Identification of emission sources of umbral flashes using phase congruency

Abstract

The emission sources of umbral flashes (UFs) are believed to be closely related to running umbral and penumbral waves, and are concluded to be associated with umbral dots in the solar photosphere. Accurate identification of emission sources of UFs is crucial for investigating these physical phenomena and their inherent relationships. A relatively novel model of shape perception, namely phase congruency (PC), uses phase information in the Fourier domain to identify the geometrical shape of the region of interest in different intensity levels, rather than intensity or gradient. Previous studies indicate that the model is suitable for identifying features with low contrast and low luminance. In the present paper, we applied the PC model to identify the emission sources of UFs and to locate their positions. For illustrating the high performance of our proposed method, two time sequences of Ca II H images derived from the Hinode/SOT on 2010 August 10 and 2013 August 20 were used. Furthermore, we also compared these results with the analysis results that are identified by the traditional/classical identification methods, including the gray-scale adjusted technique and the running difference technique. The result of our analysis demonstrates that our proposed method is more accurate and effective than the traditional identification methods when applied to identifying the emission sources of UFs and to locating their positions.

High-frequency Oscillations in the Atmosphere above a Sunspot Umbra

“…The magnetic field orientation is different in the umbra from that in the penumbra; however, the propagation of slow magnetoacoustic waves is anisotropic to the orientation of magnetic fields. So, different types of magnetohydrodynamic waves are displayed inside and above sunspots at different solar atmospheric layers, such as oscillations above light bridges (Li et al 2013;Sobotka et al 2013;Yuan et al 2014;Bharti 2015;Su et al 2016;Yuan & Walsh 2016), umbral flashes (Feng et al 2014), penumbral running waves (Christopoulou et al 2000;Jess et al 2013;Löhner-Böttcher & Bello González 2015) and coronal fan structures (Yuan et al 2011;Jess et al 2012;Tian et al 2016). Slow magnetoacoustic waves are assumed to result from the interaction between the photospheric p-modes and magnetic fields, and can propagate upward along magnetic field lines, and finally reach coronal heights (Jess et al 2012(Jess et al , 2016Krishna Prasad et al 2015, 2017Yan et al 2008).…”

Identification and morphology analysis of granules using the New Vacuum Solar Telephone Observations

“…Morrone等人 [15] 8 to illustrate the comparsion test of the other identified method Kovesi [16,17] 对这一理论进行了发展, 他不但证明了相 位一致性在表征特征结构时对强度、对比度、照度具 有不变性, 而且通过计算图像的局部能量实现了对 相位一致性特征的稳定提取. 目前, 相位一致性技术 已经被用于识别和提取低对比度太阳图像特征, 如 本影点、本影闪耀, 以及冕环 [18,19] . 本文利用相位一 致性来识别米粒的特征结构.…”

Doppler shift oscillations of a sunspot detected by CYRA and IRIS

“…It is still very difficult to observe the intensity fluctuations at photospheric sunspots since their amplitudes are very small (Beckers & Schultz 1972;Bellot Rubio et al 2000). Although some authors have detected the very weak intensity fluctuations in G-band, TiO, or visible continuous images (Nagashima et al 2007;Yuan et al 2014;Su et al 2016), in the chromosphere the intensity oscillations of sunspots are called "umbral flashes", which are often accompanied by the up and down motions with periods of about 2−3 min (Wittmann 1969;Phillis 1975;Rouppe van der Voort et al 2003;Feng et al 2014).…”