- Email: [email protected]
International Solar Cycle Studies [ISCS] Working Group 2: solar magnetic field variability - from the lower atmosphere through the inner corona
Adv. Space Res. Vol. 29, No. 10, pp. 1583-1587,2002
0 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved
Pergamon
Printed in Great Britain 0273-l 177/02 $22.00 + 0.00
www.elsevier.com/locate/asr
PII: SO273-1177(02)00220-X
INTERNATIONAL SOLAR CYCLE STUDIES [ISCS] WORKING GROUP 2: SOLAR MAGNETIC FIELD VARIABILITY - FROM THE LOWER ATMOSPHERE THROUGH THE INNER CORONA Richard
A. Harrison1
l Space
Science
‘Naval
Research
and Donald
Michels2
Appleton Laboratory, Didcot, Oxfordshire OX11 Dept., Rutherford Code 7666, Washington DC 20375-5352, USA Laboratory,
OQX,
UK
ABSTRACT This report is a summary of activities and plans relating to the International Solar Cycle Studies (ISCS) Working Group 2, which is concerned with solar magnetic field variability, from the lower atmosphere through the inner corona. Whilst the Working Group carries a rather general title, the activities are focusing on several well defined topics - in particular the onset of coronal mass ejection events. Recognising the large number of scientific meetings worldwide, the working style of this group is aimed at improving communication, information exchange and collaboration making use of existing meetings and with a minimum of red tape. The core of the act,ivity is through t,he use of the World Wide Web and e-mail. In this way, this Working Group does not introduce extra effort, but provides a better focus for on-going projects. 0 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.
INTRODUCTION The Sun’s atmosphere is a complex environment where the interplay between the ambient plasma and the solar magnetic fields produces a stunning array of transient and dramatic phenomena. This highly dynamic environment is worthy of study for many reasons beyond pure solar physics research. For example, it generates activity which has direct, impacts on the Earth, and it provides a means for the study of processes which occur on other sta,rs, such as mass loss. For all of these reasons, ISCS Working Group 2 homes in on the variability of t)he solar magnetic fields. Specifically, Working Group 2 covers the two areas: - magnetic phenomena having different space and time scales: - solar flares, mass ejections and interplanetary consequences. In basic terms, Working Group 1 is concerned with the solar core to the solar surface, and Working Group 3 is concerned with the corona and outwards through the heliosphere. Thus, Working Group 2 sits in the middle, mainly concerned with the lower atmosphere and inner corona. Naturally, this leads to some overlap, for example, coronal mass ejections (CMEs) are of major concern for Working Groups 2 and 3. We are more concerned, here, with the onset of CMEs and Working Group 3 will place more emphasis on propagation through the heliosphere. The activities of Working Group 2 are open to anyone and the range of topics which can be covered within the two areas defined is clearly huge. However, the main aim is to provide a forum for multidisciplinary observations of the kind which are required to unra,vel many of the basic solar processes. Thus, we are attempting to encourage multi-wavelength, multi-scale campaigns to address certain issues. For example, the study of coronal mass ejection onsets requires the use of coronagraphs and underlying spectrometer and imaging observations 011 t,he disc. The co-ordination of relevant observing programmes and the analysis and interpretation of the multi-instrument datasets lies at the heart of the work of this Group. The basic aims of the Working Group are to provide efficient
1583
R. A. Harrison and D. Michels
1584
communication through meetings and the dissemination of information, to enhance the multiinstrument campaign activities. Having said that, the facilities provided by Working Group 2 can be used in other ways, to advertise activities and encourage information exchange and collaboration for a variety of projects. Thus, we have a spectrum of projects making use of the Working Group 2 activities in different ways. AREAS
OF ACTIVITY
The principal tools of this Working Group were envisaged to be the multi-instrument observations addressing specific solar questions, centred on Solar and Heliospheric Observatory (SOHO) spacecraft Joint Observing Programmes (JOPs). This new breed of collaborative observation work appeared to require a basic communication and information tool to enhance the analysis and intrepratation of the data, or even the planning of observations. However, it was recognised early on that the efforts of this Working Group should not be related exclusively to the SOHO JOPs; any Indeed, with a basic definition of how the campaigns may be included in the Group’s activities. Working Group would work, it was decided that any groups or individuals who could make use of the Working Group 2 activities for enhanced information exchange, collaboration etc... should be free to do so. It was decided also that the Working Group activities should not add a layer of red tape, but should be geared toward the encouragement of collaboration and ease of communication. This is being done with two major efforts. First, through the arrangement and encouragement of meetings. Every effort is being made to not introduce extra meetings, but to make use of existing meetings where sessions can be tuned to the Working Group needs. This is the case for sessions at the 1999 and European Geophysical Society (EGS) S cientific Assembly in The Hague, The Netherlands, the International Association for Geomagnetism and Aeronomy (IAGA) meeting in Birmingham, England. The second approach is through the setting up and use of a dedicated Web site, and harrison/iscs.html. communication via e-mail. The Web site address is http://solg2.b nsc.rl.ac.uk/ A particular desire is to enhance the communication between judgement on the success of this can only be made later!
