History

Under construction!

Brief history of the sub-department

Atmospheric Physics started at Oxford shortly after World War 1 when F. A. Lindemann was Dr Lee's Professor of Experimental Philosophy and therefore Head of the Clarendon Laboratory. Lindemann was interested in the upper atmosphere and was responsible for appointing a young scientist then at Farnborough, G. M. B. Dobson, as a University Lecturer. Together they worked on the analysis of observations of meteor trails, from which they deduced that the temperature did not decrease with altitude above the tropopause, as had previously been supposed, but rather that there was a region where temperature increased substantially with height. Dobson inferred correctly that the cause of this was heating by ozone in the stratosphere, and he set out to make measurements of the ozone amounts and their variability. In 1923 he produced the first Dobson Ozone Spectro-meter, to be succeeded in 1931 by his Spectrophotometer - a device which is still in use worldwide, with a network of over 150 instruments making daily observations. (The famous `Antarctic Ozone Hole' was discovered from data collected by one of these instruments.) For many years, `Number One' was located in Dobson's original hut on the roof of the Department. It is now in the Science Museum, South Kensington.

In 1929 Dobson became the first Reader in Meteorology, and in the same year he was elected a Fellow of the Royal Society. In 1948 he was joined at Oxford by a new lecturer in Meteorology, A. W. Brewer, and together they made their classic study of atmospheric water vapour. The `Brewer-Dobson Circulation' is generally accepted as the breakthrough in understanding why the stratosphere is so remarkably dry. Its details are still a major subject of study to this day in Oxford and elsewhere.

After Dobson retired, Brewer became Reader, and with one of his research students, J. T. Houghton, made measurements of atmospheric radiation and radiometric measurements of water vapour from aircraft and balloons. Dr Houghton became Reader in 1963 and was appointed to a personal Chair in 1973. He expanded the Department, adding two further lecturerships, and in 1970 moved it from the Clarendon to the `Old Zoology' Building. He also introduced it into the space era, with a proposal for a radiometric temperature-sounder on the NASA (See Appendix 1 for a list of abbreviations and acronyms) satellite Nimbus D. This and subsequent Nimbus instruments flew in 1970, 1972, 1976 and 1978. In the same period an instrument (`VORTEX') was jointly developed with the Jet Propulsion Laboratory in California and became the first temperature sounder of the planet Venus in December 1978.

F.W.Taylor was Principal Investigator for VORTEX, having gone to JPL in 1970 after completing a D.Phil.~in the Department on the development of the Pressure Modulator Radiometer. Dr Taylor returned as Acting Head of Department in 1979 when Professor Houghton went on leave of absence to head the Appleton Laboratory (now merged with Rutherford and Daresbury to form DRAL). This brought the Department a substantial involvement in two more of NASA's large space projects - the ATMOS spectrometer on the Space Shuttle and the Galileo mission to Jupiter. A large and complicated space instrument, ISAMS, was accepted for NASA's Upper Atmosphere Research Satellite. Three other major space experiments with substantial Oxford involvement began in the next few years: the ATSR, to measure sea-surface temperatures from ERS-1, the EOR mesospheric water-vapour experiment on EURECA, and the PMIRR atmospheric sounder for Mars Observer. The beginnings of the Oceanography Group (originally under Dr D. L. T. Anderson) and the Middle Atmosphere Dynamics Group (under Dr D. G. Andrews) also date from about this time.

In 1984, with Prof. (now Sir John) Houghton moving to the Meteorological Office as Director-General, Dr Taylor became Reader and Head of Department. A research team in planetary atmospheres was built up and is now one of the leading European groups. In 1987, the department was renamed and further expansion agreed.

In August 1990, Atmospheric, Oceanic and Planetary Physics became formally a sub-department of the newly-unified Physics Department and Dr Taylor was appointed to the new Halley Professorship of Atmospheric Physics.

Two new lecturers were appointed in 1991, bringing a significant increase in the number of senior staff in the sub-department; another lecturer was added in 1996. The Nonlinear Systems Group, previously in the Clarendon, also joined AOPP until its transfer to the University of Manchester in 1996. The Geophysical Fluid Dynamics laboratory (led by Peter Read) was also added to the sub-Department at this time, having previously been at the Met Office and then in Oxford as part of the Hooke Institute.

