Coronal Disturbances and Their Terrestrial Effects

Origin and development of transient coronal holes

“…The term transient coronal hole (TCH) was introduced by Rust [1983] to describe voids in Skylab Xray images that occurred within 0.2 R© of Ha filament eruptions associated with long-decay X-ray enhancements (LDEs). In 11 of 21 candidate events, Rust found voids that "were as dark as nearby 'permanent' coronal holes" (p. 31).…”

“…The search for TCHs was motivated by the idea that transient high-speed wind flows following coronal mass ejections (CMEs) could come from the same kind of open magnetic structure that gives rise to long-lived high-speed wind streams at I AU. The short (<48 hours) lifetimes of the Skylab TCHs further suggested [Rust, 1983] ten it may not be appropriate to equate such dimming regions with TCHs. We will adhere to a stricter TCH definition that the TCH be easily observed in direct SXT images, rather than in a difference image.…”

“…Only a limited number of TCHs have been discussed in the references cited above, but the basic interpretation of Rust [1983] electron heat fluxes to determine the connectivity of the magnetic clouds to their solar footpoints. Some clouds were completely disconnected from one footpoint, others were completely connected to both footpoints, and the periods of complete connection were randomly distributed throughout the clouds.…”

X‐ray coronal changes during Halo CMEs

“…Hudson have recently summarized our current state of knowledge, pointing out a variety of signatures for mass loss revealed by the X-ray images. These signatures often take the form of X-ray dimming related to the formation of voids in the visible corona [Hansen et al 1974] and to "transient coronal holes" as noted from the soft X-ray observations from Skylab [Rust 1983]. …”

The Solar Sources of Geoeffective Structures

“…Such "dimming regions", best ob served in X-ray and EUV images, imply that material is evacuated from the low corona. Transient dimmings in soft X-rays observed during Skylab were called "tran sient coronal holes" by Rust [1983]. The images ob tained by the Yohkoh Soft X-ray Telescope (SXT) now reveal areas of subtle dimming, or depletion above or near brightening X-ray arcades.…”