observers
and theorists
but
any
The plan is not to define an all encompassing scheme covering all SOHO JOP or solar multiinstrument activities. Each team running such an activity should decide for itself whether or not the ISCS framework allows a useful forum for the development of their activities. If anyone finds this approach attractive they should contact either of the Working Group coordinators. (See the Web site for information). The first ISCS Working Group meetings took place at the COSPAR Nagoya Scientific Assembly in the summer of 1998, where some 24 papers were presented relating to the three established working groups. Some 60 people attended the sessions. As the ISCS Working Group 2 approach matures, we anticipate a number of multi-disciplinary efforts linking in to the activities. A number of efforts are already making use of the Working Group 2 approach and these are listed at the Web site. They include a major multi-disciplinary effort to observe and study CME onsets, the study of large-scale chains on the solar disc, studies of small scale transients in the quiet Sun network, and numerical MHD modelling. These activities are using the Working Group 2 approach in different ways, from a full scale collaborative observation programme, to the advertising and open discussion of new theoretical results. A number of other efforts are being co-ordinated at this time and will be posted at the Web site as appropriate. The first affiliated activity was the CME onset study and the activities of this group are outlined in the next section, as an example of how the ISCS framework may be used. CME
ONSET
STUDIES
The onset phase of CMEs is still shrouded in mystery. There are a number of candidate processes which can result in the ejection of coronal material into space. One of these is a pressure pulse
ISCS Working Group 2 Report
1585
which in solar conditions, would mean a response to a flare-like event. This we can rule out on the basis! of studies of the relative locations and times of solar flare and CME activity (see e.g. Harrison, 1991, 1995). Other possible mechanisms would include magnetic buoyancy, magnetic Convincing models exist which can mimic the expansion of evolution and magnetic reconnection. a CME-like event through the driving of shear in the footpoints of coronal arcades (e.g. Klimchuk, 1990; Steinolfson, 1991) or through the reconnection of magnetic fields in certain configurations H owever, although such models have realistic (e.g. Antiochos, DeVore and Klimchuck, 1999). features it is often very difficult to see how the prominence or flare fits into the picture. Many with flares CMEs include prominence eruptions; many do not. CMEs often occur in association but it is clear that neither drives the other. The best statement that one can make is that these are all consequences of the activities (the CME, including the prominence eruption, structures within the same driving mechanism, e.g. magnetic shear, but manifested in di magnetic configuration (Harrison, 1996). Prior to SOHO most studies of CME onsets were limited to basic considerations of relative timings and locations, and to statistical studies. It was recognised that with SOHO we had the opportunity to perform multi-instrument studies which could allow the detection of a CME through an observations unprecedented range of altitudes, as well as in space, combined with spectroscopic This would allow detailed plasma diagnostic techniques to be used in the of the onset region. observation of the lead up to the CME, and the onset, in the source region itself. Therefore? a multi-instrument SOHO Joint Observing Programme (JOP) was designed to provide such an observation. This SOHO JOP expanded to include ground-based and other space instrumentation and became the first major campaign to be included as an ISCS Working Group 2 activity. In the SOHO scheme of things, this is JOP 3 and 67 and the basic observing scenario is to study the solar near-limb regions with extreme ultraviolet (EUV) spectroscopy with supporting coronagraph data. These JOPs have been run on many occasions since October 1996, initially as a stand-alone SOHO JOP, but later being run with a larger community involvement under the IACG (Inter Agency Consultative Group) and ISCS umbrellas. As the Sun has become more active a number of ejecta have been identified. Some very early results have been presented (Harrison, 1997a) and they reveal a remarkable rather ‘inactive’ low corona under CME events, although coronal dimming is reported for the million degree emission lines. The analysis and interpretation of the events observed is expected to continue for some time, whilst, in parallel, further observational runs will be made. Regarding the ISCS involvement, the CME onset study team is spread over many countries and communication via the ISCS framework is a useful approach. The publications are posted on t,he Web page and the page is used also to post images/data for discussion. Also posted at the Web site is the CME onset meeting details for those sessions arranged under ISCS sponsorship. These include (i) a workshop on the results of the CME