Solar cycle variations of the EUV network characteristics from SDO/AIA

Abstract

It is well-known that there is a close relationship between the supergranules, magnetic field and the Extreme-UltraViolet (EUV) network of the solar atmosphere. We have obtained the network characteristics from the imaging data from the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory (SDO) in the lines He II 304 Å and C IV 1600 Å. The changes in the network index and contrast with reference to the sunspot cycle are examined for a duration of about 10 years from 2010 to 2020. The cross correlation between network properties and monthly sunspot number are obtained. For the He II line, the network index and contrast show a negative correlation with the sunspot cycle. This negative correlation is probably related to the anomalous behaviour of the He lines, noticed earlier. The cross correlation of network properties with the sunspot number for the C IV line shows a general positive correlation, which is usually observed in chromospheric and transition region lines. A comparison of the characteristics of the two lines shows that the network index is more than double for the He line while the contrast is almost comparable. These findings can have significance in line emission mechanisms, flux transfer and solar irradiance.