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HINODE Operation Plan (HOP)

accepted on


 HOP No.

 HOP title

HOP 0179

Relationship between small-scale magnetic fields and convection

plan term


@ @


 name : Ishikawa, Tsuneta @  e-mail : ryoko.ishikawa[at]nao.ac.jp

contact person in HINODE team

 name : Sekii @  e-mail : sekii[at]solar.mtk.nao.ac.jp

 abstract of observational proposal
Ishikawa and Tsuneta (2010) found that the 2hr-summed linear polarization map shows a very clear cellular structure with a typical scale of 5-10" and that the cellular structure coincides in position with the negative divergence of the horizontal flow field, i.e., mesogranular boundaries with downflows. These results (unexpectedly!) indicate that mesogranular flows play an important role on the generation and distributions of the photospheric magnetic fields.

In this study, I will clarify the role of large-scale convection namely mesogranulation and supergranulation on the generation, organization, and maintenance of the small-scale photospheric magnetic fields (Transient Horizontal Magnetic Fields). The lifetime of the mesogranules ranges from 30 min to 6 hrs depending on studies (e.g., Roudier et al. 1998 and Shine et al. 2000), while those of supergranular flow patterns are ~20 hrs. In order to see the temporal evolution of such larger scale convection pattern with longer turn-over time, the observation of the vector velocity fields with much longer than mesogranular and supergranular lifetimes is ideally required. I stress that such a long duration observation with no or minimum interruption is needed to obtain  high quality data that allows to address the fundamental question raisedin this HOP proposal. I will compare the temporal evolution and distribution of small-scale magnetic fields with that of mesograules and supergranules.

Second important topic in this study is to find a potential influence ofglobal magnetic fields on the small-scale magnetic fields. It is pointed out that non-negligible amount of toroidal flux tubes buoyantly rising through the bulk of convection zone fail to emerge to the surface (e.g., Magara (2001)). Such magnetic fields accumulated in the photosphere might be a source of small-scale magnetic fields. At the same time, we now know that the histograms of the intrinsic magnetic field strengths are exactly the same in the polar region, the quiet sun, and a weak plage region (Ito et al. 2010 and Ishikawa and Tsuneta 2009). But, this is almost a snapshot data in spatial and time domain, and moreobservations with Hinode are apparently desired.

I, therefore, would like to perform the continuous observation with 24 hrs (at least 20 hrs) at disk center and in the active region belt at the meridian. By summing magnetograms obtained for 24 hrs, ultra high S/N will be achieved, and such deep exposure magnetograms in different regions would allow us to explore the hidden global magnetic field with much weaker field strength, if any.

Please note that 20 hrs is comparable to the lifetime of supergranules. I may request second run with longer duration after analyzing the data set to be taken this time.

 request to SOT
5250 Sh-less IQUV at blue and red wing, FOV 51"x82", 1 min cadence.
Data volume: 208Mbits/1H => ~5G for 24 hrs.

Note: Before the observation, please run 5250 wavelength scan to find the suitable wavelength offsets.

 request to XRT

 request to EIS

 other participating instruments

Observation target:
1. Quiet Sun at the disk center
  Set the pointing of (0",0") at the middle of observation.
2. Quiet Sun at the meridian in the active region belt
  Set the pointing of EW=0" at the middle of observation.

Observation duration:
Continuous observation for 24 hrs (at least 20 hrs).

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