Small-scale dynamics in the chromospheric network in coronal holes from TRACE/BBSO observations

Low-lying small-scale dynamics, e.g., spicules, macrospicules and microflares, in coronal holes are believed to play an important role in coronal heating and solar wind acceleration. To investigate plasma motion in small-scale dynamics in relation to their magnetic settings, we made high-spatial and temporal resolution UV/EUV observations of coronal holes by the Transition Region and Coronal Explorer (TRACE) in September 2004 jointly with BBSO Hα and magnetogram observations. We focused on macrospicules as the events in this study. We identified 72 macrospicules in coronal holes. 59 of 72 events were in the form of a spiked jet and 6 were in the form of an erupting loop. As in our previous BBSO observations, spiky macrospicules were rooted in compact bipolar fields at the edges of the magnetic network. Most spiky events showed brightenings at their base in CIV 1550 Å images. This strongly suggests that spiky macrospicules are driven by reconnection between the network bipole and open magnetic fields. Moreover, 80% of the spiky events were seen in both Hα blue and red-wing images, which indicates that plasma was launched upward at the beginning and then fell back down. However, 20% spiked-jet macrospicules were seen in only Hα bluewing images, indicating that plasma in the events ejected up to the corona and did not fall back. The erupting-loop macrospicules were located between positive and negative network fluxes, which is consistent with previous our results. These results support scenarios of coronal heating and solar wind generation through fine-scale explosive reconnection events seated in the magnetic network.