Eugene PARKER - Médaille de l'ADION 1996

La médaille de l'ADION, fondée par Jean-Claude Pecker en 1962, honore chaque année une personnalité scientifique de notoriété mondiale, dont les contributions ont marqué de façon importante les recherches développées à l'Observatoire de la Côte d'Azur.

C'est Monsieur Eugene Parker, Professeur Emérite à l'Université de Chicago (USA), qui a reçu le mardi 3 juin 1997, à 14h30, à l'Observatoire de Nice, la médaille 1996 de l'ADION.

Membre de l'Académie des Sciences des Etats-Unis il est aussi récipiendaire de la Médaille Nationale des Sciences des Etats-Unis. Monsieur Parker est un grand spécialiste mondial de l'astrophysique solaire, stellaire et galactique. Il est, en particulier, un des fondateurs de la physique des plasmas spatiaux et est un véritable pionnier sur des domaines essentiels tels que le vent solaire ou la génération du champ magnétique à grande échelle par des effets tourbillonnaires. Ses travaux continuent de marquer fortement les recherches développées à l'Observatoire de la Côte d'Azur.

La médaille a été remise au Professeur Eugene Parker par Monsieur José A. de Freitas Pacheco, Directeur de l'Observatoire de la Côte d'Azur, en présence de Madame Frisch, Présidente de l'ADION, de Madame Mathieu-Obadia, représentant le Maire de Nice et de Madame Saint-Cricq, représentant le Délégué Régional du CNRS. Le discours d'éloges au candidat a été prononcé par Annick Pouquet-Davis, du laboratoire Cassini, Directrice de Recherche au CNRS. (Son discours est reproduit ci-après).

Le Professeur Parker a présenté ses travaux dans sa conférence intitulée :

``Spontaneous Discontinuities in Magnetic Fields"

La cérémonie s'est terminée autour d'un buffet offert par l'ADION.





Département Cassini de l'OCA

Dear Professor Parker,

It is a pleasure and an honor to introduce Gene Parker on the occasion of his receiving the medal of the ADION for 1997. One of the requirements to obtain such a medal is that the work be influential, obviously, but influential not only in general, but more specifically for the scientists working here at OCA. Well, this is not difficult because we are an Observatory, and you contributed to many facets of Astrophysics; we all share a common interest in the Sun, and in magnetic fields as well. So, I shall try in the next five minutes to remind you in that light of some of the high peaks of Gene's scientific career. I might add that, as you know, an understanding of the magnetic field of the Sun and of the solar wind, because of the solar-terrestrial connection, is a necessary step in the understanding of our ''close'' environment.

You have pursued with energy a few well-chosen topics and you make us understand them because you always stick to first principles: what are the characteristic time and length scales at hand? What are the forces at play, that move and push things around?

As Uriel told you yesterday, Rocard (père) said that MHD was fine, as long as you did not stay too long with it. So, MHD must be one of those wonderful and rare things in life that are good either way, because you remained faithfully with it!

It all began with a BS from Michigan, followed by a PhD at Caltech in 1951. Your first job as a researcher was in Utah, followed by an interesting episode, the moral of which being that it does not only happen to the bad guys. You told us in Kittila that you applied for a job at the University of, if I remember correctly, Alaska and got bumped out! I see that as an encouragement whereby being bumped out is not necessarily the promise of a bleak future. In your case, indeed quite the opposite.

So you settled for Chicago, where you held a job at the Institute for Nuclear Studies, then in the Astronomy Department, obtaining in 1987 the chair of Chandrasekhar and being presently retired with the title of Professor Emeritus.

I asked you what you meant by retirement, when I witness you being quite active. Your answer yesterday night was that you leave the hacking to the young, but keep a keen interest in the output, be it theoretical, and of course observational, and in compiling the output to draw your conclusions. In that light, the Themis instrument of which our Institute is a full participant should arouse your curiosity and keen interest in small scale structures that it is built to unravel.

In the mid fifties Walt Roberts. the founder of NCAR, offered you a position which you declined to take; but you kept close contacts with both NCAR (you served on the board of trustees of UCAR) and HAO. The HAO connection here at OCA is strong, with several persons having held post-docs there, among whom a 1996 vintage new member of our laboratory, F. Paletou.

I might add at this point that I got some of this insider information from B.C. Low who very kindly provided it to me.

