1980年5月21日—22日耀斑后冕拱(Post-flare coronal arch)的加热机制和稳定性

本文提出了快撕裂模加热是1980年5月21日—22日耀斑后冕拱长达10多小时的有效加热机制。作者计算了撕裂模所提供的能量和相应的增长率,并讨论了该冕拱的MHD平衡和稳定性问题,主要结论如下:1.对5月21日冕拱,当密度取1.6×109cm-3（实测值）时,剪切宽度α_α=1.8×108cm（冕拱小半径的十分之一）剪切磁场为18—32×10-4T,所对应的增长率为1.79×10-5s-1—2.66×10-5s-1,不稳定的增长时间为15.5h—10.4h,这组解与观测到的冕拱存在10多小时相符。所以,撕裂模是冕拱合理的有效加热机制。2.该冕拱之所以维持10多小时之久,除撕裂模加热与辐射损失平衡外,在力学上必须处于平衡态,其平衡条件为B_φ（冕拱轴向磁场）=2B_θ（冕拱的环向场）,和气压梯度dp/dr大于零。若冕拱满足该力学平衡条件,则利用能量原理可得到该系统对腊肠扰动、扭曲扰动、螺旋扰动均是稳定的。 

THE HEATING MECHANISM AND STABILITY OF THE GIANT POST FLARE ARCH OF 21-22 MAY, 1980

It is proposed in this paper that the fast tearing modes in cylindrical geometry is an effective heating mechanism for post-flare coronal arch of 21-22 May,1980 which have remained visible for more than 10 hours after the flare onset.The magnetic energy supplied by tearing modes,corresponding fast tearing modes grow the rate r_t and growth time r_t-1 are calculated.The MHD equilibrium and stability of the arch are discussed.Main conclutions are as follows:(1)When density of the arch is given by the observational value,for different shearing width,the equilibrium can be made between radiative loss and tearing modes heating by taking different shearing magnetic field.But,in considering that corresponding tearing modes growth rate must be coincide with observation time,only one situation is reasonable.For coronal arch of 21-22 May,n_e=1.6×109 cm,only shearing width a_a=1.8×108cm(1/10 minal radius of the arch),shearing magnetic field B=18-32×10-4T,r_t=1.79×10-5-2.66×10-5s-1,r_t-1=15.5-10.4h,this solution is in agreement with observational value.The free energy which supplied by tearing modes can afford the radiative loss.So,fast tearing modes is an effective reasonable heating mechanism for the coronal arch.(2) According to the discussion for MHD equilibrium and stability of the arch,the arch which lasted more than 10 hours,must be in mechanical equilibrium besides the equilibrium between tearing modes heating and radiative loss.The equilibrium conditions are B_Ф (axis magnetic field of arch)=2B_θ(toroidal field intensity) and (dp/dr)>0.If the equilibrium conditions are satisfied,the arch is in stability for sausage,kink,screw perturbation by the energy principle.The axis magnetic field and toroidal field components can not be observed directly but an average pressure of 1.4 bar in the arch was observed,usually p_a (over the major active region)=2 bar.It can be thought that the arch of 12-22 May is in equilibrium condition and in a stable state.(3)According to observation and calculation for 21-22 May arch,when the tearing modes work,the thermal conduction in the coronal arch can be neglected.