background

I make it into this volume by the skin of my teeth. In 1957, I remember, as a schoolboy, greeting the arrival on the scene of Sputnik with amazement and no sense that within a decade I would be involved in space science. It all seemed remote from the west country of England where I was growing up.

By 1966 things had changed. I had come to London where possibilities seemed greater. What set me off on my space science career was what in retrospect was the most enormous piece of luck, although I did not recognise it at the time. I was about to graduate (in Mathematics) from Queen Mary College, London and I was set on doing a doctorate with Vincente Ferraro who had been my undergraduate tutor. Fate intervened. Ferraro had a coronary and was ordered to cut back on his work load. He sent me across town to Imperial College where Jim Dungey had recently arrived. Jim was appointed first as a Reader then rapidly given a chair (Professorship) of which more below.

One says of teachers that they ‘taught me all I know’. Of course, everyone says this about influential teachers. Jim did that, but also, by his remarkable prescience or intuition of the magnetosphere, he gave me an enormous headstart in space physics. Happily, as I shall reveal below, in this case I have documentary proof. The effect was that by 1970, I had a way of understanding the magnetosphere that worked but was not generally accepted for another decade or so.

I remember an interview with a tired-looking Ferraro when he explained that he was not going to take me on but that he had recommended me to Dungey. He was a very nice man and I think that he felt badly about sending me off. As if to apologise, he gestured with a sweep of his hand to a shelf of yellow-spined JGR’s on his bookshelves and said something like “I cannot keep up with the rate of new material. One of these comes every month!”. I shudder to think what he would make of what now appears monthly in just JGR-Space Physics. In those days, JGR covered all geophysics and contained maybe half a dozen papers on any space-related topic.

I went across town to meet Jim Dungey in either January or February 1966. I immediately liked him and, what was more important, he accepted me. He decided to take me on after an interview where I remember him doing most of the talking. As far as I can recall, he outlined two potential research problems. One was about the generation of magnetohydrodynamic waves on the boundary between solar wind and magnetosphere and the other was the acceleration of charged particles at neutral points. What else we discussed, I do not know. However, I was sold on the subject.

The former topic became central to my PhD thesis and I have worked on magnetospheric magnetohydrodynamic wave problems throughout my career. Here was an area where there was a lot of work to do and another paper is required to do justice to the way the field has developed since then. However in terms of what I remember of that magic time when I was a PhD student the subject of my thesis is an almost incidental fact.

IMPERIAL COLLEGE

The research group I joined at Imperial in 1966 was small. As I remember, there were three other students, one post-doc, two faculty other than Jim and two US visitors, Bill Ross (from Penn State) and Ted Speiser who had been one of Jim’s students at Penn State. Later another student, more or less a twin with me, Maha Abdalla, joined the group. Subsequently, in the summer of 1967, an undergraduate student, Stan Cowley, came to work for the post-doc, Roger Etherington (an endearing but fierce anarchist who sadly was to die from Hodgkin’s disease within a few years).

The group was small but well connected. Americans at the time seemed to travel more freely than others and there was a regular stream of visitors to the group who came through, no doubt to talk to Jim but also because London was an exciting place to be at that time. David Beard came so often that we named a room after him (also known as the ‘magnetospheric cavity’). Norman Ness who had just discovered the magnetic tail of the Earth (of which more below) was a regular visitor. I remember Fred Scarf whose enthusiasm for measuring waves from spacecraft seemed unusual at the time and yet fundamentally so sensible. Non-US visitors included Roger Gendrin and Valeria Troitskaya. Devrie Intriligator, who was later to convince me Los Angeles was a good place to live, spent a summer with a desk in the office I used. In my years as doctoral student I shared the office with, at different times, Ira Bernstein (the plasma physicist), Carl McIlwain, Alfredo Baños, Chuck Sonett and the South African, Desmond Clarence. All this provided a wonderful education.

