GENERAL OVERVIEW

ORGANIZATION OF THE EUROCONFERENCES

For each event the coordinator of the project was assisted by a chairman belonging to the inviting institute who helped by two committees of organization (science and local). For the first event the chairman was Dr. Vazquez (Canaries), for the second Dr. Alissandrakis (Greece), for the third one, Dr. Hofmann from Potsdam (Germany). The budget of each event consists of EC funds, plus a part from the inviting institute and finally of national funds which support the participants who are not speakers or young persons. Without the support of EC, this kind of meetings could not have not been organized.

Each Euroconference was organized in 4 full days on Wednesday, Thursday, Friday and Saturday. The visit of the observatory nearby, if there is one, was on Sunday. This organization is suitable for utilizing cheaper flights within Europe. The two first days was focused on a specific solar physics topic with presentations of new observation and discussions on available models. The following day was devoted to

technical problems around optics, devices and detectors adapted to the specific observations The last day was devoted to the organization of network, of transverse cooperations and of transfer of informations between the different groups. In addition, the meeting was of the preferable type in which talks are limited largely to extensive reviews while the ''show-and-tell'' presentations are largely done in the form of posters plus brief oral introductions. This is an excellent formula. The reviewers get enough speaking time to take their task sufficiently serious and come up with proper reviews rather than just advertising their own latest results. They gave high-quality lectures very understandable for non specialists in the field. The relatively few oral contributions, a small fraction of the total, were well selected. The poster introductions gave the presenters a valuable opportunity to present their product. Given long enough poster session, which often is sorely lacking, but not in this meeting, such brief presentations indeed generate interest and the appropriate markings in the abstract booklet, to be followed by extensive discussion at the selected posters.

Exchange of observations and transfer of data through Data Bases Centers

defined among these different laboratories during the conferences. All the laboratories have access to Internet. The advance publicity of the conferences was done mainly through the network of solar physic laboratories by electronic mail and by WWW (netscape) which is developing quickly among our community. We have developed a special sub-network of interested universities and institutes where seniors have in charge to inform the young scientists of their universities about the Euroconferences.

TRAINING ASPECT

The large number of young participants at the meeting was striking since solar physics is a mature and established field with an overly senior age profile. Rejuvenation appears to work.

One of the main objectives of these Euroconferences was the training of students in the field of research ''Magnetic fields and Oscillations'' in Solar Physics. In the last few years we have got much new instrumentation, mainly in space with SOHO. SOHO (Solar and Heliospheric Observatory) is an ESA/NASA mission launched in December 1995 with 12 instruments on board. Lost by the end of June 1998 it was

successfully recovered during August 1998 and fully operational again in October 1998. The European students have to be familiarized with the data reduction of the different instruments and to learn what kind of science we are able to do. They have to be able to propose observing programs and to be the planners of the different instruments. The operations center, due to its location at Goddard Space Flight Center (in Maryland, USA) is very favorable to American scientists so it is important to make publicity among the young European generation in order that they accept some mobility for a few months to be planners of the instruments on SOHO. I think that this was well accomplished in the working group ''Coordinated observations between space and ground based observatories'', managed by B. Fleck, the SOHO project scientist for ESA.

Students (Ph.D. and Post.Doc.) were trained with this objective in mind. We attracted young scientists from different EU countries which are not so much involved in the SOHO project and the discussion started between them, the leaders of the working groups and the keynote speakers. The conference sessions and the social events were good opportunities to mix people belonging to different groups. For some of them these Euroconferences were the ideal place to present what they were doing using the poster sessions and to place their own work in a larger context.Some collaborations started already during the meeting between researchers and students. All the seniors were particularly glad to meet high-quality post.doc. candidates for solar physics research and particularly for the European Solar Magnetometry Network contracted by R. Rutten. This experience was particularly gratifying in view of the worrisome stagnancy in the US production of young solar physicist.

