CME升空，带高频碎片型II突发发射
CME liftoff with high-frequency fragmented type II burst emission
摘要：
目标：太阳射电II型爆发很少出现在频率高于几百兆赫的地方。由于公制II型爆发被认为是传播冲击波的特征，因此了解这些冲击和II型爆发是如何形成的是很有意义的。特别是，如何产生高频、碎片化的II型爆发？冲击加速度或周围介质的差异是否可以解释与“典型”度量II型的差异？方法：我们详细分析了一个不寻常的度量II型事件，并与白光，EUV和X射线观测进行了比较。由于射电事件与耀斑和日冕物质抛射（CME）有关，我们研究了它们之间的联系。然后，我们利用数值MHD模拟研究的冲击结构引起的爆发日冕物质抛射模型日冕，包括密集的环路。结果如下：我们的模拟结果表明，II型爆发的碎片部分可以形成时，日冕冲击的质量喷射驱动通过一个系统的密集环覆盖的活动region.To产生碎片的发射，等离子体发射的条件必须是更有利的环内比环间区域。与我们的模拟模型一致的明显假设是，在密度更高的环之间的空间中，冲击强度显著降低。后来，更典型的II型爆发出现时，冲击退出密集环系统，最后，在活动区之外，II型爆发消亡时，改变几何形状不再有利于电子冲击加速。
英文摘要：
Aims: Solar radio type II bursts are rarely seen at frequencies higher than a few hundred MHz. Since metric type II bursts are thought to be signatures of propagating shock waves, it is of interest to know how these shocks, and the type II bursts, are formed. In particular, how are high-frequency, fragmented type II bursts created? Are there differences in shock acceleration or in the surrounding medium that could explain the differences to the "typical" metric type IIs? Methods: We analyse one unusual metric type II event in detail, with comparison to white-light, EUV, and X-ray observations. As the radio event was associated with a flare and a coronal mass ejection (CME), we investigate their connection. We then utilize numerical MHD simulations to study the shock structure induced by an erupting CME in a model corona including dense loops. Results: Our simulations show that the fragmented part of the type II burst can be formed when a coronal shock driven by a mass ejection passes through a system of dense loops overlying the active region.To produce fragmented emission, the conditions for plasma emission have to be more favourable inside the loop than in the interloop area. The obvious hypothesis, consistent with our simulation model, is that the shock strength decreases significantly in the space between the denser loops. The later, more typical type II burst appears when the shock exits the dense loop system and finally, outside the active region, the type II burst dies out when the changing geometry no longer favours the electron shock-acceleration.
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