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Much of coronal hole (CH) research is focused upon determining the boundaryand calculating the open flux as accurately as possible. However, the observedboundary itself is worthy of investigation, and holds important clues to thephysics transpiring at the interface between the open and closed fields. ThisLetter reports a powerful new method, an application of the correlationintegral which we call correlation dimension mapping (CDM), by which theirregularity of a CH boundary can be objectively quantified. This methodhighlights the most important spatial scales involved in boundary dynamics, andalso allows for easy temporal analysis of the boundary. We apply this method toan equatorial CH bounded on two sides by helmet streamers and on the third by asmall pseudostreamer, which we observed at maximum cadence for an hour on 2015June 4. We argue that the relevant spatial scales are in the range of $\sim5-20$ Mm, and we find that boundary complexity depends measurably upon thenature of the neighboring closed structure. The boundary along thepseudostreamer shows signs of highly-localized, intermittent complexityvariability, likely associated with abrupt changes in the magnetic topology,which would be elegantly explained by interchange reconnection. By contrast,the helmet streamer boundary supports long-lived high-complexity regions. Thesefindings support the recent predictions of interchange reconnection occurringat very small scales in the corona.

Statistical Evidence for Small-Scale Interchange Reconnection at a Coronal Hole Boundary