Evolution of Subsurface Zonal and Meridional Flows in Solar Cycle 24 from Helioseismological Data. (arXiv:2012.15555v2 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Getling_A/0/1/0/all/0/1">Alexander V. Getling</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kosovichev_A/0/1/0/all/0/1">Alexander G. Kosovichev</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhao_J/0/1/0/all/0/1">Junwei Zhao</a>
The results of determinations of the azimuthal and meridional velocities by
time-distance helioseismology from Helioseismic and Magnetic Imager (HMI)
onboard Solar Dynamics Observatory (SDO) from May 2010 to September 2020 at
latitudes from -60{deg} to +60{deg} and depths to about 19 Mm below the
photosphere are used to analyze spatiotemporal variations of the solar
differential rotation and meridional circulation. The pattern of torsional
oscillations, or latitudinal belts of alternating `fast’ and `slow’ zonal flows
migrating from high latitudes towards the equator, is found to extend in the
time–latitude diagrams over the whole time interval. The oscillation period is
comparable with a doubled solar-activity-cycle and can be described as an
extended solar cycle. The zonal-velocity variations are related to the
solar-activity level, the local-velocity increases corresponding to the
sunspot-number increases and being localized at latitudes where the strongest
magnetic fields are recorded. The dramatic growth of the zonal velocities in
2018 appears to be a precursor of the beginning of activity Cycle 25. The
strong symmetrization of the zonal-velocity field by 2020 can be considered
another precursor. The general pattern of poleward meridional flows is
modulated by latitudinal variations that are similar to the
extended-solar-cycle behavior of the zonal flows. During the activity maximum,
these variations are superposed with a higher harmonic corresponding to
meridional flows converging to the spot-formation latitudes. Our results
indicate that variations of both the zonal and meridional flows exhibit the
extended solar-cycle behavior, which is an intrinsic feature of the solar
dynamo.
The results of determinations of the azimuthal and meridional velocities by
time-distance helioseismology from Helioseismic and Magnetic Imager (HMI)
onboard Solar Dynamics Observatory (SDO) from May 2010 to September 2020 at
latitudes from -60{deg} to +60{deg} and depths to about 19 Mm below the
photosphere are used to analyze spatiotemporal variations of the solar
differential rotation and meridional circulation. The pattern of torsional
oscillations, or latitudinal belts of alternating `fast’ and `slow’ zonal flows
migrating from high latitudes towards the equator, is found to extend in the
time–latitude diagrams over the whole time interval. The oscillation period is
comparable with a doubled solar-activity-cycle and can be described as an
extended solar cycle. The zonal-velocity variations are related to the
solar-activity level, the local-velocity increases corresponding to the
sunspot-number increases and being localized at latitudes where the strongest
magnetic fields are recorded. The dramatic growth of the zonal velocities in
2018 appears to be a precursor of the beginning of activity Cycle 25. The
strong symmetrization of the zonal-velocity field by 2020 can be considered
another precursor. The general pattern of poleward meridional flows is
modulated by latitudinal variations that are similar to the
extended-solar-cycle behavior of the zonal flows. During the activity maximum,
these variations are superposed with a higher harmonic corresponding to
meridional flows converging to the spot-formation latitudes. Our results
indicate that variations of both the zonal and meridional flows exhibit the
extended solar-cycle behavior, which is an intrinsic feature of the solar
dynamo.
http://arxiv.org/icons/sfx.gif
