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Register a new userNumerical simulations of macrospicule jets under energy imbalance conditions in the solar atmosphere
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Added by
J.J. Gonz\\'alez-Avil\\'es
Publication date
2021
fields
Physics
and research's language is
English
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Using numerical simulations, we study the effects of thermal conduction and radiative cooling on the formation and evolution of solar jets with some macrospicules features. We initially assume that the solar atmosphere is rarely in equilibrium through energy imbalance. Therefore, we test whether the background flows resulting from an imbalance between thermal conduction and radiative cooling influence the jets behavior. In this particular scenario, we trigger the formation of the jets by launching a vertical velocity pulse localized at the upper chromosphere for the following test cases: i) adiabatic case; ii) thermal conduction case; iii) radiative cooling case; iv) thermal conduction + radiative cooling case. According to the test results, the addition of the thermal conduction results in smaller and hotter jets than in the adiabatic case. On the other hand, the radiative cooling dissipates the jet after reaching the maximum height ($approx$ 5.5 Mm), making it shorter and colder than in the adiabatic and thermal conduction cases. Besides, the flow generated by the radiative cooling is more substantial than the caused by thermal conduction. Despite the energy imbalance of the solar atmosphere background, the simulated jet shows morphological features of macrospicules. Furthermore, the velocity pulse steepens into a shock that propagates upward into a solar corona that maintains its initial temperature. The shocks generate the jets with a quasi-periodical behavior that follows a parabolic path on time-distance plots consistent with macrospicule jets observed dynamics.
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It is known that hydrodynamic triangular jets are unstable to antisymmetric kink perturbations. The inclusion of magnetic field may lead to the stabilisation of the jets. Jets and complex magnetic fields are ubiquitous in the solar atmosphere, which suggests the possibility of the kink instability in certain cases. The aim of the paper is to study the kink instability of triangular jets sandwiched between magnetic tubes/slabs and its possible connection to observed properties of the jets in the solar atmosphere. A dispersion equation governing the kink perturbations is obtained through matching of analytical solutions at the jet boundaries. The equation is solved analytically and numerically for different parameters of jets and surrounding plasma. The analytical solution is accompanied by a numerical simulation of fully nonlinear MHD equations for a particular situation of solar type II spicules. MHD triangular jets are unstable to the dynamic kink instability depending on the Alfven Mach number (the ratio of flow to Alfven speeds) and the ratio of internal and external densities. When the jet has the same density as the surrounding plasma, then only super Alfvenic flows are unstable. However, denser jets are unstable also in sub Alfvenic regime. Jets with an angle to the ambient magnetic field have much lower thresholds of instability than field-aligned flows. Growth times of the kink instability are estimated as 6-15 min for type I spicules and 5-60 s for type II spicules matching with their observed life times. Numerical simulation of full nonlinear equations shows that the transverse kink pulse locally destroys the jet in less than a minute in the conditions of type II spicules. Dynamic kink instability may lead to full breakdown of MHD flows and consequently to observed disappearance of spicules in the solar atmosphere.
We present two-dimensional simulations of wave propagation in a realistic, non-stationary model of the solar atmosphere. This model shows a granular velocity field and magnetic flux concentrations in the intergranular lanes similar to observed velocity and magnetic structures on the Sun and takes radiative transfer into account. We present three cases of magneto-acoustic wave propagation through the model atmosphere, where we focus on the interaction of different magneto-acoustic wave at the layer of similar sound and Alfven speeds, which we call the equipartition layer. At this layer the acoustic and magnetic mode can exchange energy depending on the angle between the wave vector and the magnetic field vector. Our results show that above the equipartition layer and in all three cases the fast magnetic mode is refracted back into the solar atmosphere. Thus, the magnetic wave shows an evanescent behavior in the chromosphere. The acoustic mode, which travels along the magnetic field in the low plasma-$beta$ regime, can be a direct consequence of an acoustic source within or outside the low-$beta$ regime, or it can result from conversion of the magnetic mode, possibly from several such
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