AAS-Biographical memoirs-Giovanelli

Ronald Giovanelli was born in Grafton, New South Wales, on 30 April 1915, the only child of Irwin Wilfred Giovanelli and his wife Gertrude May, née Gordon.

Ronald's great-grandfather, Guiseppe Giovanelli, migrated from Ravenna, Italy in the 1850s, reputedly for political reasons as a supporter of Garibaldi after his unsuccessful defence of the newly-formed Roman Republic against the French and Austrians. He married in Sydney and his son George Henry (1857-1920) lived and died in Grafton, New South Wales, marrying Lucy Ellen Arkey in 1878. They had a family of ten, Irwin Wilfred being born on 7 August 1887.

Irwin attended school in Grafton and then left to study at the Teachers' College. He returned to become one of the first teachers at Grafton High School. During his career as a mathematics teacher he became well known and highly respected throughout New South Wales both as teacher and headmaster. Ronald spent his early years attending primary schools in the small country towns of Milton, Trundle and Forbes under the headmastership of his father. It is likely that this association was responsible for his own dedication to the teaching of physics and astronomy, even when this involved the hardship of an excessive work load.

Ronald's secondary education was delayed for two years until he reached the age of twelve, when it was felt that he was old enough to leave home and board privately in Sydney while attending Fort Street Boys' High School, one of the leading schools in New South Wales. He excelled academically at Fort Street, where he was made a prefect and won a Public Exhibition to the University of Sydney. While at school he also studied the piano, the beginning of a lifelong association with the arts. His generation of the family showed considerable talents in both science and music; another grandchild of George Giovanelli was a PhD in plant physiology and two others graduated at the top of the New South Wales State Conservatorium of Music. One later became a leading concert pianist. While still at Fort Street, Ronald proved to be a good sportsman and he later became an excellent tennis player.

In 1933 he proceeded from Fort Street Boys' High School to Sydney University, where he graduated in science in 1937 with First Class Honours in physics. He was awarded his MSc in 1939 and his DSc in 1950. The scientific research that earned him these degrees also led to the award in 1949 of the Edgeworth David Medal. This award, by the Royal Society of New South Wales, was for the most distinguished research contributions by a scientist under the age of 35 years.

Giovanelli's long working association with the Commonwealth Scientific and Industrial Research Organisation (CSIRO) is discussed below, but there was also a lighter side to this association. During and after the war years the staffs of the National Standards Laboratory (NSL) and the contiguous Division of Radiophysics joined together in social events: dances, concerts, sporting contests, bushwalking expeditions, parties and other social gatherings. Ronald's interests in music, tennis and generally in good fellowship ensured his involvement in many of these activities. Among his many friends was Alan (A.F.A.) Harper, who writes that:

...it was a delight to count Ron as a friend, as so many did. While dedicated to his special interests at the time, he had a puckish sense of humour and was well able to relax with his friends, all of whom regarded him with affection even when he was being difficult.

The Standards and Radiophysics Laboratories were predominantly staffed by single men and women, so it is not surprising that many found their life-time partners within the same laboratories. There were more than ten such 'in-house' marriages, one of which was that of Ron with Katherine Hazel Gordon on 8 February 1947. They had two children, Lesley Anne (born 1948) and Phillip Gordon (born 1950).

Kath Gordon was one of the first laboratory assistants in NSL and was (and still is) an enthusiastic and extremely talented painter. Consequently their married life was one of widespread contacts with both scientists and artists from all over the world. In their many sojourns in the USA, the UK, France, West Germany, Holland, Italy and India, the Giovanellis were always greeted by friends and frequently stayed in the homes of friends. These included many of the leading solar astronomers in the various countries. In Australia, Ron was very much a family man, retaining a wide circle of family contacts and always ready to give support and assistance to his relatives as well as to his other friends and colleagues.

Ron Giovanelli died after a long illness on 27 January 1984 in the Royal Prince Alfred Hospital, Sydney.

Standards of physical measurement

Accurate standards of physical measurement were urgent requirements for isolated Australia during World War II. CSIRO (then CSIR) responded in 1940 by recruiting a number of physicists for training in England. It was then that Giovanelli commenced his long association with CSIRO when he was awarded a Science & Industry Scholarship for training at the National Physical Laboratory (NPL). The objective was the creation of a nucleus of staff to establish an Australian National Standards Laboratory, now known as the Division of Applied Physics, National Measurement Laboratory. Giovanelli and two other young trainees joined six other Australians already stationed at NPL under the direction of G.H. Briggs, Officer-in-Charge of the Physics Section of the NSL.

As temporary expatriates living under war-time conditions, these nine Australians became a very close-knit group of life-long friends.

Three, including Giovanelli, were bachelors who shared a boarding house at Teddington. He was also one of six who formed the 'Australian Section' of the NPL Home Guard. Other activities included visits to scientific meetings at the Royal Institution in London and a visit to Cambridge University where Giovanelli's earlier work at Mt. Stromlo gained him a memorable meeting with Sir Arthur Eddington.

At NPL he specialised in optics, light and photometry, and was extremely busy working with NPL personnel and at the same time arranging for the purchase and dispatch of equipment for the Australian laboratory. Most of the nine Australians returned to Sydney in late 1940, but Giovanelli continued at NPL to deal with outstanding orders for equipment.

