Magnetic and Velocity Field Topology in Active Regions of Descending Phase of Solar Cycle 23
- PDF / 1,841,629 Bytes
- 26 Pages / 439.37 x 666.142 pts Page_size
- 111 Downloads / 211 Views
Magnetic and Velocity Field Topology in Active Regions of Descending Phase of Solar Cycle 23 R.A. Maurya1
· A. Ambastha2
Received: 28 March 2020 / Accepted: 30 June 2020 © Springer Nature B.V. 2020
Abstract We analyze the topology of photospheric magnetic fields and sub-photospheric flows of several active regions (ARs) that are observed during the peak to descending phase of Solar Cycle 23. Our analysis shows clear evidence of hemispheric preferences in all the topological parameters such as the magnetic, current and kinetic helicities, and the ‘curldivergence’. We found that 68%(67%) ARs in the northern (southern) hemisphere with negative (positive) magnetic helicity. Same hemispheric preference sign is found for the current helicity in 68%(68%) ARs. The hemispheric preferences are found to exist statistically for all the time except in a few ARs observed during the peak and the end phases of the solar cycle. This means that magnetic fields are dominantly left(right)-helical in scales smaller than individual ARs of northern(southern) hemisphere. We found that magnetic and current helicity parameters show equatorward propagation similar to the sunspot cycle. The kinetic helicity showed similar hemispheric trend to that of magnetic and current helicity parameters. There are 65%(56%) ARs with negative (positive) kinetic helicity as well as divergence-curl, at the depth of 2.4 Mm, in the northern (southern) hemisphere. The hemispheric preference of the kinetic helicity becomes more evident at larger depths, e.g., 69%(67%) at the depth of 12.6 Mm. A similar hemispheric trend of kinetic helicity to that of the current helicity supports the mean-field dynamo model. We also found that the hemispheric preference of all the parameters increases with the field strength of ARs. The topology of photospheric magnetic fields and near-surface sub-photospheric flow fields did not show good association but the correlation between them enhances with depths, which could be indicating more aligned flows at deeper layers of ARs. Keywords Helioseismology: observations · Helicity: current, magnetic · Active Regions: magnetic fields, velocity field · Solar Cycle: observations
B R.A. Maurya
[email protected]
B A. Ambastha
[email protected]
1
Department of Physics, National Institute of Technology Calicut, Calicut 673601, India
2
Udaipur Solar Observatory, Physical Research Laboratory, Udaipur 313001, India
106
Page 2 of 26
R.A. Maurya, A. Ambastha
1. Introduction Solar active regions (ARs) are three-dimensional magnetic structures extending from the interior below the photosphere to the coronal heights. They consist of magnetic flux tubes that emerge from the convection zone and extend into the solar atmosphere (Hood, Archontis, and MacTaggart, 2011, and the references therein). The solar interior near the photosphere is an excellent conductor where a frozen-in-field condition is valid (Priest, 2014). Over a period of time, near the photosphere, plasma flows may evolve with magnetic fields, and may swirl around them. A
Data Loading...
