Author(s): R.A. Harrison (CDS), E. Antonucci (UVCS), D. Michels (LASCO), P. Lemaire (SUMER), J.-P. Delaboudiniere (EIT), P. Scherer (MDI)

Progress:

Draft Scheme                            February 15/June 6, 1994              
Discussion at SPWG                      June 14 1994

Detailed PlanMinor Revision             June 22, 1994
                                        November 4/November 24, 1994

CDS ID: EJECT

Objective: To study the onset phase of coronal mass ejections

Scientific Case: A Coronal Mass Ejection (CME) represents a significant restructuring of the solar corona. Some 10^12 -10^13 kg of matter can be expelled from the corona as a magnetic loop system, some tens of degrees across, expands into interplanetary space at speeds of several hundred km/s. Such events often involve prominence eruption and even flares, though the relationships are unclear. Also, soft X-ray brightenings within huge coronal loops have been associated with such events. Numerous models have been presented to explain the CME onset but we have very little information on the properties of the source magnetic structures, on the plasma within them and on the precise sequence of events leading to eruption. Studies of such structures as they erupt will not only allow us to predict the onsets of CMEs and understand their relationship to flare/prominence activity, they will pave the way to predicting geomagnetic activity since such activity is generated by CME-magnetospheric interaction.

Since mass ejection involves the eruption of hot (10^6 K) coronal plasma and cool (10^4 K) prominence material, with activity in the high corona, low corona and chromosphere, observations of this kind require a multidisciplinary approach, with large fields of view and a large temperature range.

This study is designed as a "first look" exercise, to be refined as we learn to view and study CME onsets. It homes in on events near the limb, i.e. CMEs which are unlikely to be Earth-directed and, therefore, undetected by the SOHO particle instruments. Thus, in parallel, a CME study should be made for disc eruptions.

Method: The basic method is for CDS, SUMER, and EIT to monitor specific structures as they approach and cross the west limb of the Sun. Meanwhile, LASCO and UVCS provide supporting data by concentrating on observations in the corona above. The following points are taken into account:

CMEs are huge - on average 45 deg (heliographic) across at the solar limb. Thus, we need large fields of view.

There are clear associations between CMEs and prominences and active regions. Such regions should be among our initial targets.

Past studies suggest that temporal resolutions of order 5 arc minutes are appropriate.

Since this is a sit-and-wait programme, the observing schemes are chosen to provide useful data in the event of no eruption.

Pointing and Target Selection: A target should be chosen, such as a prominence or active region, which is at about W40 deg. The programme should be run on that target for as much time as possible, i.e. about 6 or more hours per day, for the following 5-6 days until it is well beyond the limb. Prime targets should be (i) large prominences (which can be identified in ground based H data), (ii) active regions which have recent history of activity (again, identified using ground based H data), (iii) prominences associated with regions of emerging magnetic flux (identified using H and magnetogram data), (iv) large active region interconnecting loops (identified using X-ray images - e.g. Yohkoh).

Operating Details:

The following raster and image details give the basic operations which should be repeated throughout the CME programme.

CDS

This scheme involves the largest field of view with a selection of lines appropriate for a wide temperature range. This should provide temperature, density, abundance, flow and morphological information over a large area in the CME source region. Note: Since we are summing across lines, lines are selected which are appropriately separated from surrounding lines. Mg and Fe ranges are used to cover the temperature range, with some density coverage.

Normal incidence operation

4x240 arcsec slit

4x4 arcmin field of view - i.e. 60 location raster

3 Sec exposure at each location

Total duration = 60x3 = 3 min per raster.

Line Selection - Synoptic Line Selection [NIS]

Ion Wavelength(Å) LogTe Comment

He I 584.33 4.3 cool, granulation, depleted in coronal holes

Mg VI 349.13 5.6

Mg VIII313.73 5.9

Mg IX 368.06 6.0 good for c.hole boundary/structure

Mg X 624.94 6.1

Fe XI 369.16 6.1

Fe XII 364.47 6.2

Fe XII 338.26 6.2 density sensitive ratio w. 364.47

Fe XIII 320.80 6.2

Fe XIII 318.14 6.2 density sensitive ratio w. 320.80

Fe XIV 334.17 6.3

Fe XV 327.02 6.3

Data Compression: Sum 11 pixels across each line

Telemetry = 12 lines x 120 pixels x 16 bits / 10000 = 2.3 Sec. No bottleneck.

SUMER

The SUMER operation includes one wavelength selection with a wide range of lines which complements the CDS selection. Particularly useful for flow and morphological study.

1x300 arcsec slit

300x300 arcsec field of view - centred on CDS field

0.76 arcsec steps - 4 steps over 2 Sec - accumulate simultaneously.

Total duration = 395 steps x 0.5 Sec = 197.5 Sec per raster (3.3 min)

Line Selection - 1204-1244Å (Covers: Si III 1206Å, H I Ly 1216Å, N V 1238Å,

Fe XII 1242Å.)

EIT

The EIT images will provide an overview of the CME source area and surrounding structures with images in each of four bands covering the target area.

Extract 8x8 arcmin field - centred on CDS field

10:1 compression (2.5 arcsec) with all four bands

Total extraction time - 4 Min.

UVCS

To be operated in either of two modes:

Orientation - field of view extending into corona above CDS/SUMER target area.

7 slit locations - between 1.4 and 2.0 solar radii - 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0 R

dwell time - 10 Sec - Total duration 70 Sec

Mode 1: To derive outflow velocity from Doppler dimming of H I and O VI and to measure proton kinetic temperature, electron temperature and density over a good

spatial region.

