Transient Coronal Holes as Seen in the Hei1083 nm MLSO Observations

Abstract

Observations from Yohkoh SXT and SOHO EIT have shown that dimming regions often appear on the solar disk near the location of a coronal mass ejection (CME). We now can see brightenings in He I 1083 nm observations made at the Mauna Loa Solar Observatory (MLSO) that form at the same time and are cospatial with the EUV intensity dimmings observed from space. The He I 1083 nm brightenings are induced by a decrease of the overlying coronal radiation. The EUV and X-ray dimmings and He I 1083 nm brightenings can thus be interpreted as different manifestations of the decreased coronal density caused by the ejection of coronal material during the eruption, i.e., as transient coronal holes. In this paper we present examples of transient coronal holes that form during the CME onset as seen in He I 1083 nm data and compare them with simultaneous observations in the Fe XII 19.5 nm line. We find that there is good agreement in both shape and size of the transient coronal holes at these two wavelengths. The 3 minute cadence of the He I 1083 nm observations taken at MLSO is used to determine the appearance and evolution of transient coronal holes with high temporal accuracy. Additional data in the Hα line and in broadband visible light are used to investigate the relation of transient coronal holes to the flare, filament eruption, and CME. The cases presented here illustrate how the higher time cadence of the MLSO observations can complement space data to establish the chronology of the various manifestations of solar activity associated with a CME.