FIRST EUROCONFERENCE IN CANARIES 1996

The first euroconference organized in Tenerife in October 2-7 1996 organized by M. Vazquez and the SOC was focused on the topics of the Sunspots: what do we know now ? what could we learn with the new instruments ?

We had a first lecture made by Dr Casanovas about the first observations of the sunspots by the Chinese 3000 years AC over quiet lakes and then later by Galileo at the beginning of the Seventeenth century. Although the sunspots have been observed and understood by Galileo in 1611 and even before or simultaneously by other observers, Ch.Scheiner, A.T. Harriot, J.Fabricius, they remain a very deep topics of uncertainties. The energy of the Sun comes from the inner core where thermonuclear reactions take place. The energy is transported by different mechanisms : the radiation (the sun light), the kinetic energy (the gas of the sun is dynamic and particularly animated by convection motion, like water in a heating can), then the global motions in the sun, poloîdal and toroîdal, generating magnetic field like in a dynamo effect. The magnetic field is concentrated along field lines which emerge at the solar surface and form the sunspots. The material inside the field lines cannot be heated by convection, and stays cooler than its surrounding atmosphere. They appear on the films darker than the photosphere. The emergence of flux tubes has a maximum of activity every 11 years. Different events or instabilities such as the flares or eruptions of filaments are associated to the birth of sunspots. So it is crucial to understand the relationship between the convection and the magnetic field which is called the magnetoconvection science, including the studies of the long term variation of the solar activity and of the energy of bipolar groups. We have invited keynote speakers and observers who compared their models in 1 or 2 D with the observations. It appears that it is difficult to make a 3D simulation up to now, and theoretical sunspots are still like slabs. Nevertheless new technics like tomography were presented to solve this 3D problem and are very promising. The sunspot exhibits in the outer atmosphere fine structures which are the emerging flux tubes. The magnetic field is concentrated in very thin tubes certainly at the limit of the spatial resolution of Themis. The physics in concentrated magnetic field tubes is different from the external atmosphere, the radiation is polarized. We use this property to derive the strength of the magnetic field. Different technics of computation have been presented. The observed motions may be waves travelling along the tubes. The direction of the motions around sunspots is radial according to spectral signatures of lines formed at a temperature close to 4 000 · K, the matter goes from the center of the sunspot to the edge or penumbra, it is well known as the Evershed effect. But in higher temperatures (10 000· K) the motion is reversed. The theoreticians try to modelize this phenomena by siphon flows due to pressure difference but some inconsistency remains, we would expect to observe higher fields outside the sunspots than inside which is unrealistics or may be due to unresolved structures?

An other important part of the meeting was devoted to the new observations obtained with the instruments of the SOHO mission.It was the first meeting where such results have been presented. The first results of helioseismology, a science which allows to "see" what is inside the sun, did not show the well expected g mode (oscillations which would be reflected on the core of the sun). We have to wait two years of observations for the confirmation of this statement and/or the theory has to be adapted to these new results.

From the spectrographs observing the atmosphere, the chromosphere and the prominences, interesting results have been presented which also ask questions more than solve problems.

SECOND EUROCONFERENCE IN IOANNINA (GREECE) 1997

The second Euroconference on the Advances in Solar Physics (ASPE97) organized by C. Alissandrakis and B.Schmieder in October 1997 dealt with "Three-Dimensional Structure of Solar Active Regions". Active Regions are the superficial manifestation of strong magnetic fields (10 Tesla), created in the solar interior by a dynamo mechanism, bouyantly rising to the surface of the Sun. Active Regions represent an important topic of study because they provide information on the general cycle of solar activity, a prototype of late-type stellar activity. Moreover, particularly violent episodes of activity, such as coronal mass ejections, or flares emitting high-energy radiation and particles, can disturb the earth's magnetosphere and cause aurorae, disrupt communications, affect satellite orbits, etc. The Euroconference focused on the geometry and structure of Active Regions throughout the whole atmosphere (from the lowest visible layers out to the corona and the heliosphere), both from the observational and the theoretical point of view. Tomography of Active regions was achieved.

