Science JOPs: JOP 014
Title: SOLAR WIND FROM CORONAL HOLES
Lead Person: Ester Antonucci
Authors: E. Antonucci and J. Kohl (UVCS), A. Fludra (CDS), T. Hoeksema (MDI), P. Lemaire (SUMER), R. Howard (Lasco)
SOHO Instruments involved: UVCS, SUMER, CDS, LASCO, EIT, MDI
Collaborating GBO: Possible collaborations: white light coronagraphs (polarization), radio observatories
First proposed: SPWG January 1995
Object: Coronal Holes
SOLAR WIND FROM CORONAL HOLES (JOP 014)
To identify and characterize the coronal sources of the solar wind: Coronal Holes contribution
The primary scientific goals of the observing program are the following:
(See JOP 006)
This observing program is dedicated to coronal holes observed preferably at high latitudes, but not necessarily in polar regions (Jop 002 deals with the physics of polar coronal holes). Although the best seeing conditions are indeed reached for polar coronal holes, being the contribution to the emission along the line of sight from active regions or the quiet sun negligible, in this case the characterization of the base of the coronal hole by means of disk observations is not at all optimum. For non-polar coronal holes this basic information on the boundary conditions of the solar wind can be obtained with accuracy observing the coronal hole on the disc a few days before approaching the limb, when the coronal hole region can be observed in the extended corona with the coronagraphs. The contribution to the emission from active regions adjacent to the coronal hole should not significantly influence the extended corona for large coronal holes during solar minimum.
This program is limited to:
Pointing and Target Selection
It is desirable to begin to observe the target region (coronal hole) a few days before arrival at the limb, in the inner corona, in order to fully characterize the solar wind source. The coronagraphs shall start the joint observation when the target is approaching the west limb, continuing for the period of visibility at the west limb.
The UVCS observations consists of a mirror scan.
Channel I: Ly , Fe XII 1242, N V 1239, S X
1196 (S X 1213) profiles
Channel II: O VI 1032, O VI 1037, Mg X 610, Ly 1026, Si XII 499, Si XII 521, Ly profiles
Channel III: VL polarized 4500--6000 Å.
To determine electron density, proton/ion kinetic temperature, outflow velocity.
Observing Sequence JOP--14
N--Predicted Counts )
CDS primary diagnostic from coronal holes will be determination of temperature and density, and identification of small scale structures within the coronal hole. Several CDS studies have been proposed, for example, TGRAD (temperatures gradient in a coronal hole from Grazing Incidence measurements). Here we describe an observing sequence using Normal Incidence spectra, based on studies CHOLE, CHSTR, BOUND (see the CDS Blue Book). CDS parameters are given below:
Line selection: Fe VIII (370.43), Fe X (365.57), Fe XI (356.54), Fe XII (364.47), Fe XII (338.17), Fe XIII (348.18), Fe XIV (334.17), Fe XVI (335.40), Si IX (349.87), Si IX (341.95), Mg IX (368.06), Mg X (624.94), O III (599.59), Ne VI (562.83), He I (584.33)
Solar Feature Tracking: May be used during prolonged observations if the target is near the disk center
Two different scans will be done: one for disc observation, and another for off-limb observations.
(The C II 1037 line and the N I 1242 lines will be used to measure the scattered light level; they are within the 50 pixels O VI and N V windows)
As in JOP 006.
The LASCO primary observables for coronal hole structures will be to determine electron densities, kinetic temperatures, velocities associated with the hole, structures within the hole and structures at the boundaries of the hole. The observations are from the C1 telescope. The C2 observations to obtain electron densities will be taken as part of the normal LASCO synoptic program.
Telescope: C1 Passbands: Fe X and Fe XIV FOV: 512 x 256 pixels ( 48 x 24 arc min) Wavelengths: 6 + 1 off band Resolution: Full spatial resolution Compression: Rice (lossless) TM Downlink: 21 minutes Cycle Repeat: Once at beginning, middle and end of period
A cycle will require several repeated exposures at each wavelength step with on-board summing to be able to obtain a total exposure time at each wavelength step of about 5 minutes.