Comparison of Hα and Heiiλ304 Macrospicules

Abstract

Simultaneous observations of limb macrospicules were carried out in Hα by the Big Bear Solar Observatory (BBSO) and in He II λ304 by the Extreme-Ultraviolet Imaging Telescope (EIT) on board SOHO. For the first time, Hα and He II macrospicules are compared, with high spatial and temporal resolution and image enhancement. Data were obtained on 1996 October 6, 7, and 8. The target of the first and last day was the north pole; on October 7, it was the quiet west limb. BBSO uses a 12 bit digital camera to obtain high-resolution Hα filtergrams at -0.65 A, line center, and 0.65 A. The pixel resolution ranges between 017 and 033, and temporal resolution ranges between 30 and 90 s. EIT images have a fixed pixel resolution of 25 and temporal resolution between 1 and 7 minutes. We found the following: within the common field of view of BBSO and EIT, all 53 identified He II λ304 macrospicules have counterparts in Hα. However, morphologies of He II λ304 and Hα macrospicules are completely different. He II λ304 macrospicules are typically in the form of an elongated ejection, whereas Hα macrospicules are either looplike bright features or much shorter jets. In the polar region, 55 (over 50%) Hα macrospicules do not show any corresponding He II λ304 macrospicules. As expected, He II λ304 macrospicules occur much more frequently in the polar coronal hole area than in the equatorial region. However, Hα macrospicules occur at an equal rate in the pole and in the equatorial limb. Equatorial Hα macrospicules tend to be confined because of their looplike structure and the lack of jetlike structure. Based on common properties of different events, we propose that the disk counterparts of macrospicules might be Hα - 1.0 A jets or a subset of explosive events. If this assumption is true, macrospicules are the results of magnetic reconnections, likely due to the network-ephemeral region or network-intranetwork interactions. We propose that magnetic reconnection occurs at about the same rate in the polar coronal hole and in the quiet regions. Hα macrospicules are direct manifestation of magnetic reconnection. He II λ304 images detect substantially taller structures that are substantially hotter. Because of dominant vertical line configuration near the pole, reconnection tends to produce He II λ304 macrospicules; in the noncoronal hole regions, He II macrospicules become undetectable because of the inclined magnetic field configuration.