The polarity reversal of polar fields is one of the most important observational targets for better understanding of the solar cycle, i.e., details of the dynamo mechanism. One of observational approaches is to track magnetic flux patches as long as possible and determine how each magnetic flux patch behaves in the high latitude region where the polarity reversal may be on going. In the proposer(Iida)'s dissertation (Iida 2012), he developed an auto-patch tracking algorithm and continuously tracked a huge amount of magnetic flux patches (1016.5 - 1019 Mx) in Quiet Sun with very long time (~5 days in new year holiday period) series of FG magnetogram observations. He determined how frequently each of four surface behaviors, i.e., splitting, merging, cancellation and emergence, is observed in Quiet Sun. The same analysis would be useful for the high latitude region where the polarity reversal may be on going. Hinode SOT has never acquired such long period series of observations for the high latitude region and this HOP proposal is to acquire such a unique dataset.
The target region will be an active region remnant rushing to the poles, which induces the polarity reversal at the high latitude. The old-cycle polarity is still dominant in the south pole, but it is expected that the polarity reversal at the south pole will happen within one year. That means that the magnetic behaviors important for the polarity reversal are NOW on-going near the pole-side edge of the active region remnant rushing to the poles.
HOP 81 and HOP 206 have been regularly monitoring the magnetic field at the polar region, but the temporal cadence of SP maps is poor and we cannot investigate how each magnetic patch behave, such as merging and canceling. A long time series of FG magnetograms with a medium cadence will allow us to monitor how they behave. Since a lot of magnetic patches exist on the solar surface, a statistical study with tracing a lot of magnetic patches in high latitude may draw a new insight to the polarity reversal process. The long time series of SDO/HMI magnetograms is also useful for tracking, but it is only for magnetic patches larger than patches resolved with SOT. Magnetic patches experience patch behaviors in the time scale much shorter than 1 hour and a large amount of patch-patch interactions (splitting and canceling) are observed more frequently in smaller magnetic flux elements that can be resolved only with SOT (Iida et al 2012). Thus, high spatial resolution data from SOT has a great advantage over HMI data.
A continuous long-time observation is essential for archiving the purpose. Longer than 2 days. Hopefully 3 days. Also, this April (April 2013, B0 angle still 4-6 deg) would be the last chance for acquiring this kind of unique dataset with Hinode, because the polarity reversal is still on-going at the south pole. North pole in September-October is too late because of its polarity reversal situation. Our proposed observables and their scientific targets are briefly summarized below, but this unique dataset can be used more extensively for other studies.
1. FG magnetogram - Track behaviors of magnetic patches and determine the frequency of, especially, cancellations
2. FG Dopplergram, EUV spectra and images - Where canceled magnetic flux goes? Submerging or upwarding? |
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