Following ISAMS and ATSR in 1991, the EOR instrument was launched in July 1992 and PMIRR in September 1992. The latter was lost, with Mars Observer, a year later. It was rebuilt for the Mars Climate Orbiter, launched in December 1998 and unfortunately lost again on reaching Mars in September 1999! The CIRS instrument was built for the Cassini mission to Saturn and Titan, which was launched successfully in October 1997.

With the end of Prof Taylor's term of office as Head of the Subdepartment in 2000, Dr David Andrews took over the headship, becoming Professor in 2004. The Climate Dynamics group was also initiated at this time when Dr Myles Allen joined the Subdepartment as Lecturer, and saw the beginnings of the Climateprediction.net project.

The next major Earth observing instrument designed and constructed in Oxford was HRDLS, launched on the Aura spacecraft in 2004. Despite a problem with a blockage in its field of view, the instrument operated more or less successfully until March 2008 when the chopper experienced an anomaly.

One year later (in 2005), the Mars Reconnaissance Orbiter was launched with the Mars Climate Sounder instrument on board - the successor of the ill-fated PMIRR instruments on Mars Observer and Mars Climate Orbiter. MRO successfully reached orbit around Mars and continues to operate in 2009. In the same year, ESA launched the Venus Express orbiter, going into orbit around Venus in 2006. The Department has a strong involvement in the VIRTIS infrared instrument team.

Prof. David Marshall joined the Department in 2006, restoring oceanography to its research programme, and in 2008 Prof Peter Read took over as Head of sub-Department. 2009 saw AOPP begin a new exploration of the Moon with the launch of NASA's Lunar Reconnaissance Orbiter mission carrying the Lunar Diviner instrument, similar in design to MCS, with the aim of searching for water ice on the Moon's surface.

The Virtual Dobson Room

Introduction

The apparatus in this display case traces the history of the Department of Atmospheric, Oceanic and Planetary Physics from its beginnings as a Meteorology Group in the Clarendon Laboratory to its present activities in Earth orbit and beyond.

Meteorology and Solar System studies has been on the teaching syllabus at Oxford for centuries, but the origins of the modern department can be traced to shortly after World War 1, when F.A. Lindemann (later Lord Cherwell) was Dr. Lee's Professor of Experimental Philosophy and therefore Head of the Clarendon Laboratory. Lindemann was interested in the upper atmosphere and was responsible for appointing a young scientist, Gordon Dobson, as a University Lecturer.

G.M.B.Dobson (1889-1976)

Dobson was an experimentalist of unusual ingenuity who devoted much of his life to the observation and study of atmospheric ozone. The results were to be of great importance in leading to an understanding of the structure and circulation of the stratosphere. He came to Oxford in 1920 to take up the position of University Lecturer in Meteorology, having previously been Director of the Experimental Department at the Royal Aircraft Establishment, Farnborough, during the War. Together Lindemann and Dobson worked on studies of meteor trails, from which they deduced that the temperature profile above the tropopause was not constant - as simple theory would predict and the name 'stratosphere' implies - but rather that there was a region where temperature increased substantially with height.

Dobson inferred correctly that the cause of the warm stratosphere was heating by the absorption of ultraviolet solar radiation by ozone, and he set out to make measurements of the amounts and their variability. He decided to measure ozone by observing its absorption in the solar ultraviolet spectrum, as Fabry and Buisson had done a few years before. Dobson's first spectrograph employed a Fabry prism, an optical wedge consisting of gelatine and carbon black between quartz plates designed by T. Merton of the Clarendon Laboratory, and a filter consisting of a mixture of chlorine and bromine vapour to cut out unwanted solar radiation at longer wavelengths. A special tank was built to ensure consistent development of the photographic plates. To measure the line intensities Dobson built a photoelectric microphotometer using a potassium photocell, the current from which was measured by an electrometer also made in the Clarendon Laboratory.

Ozone Measurements

The first spectrograph was built in the summer of 1924 at Dobson's laboratory and workshop in a hut built for the purpose in the grounds of his home, Robin Wood, Boars Hill. Extensive measurements made from Boars Hill during 1925 established the main features of the seasonal variation of ozone, the maximum in the spring and the minimum in the autumn, and also demonstrated the close correlation between ozone amount and the meteorological conditions in the upper troposphere and lower stratosphere.

The results of the 1925 ozone measurements were of such interest that Dobson decided to make measurements at a number of locations in Europe to study the relation between ozone distribution and synoptic meteorological variables. The winter of 1925-26 was spent building five spectrographs and calibrating them at Boars Hill. Measurements were begun in mid-1926 and by the end of 1927 ozone values had been calculated from over 5000 spectra. From these the distribution of ozone relative to pressure systems and a limited indication obtained of the variation of mean ozone with latitude was obtained.

