Variation in the width of transition region network boundaries

Abstract

The transition region network seen in solar extreme ultraviolet (EUV) lines is the extension of the chromospheric network. The network appears as an irregular web-like pattern over the solar surface outside active regions. The average width of transition region network boundaries is obtained from the two-dimensional autocorrelation function of SOlar and Heliospheric Observatory (SOHO)/Coronal Diagnostic Spectrometer (CDS) synoptic images of the Sun in two emission lines, He I 586 Å and O V 630 Å during 1996 – 2012. The width of the network boundaries is found to be roughly correlated with the solar cycle variation with a lag of about ten months. A comparison of the widths in the two emission lines shows that they are larger for the He I line. The SOHO/CDS data also show large asymmetry in boundary widths in the horizontal (x) and vertical (y) image directions, which is shown to be caused by image distortions that are due to instrumental effects. Since the network boundary widths are related to the magnetic flux concentration along the boundaries, the results are expected to have implications on the flux transport on the solar surface, solar cycle, and the mass and energy budget of network loops and jets.