onset efforts, arranged for the European Geophysical Society assembly in The Hague (April 19-23 1999 - ‘Multi-Instrument Campaigns to Study Solar Coronal Mass Ejection Onsets and Propagation’ - Conveners: Richard A. Harrison and Volker Bothmer), and (ii) a session on solar events and heliospheric consequences, arranged at the International Association for Geomagnetism and Aeronomy meetings in Birmingham (July 1999 - ‘Cycle 23 Solar Events and Heliospheric Consequences’ - Conveners: Barbara Thompson and Richard A. Harrison). Introducing a body like the ISCS will rarely generate a t’otally new set of productive projects. People do not redirect their research efforts as a result of the setting up of a new umbrella organisation. The aim should be to enhance on-going efforts and incorporate these into the ISCS framework and this is what has happened for the Ch4E onset effort. The ISCS Working Group 2 approach has enhanced communication and the exchange of meeting information, publication information and the viewing of data for the CME onset work and, in this way, it is proving to be a useful and succcessful tool. OTHER
AREAS
R. A. Harrison and D. Michels
1586
Other groups those here.
are using the ISCS
Working
Group
2 facility
for their own purposes,
and we list
One group, led by I. Chertok, have been investigating large-scale ‘chains’ on the solar disc, through the analysis of data from the solar Yohkoh mission, the Transition Region and Coronal Explorer (TRACE) and the Nobeyama Radioheliograph. These chains are relatively weak but large features of solar activity which suggest some kind of link of across large areas. The effort in this case has centred on the display of data, analysis and discussion as a means to advertise the work via the Working Group 2 Web site, rather than the organisation of observations. Indeed, the approach has been to open the topic for discussion well before publication. In a similar approach, A.I. Podgorny and I.M. Podgorny have introduced their 2-D and 3-D MHD The models have been applied to a number of modelling, via the Working Group Web site. phenomena, such as current sheets in the solar atmosphere, reconnection during substorms and in flares, and post-flare loops (Podgorny and Podgorny, 1997a,b). Again, the Web site has opened up a facility for discussion within the ISCS community. Another multi-instrument effort centred on a SOHO JOP is also starting to use the ISCS Working Group 2 approach for data inspection and communication. Reflecting the statement in the introduction that this Working Group is concerned with magnetic phenomena having different space and time scales, this effort is at the other end of the scale-size spectrum to the CME work discussed above. Specifically, it is a multi-instrument campaign to study quiet Sun, small-scale transient phenomena, aimed at identifying the processes leading to coronal heating and solar wind acceleration. It comes out of a series of extreme ultraviolet studies of the transient events known as ‘blinkers’ which have been made in the last year and a half (Harrison, 1997b). They appear to be basic features of the solar atmosphere in the few hundred thousand K region and appear as increases in intensity of order 50 % over lo-20 minutes. Some tens of thousands of these transient events may be on the disc at any point in time. Spectroscopic analyses of these events are in progress in an effort to identify their role. However, to determine their characteristics properly cam it is clear that we require comparisons to other data-sets, i.e. we require multi-instrument paigns. These have started recently. In particular, it is assumed that the events are the site of the conversion of magnetic energy to particle energy, so we must compare magnetic field observations of the photosphere to the transient EUV events. In addition, it is recognised that in the longer wavelength ultraviolet region, we witness the so-called explosive events (Innes et al. 1997), which are small, jet-like events also found in the quiet Sun. To determine the relationship between these jets and the blinker events and to build in the magnetic mapping, the observational effort now includes EUV, UV spectroscopy and magnetograph data. These observation campaigns are under way and will be advertised on the ISCS Working Group 2 Web site to enhance the data exchange and communication. CONCLUSION The community should use Working Group 2 as it sees fit. If specific collaborating groups feel that the ISCS umbrella is a useful one for communication and meeting arrangement, then they are very welcome to join in. We do not plan to cover all areas of solar physics but would prefer that individual teams running specific campaigns join the effort and use it as they wish. The basic aim is to improve the efficiency of a number of multi-disciplinary programmes through communication and information distribution. People should visit the Web site for more information and, of course, we welcome any comments and suggestions. Several groups are clearly using the Working Group 2 a,pproach for different reasons and we anticipate additional groups coming in as time progresses.