The scientific power of performing "coordinated observations" in the field of Solar Physics emerged clearly during this Euroconference. To deduce the full three-dimensional structure of active regions it is necessary to combine multiwavelength data, since the different layers of the solar atmosphere are best observed in specific parts of the electromagnetic spectrum (as governed by their different temperatures or spectral line emissions).

Hence, scientists must conduct coordinated observations, using data obtained nearly simultaneously from a variety of different instruments, both ground-based and space-based. This has become increasingly easier with the development of means of fast communication (e-mail, real-time WWW sites), that allows a rapid exchange of information on the best solar active region to observe and the current data from other observing sites. Moreover, and perhaps more importantly, scientists have learned in the past years how to efficiently combine such huge sets of data, in order to obtain physical results. During the Conference we witnessed how wide-spread and successful such an approach has become, as was testified by the large number of contributions describing or utilizing coordinated observations.

The many contributions dealing with SOHO observations showed how well the mission is performing. While at the 1996 Euroconference (ASPE96) many of the SOHO related talks were essentially a presentation of new observations, during ASPE97 we heard about the physical results that are being produced by the mission. The array of instruments onboard SOHO provides observations with enough temperature coverage to infer the real 3-D structure in the corona, as shown by several presentations (e.g. those by P. Brekke, N. Brynildsen, M. Aschwanden). The comparison of EUV (produced in the chromosphere-to-corona transition region) data obtained from SOHO (such as the images obtained by the EIT, that provide the geometry of the magnetic structures) with radio (produced in the corona) maps obtained from the ground (e.g. with the VLA telescopes) allows one to accurately deduce at which height in the solar atmosphere the radio emission is produced. In turn, from the radio emission one can derive the electron density, and the temperature in all of the points of the structure, hence deriving all of its physical conditions in three-dimensions.

Another rapidly developing theme, very well covered during the Euroconference, was that of the comparison between theoretical models and observations of active regions and their structure. The structure of active regions in the higher layers of the atmosphere (corona) is essentially determined by the magnetic field, since the plasma pressure is extremely low. However, a direct measure of the magnetic field in the corona is currently beyond the instrumental capabilities, so scientists have adopted the method of "extrapolating" the magnetic field structure, measured at photospheric layers, all the way to the corona, using various sets of assumptions about both the field and the plasma parameters.

Up to few years ago, the comparison between such "theoretical" (numerical) models and the observations was mostly limited to the morphology of the structures, i.e. they tried to reproduce the shape, length and orientation of the loops observed in the corona. As we witnessd at ASPE97, these methodologies are rapidly advancing, introducing more and more realistic assumptions, such as mechanisms of coronal heating in order to determine the plasma content of the fluxtubes, and their emission at various wavelengths. These computations are finally compared with the parameters derived by observations such as those performed on SOHO, in order to derive the physics of the solar structures.

THIRD EUROCONFERENCE IN POTSDAM 1998

The third Advances in Solar Physics Euroconference was held in Potsdam, Germany in September 1998 organized by B. Schmieder, A. Hofmann, and J. Staude. The conference topic ''Magnetic Fields and Oscillations'' was wideenough to cater to a range of interests.

Magnetic fields are of course the major agent that make the Sun a most interesting star to see close up, while oscillations in the Sun is a topic where large advances have been made in recent years. The combination, waves in magnetic structures, play a key part in the search for the holy grail of solar atmospheric heating. Let me illustrate this by simply summarizing the invited reviews. Instrumental aspects of solar polarimetry where ably reviewed by M.~Collados (IAC Tenerife).

