A brief history of solar-terrestrial physics in Australia

Solar-terrestrial physics research in Australia began in 1792 when de Rossel measured the southern hemisphere geomagnetic field at Recherche Bay on the southern tip of Tasmania, proving the field magnitude and direction varied with latitude. This was the time when the French and British were competing to chart and explore the new world. From the early twentieth century Australian solar-terrestrial physics research concentrated on radio wave propagation and communication, which by the 1950s fed into the International Geophysical Year in the areas of atmosphere and ionosphere physics, and geomagnetism, with some concentration on Antarctic research. This was also the era of increased studies of solar activity and the discovery of the magnetosphere and the beginning of the space age. In the 1960s, Australia became a world leader in solar physics which led to radio astronomy discoveries. This paper outlines the historical development of solar-terrestrial physics in Australia and its international connections over the years and concludes with examples of specific research areas where Australia has excelled. © 2016 The Author(s). This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. Background Australia, being an isolated and relatively newly discovered continent, does not experience the advantages or disadvantages of Europe which is steeped in history. By the turn of the twentieth century Europe and the UK could claim over 800 years of well-established and successful University development in education and research. Correspondingly, Australia was a colony of the British Empire comprising a group of independent states which combined into the Commonwealth of Australia with a constitution in 1900. Internal communications were the first priority to be considered by the new nation, followed by reliable connections to the rest of the world. Then followed the disturbing war years, and more recently the space age, all of which bolstered the advancement of discovery and technology. Over these times, since the ionosphere and magnetosphere were discovered, solar-terrestrial physics (STP) was fundamental and made a vitally important contribution to this chain of events. Now in the twenty first century we are experiencing a rapid expansion of digital and space technology, and this is providing opportunities to embark on large scale instrumentation accumulating and assimilating vast quantities of data never before imagined. Due to space limitations this paper can only briefly outline the role STP played in Australia’s development from a primitive colony to an advanced technology dependent country in just over two centuries. A fuller account of radio science and ionospheric research in the British Empire between the two world wars is included in Anduaga (2009). As well as being initially dependent on the UK some of Australia’s experience involved New Zealand scientists and more detail on this has been provided by Fraser (2005). “The pre-1900s” section considers the beginnings of communications while “The twentieth century” section describes the early modern era where Australia takes advantage of high frequency communication leading into ionospheric research. Activities associated with Australian STP over the interval between the two world wars are covered in “Between the two world wars 1918–1939” section, while post world war II achievements are documented in “Post world war II: 1945–1980” section. Finally, “The modern era: post 1980” section considers the post 1980 era up to the present. This section is necessarily brief as most modern information is now Open Access *Correspondence: [email protected] Centre for Space Physics, University of Newcastle, Callaghan, NSW 2308, Australia Page 2 of 11 Fraser Geosci. Lett. (2016) 3:23 available on specific institutional websites and online literature. Emphasis has been placed on the middle twentieth century, an extremely interesting time to be an STP researcher in Australia. The pre‐1900s Following the Abel Tasman and James Cook discovery voyages a French expedition led by Bruni d’Entrecasteaux sent to find lost explorer La Perouse was caught in a storm in 1792 and sought refuge in Recherche Bay on the southeast tip of Van Diemen’s Land, now Tasmania. Over the following 2 years, the d’Entrecasteaux expedition with physicist Elisabeth Paul Edouard de Rossi (male) undertook pioneering research of worldwide importance, showing that the geomagnetic field increased in strength with increasing latitude. Details of this work were reported by de Rossel (De Rossel 1808; Lilley and Day 1993). Without a method to directly measure the strength of the geomagnetic field the instrument of the time was a dip meter (Fig. 1a). The dip meter was set up vertically and stable, the needle set oscillating and the time for typically 100 oscillations recorded. Since the oscillation period, and consequently, the geomagnetic field strength varies with latitude this provided a simple method to compare field strength between hemispheres and with latitude. The period of oscillation was then plotted against dip angle as shown in Fig. 1b. The curve for an ideal geocentric dipole is superimposed for comparison. It is interesting to note that these measurements predate the Humboldt 1798–1803 South American observations (Humboldt and Biot 1804). In nineteenth century Australia the six separate colonies relied on shipping to provide communication links between their widely dispersed