# Kelvin--Helmholtz instability in a twisting solar polar coronal hole jet observed by \emph{SDO}/AIA

## TL;DR

This study models the Kelvin-Helmholtz instability in a twisting solar coronal jet using MHD theory and observations, identifying conditions that suppress or enable instability and matching growth times with observed jet features.

## Contribution

The paper presents a theoretical model of KH instability in a twisting solar jet, incorporating observational data to determine instability conditions and suppression mechanisms.

## Key findings

- Magnetic field twist influences the width of instability windows.
- A magnetic field of 1.3-1.4 G suppresses KH instability.
- KH instability growth times match observed jet blob evolution.

## Abstract

We investigate the conditions under which the fluting ($m = 2$), $m = 3$, and $m = 12$ magnetohydrodynamic (MHD) modes in a uniformly twisted flux tube moving along its axis become unstable in order to model the Kelvin--Helmholtz (KH) instability in a twisting solar coronal hole jet near the northern pole of the Sun. Using a twisting jet of 2010 August 21 by \emph{SDO}/AIA and other observations of coronal jets we set the parameters of our theoretical model and have obtained that in a twisted magnetic flux tube of radius of $9.8$~Mm, at a density contrast of $0.474$ and fixed Alfv\'en Mach number of ${\cong}0.76$, for three MHD modes there exist instability windows whose width crucially depends upon the internal magnetic field twist. It is found that for the considered modes an azimuthal magnetic field of $1.3$--$1.4$~G (computed at the tube boundary) makes the width of the instability windows equal to zero, that is, it suppress the KH instability onset. On the other hand, the times for developing KH instability of the $m = 12$ MHD mode at instability wavelengths between $15$ and $12$~Mm turn out to be in the range of $1.9$ to $4.7$~minutes that is in agreement with the growth rates estimated from the temporal evolution of the observed unstable jet's blobs in their initial stage.