In 1941 he returned via the USA and Canada where he established valuable and long-standing contacts at the National Bureau of Standards (Washington, DC) and the National Research Council of Canada (Ottawa).

On arrival back in Sydney, Giovanelli became an officer of the Physics Section of NSL, being responsible for optics and photometry. As with the other NPL trainees, he was initially wholly concerned with setting up the equipment purchased abroad and with the training of staff. His fellow workers at that time recall that he was most concerned that he was not able to make a more direct contribution to the war effort. He need not have worried, because a series of problems soon presented itself.

War-time and post-war optics

A problem which has been encountered by various countries at the onset of war is a shortage of optical glass. Such was the experience of the USA in 1917 and of Australia in 1939, the reasons being that overseas orders were not met and the manufacturing techniques were not available locally. Australian approaches to glass manufacturers in the United Kingdom and elsewhere were met with a 'wall of secrecy'. However, it was found that, following their 1917 problem, the USA had maintained two important centres of research and small-scale production of optical glass. One of these, the National Bureau of Standards in Washington DC, was thrown open to Australian scientists, including G.H. Briggs and Giovanelli of the Australian NSL.

The information made available to this team led to the manufacture of high-grade optical glass in Australia. Some 620 melts were made and all had their refractive indices and homogeneity measured at NSL. Australia's war-time requirements were met and the foundations were laid for post-war optical industries. Optical glass was even exported during the war to India.

Another of Giovanelli's war-time projects was the development of goggles for anti-aircraft spotters. In the tropics these spotters often suffered eye damage following the observation of dive-bombing aircraft approaching from the direction of the sun. The solution was tinted lenses with small centrepieces of very dark glass just large enough to cover the sun. Another successful project was that relating to 'dark adaptation' by pilots and gunners of aircraft. The solution, briefly, was the use of red light of correct intensity to illuminate instrument panels.

At the conclusion of the war, the NSL turned to the task of providing calibration and other measurements of a wide range of physical quantities. Meanwhile, however, the war had left a new set of problems in optics, one being a serious shortage of optical scientific instruments for use in teaching in the rapidly expanding universities. In particular, some 1300 microscopes were needed, and tests of these were carried out at the NSL by W.H. Steel under the direction of Giovanelli.

The main objectives of the laboratory remained the provision of standards of physical measurement and the development of lines of worthwhile research necessary in such a laboratory to attract and hold high calibre scientific staff. Giovanelli was initially in charge of a group concerned with light and photometry and the establishment of calibration facilities and other properties; he was later head of the section of the Division of Physics in CSIRO concerned with these matters. The fields of measurement included colorimetry, spectrophotometry, photometry, haemoglobinometry, reflectance and the properties of optical glass prisms and lenses. The optical workshop, which had made a significant contribution to the war effort, was crucial to many of the Division's subsequent projects in both measurements and in Giovanelli's own concern with solar observations discussed below.

Throughout his career, Giovanelli spent much of his time on national and international committees and related activities. His war-time activities with optical munitions led to his service on the Optical Munitions Panel, responsible for the planning of Australian research and development in this field. Later he served for many years on the National Standards Commission, 1959-1976, where he contributed greatly to Australian Standards in the fields of optics, photometry and colorimetry.

The work of the Optical Munitions Panel and the development of optical research in Australia is discussed in some detail in an article by H.C. Bolton in the Historical Records of Australian Science (5[4], [1983], 55).

Solar observational astronomy

The major portion of Giovanelli's professional career was as a physicist concerned with optical measurements as outlined above. However, this was not his main research interest, which was solar astronomy. After graduating in science at Sydney University, he found few opportunities offering for a career in physics. He made a most fortunate choice of a Research Fellowship at the Commonwealth Solar Observatory at Mt. Stromlo, near Canberra. Here he spent the years 1937-39 gaining experience in optical observations of phenomena in the solar atmosphere. He made many observations and developed an intense interest in this work which remained his main professional concern for the rest of his life.

This early work was concerned mainly with solar flares and related phenomena occurring usually in the vicinity of sunspots. The physical causes were not understood and speculation tended to centre on vortex motions or other hydrodynamic effects. The equipment available at Mt. Stromlo was not of outstanding quality and so Giovanelli concentrated on obtaining sufficient data to allow good statistical results to be determined. These included correlations of flares with geophysical effects such as auroras, and the main structural characteristics of the optical flares and their relationship with sunspots. From all of these results Giovanelli concluded that flares are basically an electromagnetic phenomenon in which electrons are accelerated by electric fields induced by changing magnetic fields. The theoretical development of this idea had to wait until the end of the war. It is discussed in the following section.

The flare phenomenon and other problems in solar physics led Giovanelli to decide that a solar optical observatory should be created within the CSIR, but this project had to be postponed for more than a decade.

In the early 1950s the pressure of work connected with standards of measurement fell to a level where Giovanelli was able to return to solar observations. His ambitious project was a world-class solar observatory on Australia's highest mountain, Mt. Kosciusko. This project advanced as far as a sky brightness photometer, but for various reasons was then abandoned. A much less ambitious first step was made in 1954 on the roof of the NSL near the centre of Sydney. This was a poor site because of haze, but had the compensating advantage during its developmental phase of being situated above established workshop and laboratory facilities. The observations undertaken comprised a flare patrol, providing continuous monitoring of flares or localised enhanced chromospheric emissions. This programme did not require high quality seeing and so the poor quality seeing was not important.