coastal cities. In 1850, it took 60–80 days for mail to arrive from Europe. By 1859, Sydney, Melbourne, Adelaide and Tasmania were connected by telegraphic service. However, Australia needed to connect to the newly laid undersea telegraphic cable which connected England to Batavia (Jakarta) in Indonesia. An overland telegraph connection between Adelaide and the Port of Darwin was surveyed and constructed over 1870–1872 (Overland Telegraph 2015). The telegraph was successfully strung over 3200 km (Fig. 2a) using more than 36,000 wrought iron poles, placed 80 m apart with repeater stations every 250 km. The signal was carried by one strand of number eight fencing wire (Fig. 2b), and powered by Meidinger gravity cell batteries, a forerunner to the common lead–acid battery. All repeater stations were manned fulltime by a telegraphist and maintenance staff. Needless to say, the line suffered many breakdowns in the harsh desert environment where thunderstorms were a problem. Parts of the telegraph line were still being used until 1980, but there is no record of the Adelaide–Darwin line closure. The twentieth century The importance of high frequency radio in Australia On 1 January 1901, Federation of the Australian colonies was achieved after a decade of planning. This established the Commonwealth of Australia as a Dominion of the British Empire. During the early years of the century, telegraphy continued to be the primary medium of communication over this vast country. Prior to about 1920, Fig. 1 a De Rossel’s dip meter instrumentation 1792. b Period of oscillation variation with magnetic dip angle at various locations in latitude (after De Rossel 1808; from Lilley and Day 1993) Page 3 of 11 Fraser Geosci. Lett. (2016) 3:23 most radio propagation experimentation took place at long and medium wavelengths. In the mid-1920s, it was realized that much shorter wavelengths could be used for long-distance propagation, which resulted, in 1926, of the introduction of shortwave high frequency (HF) wireless telegraphy stations, using relatively low power, and directional antennas (Padula 2015). HF radio provided a means of communicating throughout Australia and to the rest of the world. News and other programs, including School of the Air to educate children in remote areas, were broadcast through Radio Australia. Typical early receiving systems are illustrated in Fig. 2c, d (Padula 2015). From the research as well as application point of view, the ionosphere and upper Fig. 2 a Overland telegraph route over Adelaide to Port Darwin 1870. b Overland telegraph poles with single wire and insulator. c Pedal radio circa 1930. d Transceiver circa 1960 Page 4 of 11 Fraser Geosci. Lett. (2016) 3:23 atmosphere became important in understanding the predictions of HF circuit conditions. Over the second half of the twentieth century, this will be seen to become even more important through aircraft navigation, defence applications, Antarctic and general communications, and over the horizon radar. Modern history After World War I, British science was redesigned to suit the political ideals of the British Empire. However, it was also noted that the Australian scenario was significantly different from the UK approach. For example, mining development was forging ahead using Australia’s vast natural resources, and there was a need for efficient communications and aviation services spanning large distances. The first direct evidence of the existence of electrified regions in the upper atmosphere was carried out by Appleton and Barnett in Southern England (Appleton and Barnett 1925). This experiment initiated the subsequent development of the major new science of upper atmosphere geophysics using radio waves. Australian scientists were to play an important role, both in England and at home, in the early discoveries. The Australian Federal Government established the Council for Scientific and Industrial Research (CSIR) in 1926 (White and Huxley 1975) and provided significant support funding. In the same year, the Australian Radio Research Board (ARRB) was established (White and Huxley 1975), following the British precedent (RRB-UK) which had just commenced research on the ionosphere, now a prestigious and autonomous discipline. The ARRB from 1927 was the first, using Australian Federal Government funding to sponsor university research. Two major research activities were supported. At the University of Sydney, John Madsen led extensive contributions to studies of the electrified regions of the atmosphere, now known as the ionosphere. The University of Melbourne under Thomas Laby devoted primary attention to “atmospherics” or lightning discharges, a major source of radio communication disturbance. Following the establishment of the ARRB and up to the start of World War II, Australian physicists and engineers were becoming familiar with the variation in the properties of the ionosphere, particularly the vertical distribution of ionization and many interesting and important studies were published. David Martyn, a University of London graduate, was one of the four scientific officers selected to join the ARRB in 1929, and was assigned to Melbourne. Martyn was a complex man but an excellent theoretician. Early on he developed an important theorem showing information on obliquely incident waves, can be obtained from those of vertical incidence (Martyn 1935). Following a visit to the UK in the mid-1930s, Martyn introduced UHF studies into Australia and was appointed head