The new liquid-crystal modulators as well as the increasing sophistication of spectral Stokes vector inversion and of telescope polarization modeling turn polarimetry from an art into a highly precise diagnostic, replacing the simple $V$-profile magnetography of the past decades into quantitative and reliable Stokes vector measurement at high angular resolution. The HAO Advanced Stokes Polarimeter at the NSO/Sacramento Peak Dunn Telescope has led the way; the upcoming IAC Stokes instruments at the German and Swedish telescopes on Tenerife and La Palma promise high resolution; THEMIS spectro-polarimetry should excel particularly in S/N. O.~Steiner (Freiburg) reviewed flux-tube dynamics including his numerical simulations with M.~Sch/"ussler, M.~Kn/"olker, and U.~Grossmann-Doerth in a beautifully presented talk. The simulations are 2D, of flux ''sheets'' rather than 3D flux ''tubes''; when the chair wondered whether all said was bound to turn out wrong since 3D reality was acknowledged to differ intrinsically, Steiner's reaction ''yes indeed, but the 2D results fit the data so nicely'' earned laughter but also respect because these simulations indeed come a long way to explain observed solar phenomena --- the surrounding down drafts earlier diagnosed from the ''V-profile area asymmetry'', the highly dynamical nature of convective buffeting, the formation of magnetic flux concentrations producing the ''V-profile zero crossing shift'', and the excitation of outward-bound shocks that are likely to explain spicules. Even while limited to two dimensions, these so-called ''Freiburg'' simulations represent a large advance in our understanding of the basic building blocks of photospheric magnetism. Much larger flux tubes break through the solar surface in the form of sunspots. No detailed radiative transfer simulations exist yet for them; E.~Wiehr's (Goettingen) review on sunspot penumbrae was therefore observationally oriented. Sunspot penumbrae present perhaps the most complex field configuration observed at photospheric levels, with their dynamic nature as evidenced by the Evershed flow a continuing source of puzzle. The observational emphasis shifts to speckle image reconstruction to obtain high-resolution spectra. Even these may yet fail to reach the scales of the intrinsic morphology, however.

The review of R. Rutten (Holland) emphasized by the contribution of M. Carlsson (Norway) gave a new insight of the chromosphere region located between the solar surface and the corona where normally the plasma temperature goes through minimum before rising again in the outer layers of the atmosphere, the corona. Using ground-based observations as well as space observations obtained by SUMER on SOHO, they showed that the perceived heating of the chromosphere could be regarded as the effect of shock waves in non-magnetic regions. Small, bright regions are very clearly distinguished in the chromosphere, and they are not associated with small magnetic elements, as was previously assumed, but are signatures of shocks.

With J. Staude's (Potsdam) review of sunspot oscillations the focus shifted from penumbrae to umbrae. Umbral flashes are known since Beckers' description in in 1968 and penumbral waves since Giovanelli's 1972 analysis. Both oscillatory phenomena are not understood, while magnetic field oscillations in sunspots were controversial for manyyears. New two-dimensional observations from Tenerife and SOHO have proved the existence of the latter in the sunspot photosphere, and this is a challenge to theorists. The SOHO measurements provided by the spectrometer SUMER, support resonant transmission of magneto-atmospheric waves in the umbral atmosphere.

Oscillations in the solar interior, having to do with solar magnetism, were discussed by A.G. Kosovichev (still Russian but working at Stanford University in the group of SOHO). This keynote speaker is working on the magnetograms provided by the Michelson Doppler Imager (MDI) aboard SOHO with a cadence of one full disk magnetogram every 90 minutes and more frequent observations, with a few minutes cadence, for a small region. He showed new local helioseismology results based on the promising new technique of time-distance analysis, in which the response of the solar surface to localized impulse excitation is measured space-time wise from the surroundings. Stochastically excited waves are measured through time averaging. One interesting result was that flares appear to provide sufficiently strong impulses below the photosphere to permit direct registration of seismic waves propagating through the solar interior. An additional and exciting prospect is the possibility to map the subsurface structure of active regions even before they appear on the surface.

The final review talk was by C. Chiuderi (Florence) who reviewed the physics of MHD waves in magnetic structures masterfully. He emphasized the importance of the fact that the familiar decomposition of wave modes into distinct types breaks down in the nonlinear regime. Even more important is that the resulting nonlinear interaction between waves and medium leads to marked enhancement of energy dissipation possibilities.