In fact Jim’s group was a subgroup of a cosmic ray group which at some time changed its name to ‘Cosmic Rays and Space Physics’ and was headed by Harry Elliot. The other part of the group was firmly experimental. People went off to fly balloons in Africa and the like but the new activity was building space instrumentation. There was a large involvement in the British Ariel programme and the new ESRO (European Space Research Organisation) programme - the joke was that the initials HEOS for the ESRO spacecraft launched in 1972 stood for ‘Harry Elliot’s Own Satellite’! Through this group I met people like André Balogh, Bob Hynds, and Peter Hedgecock who were going to become close colleagues later as well as George Haskell (with whom I worked and who later got me strongly involved in space politics). The division in the group also marked elements in the origin of the field of work. I remember crudely classifying people in the field by their origins - either as radio (ionospheric) physicists or ‘sawn-off’ cosmic ray men. I guess temperamentally the Dungey group was more the former, Elliot’s clearly the latter.

space physics in 1966

The education I received in research working with Jim went much further than working on my particular thesis topic. The smallness of the group meant that one knew what everyone was working on. In fact, the first thing I remember intensely thinking about was not associated with my thesis at all. 1966 had seen the publication of a paper by Kennel and Petschek [1966] which purported to provide a quantitative means of understanding the trapping of radiation belt particles. This paper, combining as it did microscale processes and global effects, was very influential in my own coming to terms with what space plasma physics was about. It needs to be understood that the notion of how collision-free media behaved was still controversial. A critical element of the Kennel-Petschek story was the non-linear (pitch angle) diffusion of particles which was self-sustaining because particles released energy as they diffused. The notion of diffusion being a saturation process was central in the recently derived theory for the saturation of electrostatic plasma oscillations derived both in the USSR [Vedenov et al., 1962] and in the USA [Drummond and Pines, 1962] at around the same time. I believe the junior faculty member, Jeff Klozenberg, who had come to Jim from Culham Laboratory, had been to a summer school in France in 1966 and paid the price of his ticket by lecturing to us on quasilinear theory through the autumn of that year.

Jim Dungey dominated activity in the group. Once I started working with Jim, I realised that his mode of thinking was regarded by many as eccentric. This could put people off attending to what he was saying. His presentation was the thing that was really different. He speaks and writes ‘telegraphically’, i.e. in short sentences, which express only the essence of an argument. I found his brevity immensely appealing (perhaps because I have never developed the knack myself). Jim’s response to ideas was always interesting. Assuming you had already grasped the obvious, he would leap to a further implication that you had not yet reached. Once one had the hang of it, one learnt a lot.

It is hard to get back into the mind of the time. So much of what seemed radical and off the wall at that time is now commonplace. In preparing this article I sat and tried to think what I learnt then and what I learnt later. Shockingly, I concluded that just about every useful idea I have exploited in a career in solar terrestrial physics spanning thirty years had its seed in ideas picked up whilst a student at Imperial College. However it did not seem like that at the time. What has happened in the intervening years is that the old orthodoxies have been swept away and the old barriers to understanding have gone with them. In order to patch together the feelings of the time, I would like to explore this a little.

Jim Dungey’s greatest contribution to magnetospheric physics must be his open magnetosphere model. It was launched on the world in a famous Phys. Rev. Lett. in 1961 [Dungey, 1961], but in 1966 it was clear that Jim’s ideas in this sphere were still regarded by many people working in solar terrestrial physics as from the radical fringe. A direct benefit to me was that accepting the basic ideas of the open model in the sixties, gave me a ten year head start in my career. It all seems so straightforward now that magnetic reconnection couples the solar wind and magnetosphere differently when the interplanetary field is northward or southward. It is hard to see why people had trouble coming to terms with the idea.