of the newly established ARRB Radio Physics Laboratory (RPL) at the University of Sydney. The structure of research science management in Australia following the establishment of the CSIR and ARRB remained stable up until the end of World War II, when in 1949 the CSIR became the Commonwealth Scientific and Industrial Research Organisation (CSIRO) with a Division of Radiophysics absorbing the University of Sydney’s RPL. By this time, the University of Melbourne’s atmospheric program had closed down in 1939. To continue regular monitoring of ionospheric conditions following the end of the war, the Ionospheric Prediction Service (IPS) was established in 1947 for what has now become known as space weather forecasting, and is currently located within the Bureau of Meteorology (Space Weather Services 2015). Australia administers some 43 % of the Antarctic continent and established permanent stations for upper atmosphere observations on the edge of the continent or nearby beginning in 1947 at Casey, Davis Mawson and Macquarie Island (Marchant et al. 2002). This provided Australian scientists with access to the high latitude outer regions of the magnetosphere from a low manmade noise environment. Between the two world wars 1918–1939 Following the discovery of the ionosphere, Appleton and Ratcliffe (1928) predicted, according to magneto-ionic theory that radio waves which were left hand polarised in the northern hemisphere, should be right hand polarised in the southern hemisphere due to the oppositely directed geomagnetic field. This was confirmed by Green, of Madsen’s Sydney Group in 1930 (Green 1932), although not comprehensively published until a few years later (Green 1934). Green also measured the height of reflection of the E and F ionospheric layers and found them consistent with the northern hemisphere (Green 1932). At this time technology was also developing, with Geoffrey Builder from Western Australia, travelling to the UK and undertaking postgraduate studies under Appleton (Appleton and Builder 1932). Returning to the Sydney Group Builder built an 80 m band pulse transmitter, installed at the University with a receiver at the southern Sydney suburb of Liverpool. The first equivalent heightfrequency ionograms in Australia were produced and provided to researchers by O. O. Pulley in 1935, a Sydney graduate under Madsen, while H. B. Wood in 1936 provided the first fully automated frequency sweep recorder covering 1.6–10 MHz in 5 min (Pulley 1934; Wood 1936). Figure 3 shows sweeps from 2.4 to 6 MHz for the O wave in the upper panel and X wave in the lower panel. The critical frequencies of the E and F-regions can be seen at 120 and 210 km, respectively. Page 5 of 11 Fraser Geosci. Lett. (2016) 3:23 Over this time, Victor Bailey at Sydney collaborated with Martyn in examining what was called the ‘Luxemburg Effect’; the modulation of one wave travelling through the ionosphere by another. The effect is due to the nonlinear effects of the medium (Bailey and Martyn 1934). The effects of solar disturbances on the ionosphere were also of interest to Australian radiophysicists engendered by collaboration between the Sydney Group and the Commonwealth Solar Observatory in Canberra. This was world’s first research in solar variability understanding and associated ionospheric effects. In 1937, Martyn, George Munro, and colleagues reported that bright hydrogen emissions on the solar disk occurred almost simultaneously with an increase in ionospheric D-region absorption (Martyn et al. 1937). Munro, a New Zealander arrived in Sydney after spending time at Slough UK, found other ionospheric disturbances with durations of 10–60 min and showing a time lag in arrival between Canberra and Sydney corresponding to a speed of 5–10 km s−1. This was the discovery of the phenomenon travelling ionospheric disturbances (Munro 1950), which are now known as a signature of atmospheric gravity waves generated in the auroral thermosphere. Figure 4 from Munro (1950) shows ionospheric traces where virtual height dips and peaks and the crossover point of the O and X rays. Over 1935–1937, Ron Giovanelli at the Solar Observatory was the first to recognise the relationship between sunspots and solar flares. The probability of flare occurrence was proportional to the sunspot group type, the group area and the rate of change of spot size (Giovanelli 1939). Post world war II: 1945–1980 Over this period, Australia’s STP research flourished with expansion of the National University System from 10 institutions in 1960 to 19 institutions in 1975, the injection of significant Federal government funding and the establishment of major research facilities. The STP field of study expanded too, from the ionosphere through the newly discovered magnetosphere and Van Allen radiation belts to solar radiation and radio astronomy where Australia became a world leader. Other research programs were developing at this time. Ionosphere and atmosphere research flourished at the University of Adelaide, following the rich physics history of leadership under A. P. Rowe and L. G. H. Huxley. There Graham Elford and Basil Briggs established radar meteor research, MF and HF ionospheric research and radio astronomy all at the Buckland Park field site. Meanwhile, the newly established La Trobe University under Keith Cole, who previously worked with D. F. Martyn, Fig. 3 An original ionogram from the first swept frequency ionosonde. Upper trace is O wave and lower trace the X mode (adapted from Pulley