WORKING GROUPS

The reviews, oral contributions, and poster presentations were by no means all of the meetings. The ASPE formula also adds extensive plenary working group sessions on topics that involve planning of Europe-wide collaboration. At these meetings these concerned:

1) Solar observing techniques (W.G. chaired by H. Woelh (Germany) and by G. Ceppatelli (Italy) . Some new instruments are close to be fully operational like the Franco-Italian THEMIS and the Dutch DOT, it was interesting to point to the recent progress and to see how difficult it is to upgrade the techniques and make a big step in this area. Some connection with the industry has been achieved.

Two fields of technical research are open. Contacts between specialists were made for the development and the adaptation of CCD cameras for specific problems and collaborations were established to develop the techniques of active optics of telescopes in order to overcome the image deteriorations caused by the Earth's atmosphere

2) Solar data bases (W.G. chaired by T. Roudier (France) and M.Messerotti (Italy). A network of ground based observatories at different longitudes may cover a solar activity event in time. To maximise the scientific output for such cases, we are developing a "Whole Sun Catalogue" (WSC) planned as a central platform of information about all the observations throughout the world on any particular solar event. Reports on the technical developments were given and a round table was used to discuss and convince all the observers of the benefit of such developments. Everybody should feel concerned, otherwise it is not valuable to do this.

3) Coordination between SOHO and ground-based observing. The group was very well chaired by B. Fleck and interesting results were presented. The observations of SOHO now start to be the new boundary conditions of theory development and it was striking to see, for example the interaction of theorists in MHD (magneto-hydrostatic science) with the observers of prominences: these cold clouds standing in the corona, supported and isolated by magnetic fields.

4) Preparations for the August 11, 1999 solar eclipse (W.G. chaired by F. Clette, Belgium). The maximu of the eclipse will go through a large part of Europe from England to the north of France, then going through Romania, Bulgaria and reaching Turkey. It is very important to coordinate the observations. F. Clette, develops a network between observers and engineers,who present some typical instrumentation in order that the observations could be compatible between them.

VISITS OF THE OBSERVATORIES AND SOCIAL EVENTS

Generally the visits to observatories and the social events were good opportunities to mix people of different horizon even if the visits to ovbservatories have a more training direct aspect.

In 1996 the visit of the Observatory of Tenerife was achieved on the last day. Students and others were dispatched in small groups and could discuss all the day long with the specialists. In particular the new born telescope Themis attracted many scientists who wanted to discuss the new technology developed around the vector magnetograph with mirors without polarization and adaptative optics.

In 1997 the visit of old greek theaters and ruines were the times of lot of exchanges between seniors and young scientists.

In 1998 various well-organized excursions did more than generate the usual (valuable) opportunity for shop talk and gossip. Visiting Einstein's summer house in the Havel-side village of Caputh where the meeting was held, gave a sobering impression of the great man's lifestyle. No luxury, essentials only. The pleasure of a garden and a nearby lake to sail upon. Books to generate thoughts, a terrace to catch the evening sun. A pity he had to leave for ever, not long after he acquired it. Visiting the Einsteinturm at Potsdam, presently being renovated, together with the great refractor in the giant dome next door, illustrated the long tradition of Potsdam astrophysics, with Freundlich and Schwarzschild as perhaps the most prominent giants, a memorable experience for any astrophysicist.

CONCLUSION AND PERSPECTIVE

We achieved our main aim: to attract young people in solar physics, stimulating everybody to take advantage of the new facilities open in the field, and to bring together different groups: theorists, observers and engineers.

