Three-phase Evolution of a Coronal Hole. I. 360° Remote Sensing and In Situ Observations

Stephan G. Heinemann*, Manuela Temmer, Stefan J. Hofmeister, Astrid M. Veronig, Susanne Vennerstrøm

*Corresponding author for this work

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    Abstract

    We investigate the evolution of a well-observed, long-lived, low-latitude coronal hole (CH) over 10 solar rotations in the year 2012. By combining extreme ultraviolet (EUV) imagery from the Solar TErrestrial RElations Observatories (STEREO-A/B) and the Solar Dynamics Observatory (SDO), we are able to track and study the entire evolution of the CH having a continuous 360° coverage of the Sun. The remote sensing data are investigated together with in situ solar wind plasma and magnetic field measurements from STEREO-A/B, the Advanced Composition Explorer (ACE), and WIND. From this, we obtain how different evolutionary states of the CH as observed in the solar atmosphere (changes in EUV intensity and area) affect the properties of the associated high-speed stream measured at 1 au. Most distinctly pronounced for the CH area, three development phases are derived: (a) growing, (b) maximum, and (c) decaying phase. During these phases the CH area (a) increases over a duration of around three months from about 1 · 1010 km2 to 6 · 1010 km2, (b) keeps a rather constant area for about one month of >9 · 1010 km2, and (c) finally decreases in the following three months below 1 · 1010 km2 until the CH cannot be identified anymore. The three phases manifest themselves also in the EUV intensity and in in situ measured solar wind proton bulk velocity. Interestingly, the three phases are related to a different range in solar wind speed variations, and we find for the growing phase a range of 460–600 km s−1, for the maximum phase 600–720 km s−1, and for the decaying phase a more irregular behavior connected to slow and fast solar wind speeds of 350–550 km s−1.
    Original languageEnglish
    Article number151
    JournalAstrophysical Journal
    Volume861
    Issue number2
    Number of pages12
    ISSN0004-637X
    DOIs
    Publication statusPublished - 2018

    Keywords

    • Solar wind
    • Sun: corona
    • Sun: heliosphere
    • Sun: UV radiation

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