HOP 0085

abstract of observational proposal

The main scientific objectives are:

A) Measure electron densities, temperatures and flows in plume-interplume areas using EIS lines. Also, by a combination with SOHO/CDS-NIS2 observations of high-FIP (e.g. Ne) lines study the FIP effect in plumes (EIS observes lines from low- and medium- FIP elements).

B) Use the above measurements to study in detail the quasi-periodic 10-minutes fluctuations at the plume bases, with simultaneous TRACE 171 A high-cadence images.

C) Use the SOT measurements of photospheric magnetic field and TRACE 171 A high-cadence images to see if the formation of plumes can be linked to flux emergence and reconnection.

SCIENTIFIC BACKGROUND:
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Plumes are ray-like structures ubiquitous in coronal holes, in particular during solar minimum. Despite many observations from SOHO and other instruments, the contribution of plumes to the fast solar wind is still a matter of debate. Line-of-sight measurements of line shifts with SOHO/SUMER suggest outflow speeds of the order of 10-20 km/s at the base of the coronal holes (see, e.g. Wilhelm et al 2000), and very small at the base of polar plumes.

Doppler dimming techniques applied to SOHO/SUMER and UVCS spectra taken at larger heights have produced contradictory results (see, e.g. Gabriel et al. 2003, Teriaca et al., 2003), with outflows speeds of the order of 60 km/s attributed to either plume or inter-plume regions by different analyses.

Quasi-periodic 10-minutes fluctuations in intensity have been observed in plumes (cf. DeForest and Gurman 1998) and have been interpreted as slow magnetoacustic waves propagating at 75-150 km/s, however detailed spectroscopic observations have been lacking.

With SOHO/CDS we were able to measure temperatures, densities and chemical abundances near the footpoints (see Del Zanna et al 2003), however the limited resolution of CDS did not allow accurate measurements of flows and densities with high cadence.

The origin of the formation of plumes might be related to magnetic reconnection
processes occurring in the low atmosphere, but SOHO/MDI measurements have precluded conclusive evidence. A combination of Hinode/SOT magnetic field measurements together with high-resolution (TRACE) coronal images is necessary.

NOTE:
A previous campaign during Oct 30 -Nov 3 2007 was run (HOP 44) over the
north polar hole, with SOHO/CDS/UVCS/SUMER, however it turned out that polar plumes were not present.

Indeed, some plumes similar to the so common quiescent during the
previous minimum have only started to appear in June 2008.

Due to operational constraints, the EIS field-of-view could only reach 150" above
the solar limb, while it is now possible to observe at larger heights.

request to EIS

EIS is the primary instrument. EIS observations are required.

Study GDZ_LT_PLUME_160x340_1 (Volume: 51 Mbit, Run time: 58m 37s) will be run to fill data allocation. Further details to be provided.

Run GDZ_LT_PLUME_160x340, a raster covering 160"x344" in 1h (51 Mbits total volume).
The EIS CCD extraction window should be shifted so the EIS FOV covers about 100" on-disc (or more depending on how the coronal hole is extended) and 200" off-limb.

After, run GDZ_LT_PLUME_10x180 with 10 repetitions at each pointing and 5 pointings shifted by 10", to cover an area of 50"x180" at the base of a plume, for a total of 2h 16m, 75 MBits.

Then, repeat GDZ_LT_PLUME_160x340. The whole sequence should last about 4h 16m for a total of 177 MBits.

Run GDZ_LT_PLUME_160x340, a raster covering 160"x344" in 1h (51 Mbits total volume). The EIS CCD extraction window should be shifted so the EIS FOV covers about 100" on-disc (or more depending on how the coronal hole is extended) and 200" off-limb.

After, run GDZ_LT_PLUME_10x180 with 10 repetitions at each pointing and 5 pointings shifted by 10", to cover an area of 50"x180" at the base of a plume, for a total of 2h 16m, 75 MBits.

Then, repeat GDZ_LT_PLUME_160x340. The whole sequence should last about 4h 16m for a total of 177 MBits.

ACRONYM: GDZ_LT_PLUME_10x180
OBJECTIVE: Monitor with a 3m cadence and low telemetry an area of 10'x184", to measure flows and electron densities in a plume located inside coronal holes.
TARGET : Coronal hole region
EXPOSURE TIME : 25s
RASTER : Scanning
SLIT : 2"
STEP_SIZE : 2"
FOV : 10"x184"
SPECTRAL WIND.: 15
DATA COMP. : JPEG90
RASTER DURATON: 2m 21s
DATA volume : 1.49 Mbits
LINES : He II, O V, Si VII, SiX, Ca XVII
Fe VIII X,XI,XII,XIV,XVI, XXIII
POINTING: the base of a plume inside a coronal hole region.
INSTRUCTION TO PLANNERS:
*** shift the EIS CCD extraction window if needed, so as to have SOT and EIS to observe the same on-disc region. Study (duration 2m 44s) must be repeated 10 times following the region (27m - 14.9 Mbits). Then the sequence should be repeated 5 times changing everytime the pointing by 10" (total of 2h 16m, 75 MBits) in order to scan across the base of a plume. It is essential to coordinate with TRACE planners so TRACE 171 A band is observed during the same period of observation.

ACRONYM: GDZ_LT_PLUME_160x340
OBJECTIVE: Measure Te, Ne on-disc and off-limb in a plume-interplume area in a polar coronal hole. The EIS raster covers 160"x340" with low telemetry and is designed to have transition region lines, with a few hotter ones aswell.
TARGET : Coronal hole region
EXPOSURE TIME : 40s
RASTER : Scanning
SLIT : 2"
STEP_SIZE : 2"
FOV : 160"x344"
SPECTRAL WIND.: 16
DATA COMP. : JPEG90
RASTER DURATON: 58m 37s
DATA volume : 51 Mbits
LINES : He II, O V, O VI, Si VII, S VIII, Si X, Ca XVII
Fe VIII X,XI,XII,XIV,XVI, XXIII
POINTING: the pointing should be such as the base of a plume inside a coronal hole region is observed, as well as its extension off-limb.Make sure that the base of the plume is observed by SOT.
INSTRUCTION TO PLANNERS: *** shift the EIS CCD extraction window if needed to adjust the pointing. It is important to coordinate with TRACE planners so TRACE 171 A band is observed during the same period of observation.