The impact of the European Conferences has been of different kinds, they stimulated triangle exchange of knowledge between according to the venues and the choosen topics. In general, groups of different types of research (technology, observation, theory). They were considered as training courses for young persons and researchers not specialized in the same field. We think that it is very important to maintain a good European level in know-how in Solar Physics and that the benefit of the new instrumentation should not be transfered to the US where facilities are more available. We want to transfer our knowledge to the less favoured countries where there are already good physicists which train good students, but no money to allow participation in the construction of new instruments or to send the students abroad. The Euroconference in the University of Ioannina was very helpful for the young researcher in Greece; it also improved the mobility of European researchers; personal contacts are very useful for that. Some students from Greece and from Spain, after the two first events, applied for post doc positions in laboratories in France, in the UK, in Norway. We meet during the last Euroconference in Potsdam high-quality post.doc. candidates for solar physics research and particularly for the European Solar Magnetometry Network contracted by R. Rutten and the exchange of information was very successful. We hope that the students were impressed by the new perspectives in Solar Physics.

A disappointment was the slow achievement of the new magnetograph, THEMIS. Because of its new concept of a telescope without instrumental polarization, THEMIS could not be operational before our third Euroconference, and we were still discussing improvements of the instrument. Just by the end of the summer in 1998 they started to get some observations. The primary mirror was not fulfilling the requested specification, and the THEMIS group have to wait until November 1998 to get a better one. So the first scientific results would be expected early in spring 1999, and we would like to extend slightly our series of conferences with a short session to show the capabilities of THEMIS to the young researchers.

We propose to add a one and a half day meeting in 1999 about these topic, concurrent with another meeting and at low cost (see ¢Reports of New Departures¢).

SOC OF THE 3 EUROCONFERENCES

The permanent staff is composed by four members : B.Schmieder (Observatory

of Paris, France), M.Vazquez (Instituto de Astrofisica de Canarias, Spain), P.Brandt (Kiepenheuer Institute, Germany), O.Kjeldseth-Moe (University of Oslo, Norway) Sub-network of universities, laboratories and observatories involved in the project and their responsible :

France: Observatoire de Paris (J.C.Henoux), Observatoire du Pic du Midi (R.Muller), ESA: V.Domingo, B.Fleck,

Germany: Kiepenheuer Institute (P.Brandt, H. Woehl), Astrophysikalisches

Institut Potsdam (A. Hofmann, .J.Staude), Max-Planck Institut fuer Aeronomie in Lindau (W.Curdt),

Spain:Instituto de Astrofisica de Canarias (M.Vazquez),

Italy: Observatory ofTrieste (M.Messerotti), University of Florence (E.Landi),

Portugal:Observatory of Coimbra (A.Garcia),

Greece: University of Ioannina(C.Alissandrakis),

Austria: Institut fuer Astronomie, Universitaet Graz(Hanslmeier)

Norway: University of Oslo (O. Engvold, O.Kjeldseth-Moe),

UK:University College London Holmbury (R.Bentley), University of St Andrews

(E.Priest), Rutherford Appleton Laboratory (R.Harrison), University of

Birmingham (G.Simnett),

Sweden: Royal Swedish Acad. of Sc., Stokholm (G.Scharmer)

PUBLICATIONS OF THE SERIES OF EUROCONFERENCES (CONTRACT ERBFMMACT 950045)

Book : Astronomical Society of the Pacific Conference Series Volume 118:

"First Advances in Solar Physics Euroconference:

Advances in the Physics of sunspots" edited by Schmieder B., del Toro

Iniesta J.C. and Vazquez M.

Annual report 1996 edited by M Saniga (Slovakia, Tatanska Lomnica)

Annual report 1997 edited by A.Antalova and Kucera A.(Slovakia, Tatanska

Lomnica)

Book : Astronomical Society of the Pacific Conference Series (in press)

"Second Advances in Solar Physics Euroconference:

"Three-Dimensional Structure of Solar Active Regions"

edited by Schmieder B., Alissandrakis

Annual report 1998 edited by A.Antalova and Kucera A.(Slovakia, Tatanska

Lomnica) (in press)

Book : Astronomical Society of the Pacific Conference Series (in press)

"Third Advances in Solar Physics Euroconference:

"Magnetic Fileds and Oscillations"

edited by Schmieder B., J.Staude, A. Hofmann (in preparation)

Meudon December 8 1998

Brigitte Schmieder

Observatoire de Paris

France