Electric current helicity in the solar atmosphere
Electric current helicity in the solar atmosphere
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DOI：
10.1007/bf00158402
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发表时间：
1990-09
期刊：
影响因子：
2.8
通讯作者：
N. Seehafer
中科院分区：
文献类型：
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作者：
N. Seehafer
在太阳磁学理论中，由于太阳自转而产生的动力学和磁螺旋度起着关键作用。主磁场的发电机假定在对流区工作。太阳的自转也可能是大气中产生直流电流的最终原因，而直流电流是耀斑产生所需的能量来源。那么在大气中，电流螺旋度HC=B·▽×B是一个伪标量，它在赤道平面上是反对称的。对16个活动区域的考察，利用测量光球磁场的外推法估计了它们的电流螺旋度，结果表明，电流螺旋度在北半球主要为负，在南半球主要为正。根据标准发电机理论，在对流区由α效应产生的大尺度电流的螺旋度在符号上正好相反。电流的产生是由于太阳黑子和其他磁元素的旋转运动符合全球的微分旋转，即北半球逆时针，南半球顺时针，然而，可以解释所发现的规律。在一些备选的全球场发电机模型中，发电机运行在对流区的底部，由α效应产生的大尺度电流螺旋度具有所需的符号。
In the theories of solar magnetism, kinetic and magnetic helicities, which arise as a consequence of the rotation of the Sun, play a key role. The dynamo for the main field is assumed to operate in the convection zone. The solar rotation also may be the ultimate cause for the generation of dc electric currents in the atmosphere, needed as the energy source for flares. Then in the atmosphere the electric current helicity,HC=B· ▽ ×B, which is a pseudo-scalar quantity, should be antisymmetric about the equatorial plane. An inspection of 16 active regions, for whichHChas been estimated by using extrapolation of measured photospheric magnetic fields, leads to the result that the electric current helicity is predominantly negative in the northern and positive in the southern hemisphere. The helicity of the large-scale currents generated according to standard dynamo theory by the alpha effect in the convection zone is just opposite in sign. Current generation due to rotational motions of sunspots and other magnetic elements in accordance with the global differential rotation, i.e., counter-clockwise in the northern and clockwise in the southern hemisphere, however, can explain the rule found. Also in some alternative dynamo models for the global field, in which the dynamo operates at the base of the convection zone, the large-scale current helicity generated by the alpha effect has the sign needed.