effect on the oscillations. Results. Our results show that the frequently used pendulum model does not suffice to fully estimate the period of the prominence oscillation, in addition to showing that the influence of the source and the thread-like prominence structure needs to be taken into account. Repeated reflections and transmissions of the initial shock wave occur at the specific locations of multiple high-temperature and high-density gradients in the domain. This includes the left and right transition region located at the footpoints of the magnetic arcade, as well as the various transition regions between the prominence and the corona. This results in numerous interferences of compressional waves propagating within and surrounding the prominence plasma. They contribute to the restoring forces of the oscillation, causing the period to deviate from the expected pendulum model, in addition to leading to differences in attributed damping or even growth in amplitude between the various threads. Along with the global longitudinal motion that result from the shock impact, small-scale transverse oscillations are also evident. Multiple high-frequency oscillations represent the propagation of magnetoacoustic waves. The damping we see is linked to the conversion of energy and its exchange with the surrounding corona. Our simulations demonstrate the exchange of energy between different threads and their different modes of oscillation.

Magnetoacoustic Nonlinear Periodic Wave and Soliton Structures in Degenerate Pair Plasmas in the Presence of Exchange-Correlation Force

By employing a two-fluid quantum magnetohydrodynamic (QMHD) model, linear and nonlinear aspects of magnetoacoustic wave propagation in dense magnetized electron–positron (e-p) plasma are examined in the presence of exchange-correlation potential as well. The degenerate plasma pressure and the Bohm potential effects are already taken in the model. The reductive perturbation method (RPM) is used, and the modified Korteweg–de Vries (modified KdV) equation (or KdV equation containing linear drift term) is derived for nonlinear magnetoacoustic wave propagation in degenerate pair plasma under periodic boundary conditions. The well-known Sagdeev potential approach is opted to obtain the analytical solution of magnetoacoustic cnoidal wave and soliton in dense pair plasmas. The numerical plots of magnetoacoustic cnoidal wave and soliton structures are also presented, and the condition of their formation in dense e-p plasma is discussed in detail. The parametric analysis in the absence and the presence of exchange-correlation potential effects of electrons and positrons is discussed. Moreover, the parametric analysis of the variations of plasma density and magnetic field intensity on the formation and propagation of nonlinear structures in dense e-p plasma in the presence of exchange-correlation force effects in the model is also done using the astrophysical plasma parameters mentioned in the literature for pulsars (or white dwarfs).

How Negative Energy and Kelvin–Helmholtz Instabilities Grow by Longitudinal Waves in Solar Atmospheric Jets

Abstract We model the propagation of slow magnetoacoustic body waves in solar jets in the course of negative energy wave excitation in the context of magnetohydrodynamic theory. Explicit approximate expressions are provided for the dispersion relation of slow body waves, providing insight into the influence of the steady flow speed, radiative cooling, and plasma-β at a glance. Analytic expressions are provided regarding critical speeds in the presence of backward waves, negative energy wave speeds, and instabilities. The buildup of the Kelvin–Helmholtz instability above the negative energy wave instability is expressed through analytic expressions that provide insight into the interplay of equilibrium conditions and dispersive effects as they affect the instability growth rate of slow body waves at various altitudes. As slow magnetoacoustic waves propagate with the same speed in the long-wavelength limit, slow body kink waves experience stronger dispersion than sausage waves. Backward waves are also probable at lower steady flow speeds for medium wavelengths when the jet hosts slow body kink waves that provide greater domains for dissipative processes. Slow body sausage waves grow faster while nearing the long-wavelength limit, while the internal plasma-β decreases the instability growth rate. The seismological aspect is that energy transfer to the external medium is observed on various timescales. The observational aspect is that slow body kink waves may exist at higher altitudes as energy has already been extracted to the external medium due to negative energy unstable slow body sausage waves in earlier stages contributing toward coronal heating.

Spatial variation in the periods of ion and neutral waves in a solar magnetic arcade

Context.We present new insight into the propagation of ion magnetoacoustic and neutral acoustic waves in a magnetic arcade in the lower solar atmosphere.Aims.By means of numerical simulations, we (a) study two-fluid waves propagating in a magnetic arcade embedded in the partially ionised, lower solar atmosphere and (b) investigate the effect of the background magnetic field configuration on the observed wave-periods.Methods.We considered a 2D approximation of the gravitationally stratified and partially ionised lower solar atmosphere consisting of ion plus electron and neutral fluids that are coupled by ion-neutral collisions. In this model, the convection below the photosphere causes the excitation of ion magnetoacoustic-gravity and neutral acoustic-gravity waves.Results.We find that in the solar photosphere, where ions and neutrals are strongly coupled by collisions, ion magnetoacoustic-gravity and neutral acoustic-gravity waves have periods ranging from 250 s to 350 s. In the chromosphere, where the collisional coupling is weak, the wave characteristics strongly depend on the magnetic field configuration. Above the footpoints of the considered arcade, the plasma is dominated by a vertical magnetic field along which ion magnetoacoustic-gravity waves propagate. These waves exhibit a broad range of periods, and the most prominent periods are 180 s, 220 s, and 300 s. Above the main loop of the solar arcade, where mostly horizontal magnetic field lines guide ion magnetoacoustic-gravity waves, the main spectral power reduces to the period of about 180 s, and no longer wave-periods exist.Conclusions.In photospheric regions, ongoing solar granulation excites a broad spectrum of wave-periods that undergoes complex interactions: mode-coupling, refractions through the inhomogeneous atmosphere, real physical absorption, and conversion of wave power. We found that, in addition, the magnetic arcade configuration with a partially ionised plasma drastically changes the image of wave-periods observed in the upper layers of the chromosphere and corona. Our results agree with recent observational data.

