Solar fine-scale structures. I. Spicules and other small-scale, jet-like events at the chromospheric level: observations and physical parameters

摘要

Over the last two decades the uninterrupted, high-resolution observations ofthe Sun, from the excellent range of telescopes aboard many spacecraftcomplemented with observations from sophisticated ground-based telescopes haveopened up a new world producing significantly more complete information on thephysical conditions of the solar atmosphere than before. The interface betweenthe lower solar atmosphere where energy is generated by subsurface convectionand the corona comprises the chromosphere, which is dominated by jet-like,dynamic structures, called mottles when found in quiet regions, fibrils whenfound in active regions and spicules when observed at the solar limb. Recently,space observations with Hinode have led to the suggestion that there shouldexist two different types of spicules called Type I and Type II which havedifferent properties. Ground-based observations in the Ca II H and Kfiltergrams reveal the existence of long, thin emission features called strawsin observations close to the limb, and a class of short-lived events calledrapid blue-shifted excursions characterized by large Doppler shifts that appearonly in the blue wing of the Ca II infrared line. It has been suggested thatthe key to understanding how the solar plasma is accelerated and heated maywell be found in the studies of these jet-like, dynamic events. However, whilethese structures are observed and studied for more than 130 years in thevisible, but also in the UV and EUV emission lines and continua, there arestill many questions to be answered. In this review we present observations andphysical properties of small-scale jet-like chromospheric events observed inactive and quiet regions, on the disk and at the limb and discuss theirinterrelationship.