The 'flare patrol' was a world-wide co-operative effort to ensure that optical observations were available for every solar flare. Other measurements, including solar radio emissions, geomagnetic storms, auroras and other geophysical effects could then be related to particular optical flares for a better understanding of the whole complex 'flare event'. The flare patrol programme was later moved to a new observatory site at Fleurs and finally, in 1965, to the permanent site at Culgoora where it continued for many years to provide a huge accumulation of statistical data.

The flare optical observations added greatly to our understanding of the flare event. They provided comprehensive observational studies of some new effects namely the flare surge and the flare puff as a specific cause of the Type III radio burst. Optical observations were also made and analysed of the much more violent solar atmospheric disturbance responsible for the Type II radio burst. Other observations provided the distribution of flare heights in the solar atmosphere.

The second step in Giovanelli's observatory programme was the establishment in 1956 of a small observatory at Fleurs, further from the centre of Sydney and consequently with better seeing. The first instrument put into operation at Fleurs (by R.E. Loughhead and V.R. Burgess) was a conventional photoheliograph, a general-purpose instrument capable of performing a variety of tasks when used with auxiliary equipment. The decision as to which of these various tasks should be undertaken was vital to the future of solar observations in Australia, and it was early in the Fleurs era that Giovanelli made the bold decision to embark on the design and construction of a world-class filter telescope or spectroheliograph.

The sun being a highly ionised gas with magnetic fields, the basic physical properties most needed for an understanding of solar phenomena are temperature, pressure (or density), velocity and magnetic field, together with their variations in space and time. Giovanelli's ambitious decision was to attempt to measure these quantities simultaneously over extended solar regions in short periods of time. To do this required special techniques, in particular the construction of optical filters of extremely high spectral and spatial resolution to provide an image of a large part of the solar disc in the light of a small part of a particular special line. The first such filter, using the Ha line, was a 1/8 Å birefringent filter whose design and construction involved a number of physicists including W.H. Steel, R.N. Smartt, R.E. Loughhead and R.J. Bray.

The birefringent filter was finally brought into operation at Fleurs by J.M. Beckers, a young graduate of Utrecht University and now director of the Advanced Development Program at the National Optical Astronomy Observatories, USA. Of that project Beckers wrote to me as follows:

That was true on-the-job training. I loved it. It formed the basis of my future career, I will never forget that Giovanelli provided that opportunity for me.

Later the filter was used by J.T. Jefferies, another of Giovanelli's students and now the director of both the National Optical Astronomy Observatory and the Sacramento Peak Observatory in the USA. Jefferies concentrated on the measurement of (line-of-sight) chromospheric velocities over extended areas of the solar surface. This investigation provided important results and the technique was subsequently adopted by a number of other observatories around the world.

The third and final site for a CSIRO solar optical observatory was at Culgoora in north-eastern New South Wales. This site was chosen to be adjacent to a solar radio observatory and there the optical observations have continued since 1965.

The main instrument at Culgoora is a 30 cm refractor, and after some preliminary observations with a 1/2 Å filter, the 1/8 Å birefringent filter was moved from Fleurs. This filter had provided some useful results, but it was found that a substantial proportion of the light transmitted did not originate in the chromosphere but rather in the white light of the photosphere. This problem was solved by R.E. Loughhead and E.J. Tappere with the use of an additional filter, and the instrument then provided exceptionally fine observations. It led to the now widely-acclaimed technique of two-dimensional solar spectroscopy.

The remaining physical quantity to be measured was magnetic field strength, which could be studied by means of the Zeeman effect on line spectra. An even narrower band filter was desirable and was developed by J.V. Ramsay; it comprised a series of three Fabry-Perot interferometers and a prefilter to isolate light from the wing of a suitable spectral line. The instrument had a band of 1/20 Å and overcame the limitations of previous models by providing a large field of view (one-quarter of the sun's diameter) and a short exposure time (about 0.3 s.). Observations were made by obtaining filtergrams of opposite circular polarisations simultaneously in the wings of a magnetically sensitive line. In this way, plots of magnetic field strengths were obtainable with angular resolution of about 2 arc s.

Giovanelli had few opportunities to use these various instruments because of his administrative duties in Sydney. He did, however, collaborate with J.V. Ramsay in measurements of plasma velocities in magnetic regions. He also made a series of observations of motions caused by oscillations and waves in a sunspot magnetic field.

When ill health forced his retirement from administrative work in 1974, Giovanelli used the opportunity to make a further series of observations of plasma motions and structures in magnetic and non-magnetic regions.

The importance of this work is that almost all phenomena observed in the solar atmosphere are influenced by, if not caused by, magnetic structures. While the significance of magnetic fields had long before been recognised by Hale, Babcock and others, the dominance of magnetic stresses in many phenomena had been largely overlooked. The Culgoora magnetograph and associated theoretical work played an important part in overcoming this omission.