14 arcsec x 40 arcmin slit (14 x 28 arcsec pixels)

Record OVI 1032/1037Å, Fe XII 1242Å , Mg X 610,625Å, Si XII 499,521Å,

- intensities and profiles - Ly 1216 Å profile, and 4500-6000Å polarized radiation.

Mode 2: To observe a wide range of ionisation stages and to look for cool material and study its evolution in the corona.

14 arcsec x 10 arcmin slit (14 arcsec x 2 arcmin pixels)

Record Si III 1206Å, C II 1037Å, Ly 1216Å, Fe XII 1242Å, N V 1238Å,

OVI 1032/1037Å, S IV 1063/1074Å, He II 1085Å, Mg X 610,625Å,

Si XII 499,521Å, Ly 1025Å, C III 1176Å, O V 630Å, polarized radiation

4500-6000Å.

LASCO

The LASCO coronagraphs should concentrate on the quadrant of the corona above the target region for the identification of coronal transients. The specific operational details are listed below:

C1 - Fe 5303Å green line. Images every 10 minutes.

C2 - White light images every 20 minutes (including compression)

C3 - White light images every 2 hours

MDI

MDI will provide magnetogram support during the operation.

Standard resolution magnetograms of the limb area produced about 10 per day.

SWAN

SWAN has the potential for detecting cooler material crossing the inner heliosphere, possibly the reminder of prominence eruptions.

Monitor quadrant above target region.

Particle Instruments

Although this programme is geared toward non-Earth directed CMEs, some events will interact with the Earth, due to orientation, CME expansion or non-radial motion. Particle data should be monitored for such events.

Monitor solar wind for correlations with CME events.

Ground Based Instrumentation

Ground based instrumentation is essential for identifying prominences, magnetic structure and, possibly the ejecta themselves.

The following data are required:

- H images of the full Sun and target region (e.g. Big Bear, the SOON network etc)

- H limb observations (e.g. Mauna Loa Solar Observatory, Wroclow Observatory)

- Coronal white light images (from Mauna Loa Solar Observatory, Hawaii)

- Magnetogram images (e.g. Marshall SFC, Beijing, the SOON network etc)

Notes:

It is recognised that instruments on SOHO will be operating synoptic programmes which should not be interrupted and other pressures from target of opportunity operations will exist. Thus, although a single operation will last for 5-6 days, we may expect between 25 and 75% of the time dedicated to the CME Onset effort in that time.

This programme should be run on a number of occasions to ensure reasonable observations of CME onsets.

The programme described above is an initial attempt to detect and investigate CME onsets. Thus, the programme should develop with time. For example, at this time we cannot sensibly build in inter-instrument flags though their use could be envisaged at a latter time.

Inter Agency Consultative Group

The IACG campaign on CMEs, their structure, development and evolution has discussed collaborative efforts which are centred on the above operation. The IACG plan complements the scheme by building in the following collaborations:

Yohkoh (launch 1991): The Soft X-ray Telescope (SXT) instrument should be used for the identification of potential CME source regions - e.g. large X-ray emitting loops. Also, Yohkoh should be included in the programme for the study of large scale X-ray structure and its evolution before during and after the CME onset. This extends on the spatial coverage available to SOHO. The Bent Crystal Spectrometer instrument, as well as the SXT and the Hard X-ray Telescope can be used also for the identification of flares associated with ejecta. Target selection will most likely be done in discussion with both the SOHO and Yohkoh teams.

Coronas (launch 1994/5): EUV and X-ray imagers and spectrometers are available on Coronas I/F which could complement the SOHO and Yohkoh operations. The launch dates and durations are not clear at this time.

TRACE (launch 1997): The Transition Region and Coronal Experiment is an Explorer class, small mission, designed to produce EUV/UV images in a variety of wavelengths. This would be very complementary to the SOHO spectroscopic observations in the same wavelengnth range. The launch date may be 1997.

GOES (on going series): The GOES X-ray integrated Sun devices will be used to study the global X-ray response and to identify flares. If the planned GOES X-ray imager becomes available, it can be used to identify and study large scale structure and its evolution as events progress.

GRO: The BATSE device on the Gamma Ray Observatory can be used to identify flare signatures which may be associated with CME onsets.

Other Space Borne Instruments: As with the GRO and GOES instruments, supplementary information on associated flares can be given by the Interball mission. Since the mission lifetime and launch date is uncertain, the collaboration must be driven on the basis of opportunity at the time of the programme. Further, the SWATH mission may have relevant instrumentation, though this is to be confirmed.

Other Ground Based Instruments: Beyond the devices mentioned above, the IACG concluded that our understanding of radio signatures of mass ejections is far from understood. Thus, it was suggested that a comprehensive radio campaign be included. This should include many observatories covering a wide range of wavelengths, particularly for the observation of prominences, type II and type IV events, as well as flare signatures.e.g.

Nobyama - cm wavelength imaging - especially relevant for prominence observations

Potsdam - 40-800 MHz sweeps plus single frequency obs: for type II, IV observations

Nancay - multifrequency radioheliograph

Owens Valley - microwave images of flare/CME sites.

The communication between the ground based and space based groups should be coordinated through the GSFC SOHO EOF/EAF.

Since the planned SOHO launch date is July 1995 and there is a 4 month cruise phase, followed by a month long period of commissioning, if we allow 2 months for familiarisation, the first chance for a campaign of this kind is about March 1996. To maximize the chance of Yohkoh being in operation at the time, we must start the campaigns as near to this time as possible.