日冕中EUV波的研究进展

Progress of the Study on the Coronal EUV Waves

日冕极紫外(EUV)波是Thompson等人1998年首先在EIT的观测资料中发现的,在日冕中以几百km/s的速度传播的扰动现象,在1 h之内扫过了大部分太阳表面,所以这个现象开始被称为"EIT波"。首先介绍了EUV波的研究背景;然后介绍了EUV波的观测特征;第3章分别介绍了EUV波与Moreton波、耀斑及CME的关系;第4章介绍了从发现EUV波以来提出的各种理论和模型;第5章讨论到目前为止已发现的EUV波成分:一个较快的波在前面传播,一个较慢的波在后面传播;最后,对EUV波研究的未来方向及发展趋势进行了总结和展望。

Extreme Ultraviolet（EUV） waves are large-scale disturbances in the corona.They can pass through the whole solar disk in an hour at the speed of hundreds of kilometers per second. The EUV wave was first discovered by Thompson（1998） when the data from theEUV Imaging Telescope（EIT） were studied. So it was originally named EIT wave. It is now generally called EUV wave since its appearance and properties are not dependent on a specific instrument, and ‘EUV＇ is more appropriate for describing one of its important physical features. The EUV wave usually has a bright broad relatively-diffuse circular wavefront followed by an expanding dimming region.The EUV wave is thought to be the counterpart of the chromospheric Moreton wave in the corona. However, very few observation including both phenomena has been reported.Moreover, observations showed that EUV waves have two components, a faster wave in front and a slower wave following. These all indicate that the EUV wave and the Moreton wave are not the same. Though having been studied for years, the physical nature and the driving mechanism of EUV waves still remain unclear. Solar flares and coronal mass ejections（CMEs） are the two candidates to drive EUV waves. Currently, both theoretical and observational studies suggested that the flare cannot cause EUV wave, while CME is more likely to drive the EUV wave. In addition, whether EUV waves are the wave or the pseudo-wave or the hybrid wave is still unknown.There are five possible mechanisms for explaining EUV waves： fast mode MHD waves,magnetic field lines successively stretching, successive reconnection, current shell, and slow mode wave or solitary wave. The prevailing scenario of explaining the observational characteristics of EUV waves is of the combination of the first two.Take advantage of the high resolution telescope, we are convinced that EUV waves possess two components, which is supported by many observational evidences. However there are still many unsolved problems, and we hope that we can solve them in the future by development of the numerical simulations and observations of high spatial resolution and high time cadence.