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.
Small-scale chromospheric jets above a sunspot light bridge
用Hinode上的太阳光学望远镜获得了活动区NOAA 11271在Ca ii H和G波段的高分辨率宽带滤波图，以确定造成太阳黑子光桥上方动态和小规模色球喷流的物理驱动因素。我们使用半自动程序识别Ca图像中的射流。色球喷流由一个明亮的三角形斑点组成，它位于光桥上，而这个斑点的顶点延伸成一个在黑暗的本影背景下明亮的尖峰状结构。大多数喷流的表观长度小于1000公里，其中约30%的长度在1000-1600公里之间。它们的方向在+/-35度范围内。与光桥轴的法线成直角。它们中的许多聚集在2弧秒范围内的中心部分附近。可以看到喷气式飞机沿着光桥快速移动，其中大部分无法在以2分钟节奏拍摄的连续图像中识别。喷流主要位于光桥的一侧，并直接进入本影核心。在LB上的斑点的位置处或附近的斯托克斯轮廓表现出显著的净圆偏振和多个分量，包括相反极性的波瓣。磁场从光桥向它分离的影核发散。在光球层中，有一个主要的单向流动，速度为100-150米/秒，沿着光桥，这是由一片微弱的运动，也沿着光桥移动中断。LB上方的动态短寿命射流似乎是由磁场线引导的。重连事件是这种现象的可能触发器，因为它们发生在磁场急剧改变取向的位置。我们发现喷流和光球流型之间没有明确的关系。
Possible Evolution of Minifilament-Eruption-Produced Solar Coronal Jets, Jetlets, and Spicules, into Magnetic-Twist-Wave "Switchbacks" Observed by the Parker Solar Probe (PSP)
