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arXiv 1004.5318astro-ph.SR
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驱动太阳耀斑的机械能

On the Mechanical Energy Available to Drive Solar Flares

Alexander N. McClymont, George H. Fisher

摘要:

太阳耀斑能量从何而来?更具体地说,假设耀斑能量的最终来源是对流区的机械能,这是如何转化为能量耗散或储存在日冕?这个问题似乎得到了相对较少的思考,因为注意力主要集中在日冕磁场能量通过MHD不稳定性和等离子体微不稳定性快速耗散的机制上。我们考虑三种类型的耀斑理论:稳态“光球发电机”模型,其中耀斑功率代表光球下流动同时产生的电流的日冕耗散;“磁能量储存”模型,其中光球下流动再次诱发日冕电流,但在这种情况下,日冕电流是在突然释放之前在较长的时间内建立的;和“新兴通量”模型,其中新的磁通量上升到光球已经包含自由能,并不需要随后的压力光球运动。我们的结论是:光球发电机只能为非常小的耀斑提供能量;日冕能量储存原则上可以满足大耀斑的需要,尽管可能不是最大的耀斑,但有效地耦合到能源的困难可能会限制这种机制到中等大小的耀斑;太阳内部产生的新兴磁通量管可以携带足够的自由能,甚至可以为观测到的最大耀斑提供动力。

英文摘要:

Where does solar flare energy come from? More specifically, assuming that the ultimate source of flare energy is mechanical energy in the convection zone, how is this translated into energy dissipated or stored in the corona? This question appears to have been given relatively little thought, as attention has been focussed predominantly on mechanisms for the rapid dissipation of coronal magnetic energy by way of MHD instabilities and plasma micro instabilities. We consider three types of flare theory: the steady state "photospheric dynamo" model in which flare power represents coronal dissipation of currents generated simultaneously by sub-photospheric flows; the "magnetic energy storage" model where sub-photospheric flows again induce coronal currents but which in this case are built up over a longer period before being released suddenly; and "emerging flux" models, in which new magnetic flux rising to the photosphere already contains free energy, and does not require subsequent stressing by photospheric motions. We conclude that photospheric dynamos can power only very minor flares; that coronal energy storage can in principle meet the requirements of a major flare, although perhaps not the very largest flares, but that difficulties in coupling efficiently to the energy source may limit this mechanism to moderate sized flares; and that emerging magnetic flux tubes, generated in the solar interior, can carry sufficient free energy to power even the largest flares ever observed.

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