A couple of examples of the barriers to understanding ideas that then existed might illustrate the dark ages we lived in. I was sent to Jim by Ferraro. Ferraro always took a personal interest in my progress. I felt he wanted to be reassured that he had not disadvantaged me by sending me away. Ferraro’s original claim to fame was his work while a student at Imperial College with Sydney Chapman in the early thirties. Chapman and Ferraro had first suggested that the Earth’s magnetic field might be contained within a cavity by the passage through space of corpuscular material emitted from the Sun during solar disturbances. The cavity would be bounded by a thin boundary later to be called the magnetopause (which to this day is still said to carry the ‘Chapman-Ferraro’ current). The formation of such a boundary was still an interest of Ferraro’s in the late sixties. A competing idea of magnetic storms was advanced by Alfvén in the 1940’s who postulated the penetration of an electric field from interplanetary space into the Earth’s field during storm-time. Alfvén’s model completely ignores the formation of the Chapman-Ferraro boundary, which of course, to a first approximation excludes the magnetosphere from direct experience of the solar wind electric field. As a model of magnetic storms, both ideas were wrong. However because the Sun continually sends out a stream of charged particles into space, the solar wind, Chapman and Ferraro’s idea certainly explained the existence of a terrestrial magnetosphere whilst Alfvén’s idea of an electric field, although he had the direction precisely wrong, is arguably at the root of our current understanding of geomagnetic disturbances. For Ferraro the penetration of the interplanetary field remained a major puzzle. At one of the early national MIST (Magnetosphere, Ionosphere and Solar Terrestrial Physics) meetings I can remember him asking after a talk by Stan Cowley about the magnetic neutral sheet, “But where does the electric field come from?”. In similar spirit, I recall talking in La Jolla with Hannes Alfvén about his admiration for Jim Dungey. Alfvén, a man not given to acknowledging lapses, admired Jim, he said, because he not only recognised that a magnetopause would form but also that the electric field would penetrate it. Alfvén’s real admiration was for the fact that Jim had seen that a magnetopause would form. When I gently suggested that Chapman and Ferraro had got there first, he would have nothing of it “No, their idea was wrong. They did not include the solar magnetic field.”.

A second issue which might illustrate the dark ages, concerns the Earth’s tail. This was a relatively recent discovery (by IMP I in 1964) when I was a student. The presence of an extended magnetotail behind the Earth proved conclusively that the magnetosphere was not raindrop-shaped but that the magnetic field splits into northern and southern lobes containing respectively field pointing towards and away from the Earth. Its length was not clear and debate started in the pages of JGR [Dessler, 1964; Dungey, 1965]. In fact, the existence of magnetotail at all is extremely good evidence of the need for the Dungey open model magnetosphere. The field lines have in some way to be dragged out to obtain the observed configuration. One does not even need to believe in the tenets of magnetohydrodynamics to see that the body forces exerted by the field in the near tail are towards the Earth and extreme and there must be an effective mechanism for tugging in the opposite direction. Oddly the discovery of the tail did not seem to be greeted at the time by any large body of people as a triumph for the open magnetosphere model propounded by Dungey. Part of the reason for this must have been the topological nature of the sketches showing the field configuration which bear little resemblance to the actual geometry [cf. Figure 1, which I discuss later.]. However, even today an audience can seem to have trouble making the connection, but against a background of the apparently competing ideas of Chapman and Alfvén and others, it was much harder.

There were a lot of contradictory and confused ideas around in 1966. It is important to understand that fact or one cannot understand why it took so long to make the ultimate progress we did make.

enlightenment

On the issue of how the magnetosphere worked I made my own private resolution. In those days students had a lot more time to read around their work (and there was a lot less to read). Jim did not spoon-feed one and one was left very much to do one’s own background reading. As a result, I can remember coming to an independent conviction that Dungey had to be right after a bout of browsing in JGR and the limited number of conference proceedings then available. Epiphany was seeing Don Fairfield’s work [Fairfield and Cahill, 1966] which correlated the geomagnetic disturbance DS current system with southward interplanetary field occurrence. Don had been a graduate student of Jim’s at Penn State and I think that the work had been part of his thesis. Since then innumerable connections have been established between the sense of the interplanetary field and geomagnetic response. Such effects, whatever they may be, cannot be explained by magnetohydrodynamics alone. MHD effects are insensitive to the sense of the magnetic field. The reconnection process which Dungey postulated to occur at the magnetopause did depend on the sense of the external field. Once you had accepted that reconnection occurred, many related phenomena or epiphenomena were open to explanation. In particular, one was no longer puzzled by why there was a magnetopause and/or by why there was an externally driven magnetospheric electric field.