Physics of the solar atmosphere

Throughout his working life, Giovanelli's main interest was the physics of the solar atmosphere and convection zone. This interest is reflected in his numerous published papers describing both observations and theoretical studies. The latter comprise investigations in three main areas, the first being radiative transfer in stellar atmospheres in the absence of thermodynamic equilibrium. The other two studies centred on magnetic fields and their effects, the first being solar flares and the second, actively pursued during his last few years, the solar magnetic cycle and the origin and morphology of solar magnetic fields. These studies are outlined in the following three sub-sections.

In addition to these main theoretical studies, Giovanelli engaged in a number of short-term investigations of solar atmospheric phenomena. Some of these, such as the motions in the convective cells seen on the surface of the sun, involved both observational and theoretical work; for convenience they are included in this section (as a fourth sub-section). Others were carried out at the Kitt Peak National Observatory, now the National Solar Observatory (a unit of the National Optical Astronomy Observatory), in Arizona, and involved fellow workers from that institute. These are described in the section headed 'Administrator, Teacher and Colleague'.

Radiative transfer in stellar atmospheres

Prompted by the discovery that 'in the solar chromosphere the temperature of the free electrons is higher than that of the radiation', Giovanelli published in 1948 a series of papers on the subject of 'hydrogen atmospheres in the absence of thermo-dynamic equilibrium'. He formulated and solved the equations of statistical equilibrium that determine the population densities of the lower quantum states of hydrogen. The work was a significant advance because it demonstrated the importance of collisional excitation and de-excitation while previous studies had considered only radiative processes. Giovanelli's papers were published within a few months of a paper by R.N. Thomas on the same subject, and taken together these heralded the modern era of research on non-LTE (non-local thermodynamic equilibrium) in stellar atmospheres.

Giovanelli applied the theory to the specific problem of the chromospheric hydrogen spectrums to determine a value of the central intensity of Ha in good agreement with available measurements. However, he argued that 'a model consisting of adjacent hot and cold columns would be more consistent with all the observational data'. This suggestion indicates his early interest in radiative transfer in inhomogeneous media, a subject to which he returned several times in the following two decades.

During the period 1950-55 Giovanelli and his colleague J.T. Jefferies improved the original non-LTE calculations with better collisional cross-sections, and several attempts were made to provide a more accurate account of self-absorption in the chromosphere. However, progress was impeded by the assumption of coherent scattering until 1958, when J.T. Jefferies and R.N. Thomas formulated and solved the equation of transfer for non-coherent scattering.

In 1955 Giovanelli turned his attention to the theory of radiation transfer in diffusing media. He developed several methods for deriving the reflection coefficients and other properties of semi-infinite and slab diffusers, using methods introduced by the astrophysicists Eddington and Chandrasekhar. He showed how the theory could be applied to the analysis of biological material by the technique of diffuse reflection spectrophotometry. Using a solution of the two-dimensional radiative transfer equation obtained by J.T. Jefferies, he also developed a comprehensive theory for the practical problem of radiation transfer in a diffuser illuminated by a line source.

By 1957 Giovanelli's interest in radiative transfer through diffusers was focussed on the difficult problem of transfer in inhomogeneous media such as imperfectly mixed paints, clouds and the solar atmosphere. He described his first methods as 'cumbersome', but in 1959 he developed a multi-dimensional generalisation of the Eddington approximation that greatly simplified the problem. His formulation has since been exploited by many workers, notably by his student, P.R. Wilson who used it to study the radiative properties of the photospheric granulation.

During a visit to the Fraunhofer-Institut in Freiburg in 1964-65, Giovanelli returned to the problem of the non-equilibrium state of hydrogen and calcium in the chromosphere. He computed the excitation equilibrium for a wide range of electron densities and temperatures in a finite slab illuminated by the mean radiation field in the chromosphere. He used the concept of an approximate net radiative bracket to treat the effects of self-absorption in the resonance and subordinate lines. Because the results were obtained for a finite slab, they have proved useful to many authors using them to infer from observations the excitation state in a variety of chromospheric fine structures.

In 1978 Giovanelli improved and extended his earlier application of approximate net radiative brackets and used the results to calculate for the first time the effect of spectral lines on the radiative relaxation time in the chromosphere. His work showed that previous studies, which considered only continuous emission, had seriously underestimated the cooling rate in the middle chromosphere. He pointed out that the revised cooling rates could have important consequences in studies of the phase relationships between velocity and temperature variations in chromospheric oscillations.

Solar flares and magnetic reconnection

Plasma, or ionised matter, constitutes nearly all of the matter in the universe, and most of it is permeated by magnetic fields of various strengths. Occasionally, sections of these fields with opposite polarities meet one another to provide a phenomenon known as magnetic reconnection (or magnetic merging or magnetic field annihilation). In October 1983, a conference on magnetic reconnection was held at the Los Alamos National Laboratory, USA, attended by 130 scientists from more than a dozen countries. In the official records of this conference, Ronald Giovanelli was honoured as the originator of the concept of magnetic reconnection. This tribute was paid some 37 years after Giovanelli's first paper on the effect.