More extensive measurements of the variation with latitude were made during 1928 and 1929 by redistributing the instruments to places widely scattered over the world. Only the instruments at Oxford and Arosa in Switzerland remained at their old stations; the others were sent to Table Mountain in California, Helwan, Egypt, Kodal Kanal, India and Christchurch, New Zealand. As before, the photographic plates were returned to Oxford for development and measurement. By the end of 1929, therefore, the main feature of the variation of the ozone amount with synoptic conditions, with latitude and with season had been established.

Meanwhile Dobson's lectures in the Clarendon Laboratory attracted large audiences of undergraduates. In 1923 he was awarded the University's Johnson Memorial Prize, and in 1925 took his Oxford D.Sc. In 1926 he gave the Halley lecture on 'The uppermost regions of the Earth's atmosphere'. He was elected to a new Readership in Meteorology in 1927 and also appointed University Demonstrator in Physics and Chemistry. In that year he was made an Official Fellow of Merton College and became a Fellow of the Royal Society, serving on the Council from 1932 to 1933.

The Development of the Photoelectric Spectrophotometer

The inconvenience of the photographic technique led Dobson to design and build his photoelectric spectrophotometer which enabled the relative intensity at two wavelengths to be measured directly. It was completed in 1927 or 1928, the design being remarkably advanced for its day. It is probably the first spectrophotometer to use the principle of synchronous detection of a weak signal. It used a photocell with a sodium cathode made by T. C. Keeley, who had also made the photocells used in the microphotometer which Dobson built for measuring the photographic plates. This instrument, like the Fabry spectrographs, was built by Dobson himself in his own workshop.

Work on Atmospheric Pollution

In the early 193Os Dobson became concerned with the study of atmospheric pollution, and from 1934 to 1950 served as Chairman of the Atmospheric Pollution Committee of the Department of Scientific and Industrial Research Under his guidance reliable methods were developed for the measurement of smoke, deposited matter and sulphur dioxide, and a detailed survey was conducted in Leicester from 1937 to 1939.

The Move to Shotover

The second international conference on atmospheric ozone was held at Oxford in 1936 (the first had been in 1929 in Paris). In the following year Dobson moved into his new house, 'Watch Hill' at Shotover. His laboratory there was a substantial brick building with two workrooms, one large and one small, with provision to make zenith sky observations, and a well equipped workshop. A wooden hut was built near by and was used during the International Geophysical Year (195&57) as the office for collating and plotting the data sent in by the network of spectrophotometers.

Stratospheric Water Vapour

During World War II Dobson directed his attention to the humidity of the stratosphere. The work on water vapour began because the Meteorological Office had a problem with forecasting the conditions and heights when aircraft make condensation trails. He looked at the dew-point, or frost-point, method of measuring humidity and designed the frost-point hygrometer. A. W. Brewer was appointed to be the Meteorological Officer at Boscombe Down. He was responsible for flying these instruments and also did a lot of the design work. The first flights, involving working unpressurised in the stratosphere, showed that the region was unexpectedly dry. The meteorologists of the day took a long time to be convinced by the new data, having expected the air in the stratosphere to be saturated.

As a result of the study of contrails and the development of hygrometry Dobson became interested in the mechanism of freezing of water drops. Several of his students built cloud chambers in which water drops could be formed and their temperature of freezing noted. Their work confirmed the large effect on freezing temperature of different amounts of impurity and showed that pure water drops do not freeze spontaneously until a temperature of - 40 C is reached.

Post-War Work on Ozone

After World War II, international ozone work became organised under the International Ozone Commission which was set up in 1948 at the Oslo meeting of the International Union of Geodesy and Geophysics. The first Secretary was Sir Charles Normand who in 1947 had joined Dobson in Oxford after retiring as Director of the Indian Meteorological Service.

R. H. Kay, working with Dobson in the Clarendon Laboratory in 1952, adapted a chemical technique for making in situ measurements of ozone from an aircraft. Kay also played a large part, together with Normand and Dobson, in making various improvements to the spectrophotometer, including the fitting of photomultipliers which had become commercially available after the war and which greatly increased the sensitivity, the introduction of three more wavelength pairs for observations, and the development of improved methods of adjustment and calibration.

