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Solar Kinetic Energy and Cross Helicity Spectra
Chinese Acad Sci, Key Lab Solar Act, Natl Astron Observ, Beijing 100012, Peoples R China..
KTH, Centres, Nordic Institute for Theoretical Physics NORDITA. Stockholm Univ, Roslagstullsbacken 23, SE-10691 Stockholm, Sweden.;Univ Colorado, JILA, Boulder, CO 80303 USA.;Univ Colorado, Dept Astrophys & Planetary Sci, Boulder, CO 80303 USA.;Stockholm Univ, AlbaNova Univ Ctr, Dept Astron, SE-10691 Stockholm, Sweden.;Univ Colorado, Lab Atmospher & Space Phys, Boulder, CO 80303 USA..ORCID iD: 0000-0002-7304-021X
2018 (English)In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 862, no 2, article id L17Article in journal (Refereed) Published
Abstract [en]

We develop a formalism that treats the calculation of solar kinetic energy and cross helicity spectra in an equal manner to that of magnetic energy and helicity spectra. The magnetic helicity spectrum is shown to be equal to the vertical part of the current helicity spectrum divided by the square of the wavenumber. For the cross helicity, we apply the recently developed two-scale approach globally over an entire active region to account for the sign change between the two polarities. Using vector magnetograms and Dopplergrams of NOAA. 11158 and 12266, we show that kinetic and magnetic energy spectra have similar slopes at intermediate wavenumbers, where the contribution from the granulation velocity has been removed. At wavenumbers around 0.3 Mm(-1), the magnetic helicity is found to be close to its maximal value. The cross helicity spectra are found to be within about 10% of the maximum possible value. Using the two-scale method for NOAA. 12266, the global cross helicity spectrum is found to be particularly steep, similarly to what has previously been found in theoretical models of spot generation. In the quiet Sun, by comparison, the cross helicity spectrum is found to be small.

Place, publisher, year, edition, pages
Institute of Physics Publishing (IOPP), 2018. Vol. 862, no 2, article id L17
Keywords [en]
dynamo, Sun: activity, Sun: magnetic fields, Sun: photosphere
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-233286DOI: 10.3847/2041-8213/aad337ISI: 000440583700003Scopus ID: 2-s2.0-85051504860OAI: oai:DiVA.org:kth-233286DiVA, id: diva2:1240353
Note

QC 20180821

Available from: 2018-08-21 Created: 2018-08-21 Last updated: 2018-10-16Bibliographically approved

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