In fact, Jim Dungey was supremely right about the open magnetosphere but in fact he was right about lots of things, indeed rarely wrong. In 1966, he had thought about many of the basic problems of the magnetosphere in his own way. Only slowly did the rest of the world come round to that way of thinking. My luck was to meet him and pick up the rules at just the right time.

inauguration

‘History belongs to the winners.’ In planning this article, I was haunted by the fact that so much of what Dungey’s group thought was true in 1966 was proven correct that the story would all seem a little unlikely to an audience who did not remember the time in question.

Happily in pursuing evidence of what we did and did not know I came across excellent documentary proof of Jim’s overall prescience in matters solar terrestrial. Whilst I was looking for material for this article, my secretary proposed I look at Jim’s inaugural lecture. This was a great idea. The inaugural text encapsulates well the knowledge one came to take for granted at Imperial College in the late sixties. It stands well the test of time.

At Imperial College, on being appointed to a chair (the term for making the rank of professor in England) the new professor is expected to give an inaugural lecture. Jim gave his lecture on May 3rd 1966. At that time all inaugural lectures were published, a tradition that has lapsed somewhere in the intervening years. (No doubt because now we are all so busy filling the pages of journals like JGR with our outpourings instead.) Publication took the form of an annual collected volume of inaugural lectures. In addition bound off-prints were made of each lecture (published at a price of two shillings and sixpence by Imperial College).

Jim’s lecture title is rather prosaic: ‘The Magnetosphere’. After a crack about taking Patrick Blackett’s old chair, Jim mentions the long interest he has had in the origin of the aurora. He refers to Chapman and Ferraro (who are clearly both present in the lecture theatre) and their theory that that the Sun might throw out streams of ionized material and that these would then be held off from the Earth by the formation of a magnetic cavity. There is no doubt in Jim’s mind about the origin of the idea of the magnetopause here. He then goes on to outline Ludwig Biermann’s and Eugene Parker’s post-war contributions to the recognition that there could be a continuous solar wind culminating in the Mariner II spacecraft’s actual measurement of a supersonic solar wind as Parker had predicted.

Jim then goes into a concise description of the basic unifying concept of MHD, the notion that the magnetic field is frozen into the plasma and field lines move with the plasma. He then introduces another central tenet of MHD, magnetic field tension ‘appreciated by Faraday but then somewhat forgotten for a time’. Oddly he does not mention the allied concept of field pressure which is central to the formation of the magnetopause and the Chapman-Ferraro cavity. Tension, however, is the central element in the open magnetosphere, the model he is to describe later.

Next he describes the solar wind and the interplanetary field. The source of heat in the corona which causes the solar wind to flow was a mystery then as it still is now but once given the high temperature of the corona, the outflow is a consequence. The recently discovered interplanetary field sector structure is described as a simple consequence of frozen-in flow. The solar wind established, he goes on to discuss the current (i.e. 1966) state of the Chapman-Ferraro problem of defining the magnetopause shape assuming an unmagnetised solar wind incident on the Earth’s dipole field. David Beard (no doubt present) comes in for praise. There is mention of hypersonic gas dynamic flow models for the solar wind flow about the magnetosphere being developed. Almost certainly Jim had in mind the work by John Spreiter and colleagues whose first publications on the solar wind magnetospheric interaction were appearing. These workers included an upstream shock but retained the unmagnetised assumption for the solar wind for dealing with the dynamics of the interaction. Even today, thirty years on, theory has not completely included the magnetic field in our understanding of magnetosheath dynamics and so, as my colleague Margaret Kivelson and I know, one can still get involved in controversy on the topic.

Finally the text gets to what is Dungey’s magnum opus, the open magnetosphere. It is not introduced in any way that would lead one to suspect that 30 years on it would be regarded as the most important thing the speaker had done. Neither is there any indication of the passions that the model could arouse even then and the controversies and arguments that would rage for the next decade and a half until it achieved general acceptance. Rather Dungey writes in the spare economical style mentioned earlier which repays attention to each word.