Although plasma, or the 'fourth state of matter', is the main constituent of the universe, its perceived role in the affairs of man was negligible before this century. Then, with the growth of science and technology, and especially with the beginnings of the 'atomic age' and the 'space age', knowledge about this ionised state of matter assumed real importance. A fundamental feature of plasmas is the interplay of energy forms that can occur within them, between the energy of electromagnetic fields on the one hand and kinetic energy of particles on the other. A notable example of the rapid increase in the kinetic energy of plasma particles is observed in solar flares. The solar atmosphere is plasma which is heated to high temperatures as a result of the release of energy by hydrogen fusion in the solar core. The consequent thermal radiation is extremely steady, providing a uniform source of heat to the earth. However, from time to time localised regions in the solar atmosphere are heated rapidly to much higher temperatures so as to radiate strongly in the ultraviolet and X-ray parts of the spectrum. During his years at Mt Stromlo Giovanelli had studied the structure of many sunspot groups from observations of which may be inferred the distributions of the bundles of magnetic flux projecting through the solar surface. These bundles, often termed 'flux ropes', indicate the general forms of the magnetic fields which permeate the solar atmosphere. Changes in these magnetic structures must be accompanied by induced electric fields, and Giovanelli considered the possibility that these electric fields might accelerate electrons to high enough energies to excite atoms by collision and so account for the observed ultra-violet and X-ray emissions.

The physics of charged particle acceleration in induced electric fields appeared deceptively simple, and many workers used the phenomenon in attempts to explain a range of phenomena from auroral electrons to cosmic rays. There is a basic difficulty, however, in that the electrons cannot follow the electric field because they are constrained to move in small orbits around the magnetic field lines. Giovanelli was aware of this difficulty and avoided it by suggesting that acceleration takes place near 'neutral points'. In a complex group of sunspots, there will be confined regions where the magnetic field of one pair of spots happens to be equal and opposite to that of another pair so that the net field is zero. Particles in such regions might be accelerated by electric fields to high energies and so provide solar flares. These suggestions were supported by observed flare structures and magnetic structures deduced from the observed surface magnetic fields.

These ideas originated during Giovanelli's term at Mt. Stromlo, but their development into a theory of flares had to wait until the war ended and the pressure of work in optical measurements was reduced. The theory was published in a series of papers during l946-49.

This theory of magnetic neutral points found little favour for many years but nevertheless was developed by a few workers within the framework of a new treatment of plasma problems: magneto-hydrodynamics (or hydromagnetics). Here the original generally static configurations are replaced by steady flows of plasma and magnetic flux into regions where the oppositely directed flux components are destroyed and the energy converted to particle energy. It is now generally accepted that some such process is of basic importance in the phenomena of solar flares and solar eruptions. It is widely believed that magnetic reconnection is important in many other parts of the universe, notably the magnetospheres of planets, the atmospheres and perhaps interiors of many stars, and perhaps the magnetic fields of galaxies.

The solar magnetic cycle

During 1979 Giovanelli became increasingly interested in the theoretical side of the solar activity cycle. In part this was a result of his inability, because of his failing lungs, to visit high-altitude solar observatories. The change was also prompted by his belief that much of the published work in this field contained major errors in physics.

Activity in the solar atmosphere comprises a wide variety of phenomena including sunspots, flares, eruptive and quiescent prominences and many others. All of these effects are caused by magnetic fields that interact in various ways with the electrically conducting plasma. The patterns of these fields vary on time scales from as short as minutes for small structures to the 11-year sunspot cycle and the 22-year magnetic cycle for the global structures. The basic problem is to explain the origin of new magnetic fields at intervals of 11 years, with a reversal of polarity with a 22-year cycle. Prior to about 1973 it was widely believed that these cycles were caused by 'dynamo' action, the dynamo being driven by the turbulent motions known to occur in the convection zone which extends to a depth of some 2 × 10⁵ km below the solar surface. This Turbulent Dynamo Theory had been attacked, but was generally accepted as the basis of solar activity.

In 1974 Giovanelli and the author attended a seminar at Kitt Peak National Observatory (now the National Solar Observatory) where conclusive observational evidence was advanced showing that all solar magnetic fields have strengths of about 2000 gauss or more. Previous measurements indicated fields outside sunspots of only about 100 gauss or less, but these were average strengths. It now appeared that the actual fields were in the form of small 'flux tubes' surrounded by much more extensive regions of non-magnetic plasma. This result posed a new and major problem for the turbulent dynamo theory because the magnetic fields, which are supposed to be manipulated by the convective motions of the plasma, are capable of exerting stresses in excess of those provided by the plasma motions themselves. This new dynamical problem had been ignored by the dynamo theorists for more than a decade.

The mechanisms of interaction between magnetic flux tubes and the convection zone soon became and remained Giovanelli's main interest. The problem is complex: a cylindrical flux tube exerts outward magnetic pressure so that the internal plasma pressure and density tend to be less than the external and the tube tends to float upwards. However, depending on the earlier history of the tube, it may have expanded and so cooled the internal plasma. Also, plasma may enter the tube by diffusion and may move freely along the tube, which is in a medium whose temperature and pressure vary with height and so, in general, vary along the tube. Finally, if the tube is not cylindrical the magnetic stresses are complex, as occurs near the solar surface where the plasma pressure is unable to prevent the tube from expanding. Giovanelli persevered with the problem for some years, making as few simplifying assumptions as possible, and only after examining their possible influence on models of flux tubes in the convection. This work was described in a paper which had not been submitted for publication at the time of his death.

