NDLI: Periodic Appearance of Coronal Holes and the Related Variation of Solar Wind Parameters

Content Provider	Springer Nature Link
Author	Temmer, Manuela Vršnak, Bojan Veronig, Astrid M.
Copyright Year	2007
Abstract	We compared the variability of coronal hole (CH) areas (determined from daily GOES/SXI images) with solar wind (daily ACE data) and geomagnetic parameters for the time span 25 January 2005 until 11 September 2005 (late declining phase of solar cycle 23). Applying wavelet spectral analysis, a clear 9-day period is found in the CH time series. The GOES/SXI image sequence suggests that this periodic variation is caused by a mutual triangular distribution of CHs ∼120° apart in longitude. From solar wind parameters a 9-day periodicity was obtained as well, simultaneously with the 9-day period in the CH area time series. These findings provide strong evidence that the 9-day period in solar wind parameters, showing up as higher harmonic of the solar rotation frequency, is caused by the “periodic” longitudinal distribution of CHs on the Sun recurring for several solar rotations. The shape of the wavelet spectrum from the Dst index matches only weakly with that from the CH areas and is more similar to the wavelet spectrum of the solar wind magnetic field magnitude. The distinct 9-day period does not show up in sunspot group areas which gives further evidence that the solar wind modulation is strongly related to CH areas but not to active region complexes. The wavelet power spectra for the whole ACE data range (∼1998 – 2006) suggest that the 9-day period is not a singular phenomenon occurring only during a specific time range close to solar minimum but is occasionally also present during the maximum and decay phase of solar cycle 23. The main periods correspond to the solar rotation (27$^{d}$) as well as to the second (13.5$^{d}$) and third (9$^{d}$) harmonic.
Starting Page	371
Ending Page	383
Page Count	13
File Format	PDF
ISSN	00380938
Journal	Solar Physics
Volume Number	241
Issue Number	2
e-ISSN	1573093X
Language	English
Publisher	Kluwer Academic Publishers
Publisher Date	2007-03-30
Publisher Place	Dordrecht
Access Restriction	One Nation One Subscription (ONOS)
Subject Keyword	Coronal holes Solar wind Space weather Astronomy Extraterrestrial Physics, Space Sciences Astrophysics
Content Type	Text
Resource Type	Article
Subject	Astronomy and Astrophysics Space and Planetary Science

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