Figure 1 is reproduced from the lecture. Jim explains that it was his PhD supervisor, Fred Hoyle, who suggested that the interplanetary magnetic field could be important in the magnetospheric interaction (I wished I had known this reference when I talked to Alfvén.). One starts (as Alfvén’s comments implied) by ignoring the Chapman-Ferraro effect and simply adds an interplanetary field to the Earth’s dipole. The field lines then interconnect from Earth to interplanetary space. If the interplanetary medium is moving, the existence of an electric field both in space and in the Earth’s environment is natural. Even without allowance for the Chapman-Ferraro effect, current sheets form between the solar and terrestrial plasma where the field reverses and the plasmas move together. At the current sheet the frozen-in approximation breaks down and field lines break and change partners, the process being called ‘reconnection’.

The field topology of Figure 1 implies that the polar cap field lines of Earth extend into the solar wind. Although the sketch is topologically sound it does not show the extended field configuration that naturally results as field lines connecting to earth at one end and to the solar wind at the other are drawn out by the solar wind flow behind the Earth to form the tail. In this sense the tail is a natural result of the open model.

Dungey then goes on to discuss two other consequences of the open model. The first is the ionospheric circulation system predicted by the model. This is the effect that Jim himself credits with inspiring him that the open model would work. The electric field imposed on the polar cap field lines by the solar wind flow must extend down into the ionospheric levels and there it must drive horizontal ohmic currents. The most naive view of the ionosphere is to think of the ions as bound by collisions to the neutrals. In contrast the electrons can still move with the field. The horizontal current induced by the field line flow is thus opposite to the projection of the field line flow on to the ionosphere. The global pattern of current that one derives is that of the DS system. It was this very current system whose strength Fairfield had used as a measure of geomagnetic disturbance and had shown was correlated with the occurrence of southward interplanetary field just as is required for reconnection. Oddly, Jim makes no reference to Fairfield here.

The next part of the lecture is a delight for what is missing. Dungey describes some of the implications of unsteady behaviour in his model. He refers to magnetic bays and to ‘pt’ pulsations and auroral storms and the auroral oval about the pole. He describes the characteristic sudden brightening and the subsequent explosive-like behaviour of the aurorae and associated phenomenology which occurs in conjunction with a magnetic bay. He also says that at the time of magnetic bays the tail field is seen to suddenly decrease with bay onset and that the aurorae move poleward after breakup. Here is where Jim relates the bay to the DS system and mentions the correlation with southward interplanetary field found by Fairfield and Cahill. He fits all the phenomena into the framework of his reconnection model of the magnetosphere by postulating a sudden onset of magnetic reconnection in the magnetotail current sheet as the seat of activity.

The words that are missing are, of course, ‘magnetospheric substorm’. The terms ‘bay’ and ‘pt’ have now disappeared. The bay is the trace on the ground magnetogram which looks rather like a bay on a coastal map. The ‘pt’ described as having ‘a pizzicato waveform like that of a plucked string with a period of a few minutes’ is now known by the name ‘pi2’. Dungey’s description of what we know as the magnetospheric substorm would be well-recognised today.

Less well recognised now but more familiar in 1966 were the Van Allen radiation belts. He credits Alfvén with the introduction of the notion of adiabatic invariants to explain their trapped orbits. Dungey was involved in one of the critical studies that showed the external source of the belts [Nakada et al., 1965]. This important and perhaps under-recognised paper resolved the external nature of the source by looking at the particle distribution as a function of adiabatic invariants. Figure 2 (also reproduced as is from Dungey’s inaugural lecture) shows that distribution function (or phase space density) deduced for different values of adiabatic invariants (, magnetic moment, J longitudinal invariant) increases toward higher L values. The inaugural mentions the external source and suggests that the particles enter from the tail. Jim then notes that the system pumps the particles up to their final energies by a form of stochastic acceleration. We take this for granted now. These were new and even radical ideas in 1966.

The next section is specialist also. He describes waves. All the waves mentioned are electromagnetic. Kelvin-Helmholtz instability on the magnetopause is mentioned as are whistlers, one of the earliest evidences for the existence of the magnetosphere. The latter waves are very interesting from a plasma physics point of view because of the clearly structured nature of their geophysical emissions. Jim continues with some insights into the non-linear interaction of waves with particles in a collision-free plasma and the phase space ‘stirring’ that is behind phenomena like VLF-stimulated emissions.

