From what I understand, the rotational progression of the apparent "spinning" of the sun varies based on the location on the sun (equator vs. poles - each taking a different number of days to complete a full rotation - ranging from 27 to 31 days for a full rotation). Of course, the perimeter of the sun (the viewable "exterior") acts a little bit like an atmosphere - versus for example the hard, attached surface of the moon, or for that matter a baseball.
Because the sun is made up of multiple layers and different chemical actions/reactions taking place amongst these layers, combined with gravitational and magnetic factors, I think it is safe to assume that the rotation of the sun at different layers also varies. As the spin or rotation at the core assumes the act of rotation/spin, it's spinning and relating forces are carrying the progressively subsequent outer layers as a result.
Of course, during this process the forces of friction are serving to influence the rotational speed. As we get further away from the core of the sun which is serving to act as the engine of rotation, gravitation pull and friction are acting upon the speed of subsequent layers and distances from the core. The further out from the core, the lesser the gravitational impact created by the core has (simply put). Secondly and especially as the outer most layers are reached, the level of friction fighting against the spin/rotation increase - slowing the spin rate at the outer most (and most easily visible) layers.
It's sort of like watching the fluid in a blender. The closer to the center of the blender, which in the case of the blender is the engine that provides the rotation, the faster the liquid will rotate. As we move further away from the center point, the rotational speed of the liquid is reduced. The outer most point of the blender encounters a lot of friction created by the stationary walls of the blender - this friction results in a slower rotational speed versus the center. The outer most portions of the sun's atmosphere are also exposed to greater amounts of friction - which I postulate, reduces the apparent rotational speed of the sun's visible outermost layer (ie. the surface) versus the rotational speed at and/or closer to the core of the sun.