REFERENCES Antiochos, S.K., DeVore, C.R. and Klimchuk, J.A., A model for solar coronal mass ,4strophys. J. 510, 485 (1999) Harrison, R.A., Coronal mass ejection, Phil. Trans. Roy. .Soc. Lond. A 336, 401 (1991)
ejections,
ISCS Working Group 2 Report
1587
Harrison, R.A., The Nature of Solar Flares Associated with Coronal Mass Ejection, astron. Astrophys. 304, 585 (1995). Harrison, R.A., Coronal magnetic storms: a new perspective on flares and the solar flare myth debate, Solar Phys. 166, 441 (1996) Harrison, R.A., Overview of Results from IACG Campaign 3: CME Onsets, Proc. 31st ESLAB Symp. ‘Correlated Phenomena at the Sun, in the Heliosph.ere and in Geospace *, ES-4 SP-415, 121 (1997a). Harrison, R.A., EUV blinkers: The significance of va.riat,ions in the extreme ultraviolet quiet Sun. Solar Phys. 175, 467 (1997b). Innes. D.E.. Inhester, B.. Axford, A.I. and Wilhelm, Ii., Nature 386, Sll (197i). Klimchuk, j.A., Shear-induced inflation of coronal magnetic fields, Astrophys. 1. 354, i45 (1990) Podgorny, A.I. and Podgorny, I.M., Current sheet’s in t,he solar atmosphere, Adv. in Space Res. 20, 12, 2309 (1997a) Podgorny, A.I. and Podgorny, I.M., Reconnection during substorms and solar flares, Aclr. in Space Res. 19, 12, 1929 (1997b) Steinolfson, R.S., Coronal evolution due to shear motion, Ast,rophys. J. 382, 677 (1991)
0 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved
Pergamon
Printed in Great Britain 0273-l 177/02 $22.00 + 0.00
www.elsevier.com/locate/asr
PII: SO273-1177(02)00220-X
INTERNATIONAL SOLAR CYCLE STUDIES [ISCS] WORKING GROUP 2: SOLAR MAGNETIC FIELD VARIABILITY - FROM THE LOWER ATMOSPHERE THROUGH THE INNER CORONA Richard
A. Harrison1
l Space
Science
‘Naval
Research
and Donald
Michels2
Appleton Laboratory, Didcot, Oxfordshire OX11 Dept., Rutherford Code 7666, Washington DC 20375-5352, USA Laboratory,
OQX,
UK
ABSTRACT This report is a summary of activities and plans relating to the International Solar Cycle Studies (ISCS) Working Group 2, which is concerned with solar magnetic field variability, from the lower atmosphere through the inner corona. Whilst the Working Group carries a rather general title, the activities are focusing on several well defined topics - in particular the onset of coronal mass ejection events. Recognising the large number of scientific meetings worldwide, the working style of this group is aimed at improving communication, information exchange and collaboration making use of existing meetings and with a minimum of red tape. The core of the act,ivity is through t,he use of the World Wide Web and e-mail. In this way, this Working Group does not introduce extra effort, but provides a better focus for on-going projects. 0 2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.
