The twist of magnetic field lines, or magnetic helicity, is a physical property of the field that plays a crucial role in many aspects of solar activity, including the stability of magnetic flux against disruption as it rises buoyantly through the solar convection zone, the basis for supporting and thermally isolating the dense, cool material of filaments/prominences within the hot and tenuous corona, and the initiation of coronal mass ejections (CMEs). Prominences/filaments are intimately linked to the CME process, so understanding their magnetic field structure and how helical magnetic flux arises is a key issue for solar physics.
Few reliable measurements exist for magnetic fields in filaments, yet such measurements are essential to understand the structure and evolution of the filaments and the related magnetic structures such as filament channels and the overlying coronal cavity. In recent times significant progress has been made toward understanding the structure of the field in the photosphere below active region filaments (Lites 2005, Okamoto et al. 2008, 2009, Lites et al. 2010), largely because of access to the consistently high angular resolution spectro-polarimetric measurements afforded by Hinode. However, the status of observations of the field within the filament structure itself is not nearly as well-defined. Most of the observations to date have employed the Hanle effect
for prominences above the limb. Due to line-of-sight integration and lack of spatial resolution, these measurements have afforded only limited information regarding the field vector within the filament/prominences.
This proposal aims to establish an observational picture of the magnetic field vector within and under active region filaments. Active region filaments are particularly interesting because the fields are strong enough, and the filament structures are generally low enough in the solar atmosphere, that traditional Zeeman effect measurements of the field in the photosphere consistently show signatures characteristic of the magnetic structure of the filament at that level.
It is now appropriate to attempt similar measurements of the photosphere below filaments coupled with simultaneous measurements of the filament structure at chromospheric temperatures and densities. The latter measurements of filaments on the disk are made possible by significant advances within the past few years toward interpretation of polarization measurements in chromospheric lines sensitive to both the Hanle and Zeeman effects If such measurements can be obtained with good spatial resolution, and then coupled to the proven measurements of the vector field in the photosphere below the filament, we hope to develop a glimpse of the actual 3-dimensional structure of the entire filament magnetic field system.
The proposed Hinode observations would be carried out during the 3-hour period 09 - 12UT. Hinode observations will follow closely the “standard” Case 1 mode of HOP 0139 similar to that run on 05 November 2009 (FG program 0x360, SP program 0xb2). The observations needed to carry out this study include: