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Science JOPs: JOP 006


Lead Person: Ester Antonucci

Authors: E. Antonucci and J. Kohl (UVCS), P. Lemaire (SUMER), R. Harrison (CDS), T. Hoeksema (MDI), R. Howard (Lasco)

SOHO Instruments involved: UVCS, SUMER, CDS, LASCO, EIT, MDI

Collaborating GBO: Possible collaborations: white light coronagraphs (polarization), radio observatories

Collaborating S/C: Yohkoh

Campaign: yes

First proposed: SPWG June 1994

Object: Active Regions


To identify and characterize the coronal sources of the solar wind: Active Regions role

Scientific Case
The primary scientific goals of the observing program are the following:

The first goal of the investigation is to identify definitively the sources of non-transient high speed wind and of low speed wind, and to characterize the physical conditions of the different sources of solar wind at the base of the corona, as well as their evolution throughout the corona up to a few solar radii. The recent Ulysses data on solar wind are clearly showing a strong variation of the wind properties as a function of latitude, as expected, and a peculiar wind speed behavior above the streamer belt. Active regions have been recently proposed as possible sources of wind by Uchida et al. (1992) on the basis of the observations of the Soft X-ray Telescope on Yohkoh which suggest a continuous expansion of the coronal loops with a non negligible mass and magnetic field contribution to the wind. It is therefore crucial to obtain a detailed description of the physical conditions of the wind and its boundary conditions at the solar surface in correspondence to high-latitude sources such as coronal holes, to streamers at middle latitude and their interface region with the surrounding atmosphere, to the quiet sun and to active regions. In this specific observing program we limit our investigation to active regions as possible sources of solar wind.

The second goal consists in using the physical parameters of the solar wind region and its boundary at the solar surface to identify the dominant acceleration mechanisms, for example to determine the roles of thermal pressure gradients (Parker type wind), wave-particle interactions, and non-thermal electrons in accelerating the solar wind in the different regions. We also aim to distinguish between the effects of waves that damp in the lower corona (acoustic waves, fast mode MHD waves) and waves that survive to heat and accelerate the solar wind beyond the critical point.

This program is limited to:


Pointing and Target Selection

It is desirable to begin to observe the target region (active region) a few days before arrival at the limb, in the inner corona, to fully characterize the potential solar wind sources. 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-06

Corona above Active Region
N--Predicted Counts )




MDI will contribute its standard set of full disk 4" resolution photospheric magnetograms taken every 90 minutes and additional high resolution magnetograms when the region of interest is in the high resolution field of view. Potential field extrapolated coronal field lines can also be provided. Continuum intensity images are also available.

Full Disk Magnetograms

FD magnetic field observations are taken every 90 minutes. The FD images have 4" resolution and accuracy of about 20 G. They are observed in the Ni I 6768 line in the mid photosphere.

High Resolution Magnetograms

HR magnetograms are avail 3 times per day for areas within the MDI HR field of view. The middle of the HR FOV is 160" north of the center of the the disk, centered EW. The HR FOV is 785" square. The resolution is 1.23". Accuracy is about 20 G. Extra HR Magnetograms can be scheduled if the region of interest is in the HR FOV..

Continuum Images

FD and HR continuum (near Ni I 6768) are available 3 times per day. Additional images can be obtained if desired.

If real time data are required for additional images, extra VC2 data will be required.

Modeled Coronal Magnetic Field

A potential field model extrapolation of the coronal field based on the photospheric observations can be provided to approximate the locations of closed and open field regions.


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.


Synoptic observations.

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SOHO Archive
Tue Aug 6 15:23:40 EDT 1996