INTRODUCTION The Sun’s atmosphere is a complex environment where the interplay between the ambient plasma and the solar magnetic fields produces a stunning array of transient and dramatic phenomena. This highly dynamic environment is worthy of study for many reasons beyond pure solar physics research. For example, it generates activity which has direct, impacts on the Earth, and it provides a means for the study of processes which occur on other sta,rs, such as mass loss. For all of these reasons, ISCS Working Group 2 homes in on the variability of t)he solar magnetic fields. Specifically, Working Group 2 covers the two areas: - magnetic phenomena having different space and time scales: - solar flares, mass ejections and interplanetary consequences. In basic terms, Working Group 1 is concerned with the solar core to the solar surface, and Working Group 3 is concerned with the corona and outwards through the heliosphere. Thus, Working Group 2 sits in the middle, mainly concerned with the lower atmosphere and inner corona. Naturally, this leads to some overlap, for example, coronal mass ejections (CMEs) are of major concern for Working Groups 2 and 3. We are more concerned, here, with the onset of CMEs and Working Group 3 will place more emphasis on propagation through the heliosphere. The activities of Working Group 2 are open to anyone and the range of topics which can be covered within the two areas defined is clearly huge. However, the main aim is to provide a forum for multidisciplinary observations of the kind which are required to unra,vel many of the basic solar processes. Thus, we are attempting to encourage multi-wavelength, multi-scale campaigns to address certain issues. For example, the study of coronal mass ejection onsets requires the use of coronagraphs and underlying spectrometer and imaging observations 011 t,he disc. The co-ordination of relevant observing programmes and the analysis and interpretation of the multi-instrument datasets lies at the heart of the work of this Group. The basic aims of the Working Group are to provide efficient
1583
R. A. Harrison and D. Michels
1584
communication through meetings and the dissemination of information, to enhance the multiinstrument campaign activities. Having said that, the facilities provided by Working Group 2 can be used in other ways, to advertise activities and encourage information exchange and collaboration for a variety of projects. Thus, we have a spectrum of projects making use of the Working Group 2 activities in different ways. AREAS
OF ACTIVITY
The principal tools of this Working Group were envisaged to be the multi-instrument observations addressing specific solar questions, centred on Solar and Heliospheric Observatory (SOHO) spacecraft Joint Observing Programmes (JOPs). This new breed of collaborative observation work appeared to require a basic communication and information tool to enhance the analysis and intrepratation of the data, or even the planning of observations. However, it was recognised early on that the efforts of this Working Group should not be related exclusively to the SOHO JOPs; any Indeed, with a basic definition of how the campaigns may be included in the Group’s activities. Working Group would work, it was decided that any groups or individuals who could make use of the Working Group 2 activities for enhanced information exchange, collaboration etc... should be free to do so. It was decided also that the Working Group activities should not add a layer of red tape, but should be geared toward the encouragement of collaboration and ease of communication. This is being done with two major efforts. First, through the arrangement and encouragement of meetings. Every effort is being made to not introduce extra meetings, but to make use of existing meetings where sessions can be tuned to the Working Group needs. This is the case for sessions at the 1999 and European Geophysical Society (EGS) S cientific Assembly in The Hague, The Netherlands, the International Association for Geomagnetism and Aeronomy (IAGA) meeting in Birmingham, England. The second approach is through the setting up and use of a dedicated Web site, and harrison/iscs.html. communication via e-mail. The Web site address is http://solg2.b nsc.rl.ac.uk/ A particular desire is to enhance the communication between judgement on the success of this can only be made later!
observers
and theorists
but
any
The plan is not to define an all encompassing scheme covering all SOHO JOP or solar multiinstrument activities. Each team running such an activity should decide for itself whether or not the ISCS framework allows a useful forum for the development of their activities. If anyone finds this approach attractive they should contact either of the Working Group coordinators. (See the Web site for information). The first ISCS Working Group meetings took place at the COSPAR Nagoya Scientific Assembly in the summer of 1998, where some 24 papers were presented relating to the three established working groups. Some 60 people attended the sessions. As the ISCS Working Group 2 approach matures, we anticipate a number of multi-disciplinary efforts linking in to the activities. A number of efforts are already making use of the Working Group 2 approach and these are listed at the Web site. They include a major multi-disciplinary effort to observe and study CME onsets, the study of large-scale chains on the solar disc, studies of small scale transients in the quiet Sun network, and numerical MHD modelling. These activities are using the Working Group 2 approach in different ways, from a full scale collaborative observation programme, to the advertising and open discussion of new theoretical results. A number of other efforts are being co-ordinated at this time and will be posted at the Web site as appropriate. The first affiliated activity was the CME onset study and the activities of this group are outlined in the next section, as an example of how the ISCS framework may be used. CME
