日冕反常加热之谜新解

The mystery of coronal heating

日冕加热之谜是当代天文学、天体物理学中的八大难题之一。自日冕高温发现七十多年以来,人们建立了许多模型试图解决这一难题,但到目前为止,现有的模型几乎都无法给出一个完整的解答。近年来,人们从观测上取得了一系列新的发现,如从光球到日冕的超精细磁通道中的快速上升热流、二型针状体、极紫外龙卷风等。这些发现给我们一个新的启示,即日冕的加热能量很可能是直接通过热物质上升并在日冕区域沉积而实现的。但是,这些上升热流又是如何形成的呢?鉴于太阳大气中普遍存在具有磁场梯度的磁通量管,作者最近提出了磁场梯度抽运机制(magnetic gradient pumping mechanism,MGP),每一磁通量管就像一个抽水机一般,将底层热分布的等离子体中的高能端粒子抽运到高层大气中沉积,并最终形成了高温的日冕大气。这一机制为我们探索日冕加热之谜提供了一个新的思路。

The problem of coronal heating is one the eight key mysteries in modern astronomy and astrophysics. Since the discovery of extremely hot corona more than 70 years ago,many theoretical models have attempted to explain this mystery. However, so far no model can explain the coronal heating process perfectly. Recently, there have been several new discoveries,such as the observation of hot plasma ejections along the ultrafine magnetic channels from the solar surface upward to the corona, hot upflows of type II spicules, magnetic tornados, and EUV cyclones, which imply that the hot corona may be heated by hot plasma upflows directly from the underlying atmosphere. But how do these hot upflows form？ We notice the fact that the magnetic gradient is ubiquitous in the whole solar atmosphere, based on which we have proposed a new theoretical model, the magnetic- gradient pumping mechanism, to explain the coronal heating process. In this mechanism, each magnetic flux tube acts as a pump to drive the high energy particles to move upward, accumulate in the upper atmosphere, and finally form the hot corona. This model may provide a new approach to explain the mystery of coronal heating.