Empirical Mode Decomposition studies of quasi-biennial variations in helioseismic frequencies
Main category
Natural Sciences (Astrophysics and Astrononmy)
It is well-known that the Sun’s magnetic activity varies primarily on a time scale of 11yrs. It is also well known that the frequencies of the Sun’s natural acoustic oscillations vary in-phase with surface and atmospheric measures the Sun’s activity. Additionally, both atmospheric activity proxies and helioseimic frequencies exhibit variations on timescales much shorter than 11yrs, including the ‘quasi-biennial’ periodicity. Solar periodicities, including the 11yr cycle, are hard to characterise, as they vary in both length and amplitude. We have used empirical mode decomposition techniques to separate time variations in acoustic mode frequencies, the 10.7cm flux and sunspot areas into a set of intrinsic modes. We then use the Huang-Hilbert transform to characterise the periodicities of these intrinsic modes. The periodicities obtained are consistent between the different activity proxies, including the quasi-biennial periodicity. This indicates that the quasi-biennial behaviour observed at the solar surface and in the solar atmosphere is also symptomatic of the solar interior.
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