Goal ----
Follow the evolution of magnetic flux in the quiet Sun, to determine the time scales for network and internetwork flux replacement by ephemeral regions and small-scale emerging fields, respectively. This study requires continuous, uninterrupted observations for about 2 days, to track the evolution of the same supergranular cells from birth to death. The study also requires very high signal-to-noise ratios, to detect the weakest signals of the internetwork.
Motivation ----------
Using MDI measurements, the time needed by ephemeral regions to replace the total flux of the network has been estimated to be 40-70 h (Schrijver et al. 1997), 8-19 h (Hagenaar et al. 2003), or even 1-2 h according to the most recent studies (Hagenaar et al. 2008). A time scale of only 1-2 h implies an enormous amount of magnetic flux being brought to the solar surface by ephemeral regions, and a very effective way of flux removal, presumably through flux cancellations. However, little is known about these important processes because (a) all the studies are based on MDI data, with moderate angular resolution and cadences on the order of hours, and (b) there exist very few continuous time sequences of the quiet Sun lasting for 2-3 days, which is the minimum duration needed to observe at least one full lifetime of network cells. The situation is even worse for the internetwork. Indeed, the long-term evolution of internetwork fields is essentially unkwown, as no observations have ever been carried out to address this issue, neither with Hinode nor with other facilities.
We propose to determine the flux emergence and cancellation rates in the network and internetwork with unprecedented accuracy, to study how these processes contribute to the total flux budget of the quiet Sun. The required measurements will push Hinode's capabilities to a limit in terms of sensitivity, cadence, and time coverage. This program demands a significant amount of telemetry and ideally no interruptions, but because of their unique character we anticipate that the measurements will be of interest to many researchers in the field. Also, the questions they address are so fundamental that it seems reasonable to devote all the resources of Hinode for about two days to acquire a unique data set. |
|