The Characteristics of Thin Magnetic Flux Tubes in the Lower Solar Atmosphere Observed by Hinode/SOT in the G band and in Ca ii H Bright Points

Abstract

Photospheric bright points (PBPs) and chromospheric bright points (CBPs) reflect the cross sections of magnetic flux tubes at different heights of the lower solar atmosphere. We aim to study the fine 3D structures and transportation dynamics of the magnetic flux tubes using G-band and simultaneous Ca ii H image-series from the Solar Optical Telescope (SOT) on board Hinode. A 3D track-while-detect method is proposed to detect and track PBPs and CBPs. The mean values of equivalent diameters, maximum intensity contrasts, transverse velocities, motion ranges, motion types, and diffusion indices of PBPs and CBPs are 180 ± 20 and 210 ± 30 km, and , 1.6 ± 0.8 and 2.7 ± 1.4 km s−1, 1.5 ± 0.6 and 1.7 ± 0.8, 0.8 ± 0.2 and 0.6 ± 0.2, and 1.7 ± 0.7 and 1.3 ± 0.7, respectively. Moreover, the ratios of each CBP characteristics to its corresponding PBP are derived to explore the change rates of the flux tubes. The corresponding ratios are 1.2 ± 0.2, 1.2 ± 0.1, 1.9 ± 0.1, 1.4 ± 0.3, 0.7 ± 0.2, and 0.9 ± 0.4, respectively. The statistical results imply that the majority magnetic flux tubes expand slightly with increasing solar height, look brighter than their surroundings, show a higher transverse velocity, a wider motion range, and a more erratic path, but the majority of the flux tubes diffuse slightly slower. The phenomenon might be explained by the conservation of momentum combined with a decrease in density. The more erratic path leads to a swing or twist of the flux tubes and therefore guides magnetohydrodynamic waves.

Magnetohydrodynamic Waves in Multi-Layered Asymmetric Waveguides: Solar Magneto-Seismology Theory and Application

“…The existence of a wealth of magneto-acoustic oscillations within MBPs themselves has also been concluded from highcadence observations performed at different altitudes (Jess et al, 2012). Chromospheric manifestations of bright points have been confirmed to sway around their photospheric counterparts, signaling the presence of kink type oscillations (Xiong et al, 2017).…”

Seismological Determination of the Alfvén Speed and Plasma Beta in Solar Photospheric Bright Points

“…The inclination angle of bright grains in the photospheric network near the solar disk center is found to be lower than 10 • (Sanchez Almeida & Martinez Pillet 1994). The difference of diameters of BPs in the co-aligned G-band and Ca II images is a few tens of kilometer (Kühner et al 2011;Xiong et al 2017), which is much smaller than the difference of the formation heights of these lines. Thus, BPs are modeled as thin vertical magnetic flux tubes of a kG field strength.…”

Spectral Diagnostics of Solar Photospheric Bright Points

“…Based on statistical studies and detailed analysis of individual cases, a series of characteristics of PBPs have been obtained. That is, the diameters of PBPs range from 150 -400 km (Berger et al 1995;Xiong et al 2017;Liu et al 2018); the lifetimes of PBPs are about 200 -1000 s or more (Muller & Keil 1983;de Wijn et al 2005;Jafarzadeh et al 2013;Keys et al 2014;Xiong et al 2017;Liu et al 2018), and the brightness varies from 0.8 to 1.8 times the average background intensity (Mehltretter 1974;Berger et al 1995;Liu et al 2018). PBPs show random-walk characteristics, with an average speed of 0.5 -3 km s −1 (Berger & Title 1996;Nisenson et al 2003;Criscuoli et al 2012;Chitta et al 2012;Keys et al 2014).…”

“…Most of them are filling factor dependent and are derived assuming Local Thermodynamic Equilibrium (LTE) (see Solanki (1993); Steiner (2007) for review). Later on, many authors used G-band images, combined with the broadband Hα and/or Ca II (H, K) imaging observations (Berger et al 1995;Berger & Title 1996;Berger et al 1998;Manso Sainz et al 2011;Chitta et al 2012;Xiong et al 2017), while some authors used the broadband imaging at TiO 7057 Å (Cao et al fangc@nju.edu.cn haoqi@nju.edu.cn 2010; Liu et al 2014Liu et al , 2018 to study PBPs. Recently, owing to the development of adaptive optics and image processing technology, high-spatial resolution observations have been used to explore the characteristics of PBPs in detail.…”

“…Recently, owing to the development of adaptive optics and image processing technology, high-spatial resolution observations have been used to explore the characteristics of PBPs in detail. For example, a 3D track-while-detect (TWD) method was used to detect and track 27,696 PBPs in the images of G-band and Ca II H line from SOT/Hinode (Xiong et al 2017). A new algorithm was also developed to identify and track 2010 PBPs in TiO 7057 Å images observed by the New Vacuum Solar Telescope of the Yunnan Observatory (Liu et al 2018) .…”