The results are in marked disagreement with all previous conclusions and are likely to be important in developing a sound physical theory of the origin of solar magnetic fields and of the sunspot and magnetic cycles. Comparing his results with those of many published during the past quarter-of-a-century, Giovanelli found that all accounts include at least one fundamental error of physics, namely the use of Archimedes' principle to test for the ability of a magnetic flux tube to float upwards in the convection zone. This principle is not applicable to flux tubes, whose dimensions and gas content change with level. An evaluation of the change in potential energy is necessary, and the results are greatly different. In consequence all previous work in this area is invalid. Furthermore, most accounts consider only a portion of a flux tube, as if it could be isolated from the whole tube, which is not the case. Finally, inadequate attention has been paid to the fundamental role of convective motions in controlling the behaviour of individual flux tubes; and none at all to the effects of gas entry into the tubes, decisive in establishing the equilibrium field strengths.

The present, widely accepted turbulent dynamo theory of solar magnetic fields ignores these (and most other) physical effects.

Miscellaneous investigations

At various times Giovanelli studied almost every problem of the solar convection zone and atmosphere. Some of these investigations are summarised here.

Near the top of the convection zone the motions and brightness patterns may be observed, and it is found that these occur on two main scales termed the granulation and the supergranulation, with average cell dimensions of roughly 1,000 and 30,000 km respectively. The interpretation of observations of these structures is difficult and Giovanelli discussed some of the problems involved in the case of granules and later on supergranules.

As seen in the preceding sub-section, the central problem in the physics of the solar convection zone and atmosphere is the origin and effects of the magnetic flux tubes. One aspect of this problem is that of gas flow into the flux tubes from the surrounding non-magnetic regions, generally assumed to be negligible. Giovanelli considered this effect as early as 1977, showing that in the region of temperature minimum between the photosphere and chromosphere, it is important. Here the degree of ionisation is low and there is an inward diffusion of the major gas constituent, the neutral atoms. At lower levels turbulent buffeting indents tubes in the convection zone and this may also be important, particularly near the photosphere.

Radiative cooling in the upper photosphere and chromosphere is important in at least two problems: the steady-state temperature distribution, and the temperature fluctuations in compressive waves. Giovanelli made contributions to these problems by calculating the cooling effect of emissions in the spectral lines, and by using the results to calculate the resulting enhanced dissipation of compressive waves. He found that in the chromosphere the effects of line emission dominate over those of continuous emission and that this largely determines the radiative dissipation of sinusoidal compressive waves. This result is important in theories which invoke such waves as the cause of the observed outward increase in temperature of the solar atmosphere.

Administrator, teacher and colleague

Some idea of the extent and diversity of Giovanelli's interests in science and technology may be obtained from the preceding sections. In the establishment of standards and physical measurement in Australia he played a major role, both in administration and technical development. This was his main occupation during the long period 1940-74 and alone constitutes a successful career in physics. Nevertheless, during the same period he was the prime instigator in the setting up of a series of solar optical observatories, culminating in the present observatory at Culgoora, NSW. This facility has since been expanded and developed as an important unit in the world-wide system of solar observatories.

These activities as administrator on the national scene were supplemented by a variety of services on international committees and in other bodies, notably the International Astronomical Union. An important part of this work was the development of warm personal relationships with many foreign astronomers. Ron Giovanelli and his wife Kath were cosmopolitan travellers and their attendances at international symposia were usually followed by a tour of the country and a stay at a fellow astronomer's house.

Over a period of some 25 years Giovanelli was involved in the administrative functions of various scientific bodies. He was first involved with the Australian National Committee of the International Geophysical Year on 'World Days and Solar Activity 1956-59'. Later he was convener of the Australian National Committee for the 'International Year of the Quiet Sun', 1962-65. In 1962 he was elected a Fellow of the Australian Academy of Science, and subsequently served for many years on the National Committees for Astronomy, for Space Research and for International Relations.

He served on the Australian National Committee for Solar-Terrestrial Physics as chairman in 1973, member 1974-79, and again as chairman in 1979-81. He was largely responsible for setting up in 1966 the Astronomical Society of Australia, and served as president from 1968 to 1971. Giovanelli was also active within the International Astronomical Union, serving as president of Commission 12 (Solar Radiation) from 1973 to 1976.

Such was Giovanelli's dedication to physics and astronomy that he took every opportunity to teach these subjects even when it involved an addition to a full work load. Teaching took two forms: the delivery of formal lectures or courses at universities and other research institutes, and the training of students to the PhD level in astronomy.

Most of the latter form of teaching was carried out within CSIRO as part of the astronomy program described above. One of the first students involved was J.T. Jefferies, whose training was mainly in astrophysics in the field of radiative transfer. Jefferies subsequently accepted a position in the USA where he is now the most senior optical astronomer, being director of the National Optical Astronomy Observatories. Another student was J.M. Beckers, who was trained in solar observational techniques at Fleurs Observatory and who now has the very senior position of director of the Advanced Development Program at the National Optical Astronomy Obsrvatories, USA. A third student was D.G. Hall, whose more recent training was also with CSIRO in Sydney and who is now director of the Institute for Astronomy, Hawaii. Through the training of these three influential astronomers, Giovanelli has made a considerable impression on astronomy in the USA.

In 1959 Giovanelli accepted the position of Honorary Associate of the Department of Applied Mathematics, University of Sydney, in order to supervise the PhD courses of students studying solar physics. Among these students was P.R. Wilson, later professor in the same department. Giovanelli's association with this department terminated in 1974, as did his term as chief of the Division of Applied Physics at CSIRO, because of ill health.

