Physical properties of solar polar jets

Abstract

Aims. The target of this work is to investigate the physical nature of polar jets in the solar corona and their possible contribution to coronal heating and solar wind flow based on the analysis of X-ray images acquired by the Hinode XRT telescope. We estimate the different forms of energy associated with many of these small-scale eruptions, in particular the kinetic energy and enthalpy. Methods. Two Hinode XRT campaign datasets focusing on the two polar coronal holes were selected to analyze the physical properties of coronal jets; the analyzed data were acquired using a series of three XRT filters. Typical kinematical properties (e.g., length, thickness, lifetime, ejection rate, and velocity) of 18 jets are evaluated from the observed sequences, thus providing information on their possible contribution to the fast solar wind flux escaping from coronal holes. Electron temperatures and densities of polar-jet plasmas are also estimated using ratios of the intensities observed in different filters. Results. We find that the largest amount of energy eventually provided to the corona is thermal. The energy due to waves may also be significant, but its value is comparatively uncertain. The kinetic energy is lower than thermal energy, while other forms of energy are comparatively low. Lesser and fainter events seem to be hotter, thus the total contribution by polar jets to the coronal heating could have been underestimated so far. The kinetic energy flux is usually around three times smaller than the enthalpy counterpart, implying that this energy is converted into plasma heating more than in plasma acceleration. This result suggests that the majority of polar jets are most likely not escaping from the Sun and that only cooler ejections could possibly have enough kinetic energy to contribute to the total solar wind flow.

Quiet-Sun Network Bright Point Phenomena With Sigmoidal Signatures

“…Our best-fit line to this jet rise gives an LOS velocity of 150 ± 60 km s −1 . This velocity is comparable to the 80-250 km s −1 velocities derived for the prevalent small-scale chromospheric and TR jets observed by Tian et al (2014) and the 160 ± 30 km s −1 outflow speed of polar coronal jets observed by Paraschiv et al (2015).…”

The Contribution of Coronal Jets to the Solar Wind

“…Following Pucci et al (2013) and Paraschiv et al (2015), we calculate the mass and energy fluxes associated with our jets, and integrate them in time and space to find the total mass and energy injected into the SW. Different from these authors, we perform our analysis high in the corona, at r = 4 R ⊙ , and use the Poynting flux, rather than the wave-energy flux, for a more accurate calculation of the total energy flux ( § 3.1).…”

“…Fluxes due to radiation and thermal conduction are neglected (Paraschiv et al 2015). For each flux x we determine the constant background F (bg) x produced by the steady-state SW (which is zero for F wave and F Poynting ).…”

“…Using heliospheric images from SMEI (Jackson et al 2004), Yu et al (2014) estimated mass and energy contributions of 3.2 % and 1.6 %, respectively. Finally, Paraschiv et al (2015) estimated the energy provided by coronal jets to be less than 1 % of what is required to heat a polar coronal hole. They emphasized, though, that many high-temperature jets may be missed by the observations (Young 2015).…”

Observations of Multiple Blobs in Homologous Solar Coronal Jets in Closed Loop

“…They were first discovered in soft X-ray (SXR) by the YOHKOH spacecraft observations (Shibata et al, 1992). With the development of solar space telescopes and the increase of spatial resolution, more and more coronal jets are observed and investigated in SXR as well as extreme-ultraviolet (EUV) wavelengths (Shimojo et al, 1996;Shimojo & Shibata, 2000;Paraschiv et al, 2015;Nisticò et al, 2015). They are located not only in coronal holes and active region (AR) boundary where open magnetic field dominates, but also in quiet regions with large-scale, closed magnetic field (Cirtain et al, 2007;Culhane et al, 2007;Zhang et al, 2012b).…”