AN INTERFACE REGION IMAGING SPECTROGRAPH FIRST VIEW ON SOLAR SPICULES

Abstract

Solar spicules have eluded modelers and observers for decades. Since the discovery of the more energetic type II, spicules have become a heated topic but their contribution to the energy balance of the low solar atmosphere remains unknown. Here we give a first glimpse of what quiet Sun spicules look like when observed with NASA's recently launched Interface Region Imaging Spectrograph (IRIS). Using IRIS spectra and filtergrams that sample the chromosphere and transition region we compare the properties and evolution of spicules as observed in a coordinated campaign with Hinode and the Atmospheric Imaging Assembly. Our IRIS observations allow us to follow the thermal evolution of type II spicules and finally confirm that the fading of Ca II H spicules appears to be caused by rapid heating to higher temperatures. The IRIS spicules do not fade but continue evolving, reaching higher and falling back down after 500 − 800 s. Ca II H type II spicules are thus the initial stages of violent and hotter events that mostly remain invisible in Ca II H filtergrams. These events have very different properties from type I spicules, which show lower velocities and no fading from chromospheric passbands. The IRIS spectra of spicules show the same signature as their proposed disk counterparts, reinforcing earlier work. Spectroheliograms from spectral rasters also confirm that quiet Sun spicules originate in bushes from the magnetic network. Our results suggest that type II spicules are indeed the site of vigorous heating (to at least transition region temperatures) along extensive parts of the upward moving spicular plasma.

Solar Coronal Plumes

“…Because they fade in the Ca ii H passband, it has been speculated they undergo thermal evolution and may show up at higher transition region (TR) and coronal temperatures. This has been confirmed by data from the IRIS mission that revealed spicules can be observed at TR temperatures (Pereira et al, 2014). Also, the X-ray jets discussed in Section 5.1 have been recognized to belong to two categories with different properties: the standard jets and the blowout jets , the latter being analogous to the large flares often associated with CMEs (coronal mass ejections).…”

Statistical Study of Network Jets Observed in the Solar Transition Region: a Comparison Between Coronal Holes and Quiet-Sun Regions

“…It has already been claimed (e.g. Rouppe van der Voort et al, 2009;Sekse, Rouppe van der Voort, and De Pontieu, 2012;Pereira et al, 2014) that the RBEs observed in profiles of different chromospheric lines are on-disk counter parts of solar spicules. In addition, it is also reported that the doppler velocity of RBEs increases along their length in CHs when observed in the 8542Å (Ca II) spectral line using the CRisp Imaging SpectroPolarimeter instrument (CRISP, Scharmer et al (2008)) at the Swedish 1-m Solar Telescope (SST).…”

“…Tian et al (2014) concluded that the existence of network jets are consistent with the 'Magnetic Furnace Model' of solar wind (Axford and McKenzie, 1992;Tu et al, 2005;Yang et al, 2013) and thus may serve as strong candidates for supply of mass and energy to the solar wind and corona. Tian et al (2014) also suggest that some of these network jets may be the on-disk counterparts and TR manifestations of the chromospheric type-II spicules (see also Pereira et al (2014) The network jets in CHs, as reported in Tian et al (2014), have widths of 300 km with lifetimes of 20-80 s and lengths of 4-10 Mm. They calculated apparent speeds of the jets, which turned out be 80-250 km s −1 in CHs.…”

THE APPEARANCE OF SPICULES IN HIGH RESOLUTION OBSERVATIONS OF Ca ii H AND Hα

“…But spicules have clear spectral signatures in the form of Doppler-shifted, wider line profiles with increased absorption in the red or blue wings. Such signatures have been observed for spicules on disk (e.g., Langangen et al 2008;Rouppe van der Voort et al 2009;Sekse et al 2013b;Yurchyshyn et al 2013;Kuridze et al 2015) and off limb (Pereira et al 2014).…”