Magnetoacoustic solitons in Alkali-fullerene plasmas

Nonlinear propagation of magnetoacoustic waves in magnetized, collisionless, warm bi-ion plasmas with positive and negative ions of different masses and charge states are investigated. The two-fluid model is used here. Using reductive perturbation technique, the Korteweg-de Vries equation is derived as nonlinear dispersion relation, and its solution for the magnetoacoustic solitons propagating in the direction perpendicular to the external magnetic field is obtained. Using experimental values for the plasma parameters, magnetoacoustic soliton structures for K-fullerene plasma are illustrated along with some other useful alkali-fullerene plasmas.

Nonreciprocal Magnetoacoustic Waves in Dipolar-Coupled Ferromagnetic Bilayers

We study the interaction of surface acoustic waves (SAWs) with spin waves (SWs) in a ${\mathrm{Co}}_{40}{\mathrm{Fe}}_{40}{\mathrm{B}}_{20}$/$\mathrm{Au}$/${\mathrm{Ni}}_{81}{\mathrm{Fe}}_{19}$ system composed of two ferromagnetic layers separated by a nonmagnetic $\mathrm{Au}$ spacer layer. Because of interlayer magnetic dipolar coupling between the two ferromagnetic layers, a symmetric and an antisymmetric SW mode form, which both show a highly nondegenerate dispersion relation for oppositely propagating SWs. Due to magnetoacoustic SAW-SW interaction, we observe highly nonreciprocal SAW transmission in the piezoelectric-ferromagnetic hybrid device. We experimentally and theoretically characterize the magnetoacoustic wave propagation as a function of frequency, wave vector, and external magnetic field magnitude and orientation. Additionally, we demonstrate that the nonreciprocal SW dispersion of a coupled magnetic bilayer is highly tuneable and not limited to ultrathin magnetic films, in contrast to the nonreciprocity induced by the interfacial Dzyaloshinskii-Moriya interaction. Therefore, magnetoacoustic coupling in ferromagnetic multilayers provides a promising route towards building efficient acoustic isolators.

Magnetoacoustic Waves in a Magnetic Slab Embedded in an Asymmetric Magnetic Environment. III. Applications to the Solar Atmosphere

Abstract Analytical and numerical modeling of the behavior of magnetohydrodynamic waves in various magnetic geometries can offer a valuable contribution to the field of solar magnetoseismology. Based on analytical results from our previous studies, here we illustrate a few solar applications of these findings concerning the propagation of magnetoacoustic waves in a magnetic slab embedded in an asymmetric environment. Bearing in mind the simplifying assumptions made, this asymmetric model incorporating external magnetic fields can be used to describe a wide variety of multilayered solar features, some of which are observable and have already been studied in solar structures. Specific potential applications are: prominences, polar plumes and their environment, magnetic bright points, and light bridges, as well as adjacent large-scale layers in the solar atmosphere (e.g., the photosphere—interface region—corona triad, or the chromosphere—transition region—corona group). In these individual cases, the appropriate dispersion relations are derived and solved. The obtained wave propagation solutions may serve (i) not just as impetus to be confirmed by high-resolution observations but (ii) also to be exploited for further diagnostic purposes by solar magnetoseismology of these frequently studied magnetic structures.

Nonreciprocal Dzyaloshinskii-Moriya Magnetoacoustic Waves.

We study the interaction of surface acoustic waves with spin waves in ultrathin CoFeB/Pt bilayers. Because of the interfacial Dzyaloshinskii-Moriya interaction (DMI), the spin wave dispersion is nondegenerate for oppositely propagating spin waves in CoFeB/Pt. In combination with the additional nonreciprocity of the magnetoacoustic coupling itself, which is independent of the DMI, highly nonreciprocal acoustic wave transmission through the magnetic film is observed. We systematically characterize the magnetoacoustic wave propagation in a thickness series of CoFeB(d)/Pt samples as a function of magnetic field magnitude and direction, and at frequencies up to 7GHz. We quantitatively model our results to extract the strength of the DMI and magnetoacoustic driving fields.

Plasmoids and Resulting Blobs due to the Interaction of Magnetoacoustic Waves with a 2.5D Magnetic Null Point

Abstract We performed a numerical study for interpreting observations of plasma blobs occurring in the solar corona. Considering all of the previous studies and the presence of magnetic null points together with propagating magnetohydrodynamic waves in the solar corona, we guessed that the interaction of fast magnetoacoustic waves with null points could give rise to blobs under coronal conditions. The outcome of these interactions contributes to coronal jets and flares that directly affects us on Earth. The propagation of magnetoacoustic waves in the vicinity of a magnetic null point contributes to the high current density accumulation at the small scale around the magnetic null point, which has significant magnetic gradients. When nonlinearity becomes dominant, the variation of current density could result in instabilities and thus anomalous resistivity. Moreover, it is demonstrated that plasmoids with eruption events take place in the solar corona without considering the transition region. In our numerical simulation results, it is interesting that plasma blobs manifest themselves in many parameters, including current density, temperature, plasma density, flows, and magnetic fields, simultaneously and consistent with the generation of plasmoids. In this work, it is found that plasmoid instability is the reason for the plasma blobs and tiny blobs are produced by the tearing instability occurring in thin current sheets.