Giovanelli's career as a lecturer commenced in a modest way with a physics course at Sydney Technical College, but stopped in 1940 with his acceptance of a CSIRO studentship. It was resumed in 1968 at Wollongong University College (until 1974 a college of the University of New South Wales). This college on the one hand lacked a lecturer in astronomy, and on the other hand had an 18-inch Cassegrain telescope under construction. By an agreement between CSIRO and the university, Giovanelli became professor of physics at Wollongong and a member of the Professorial Board of the University of New South Wales for the academic year 1968. He worked for the university two days per week and as Chief of Division the remaining time.

In teaching he brought an infectious enthusiasm for physics education, designing courses and lecturing in plasma physics, spectral line formation and solar physics. He used his influence in CSIRO to have appropriate experts produce sets of notes and give lectures in a course called 'The Physics of Measurement', a course of outstanding quality. He also enthusiastically set about converting the telescope to a solar telescope. With the teaching courses well established and the telescope project foundering from lack of financial support, Giovanelli resigned from this university appointment at the end of 1970.

However, his love of teaching remained and in 1981 he gave a course of lectures at La Trobe University, Melbourne, on plasma physics. Finally, in 1982 he was invited to Paris and Boston to give a series of lectures at the Observatoire de Meudon and the Smithsonian Institute respectively.

As a fellow worker Giovanelli was a person of infectious enthusiasm and stimulating mind, eager to assist others without thought to his own advantage. He collaborated with many people in Australia and abroad on both observational and theoretical projects. Some of his colleagues had previously been his PhD students. These included J.T. Jefferies, J.M. Beckers and D.G. Hall mentioned above. Others were workers in other divisions of CSIRO. Some of these collaborative studies were not recorded; these include a flare study based on optical and radio observations. The latter were provided by the radio heliograph at Culgoora developed by J.P. Wild, now Chairman of CSIRO.

From time to time Giovanelli was a guest observer or consultant astronomer at a number of observatories in the USA and Europe, and collaborated with other workers there. Most time was spent at Kitt Peak Observatory and some results of work done there are mentioned in the following sub-section. Other observatories visited include the Fraunhofer Institut (now the Kiepenheuer Institut) in West Germany, where he worked with the Director, K.O. Kiepenheuer, on the problem of radiative transfer in the chromosphere. Visits to Europe usually included a stop at the Astronomical Observatory, Sonnenborg, Utrecht, The Netherlands, and some work with his friends there: C. de Jaeger and the Director M.J.G. Minnaert. In Italy he worked with his long-time friend G. Righini, the director of the Observatorio Astrophysico di Arcetri, near Florence.

Reference should be made here to an important investigation in solar physics in the form of a record of the sunspot cycle from 650 million years ago. This work was done by G.E. Williams of Broken Hill Pty. Ltd. Giovanelli did not collaborate but sponsored an extension of an earlier drilling program, and, as Williams states, "due in no small measure to Ron's strong support, CSIRO through its Science and Industry Endowment Fund, agreed in May 1982 to co-sponsor the (new) drilling." The drill cores provide a record over a period of 25,000 years of the solar cycle and of its effect on terrestrial climate at certain times in the geological past. Previous records of the sunspot cycle cover a total period of only about 10,000 years, and that in the immediate past. The new data shows that solar cyclicity has existed for at least 650 million years. This implies great stability and regularity of the physical processes involved and carries important implications for models of the activity cycle.

It was in connection with these models that Giovanelli and I collaborated during the last few years of his life. This collaboration was not a matter of working together on details, but rather a series of exchanges of ideas at regular intervals. Once again his dedication to his work is shown by an exchange on the occasion of our last meeting, when he handed me a copy of his most recent work for comment. He was aware that the end was imminent, and indeed he died on the following day.

The Kitt Peak (National Solar) Observatory visits

The USA National Solar Observatory is at Kitt Peak, Arizona, with headquarters in Tucson. At Kitt Peak National Observatory, or KPNO, Giovanelli was appointed as visiting scientist for six months in both 1975 and 1979, and then for a whole year in 1981. During these periods he completed a number of research projects, and in the words of a senior staff astronomer, W.C. Livingston, 'happily, he drew many of us in Tucson into his projects, injecting us with enthusiasm and enlarging our knowledge of solar physics in the process'.

One of these projects was the measurement of plasma velocities inside magnetic flux tubes. These flux tubes are too small to be resolved by any telescope on the earth's surface and so observations of Doppler velocities measure a composite motion of plasmas inside and outside the flux tubes. To sort out the magnetic from the non-magnetic components, Giovanelli had already devised the Line-Centre-Magnetogram (LCM) scheme, which uses the fact that Zeeman polarisation falls to zero when the detector is centred in wavelength on the magnetic line component. At KPNO this scheme was applied to the 512 Channel Magnetograph and Vacuum Telescope using various spectrum lines to provide velocity data at different levels in the solar atmosphere. Giovanelli and Slaughter found that the downflow of matter in magnetic flux tubes ranges from 0.6 km^-1 at the lowest photospheric level to near zero for the low chromosphere.