ONSET
STUDIES
The onset phase of CMEs is still shrouded in mystery. There are a number of candidate processes which can result in the ejection of coronal material into space. One of these is a pressure pulse
ISCS Working Group 2 Report
1585
which in solar conditions, would mean a response to a flare-like event. This we can rule out on the basis! of studies of the relative locations and times of solar flare and CME activity (see e.g. Harrison, 1991, 1995). Other possible mechanisms would include magnetic buoyancy, magnetic Convincing models exist which can mimic the expansion of evolution and magnetic reconnection. a CME-like event through the driving of shear in the footpoints of coronal arcades (e.g. Klimchuk, 1990; Steinolfson, 1991) or through the reconnection of magnetic fields in certain configurations H owever, although such models have realistic (e.g. Antiochos, DeVore and Klimchuck, 1999). features it is often very difficult to see how the prominence or flare fits into the picture. Many with flares CMEs include prominence eruptions; many do not. CMEs often occur in association but it is clear that neither drives the other. The best statement that one can make is that these are all consequences of the activities (the CME, including the prominence eruption, structures within the same driving mechanism, e.g. magnetic shear, but manifested in di magnetic configuration (Harrison, 1996). Prior to SOHO most studies of CME onsets were limited to basic considerations of relative timings and locations, and to statistical studies. It was recognised that with SOHO we had the opportunity to perform multi-instrument studies which could allow the detection of a CME through an observations unprecedented range of altitudes, as well as in space, combined with spectroscopic This would allow detailed plasma diagnostic techniques to be used in the of the onset region. observation of the lead up to the CME, and the onset, in the source region itself. Therefore? a multi-instrument SOHO Joint Observing Programme (JOP) was designed to provide such an observation. This SOHO JOP expanded to include ground-based and other space instrumentation and became the first major campaign to be included as an ISCS Working Group 2 activity. In the SOHO scheme of things, this is JOP 3 and 67 and the basic observing scenario is to study the solar near-limb regions with extreme ultraviolet (EUV) spectroscopy with supporting coronagraph data. These JOPs have been run on many occasions since October 1996, initially as a stand-alone SOHO JOP, but later being run with a larger community involvement under the IACG (Inter Agency Consultative Group) and ISCS umbrellas. As the Sun has become more active a number of ejecta have been identified. Some very early results have been presented (Harrison, 1997a) and they reveal a remarkable rather ‘inactive’ low corona under CME events, although coronal dimming is reported for the million degree emission lines. The analysis and interpretation of the events observed is expected to continue for some time, whilst, in parallel, further observational runs will be made. Regarding the ISCS involvement, the CME onset study team is spread over many countries and communication via the ISCS framework is a useful approach. The publications are posted on t,he Web page and the page is used also to post images/data for discussion. Also posted at the Web site is the CME onset meeting details for those sessions arranged under ISCS sponsorship. These include (i) a workshop on the results of the CME onset efforts, arranged for the European Geophysical Society assembly in The Hague (April 19-23 1999 - ‘Multi-Instrument Campaigns to Study Solar Coronal Mass Ejection Onsets and Propagation’ - Conveners: Richard A. Harrison and Volker Bothmer), and (ii) a session on solar events and heliospheric consequences, arranged at the International Association for Geomagnetism and Aeronomy meetings in Birmingham (July 1999 - ‘Cycle 23 Solar Events and Heliospheric Consequences’ - Conveners: Barbara Thompson and Richard A. Harrison). Introducing a body like the ISCS will rarely generate a t’otally new set of productive projects. People do not redirect their research efforts as a result of the setting up of a new umbrella organisation. The aim should be to enhance on-going efforts and incorporate these into the ISCS framework and this is what has happened for the Ch4E onset effort. The ISCS Working Group 2 approach has enhanced communication and the exchange of meeting information, publication information and the viewing of data for the CME onset work and, in this way, it is proving to be a useful and succcessful tool. OTHER
AREAS
R. A. Harrison and D. Michels
1586
Other groups those here.
