Cyclic behavior of solar inter-network magnetic field

TL;DR

This study uses high-resolution solar spectro-polarimetry data from Hinode to analyze the cyclic behavior of the solar inter-network magnetic field, revealing its invariance over the solar cycle and suggesting a local small-scale dynamo origin.

Contribution

It provides the first detailed analysis of the cyclic variation of the solar inter-network magnetic field using Hinode data, indicating its independence from the solar cycle and active region flux.

Findings

Inter-network magnetic flux density remains constant at about 10 G throughout the solar cycle.

The area ratio of inter-network regions decreases but remains above 60% during solar maximum.

Inter-network magnetic fields are likely generated by a local small-scale dynamo.

Abstract

Solar inter-network magnetic field is the weakest component of solar magnetism, but contributes most of the solar surface magnetic flux. The study on its origin has been constrained by the inadequate tempo-spatial resolution and sensitivity of polarization observations. With dramatic advances in spatial resolution and detective sensitivity, solar spectro-polarimetry provided by the Solar Optical Telescope aboard Hinode in an interval from solar minimum to maximum of cycle 24 opens an unprecedented opportunity to study the cyclic behavior of solar inter-network magnetic field. More than 1000 Hinode magnetograms observed from 2007 January to 2014 August are selected in the study. It has been found that there is a very slight correlation between sunspot number and magnetic field at the inter-network flux spectrum. From solar minimum to maximum of cycle 24, the flux density of solar inter-network field is invariant, which is 10$\pm1$ G. The observations suggest that the inter-network magnetic field does not arise from the flux diffusion or flux recycling of solar active regions, thereby indicating the existence of a locally small-scale dynamo. Combining the full-disk magnetograms observed by SOHO/MDI and SDO/HMI in the same period, we find that the area ratio of the inter-network region to the full-disk of the Sun apparently decreases from solar minimum to maximum but always exceeds 60\% even though in the phase of solar maximum.