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Solar jets are observed as collimated plasma beams over a large range oftemperatures and wavelengths. They have been observed in Halpha and opticallines for more than 50 years and called surges. The term "jet" comes from X-rayobservations after the launch of the Yohkoh satellite in 1991. They are themeans of transporting energy through the heliosphere and participate to thecorona heating and the acceleration of solar wind. Several characteristics havebeen derived about their velocities, their rates of occurrence, and theirrelationship with CMEs. However, the initiation mechanism of jets, e.g.emerging flux, flux cancellation, or twist, is still debated. In the lastdecade coordinated observations of the Interface Region Imaging Spectrograph(IRIS) with the instruments on board the Solar Dynamic Observatory (SDO) allowto make a step forward for understanding the trigger of jets and therelationship between hot jets and cool surges. We observe at the same time thedevelopment of 2D and 3D MHD numerical simulations to interpret the results.This paper summarizes recent studies of jets showing the loci of magneticreconnection 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 minifilament close to the dome of emerging flux. The twist can also be transferredto the jet from a flux rope in the vicinity of the reconnection by slippage ofthe polarities. Bidirectional flows are detected at the reconnection sites. Weshow the role of magnetic currents detected in the footprints of flux rope andquasi-separatrix layers for initiating the jets.  We select a few studies and show that with the same observations, differentinterpretations are possible based on different approaches e.g. non linearforce free field extrapolation or 3D MHD simulation.

Solar jets: SDO and IRIS observations in the perspective of new MHD simulations