Simulation of convective dynamo in solar convection zone: The role of small-scale magnetic fields

When (times in MT)
Wed, Feb 5 2025, 2pm - 1 hour
Event Type
Speaker
Mei Zhang
Affiliation
National Astronomical Observatories, Chinese Academy of Sciences, Beijing, China
Building & Room
CG1-3131

We report the results of a series of numerical simulations of convective dynamos, analysis of which points out the important role of small-scale magnetic fields in highly-nonlinear convective dynamos.

In the first part of the talk we show that in our simulations, with the increase of Reynolds number, the magnitude of current helicity increases dramatically, whereas the variation of kinetic helicity is moderate. The competition between the kinetic helicity term and the current helicity term of the alpha coefficient results in an interesting phenomena of the large-scale magnetic fields that resembles the “dynamo-disappear-and-recover” phenomena reported in Hotta et al. (2016). Our simulation and analysis indicate that the role of current helicity first functions to suppress the dynamo, as the convectional alpha-quenching concept states, but then functions to drive the dynamo, instead of quenching it, after a critical Reynolds number is exceeded.

In the second part of the talk we present the properties of the mean-field coefficients that we extract from our dynamo simulations. Our analysis confirms Pouquet et al.(1976)’s formula and proves that current helicity plays an important and possibly dominate role. Unlike what the convectional alpha-quenching formula predicts, in some regions the alpha coefficient is actually larger during the maximum. In the high Reynolds number case, the beta coefficient in some regions can become negative. All these point out the importance of the magnetic terms in the mean-field coefficients.
 

About the Speaker

Mei Zhang is a senior scientist in the National Astronomical Observatories of the Chinese Academy of Science and a joint professor in the University of the Chinese Academy of Sciences. She obtained her BA from Peking University in 1987, her master and PhD degrees from Beijing Astronomical Observatory of the Chinese Academy of Sciences in 1990 and 1999 respectively. From 2000 to 2004 she worked in HAO, first as a long-term visiting scientist and then as a project scientist. Upon her returning to China to take up a professor position in the National Astronomical Observatory, she becomes an affiliate scientist of HAO since 2004. Her work covers topics on coronal modelling (with BC Low in HAO) and observation, magnetic field measurement and observation, and more recently on solar interior dynamics (with Yuhong Fan in HAO and the topics of today’s talk).