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Solar Kinetic Energy and Cross Helicity Spectra
Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Colorado, USA.ORCID iD: 0000-0002-7304-021X
Number of Authors: 22018 (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
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:su:diva-159002DOI: 10.3847/2041-8213/aad337ISI: 000440583700003OAI: oai:DiVA.org:su-159002DiVA, id: diva2:1246780
Available from: 2018-09-10 Created: 2018-09-10 Last updated: 2018-09-10Bibliographically approved

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