The LCM technique was next applied to the study of oscillatory motions and wave propagation in individual magnetic tubes. The co-workers in these measurements were W.C. Livingston and J.W. Harvey and the results showed that the oscillatory motions of the gas inside the magnetic tubes mimicked closely the surrounding gas. The LCM technique was then applied to the study of wave propagation in sunspot umbrae. The principal finding was a substantial phase lag between waves at the level of chromospheric Ha and lower level Fe5233, showing that the waves are propagating outwardly.

Another of Giovanelli's KPNO projects was a study of the two types of magnetic field concentrations, apart from that occurring in sunspots, observed on full disc magnetograms. One of these is unipolar, with a predominance of one magnetic polarity; the other is mixed-polarity, defined as a ratio of minor to major components of 0.4 or more. Magnetograms taken near sunspot minimum and maximum show clear differences in the proportions and distributions of these magnetic features, and Giovanelli quantified these differences for KPNO magnetograms covering 1975-80 as a function of solar latitude and date. The results show a clear trend from sunspot minimum to maximum that may prove important in resolving the problem of the solar magnetic cycle.

The final KPNO study was carried out in collaboration with H. P. Jones and concerned a curious magnetic structure which was termed a 'magnetic canopy'. Full-disc magnetograms in moderately strong spectral lines invariably display diffuse fringes of reverse polarity fields on the limbward side, away from the disc centre. Conventional models of magnetic fields projecting from the solar surface show field lines bending away to become horizontal at considerable heights. Giovanelli suggested that the fields become horizontal at much lower levels, perhaps 500-600 km above optical depth unity. Later, refined calculations indicated heights as low as 150-250 km, with some 20-30% of the solar surface near sunspot maximum covered by canopies whose base lies lower than 750 km. Such low-lying fields have not been accounted for in present-day models of the chromosphere and transition region and may require radical modifications of these models.

Achievements and their recognition

Ron Giovanelli emerges as a major figure in Australian science, with a substantial contribution as well in the field of physical measurements. His scientific contributions comprise original research in solar and stellar physics, in instrumentation, in observations and in theory, as well as administration and teaching. In opening a commemorative colloquium in his honour, J.P. Wild, Chairman of CSIRO, noted that 'Giovanelli had played a dominant part in physics in Australia for more than forty years'.

In advancing scientific knowledge, research ability is of course a prime requirement. In addition, a pleasant personality is important where collaboration is involved. Giovanelli was so widely liked and admired that, at the commemorative colloquium, the president of the International Astronomical Union observed that 'Ron Giovanelli helped build an international community of solar physicists because he was an enthusiastic worker and people liked him'. This was true for most of the solar physicists in Europe, the USA, India and Japan, many of whom were personal friends and on a family-visiting basis.

Giovanelli's contributions to science were recognised in a series of meetings of physicists and astronomers in Australia and the USA.

The first of these tributes was paid to his contributions to our knowledge of solar-terrestrial physics. During the sixth National Congress of the Australian Institute of Physics, held in Brisbane in August 1984, a series of Solar-Terrestrial Physics Workshops was dedicated to the memory of R.G. Giovanelli. The workshops were co-sponsored by the Australian Academy of Science.

The second tribute was the 'R.G. Giovanelli Commemorative Colloquium' held in Sydney during the period 26-29 November 1984. This colloquium was titled 'Past Progress and Future Developments in Solar and Stellar Atmospheric Physics', and was coordinated by P.R. Wilson and W.C. Livingston. It was attended by 40 Australian and overseas astronomers, including representatives from observatories in the USA, France and West Germany. The official opening and welcome was made by J.P. Wild who recalled some of the early problems in which he and Giovanelli had been involved at Culgoora while they directed the radio observatory and optical observatory respectively.

During that colloquium the participants gathered around a sundial in the grounds of the Division of Applied Physics of CSIRO to participate in a ceremony of presentation and dedication to the memory of R.G. Giovanelli.

A second 'R.G. Giovanelli Commemorative Colloquium' was held during 17-18 January 1985 in Tucson, Arizona, the home of the headquarters of the National Optical Astronomy Observatories.

During this meeting a video-tape was screened that provoked a highly emotional response. Because of ill health, Giovanelli had been unable to speak at an earlier colloquium at Los Alamos on magnetic reconnection. At the request of the co-ordinator of that meeting, he prepared a video-tape which was played by E.W. Hones at the Tucson meeting. The Coordinator of that meeting, W.C. Livingston (Kitt Peak Observatory), wrote to me as follows:

As I mentioned at our meeting Ed Hones of Los Alamos showed this video that Ron had prepared perhaps six weeks before his death. In this talk Ron exudes wisdom about sunspots, prominences and magnetic reconnection. He gently abrades others for drifting into mathematics and leaving out physics . He continually reminded us how little we knew about the sun or, to put it differently, how much there was to learn . At the end of the tape there was the strangest quiet in the room – not a stir. Never, ever, have I seen this response from a room full of astronomers!

Acknowledgements

The contributions to science and technology of Ronald Giovanelli were so varied that the above record required the co-operation of a number of colleagues and friends. Thanks are due to J.M. Beckers, K.D. Cole, L.E. Cram, A.F.A. Harper, R.E. Loughhead, H. Myers, W.H. Steel and G.E. Williams.

J.H. Piddington, Senior Research Fellow, CSIRO Division of Applied Physics.

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