are using the ISCS
Working
Group
2 facility
for their own purposes,
and we list
One group, led by I. Chertok, have been investigating large-scale ‘chains’ on the solar disc, through the analysis of data from the solar Yohkoh mission, the Transition Region and Coronal Explorer (TRACE) and the Nobeyama Radioheliograph. These chains are relatively weak but large features of solar activity which suggest some kind of link of across large areas. The effort in this case has centred on the display of data, analysis and discussion as a means to advertise the work via the Working Group 2 Web site, rather than the organisation of observations. Indeed, the approach has been to open the topic for discussion well before publication. In a similar approach, A.I. Podgorny and I.M. Podgorny have introduced their 2-D and 3-D MHD The models have been applied to a number of modelling, via the Working Group Web site. phenomena, such as current sheets in the solar atmosphere, reconnection during substorms and in flares, and post-flare loops (Podgorny and Podgorny, 1997a,b). Again, the Web site has opened up a facility for discussion within the ISCS community. Another multi-instrument effort centred on a SOHO JOP is also starting to use the ISCS Working Group 2 approach for data inspection and communication. Reflecting the statement in the introduction that this Working Group is concerned with magnetic phenomena having different space and time scales, this effort is at the other end of the scale-size spectrum to the CME work discussed above. Specifically, it is a multi-instrument campaign to study quiet Sun, small-scale transient phenomena, aimed at identifying the processes leading to coronal heating and solar wind acceleration. It comes out of a series of extreme ultraviolet studies of the transient events known as ‘blinkers’ which have been made in the last year and a half (Harrison, 1997b). They appear to be basic features of the solar atmosphere in the few hundred thousand K region and appear as increases in intensity of order 50 % over lo-20 minutes. Some tens of thousands of these transient events may be on the disc at any point in time. Spectroscopic analyses of these events are in progress in an effort to identify their role. However, to determine their characteristics properly cam it is clear that we require comparisons to other data-sets, i.e. we require multi-instrument paigns. These have started recently. In particular, it is assumed that the events are the site of the conversion of magnetic energy to particle energy, so we must compare magnetic field observations of the photosphere to the transient EUV events. In addition, it is recognised that in the longer wavelength ultraviolet region, we witness the so-called explosive events (Innes et al. 1997), which are small, jet-like events also found in the quiet Sun. To determine the relationship between these jets and the blinker events and to build in the magnetic mapping, the observational effort now includes EUV, UV spectroscopy and magnetograph data. These observation campaigns are under way and will be advertised on the ISCS Working Group 2 Web site to enhance the data exchange and communication. CONCLUSION The community should use Working Group 2 as it sees fit. If specific collaborating groups feel that the ISCS umbrella is a useful one for communication and meeting arrangement, then they are very welcome to join in. We do not plan to cover all areas of solar physics but would prefer that individual teams running specific campaigns join the effort and use it as they wish. The basic aim is to improve the efficiency of a number of multi-disciplinary programmes through communication and information distribution. People should visit the Web site for more information and, of course, we welcome any comments and suggestions. Several groups are clearly using the Working Group 2 a,pproach for different reasons and we anticipate additional groups coming in as time progresses.
REFERENCES Antiochos, S.K., DeVore, C.R. and Klimchuk, J.A., A model for solar coronal mass ,4strophys. J. 510, 485 (1999) Harrison, R.A., Coronal mass ejection, Phil. Trans. Roy. .Soc. Lond. A 336, 401 (1991)
ejections,
ISCS Working Group 2 Report
1587
Harrison, R.A., The Nature of Solar Flares Associated with Coronal Mass Ejection, astron. Astrophys. 304, 585 (1995). Harrison, R.A., Coronal magnetic storms: a new perspective on flares and the solar flare myth debate, Solar Phys. 166, 441 (1996) Harrison, R.A., Overview of Results from IACG Campaign 3: CME Onsets, Proc. 31st ESLAB Symp. ‘Correlated Phenomena at the Sun, in the Heliosph.ere and in Geospace *, ES-4 SP-415, 121 (1997a). Harrison, R.A., EUV blinkers: The significance of va.riat,ions in the extreme ultraviolet quiet Sun. Solar Phys. 175, 467 (1997b). Innes. D.E.. Inhester, B.. Axford, A.I. and Wilhelm, Ii., Nature 386, Sll (197i). Klimchuk, j.A., Shear-induced inflation of coronal magnetic fields, Astrophys. 1. 354, i45 (1990) Podgorny, A.I. and Podgorny, I.M., Current sheet’s in t,he solar atmosphere, Adv. in Space Res. 20, 12, 2309 (1997a) Podgorny, A.I. and Podgorny, I.M., Reconnection during substorms and solar flares, Aclr. in Space Res. 19, 12, 1929 (1997b) Steinolfson, R.S., Coronal evolution due to shear motion, Ast,rophys. J. 382, 677 (1991)