Abstract
Solar jets are observed as collimated plasma beams over a large range of temperatures and wavelengths. They have been observed in H α and optical lines for more than 50 years and called surges. The term “jet” comes from X-ray observations after the launch of the Yohkoh satellite in 1991. They are the means of transporting energy through the heliosphere and participate to the corona heating and the acceleration of solar wind. Several characteristics have been derived about their velocities, their rates of occurrence, and their relationship with CMEs. However, the initiation mechanism of jets, e.g. emerging flux, flux cancellation, or twist, is still debated. In the last decade coordinated observations of the Interface Region Imaging Spectrograph (IRIS) with the instruments on board the Solar Dynamic Observatory (SDO) allow to make a step forward for understanding the trigger of jets and the relationship between hot jets and cool surges. We observe at the same time the development of 2D and 3D MHD numerical simulations to interpret the results. This paper summarizes recent studies of jets showing the loci of magnetic reconnection in null points or in bald patch regions forming a current sheet. In the pre-jet phase a twist is frequently detected by the existence of a mini filament close to the dome of emerging flux. The twist can also be transferred to the jet from a flux rope in the vicinity of the reconnection by slippage of the polarities. Bidirectional flows are detected at the reconnection sites. We show the role of magnetic currents detected in the footprints of flux rope and quasi-separatrix layers for initiating the jets. We select a few studies and show that with the same observations, different interpretations are possible based on different approaches e.g. non linear force free field extrapolation or 3D MHD simulation.
Highlights
Solar jets are observed as collimated plasma beams over a large range of temperatures and wavelengths
This paper summarizes recent studies of jets showing the loci of magnetic reconnection in null points or in bald patch regions forming a current sheet
The more important achievement was due to the development of theory to reply to the following questions: what is the driver of jet? What is the relationship between jet and surge? What are the physical conditions of jet and surge? We focus the sections on recent observations using the Solar Dynamic Observatory (SDO) and Interface Region Imaging Spectrograph (IRIS)
Summary
Solar jets are transient phenomena considered being means of energy and mass transport in the solar atmosphere. These are observed in multiple temperatures and wavelengths from Hα (for more than 50 years) to X-rays after the launch of the Yohkoh satellite in August 1991. Before describing the present day state of the art of jets, let us look at how surge and jet topic develops through historical studies leading to our present knowledge. The development of instruments with higher and higher spatial and temporal resolution certainly helps us make a step forward in our knowledge so that the cartoons proposed in the late 90’s become magnetohydrodynamic (MHD) numerical simulations in three dimensions (3D)
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