Objective:
to investigate the generation mechanism and possible heating of the prevalent network jets observed with IRIS
Scientific Background:
IRIS observations have revealed numerous small-scale jet-like features with apparent velocities of 80-250 km/s from the network (Tian et al. 2014). These network jets occur in both the quiet Sun and coronal holes. Their width is often ~300 km or less. Many of these jets show up as elongated features with enhanced line width in maps obtained with transition region lines, suggesting that these jets reach at least transition region temperatures. The ubiquitous presence of these high-reaching (often >10 Mm) jets also suggests that they may play a crucial role in the mass and energy budgets of the corona and solar wind. SOHO/SUMER observations have revealed persistent blue shifts of upper transition region lines in the network (e.g., Hassler et al. 1999, Peter et al. 1999, Tu et al. 2005, Tian et al. 2009) and these ~5 km/s blue shifts have been widely believed to be signatures of the nascent solar wind or mass supply to the corona. Recently, weak blue wing intensity enhancement of the order of ~2%-5%, suggesting the presence of faint upflows with speeds of 50-100 km/s, has also been reported in the network (De Pontieu et al. 2009, McIntosh et al. 2009). The obvious high-speed jet-like features in IRIS SJI images are also observed in the network, suggesting that they might be closely related to the blue shifts and the blue wing enhancement observed with the earlier instrumentation. The generation of these jets in the network and the accompanying Alfven waves is consistent with the magnetic furnace model proposed by Axford et al. (1992). Although the network jets are observed on the disk and statistically their apparent speeds are twice as large as those of the type-II spicules, it is possible that many network jets are the on-disk counterparts of type-II spicules. Many network jets are also likely the TR equivalent of the rapid blueshifted excursions seen in the chromosphere using CRISP (Rouppe van deer Voort et al. 2009). Type-II spicules have recently been debated as a possible vehicle to supply energy and mass to the corona. In fact, using off-limb observations, De Pontieu et al. (2011) suggested that type-II spicules provide enough mass and energy for heating the corona; on the contrary, Klimchuk (2012) proposed that type-II spicules can only provide a small fraction of the hot coronal plasma. However, a definitive conclusion could not be drawn because of the ambiguities posed by the long line-of-sight affecting off-disk observations. This IHOP is devoted to studying network jets using on-disk observations of IRIS, SDO/AIA, SOHO/SUMER and HINODE: since disk observations are much less affected by line-of-sight superposition, the combination of these three instruments provides a unique opportunity to investigate the generation mechanism and heating of the network jets, and their importance for supplying mass and heating to the corona. The proposed study will also provide new insight into the reconnection process in the interface region, and evaluate the contribution of these high-speed jets to coronal heating and the solar wind.
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