HOP list   Monthly Events

HINODE Operation Plan (HOP)

accepted on


 HOP No.

 HOP title

HOP 0141

Velocity flows in quiet sun magnetic loop footpoints

plan term


@ @


 name : Fisher, Keller, de Wijn @  e-mail : c.fischer[at]phys.uu.nl

contact person in HINODE team

 name : Berger @  e-mail : berger[at]lmsal.com

 abstract of observational proposal
In 2007 we obtained quiet sun measurements with the Hinode SOT Spectro-Polarimeter, in Ca IIH with the BFI and Magnesium dopplergrams with the NFI. We analyzed the data and published the statistics we found on convective collapse events, a process that intensifies the magnetic field strength up to 1-2 kG (Fischer et al. 2009).

During the data analysis we discovered velocity flows in closely-spaced, opposite-polarity magnetic flux patches. The velocities are larger than the speeds induced by the granulation flows ( see example shown in Fig. 1). In addition, we observed transverse magnetic field patches between the opposite polarities. We propose to study these transient events in detail and determine if there is a magnetic connection between the opposite-polarity magnetic patches. This would indicate a loop configuration in which the observed magnetic patches are the footpoints of a magnetic loop. It is necessary to study the flows at the chromospheric level, which not only gives further evidence of the connection between the footpoints, but can be compared to speeds obtained by theoretical studies of siphon flows in isolated flux tubes by, e.g., Thomas (1988). Simulations indicate it may be difficult to assign a velocity to the simple hred minus blueh Dopplergram using the Magnesium line images we obtained in the previous observations. Na ID1 appears to be more promising in this regard.

The siphon flow mechanism is a competitor to the previously studied convective collapse, as it also produces strong fields, but has the hadvantageh, that it does not hdrainh the corona of its mass, as a constant mass supply is given by the upflow leg of the loop (Thomas & Montesinos 1990).

 request to SOT
Instrument Observable       Priority Resolution     FOV             Cadence
SOT/NFI    NaD1 dopplergram 1        0.16" ~ 0.16" 12.80" ~ 81.92" 15 s
          NaD1 Stokes I,V  2
SOT/BFI    Ca IIH intensity 2        0.11" ~ 0.11" 19.17" ~ 88.91" 15 s
SOT/SP     Fe I full Stokes 1        0.16" ~ 0.16" 41" ~ 4.8"      58 s

 request to XRT

 request to EIS

 other participating instruments

Observation strategy: We will target the quiet sun at disk center. As we are interested in the flows, pointings away from the center could lead to projection effects and are therefore undesirable. The Spectro-polarimeter will run in dynamics mode with 1.6 s exposure time. For the field of view of 4100 ~ 4.800 this means a cadence of around 58 s. This will give us a high
enough temporal resolution to observe these transient events, which have a duration of
minutes. A dual beam mode is desired as we are searching for weak horizontal magnetic field
signatures to establish the connection between the magnetic foot points. The Narrowband Filter Imager will take simultaneous dopplergrams and magnetograms in Na ID1, and we
will record filtergrams in Ca IIH with the Broadband Filter Imager. The bright points
seen in these filtergrams will be used to compare positions of strong magnetic fields in the
photosphere and the chromosphere.
Due to the experience with the data obtained from our last proposal we suggest observation
runs of minimal 30 minutes duration, as we found about 2 events per 1 hour sequence.
This also means we will require several (we suggest at least 5) repetitions of the program to
increase our chances of following an event from beginning to end within the field of view.
The data volume is estimated at around 722 Mbits for a 1/2 hour run. We will analyze the
data with the IDL routines provided for Hinode data analysis. In addition, we will perform
height-dependent inversions with the LTE inversion code LILIA (Socas-Navarro 2001).
It is important to note that runs with SP dynamics maps and NFI Doppler diagnostics
are rare. This type of high-resolution co-spatial measurements, spanning several hundred
kilometers along the line of sight in the sunfs atmosphere promise to lead to unexpected
additional results.

HOP list   Monthly Events