HOP 0465

abstract of observational proposal

Main Objective: Observing magnetic field in the same region at disk center and limb to explore how much the magnetic field at limb is underestimated compared with at disk center.

Scientific Justification: Linker et al. (2017) and Wallace et al. (2019) argue that the open flux extrapolated from the solar photosphere underestimates the interplanetary magnetic field observed near Earth by a factor of three. One of the possible causes of this problem is the underestimation of the polar photospheric magnetic field, and Riley et al. (2019) suggested that additional polar flux can at least partially resolve the problem. Observing solar polar region is difficult because the measurement of the transversal magnetic field component is an order of magnitude less sensitive than that of the line-of-sight (Petrie, 2022). It is necessary to quantitatively analyze how much polar observations can be underestimated.

In this observation, I explore quantitatively the difference of the magnetic-field measurements between at the disk center and the limb using SOT/SP, which has the ability to accurately measure magnetic field. The same region will be observed at the limb about five days after the observation at disk center because of the solar rotation. The target regions are unipolar with coronal holes developed in mid-low latitudes regions. This configuration is same as polar region and the limb can be substituted for the polar region. This observation can be expected to investigate how much the magnetic field strength varies depending on where it is observed from. This study is for Yoshida’s Ph.D. thisis.

request to SOT

Disk center:
SP FOV 320” x 164”, Pixel size: 0.32”/pix, Binning: 2x2, Single side mode
Exposure: 4.8 sec (6 Cycles). JPEG Quality: Q75, Data rate: 600 Mbits/Map
Limb:
SP FOV 320” x 164”, Pixel size: 0.32”/pix, Binning: 2x2, Single side mode
Exposure: 4.8 sec (6 Cycles). JPEG Quality: Q75, Data rate: 600 Mbits/Map

request to EIS

No request, but if spectral data is available for coronal hole observations, we can measure temperature, density and flow speeds and we might expand our photospheric studies to studies at upper layers, such as the source of solar winds and connectivity to the heliosphere.

Study 000582:
ACRONYM: HOP81_new_study
This is the same study that is used for HOP 81. It performs a large scan of the polar region in coordination with SOT/SP measurements of the magnetic field.
TARGET : Coronal hole
EXPOSURE TIME : 50s
RASTER : Scanning
SLIT : 2" (was 1")
STEP_SIZE : 4" (was 1")
FOV : 322"x384"
SPECTRAL WIND.: 24 (was 12)
DATA COMP. : DCPM
RASTER DURATON: 1h14m
DATA VOLUME : 140 Mbits (was 150 Mbits)
LINES : Fe VIII, Fe X, Fe XI, Fe XII, Fe XIII,
He II, O V, Mg VI, Mg VII, Si VII, Si X
Fe IX, Fe XIV, Fe XV, Fe XVI, S X, Ar XI
POINTING:
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Polar coronal hole with fixed pointing.
Make sure to cover SOT FOV and the solar limb.

INSTRUCTION TO PLANNERS:
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Start this study at the beginning of the SAA free period (roughly 10-15UT). Repeat the study several times avoiding Hinode eclipses. The later part may coincide with a short SAA.
Note: The plan for FSM is the same as that for DSM.

WARNING:
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Avoid SAAs as much as possible (SAA degrades data compression factors and mutilates the data)

remarks

Dates: One observation, followed by another observation about 5 days later.
ToO. The proposer will notify when suitable regions come.

Time window:

Target(s) of interest: This is a target of opportunity. Observe by SOT/SP when there is a coronal hole or unipolar region at disk center, and then observe at
west limb after five days. Or observe by SOT/SP at east limb if there is a coronal hole or unipolar region, and then observe at disk center after five days.

Previous HOPs: None