Title: Connection between the magnetic canopy and chromospheric/lower
transition region dynamics

Short title: Canopy dynamics with SUMER & VTT

Author: Anna Pietarila

Participating SOHO instruments, and other observatories: SUMER, MDI, VTT

Scientific Objective and Justification:

The He I 1083.0 nm line is a powerful diagnostic for studying chromospheric
magnetic fields: it is sensitive to both Zeeman and Hanle
effects. Furthermore, existing inversion codes are able to take advantage
of both phenomena making detection and characterization of weak nearly
horizontal magnetic fields (i.e. the canopy) possible. A connection between
the canopy and dynamics is clearly seen in data (e.g. magnetic shadows,
McIntosh & Judge 2001, Cauzzi et al 2008). So far, however, observations of
this connection have either no real chromospheric magnetic field
information or the observations have been purely lower/mid-chromospheric
without coverage of higher parts of the atmosphere. By combining deep
raster scans of He I 10830 with SUMER time series data of the He I 58.4 nm,
O I 115.2 nm and C III 117.5 nm lines we will have measurements of the
chromospheric magnetic field (and thus do not need to rely on extrapolation
methods to find the canopy) combined with information about the dynamics in
the chromosphere and lower TR.

The choice of lines for SUMER, He I 58.4 nm, O I 115.2 nm and C III 117.5
nm, covers the upper chromosphere and lower TR. The O I 115.2 nm line shows
oscillations in both velocity and intensity, whereas the He I 58.4 nm
mainly exhibits velocity oscillations and the C III 117.5 nm line displays
explosive events. Furthermore, the He I 58.4 nm line exhibits some
interesting behavior (e.g. intensity enhancement (Jordan 1975), reduced
network/internetwork contrast (Macpherson & Jordan 1999)) and is unlike
other chromospheric and TR lines. Judge & Pietarila (2004) suggested that
the explanation for some of the peculiarities may be connected to the
magnetic field. Therefore, direct measurement of the chromospheric field
will be useful in trying to understand the He I 58.4 nm line behavior.


Observing sequences:

SOHO:

SUMER (He I 58.4 nm (2nd order), O I 115.2 nm, C III 117.5 nm)

1) raster scan: He I 58.4 nm, 300" slit, 2" step, 60 steps, 20 s exposure
2) sit and stare: He I 58.4 nm, O I 115.2 nm and C III 117.5 nm, 120" slit,
   20s exposure, 240 repetitions, three 50 pixel windows

MDI HR, horizontal strip. Used mainly for coalignment, no need for high
temporal cadence

VTT: TIP2 He 1083.0 nm (deep rasters w/ full Stokes vector), possibly
Gottingen FPI (H-alpha w/ wavelength points in the wings and core, Stokes I
only).

Target: disk center (QS network/active network/plage)

Date: during the SUMER April 2009 campaign.