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HINODE Operation Plan (HOP)

accepted on


 HOP No.

 HOP title

HOP 0220

Flows Near Active Region Neutral Lines

plan term


@ @


 name : Martinez Pillet, Harra @  e-mail : vmp[at]iac.es

contact person in HINODE team

 name : Harra @  e-mail : lkh[at]mssl.ucl.ac.uk

 abstract of observational proposal
This proposal concentrates in understanding the slow (several days) evolution that Active Regions (AR) neutral lines undergo during the latest stages of their lifetime. During the decay of an AR, the magnetic flux will spread as a result of the various surface flows giving rise to a disperse field distribution. These ARs often contain a recognizable neutral line and a round leader sunspot. The well-known and persistent cancellation of flux patches observed at the neutral line is often related to the formation through reconnection of an AR filament channel (see, e.g., van Ballegooijen, A. A.; Martens, P. C. H.,  1989, ApJ,  343, 971). This model predicts the existence of large-scale photospheric/chromospheric downflows, indicating field line submergence. At the same time, the filament flux system slowly accumulates shear that can eventually generate a non-equilibrium configuration leading to its eruption (a process dominated by upflows of various speeds near the filament axis). The generation of AR filaments has also been suggested to be due to the bodily rise of a flux rope structure from below the bottom of the photosphere (Okamoto, et al., 2009, ApJ, 697, 913). In such a case, the flows at the AR neutral line should be dominated by a slow constant rise that should be detected as persistent upflows at all heights. In any event, the flows and magnetic fields observed near AR neutral lines are a crucial aspect of the latest stages of the evolution of an AR, including the processes that lead to the fast removal of most of their flux from the photosphere.

Understanding these late stages of the lifetime of an AR are important for key solar processes such as the solar dynamo. They will reveal important clues on how much restoration of the original toroidal flux tubes that originated the AR really occurs as well as what are the processes that actually allow AR flux to disappear from the solar surface.

For these reasons, this HOP concentrates into observing AR neutral lines with an emphasis on the magnetic and flow fields at all heights from the Photosphere to the Corona. We thus require Hinode/SP data with scans of the neutral line and simultaneous co-spatial EIS scans in the wavelength range including the HeII 257 A region. This line is sufficiently cool to give clear traces of the filament material and their flows. We emphasize here that the HOP concentrates not on transient activity observed at the neutral line, but on the slow evolution observed in these filaments at time scales of days. Thus, the emphasis is not on the fast acquisition of raster scans of the selected neutral line, but on having a few (4-5) scans per day during the disk passage of the AR at various heliocentric distances (between +/-60 degrees longitude).

 request to SOT
Request to SP:

Stokes parameters with scans centered near the AR neutral line. Default SP mode is sufficient (S/N 1000, slit scan steps of 0.3 arcsec)

3-5 raster scans every day of the neutral line region covering  approximately 40 arcsec, centred on the neutral line

Request to to BFI:

Context Ca II images during the raster scans (cadence 1 every minute, not compromising SP or EIS telemetry)

 request to XRT

 request to EIS
Similar scans as SP.

Use study 454, GDZ_300x384_S2S3_40s


The pointing should ensure that EIS covers the neutral line and can measure the flows on either side of the neutral line.  

 other participating instruments


Target selection is crucial to the success of this HOP. An AR in its late evolution phases is needed as it crosses the visible Sun. An existing AR must be identified with Stereo B and later a neutral line must be also identified. Typically the AR will have a round leader sunspot and to its left a compact neutral line composed of faculae and pores. This should then be treated as a TOO and we will contact the teams when we see a suitable target.

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