Abstract. We discuss the problem of the limiting height of quiescent prominences and the relationship of this value to the photospheric magnetic field characteristics. Solar prominences are considered preeruptive states of coronal mass ejections (CMEs). We note that in a model of inverse-polarity filament, the equilibrium is stable only in the region where the photospheric magnetic field falls off with a height not faster than h -1. Current-free magnetic field calculations are compared with the observed prominence heights. It is shown that the maximum stable height of a prominence depends on the vertical gradient value and never exceeds the level where the power is equal to unity in the power-law decrease of the magnetic field. This is a new way to predict prominence eruptions and CMEs.

New XRT observations of the north polar region taken from the X-ray Telescope (XRT) of the Hinode (Solar-B) spacecraft are used to analyze several time sequences showing small loop brightenings with a long ray above. We focus on the recorded transverse displacement of the jet and discuss scenarios to explain the main features of the events: the relationship with the expected surface magnetism, the rapid and sudden radial motion, and possibly the heating, based on the assumption that the jet occurs above a null point of the coronal magnetic field. We conclude that 3-D reconnection models are needed to explain the observational details of these events.Comment: 11 pages 8 figure

We analyze multi-wavelength and multi-viewpoint observations of a helically twisted plasma jet formed during a confined filament eruption on 10-11 April 2013. Given a rather large scale event with its high spatial and temporal resolution observations, it allows us to clearly understand some new physical details about the formation and triggering mechanism of twisting jet. We identify a pre-existing flux rope associated with a sinistral filament, which was observed several days before the event. The confined eruption of the filament within a null point topology, also known as an Eiffel tower (or inverted-Y) magnetic field configuration results in the formation of a twisted jet after the magnetic reconnection near a null point. The sign of helicity in the jet is found to be the same as that of the sign of helicity in the filament. Untwisting motion of the reconnected magnetic field lines gives rise to the accelerating plasma along the jet axis. The event clearly shows the twist injection from the pre-eruptive magnetic field to the jet.

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