We all know you have written many papers (we all know the Parker 1988a, 1988b,c,d,e,f ... you have not made it in one year to the end of the alphabet), but more importantly, you are among the lucky perhaps, talented certainly who have written many significant papers (where one such paper would be considered sufficient but not guaranteed for the average scientist): to your credit is the first theory of the solar wind, a model of the dynamo, the role of cosmic rays in the galaxy, an instability that bears your name, and the hypothesis - yet to be proven right or wrong - of the existence of nano-flares on the Sun.

It was at a meeting in Heidelberg ten years ago or so where Virginia Trimble, paraphrasing loosely the Book of Genesis reminded us that at first "Lux Fiat, ... campos magneticosque"

Now, the Bible did not say that, and besides, it ain't necessarily so: magnetic fields are not necessarily primordial. You were first in conceiving of the model whereby sufficient skewed twisting of field lines could reinforce the original field. An enormous amount of work in the world has been done since then along those lines, through various devices (that came for example under the name of the alpha-effect). Here in Nice, several people in the wake of Uriel Frisch and his students, and students of his students, yesterday and today - have used their wits to crack out the problem both in the kinematic and in the nonlinear cases, and of MHD turbulence using a combination of analytical and numerical tools, the latter mostly with M. Meneguzzi in Saclay and Helene Politano here. But as you know, many difficulties and open questions remain, among which how to reconcile the old alpha-school with the russian school of Arnold (another ADION medal recipient) - together with, more recently, the Chicago boys - looking at fast chaotic dynamos; is there any physical connection between large-scale and small-scale dynamos?

One thing you made clear from the start is the importance of the dynamic sun; it is active. In fact, it seems active even when deemed quiet, we witnessed together in the cold of a finnish winter a magnificent aurora, when the sun was at a minimum. Recent satellite observations point quantitatively, if less picturesquely to the same; as many here know, the sun in fact is always quite active and I am sure you will wish to comment on that.

Another significant claim to fame for your work came quite early in your career with your explanation for the solar wind. In the mid-fifties the corona, very tenuous and at several millions Kelvin, was quite a mystery. You realised that gravity was not sufficient to hold it and that it would expand outward. Fame needs help, the baraka, that is luck. Your luck was Sputnik, and with Sputnik, a lot of other satellites from the U.S. and the U.S.S.R. followed, and an exploration of our inner environment began, confirming your model on which people still work, 40 years later, improving it for example by taking into account the hydrodynamical instabilities that can arise when considering the effect of the expansion of the wind, I am referring here to the work of Grappin and Leorat.

This solution was not unique, the sun is quite a typical star and many stars were discovered to have winds. In fact many astrophysical objects spurt out matter, sometimes at great speeds and in very collimated impressive spectacular jets. Magnetic fields again are the most likely candidates for collimation, and molecular outflows when seen at high resolution as we heard two weeks ago may in fact be collimated as well, but can nevertheless be considered as part of a wind, a more dynamical earlier version possibly of the wind, stars sending out high speed bullets, the Herbig Haro objects. Here again several people at OCA work on some aspects of this problem, on wind, on T-Tauri stars and the interstellar medium at large.

You have also contributed to an understanding of cosmic rays in the Galaxy. Finally, I will but briefly mention your essential role in the study of the solar corona and of the processes at work to heat it; your seminar is on that topic so I will not comment any further.

In all this time, you have produced more that 300 publications and 3 monographs, you have also obtained 17 medals, including several from Europe: the Gold Medal of the Royal Astronomical Society and the Sydney Chapman, the Norse Academy of Sciences, The University of Utrecht, the German Astromomical Society and in the U.S. among others the National Medal of Science and the Bowie Medal of the American Geophysical Union.

Glancing at the Table of Contents of your first book this morning, written almost 20 years ago, it was evident how much you have influenced solar research in particular, each head of Chapter being today a full slice of research by a whole community: isolated and twisted flux tubes, magnetic equilibria, topology of magnetic field lines, rapid reconnection to name a few, as well as the fields of planets, stars and galaxies. And there are two chapters on turbulent fields, the staple of our own research as I mentioned earlier.

Whereas we might focus on processes, you focus on structures. And this is in fact where we meet: intermittency, i.e. the spatial scarcity of intense structures such as vortex tubes, may be viewed as the culprit for anomalous exponents in the scaling of structure functions of random fields, you might tend to view it as fibrils: their existence, their formation, their characteristic spatial and temporal scales, their interactions and, if I may, their statistics.

I have been a participant in two meetings organized in your honor, in HAO and in Heraklion, and wish you many other such occasions.

You are about to receive one small token of our appreciation and I believe that all the members of OCA are grateful that you should have accepted, and honored us by your presence here today.

Thank you