The possibility of Kelvin-Helmholtz instability in solar spicules

Abstract

Transversal oscillations of spicules axes may be related to the propagation of magnetohydrodynamic waves along them. These waves may become unstable and the instability can be of the Kelvin-Helmholtz type. We use the dispersion relation of kink mode derived from linearized magnetohydrodynamic equations. The input parameters of the derived dispersion equation, namely, spicules and their ambient medium densities ratios as well as their corresponding magnetic fields ratios, are considered to be within the range 0 − 1. By solving the dispersion equation numerically, we show that for higher densities and lower magnetic fields ratios within the range mentioned, the KHI onset in type ii spicules conditions is possible. This possibility decreases with an increase in Alfvén velocity inside spicules. A rough criterion for appearing of Kelvin-Helmholtz instability is obtained. We also drive a more reliable and exact criterion for KHI onset of kink waves.

Kelvin–Helmholtz instability in an active region jet observed with Hinode

“…5 in Zhelyazkov 2012a), and 15.64737, respectively, and all they are in good agreement with the highest curve in Fig. 4 in Ajabshirizadeh et al 2015. Another interesting observation is the circumstance that the minima of all computed by us 'v'-shaped (see the red curve in the bottom panel of Fig.…”

“…On the other hand, their curves plotted in Fig. 4 in Ajabshirizadeh et al 2015 seem to be correct. One can see, that according to the curve corresponding to η = 0.1 for b = 0.25 the critical Alfvén Mach number, M cr A , must be a little higher than 4, in fine agreement with our computations.…”

“…In their paper, Ajabshirizadeh et al (2015), on using asymptotic presentations of modified Bessel functions, claim that the KH instability will emerge if…”

“…It is intriguing to see how accurately these two criteria predict the threshold/critical Alfvén Mach number for various studies of KH instability in untwisted moving flux tubes over recent years. In Table 1 we present the input data (η and b) for exploring the KH instability in spicules (Zhelyazkov 2012a(Zhelyazkov , 2013Ajabshirizadeh et al 2015), X-ray jets (Vasheghani Farahani et al 2009;Zhelyazkov 2013), photospheric tubes (Zhelyazkov 2013), and EUV jets (present paper). It is clearly seen that the Andries & Goossens criterion (8) provides a fairly good prediction only in the case when the ratio of axial magnetic fields, b, is of the order of 1.…”

How Rotating Solar Atmospheric Jets Become Kelvin–Helmholtz Unstable

“…In its nonlinear stage, the KHI trigger the wave turbulence which is considered as one of the main heating mechanisms of the solar corona (Cranmer et al, 2015). The development of the KHI in various cylindrical jet-environment configurations has been studied in photospheric jets (Zhelyazkov and Zaqarashvili, 2012), in solar spicules (Zhelyazkov, 2012;Ajabshirizadeh et al, 2015;Ebadi, 2016), in high-temperature and cool solar surges (Zhelyazkov et al, 2015a,b), in magnetic tubes of partially ionized compressible plasma (Soler et al, 2015), in EUV chromospheric jets (Zhelyazkov, Chandra, and Srivastava, 2016;Bogdanova et al, 2018), in soft X-ray jets (Vasheghani Farahani et al, 2009;Zhelyazkov, Chandra, and Srivastava, 2017), and in the twisted solar wind flows (Zaqarashvili et al, 2014). A review on KHI in the solar atmosphere, including some earlier studies, the reader can find in Zhelyazkov, 2015. The first modeling of the KHI in a rotating cylindrical magnetized plasma jet was done by Bondenson, Iacono, and Bhattacharjee (1987).…”