I assume we are looking for a sun like this:
SH3:

or
SH4:
But as far as I've investigated in the directory and codes, SH5 does not use normal textures (*.tga, *.dds) for the Sun_Halo effect. The sun disk is hardcoded and receives from the config files only parameters for the color, size and multiplyers, not more. The rest of the visual sun effect, the HDR light and solar radiation are calculated by the new sky shaders.