What is missing is any discussion of electrostatic waves or indeed of any of the waves that do not produce a direct electromagnetic response on the ground. This was an area of experimentation which was neglected in the early days. Not until Fred Scarf had flown his electric antenna on OGO 5 in the immediate years to come were these waves detected or their significance appreciated and only in the next decade was the Earth’s aurora seen as a source of radio waves. Subsequently, the sophistication of wave instrumentation improved substantially and later spacecraft like GEOS and ISEE had very fine plasma wave measurements. Some of the finest magnetospheric plasma physics has come out of such wave instruments and the belief expressed by Dungey that the magnetosphere could be a laboratory for plasma physics has been well borne out.

closing remarks

In respect of using the magnetosphere as a laboratory for cosmic plasma physics, the recent loss of Cluster is particularly tragic and in this respect the closing section of Dungey’s inaugural written almost exactly thirty years before the loss of Ariane 501 is extremely ironic. Whole sections of Jim’s prescient writing merit quoting. Remember these segments were written thirty years ago.

“Looking to the future I believe that progress requires bunches of satellites, though these are as yet in no published program..................”

“When one comes to study waves, bunches of satellites are also needed from several points of view. First one wants to know the geometry of waves and second their direction of propagation. For any magnetic disturbance it would be extremely useful to obtain the curl of the magnetic field because this tells one the current.”

“Steady currents are of direct interest and in the case of waves the more reliable part of hydromagnetic theory then enables one to calculate the electric field and the flow of energy which is a very important guide to the location and strength of the source of the waves. Unfortunately, few people yet appreciate the need for satellite bunches and, since satellites are being launched singly, the scientific returns are less than they could be.”

In the event, ‘Cluster’ was a much nicer name than ‘Bunch’. It was to be a wonderful mission, one I had waited for throughout my career. I trust that the idea for what would have been the ultimate space physics mission will not have died with the explosion of Ariane 501. In any event, the efforts of the hundreds of scientists who were/are part of the Cluster team showed that in the end people did start thinking Jim’s way. For my part, I was taught how to think that way earlier than most and to me it will always seem I got a serious headstart from that.

References

Dessler, A.J. Length of the geomagnetic tail, J. Geophys., Res., 69, 3913, 1964.

Drummond, W.E. and P. Pines, Non-linear stability of plasma oscillations, Nucl. Fusion, Suppl, 3, 1049, 1962.

Dungey, J.W., Interplanetary magnetic field and the auroral zones, Phys. Rev. Lett., 6, 47, 1961.

Dungey, J.W., The length of the magnetospheric tail, J. Geophys., Res., 69, 3913, 1964.

Fairfield, D. H. and L.J. Cahill, Jr., Transition region magnetic field and polar magnetic disturbances, J. Geophys., Res., 71, 155, 1966.

Kennel, C.F. and H.E. Petschek, Limit on stably trapped particle fluxes, J. Geophys., Res., 71, 1, 1966.

Nakada, M.P., J.W. Dungey and W.N. Hess, On the origin of the outer belt protons 1., J. Geophys., Res., 70, 3529, 1965.

Vedenov, A.A., E.P. Velikhov, and R.Z. Sagdeev, Quasi-linear theory of plasma oscillations, Nucl. Fusion, Suppl, 2, 465, 1962.

Figure 1. Taken from J.W. Dungey’s published inaugural lecture, the original caption of this figure reads “Outline model of the magnetosphere”. The diagram’s purpose is to show the topology but its simplicity (and the absence of a magnetopause) certainly confused the more literal-minded in the community.

Figure 2. The distribution function of energetic protons plotted against distance from the Earth for fixed values of the two adiabatic invariants, , I. The outward gradient is evident and the external source thus is pinpointed. Once again, the figure is taken from Jim Dungey’s inaugural lecture. This (informative) version of the figure is interesting to compare with that used in the actual Nakada et al. [1965] publication.

Figure 3. The author in spring 1966. It might seem in keeping with the reputation of those times that it looks as if he has just rolled a joint; in fact close inspection reveals that the item being inspected is a popsicle stick.