At the end of 1956, no less than 44 Dobson spectrometers were distributed throughout the world. The International Geophysical Year in 1956 brought a large increase in the number of ozone instruments required All new instruments came to Oxford for final calibration and comparison with No.1. The most interesting result which came out of the I.G.Y. measurements was the discovery of the annual variation of ozone at Halley Bay in Antarctica showing a sudden rise in November - very different behaviour from the northern hemisphere.

The Dobson Ozone Spectrometer is still in use world-wide with a network of over 150 instruments making daily observations. Until recently, 'Number One' was located in Dobson's original hut on the roof of the Department: it is now in the Science Museum, South Kensington. The instrument you see here is 'Number Three'.

Growth of the Department at Oxford
In 1945 the University passed a Decree conferring upon Dobson the title of Professor. Alan Brewer came to a new Lectureship in Meteorology at Oxford in 1948. Dobson had made forecasts for the Central Flying School, using 20 observations per day, but claimed they had been 'absolutely hopeless', and he wanted somebody with more experience than himself to teach forecasting in the University. Together they continued their classic study of atmospheric water vapour. The 'Brewer-Dobson Circulation' is generally accepted as the breakthrough in understanding why the stratosphere is so remarkably dry. Its details are still a major subject of study to this day in the Department and elsewhere.

Dobson retired from his university readership in 1950 and from his university demonstratorship in 1956, but work on atmospheric ozone continued all through his retirement years. His last paper was written in 1973, 62 years after his first one, and his last observation of atmospheric ozone was made the day before he had the stroke from which he died six weeks later.

After Dobson retired, Brewer became Reader, and with one of his research students, John Houghton, made measurements of atmospheric radiation and radiometric measurements of water vapour from aircraft and balloons. Dr. Houghton became Reader in 1963 and Professor in 1973. He expanded the Department, Including two further lectureships, moved it (in 1970) from the Clarendon to the 'Old Zoology' Building, and introduced it into the space era, with a proposal for a radiometric temperature-sounder on the NASA satellite Nimbus D. This and subsequent Nimbus instruments flew in 1970, 1972, 1976 and 1978, and in the same period an instrument was jointly developed with the Jet Propulsion Laboratory in California. This became the first temperature sounder of the planet Venus in December 1978. F.W. Taylor was Principal Investigator for the Venus project, having gone to JPL in 1970 after completing a D.Phil. in the Department on the development of the Pressure Modulator Radiometer. Dr. Taylor returned as Acting Head of Department in 1979 when Prof. Houghton went on leave of absence to head the Appleton Laboratory (now merged with Rutherford to form Rutherford Appleton Laboratory). This brought the Department a substantial involvement in two more of NASA's large space projects - the ATMOS spectrometer on the Space Shuttle and the Galileo mission to Jupiter. A large (180kg, 1 m3) and complex space instrument, ISAMS, was accepted for NASA's Upper Atmosphere Research Satellite and a smaller version for flight to Mars on Mars Observer. Groups doing theoretical, data analysis and modelling work on stratospheric dynamics and physical oceanography were set up.

In 1984, with Professor Houghton now at the Meteorological Office as Director-General, Dr. Taylor became Reader and Head of Department. In 1987, the department was renamed Atmospheric, Oceanic & Planetary Physics in recognition of its expansion into oceanography and experimental and theoretical studies of other planetary atmospheres. A statutory chair in Atmospheric Physics was established in 1991 with Professor Taylor as the first holder. Today, remote sensing instruments developed at least in part at Oxford are not only in Earth orbit but also in various reaches of the Solar System, the latest heading as far afield as Saturn.

Second Conference on Atmospheric Ozone, 1936

This group photograph is from the 'Second Ozone Conference' which was held in Oxford in September 1936 (the first was in Paris in 1929). The meeting attracted scientists from all over the world (16 different countries) who were working on or interested in atmospheric ozone. Dr Dobson, who was Reader in Meteorology in the Oxford University Physics Department, had done much of the pioneering work, and was the main organiser of the conference.
29 of the papers presented were published in a supplement to the November 1936 issue the Quarterly Journal of the Royal Meteorological Society, which even by today's standards represents very rapid action by the organisers and editor. (The University Library copy is date stamped 5 December showing that the issue was genuinely produced before then.)

A report of the meeting by Dr A. R. Meetham was printed in the Meteorological Magazine for October 1936 (volume 71, pages 202-205).

The next Ozone Conference was held in Brussels in 1951, under the auspices of the newly formed International Ozone Commission. Subsequent meetings were held in Oxford (1952), Rome (1954), Ravensburg (1956), Arosa (1961), Albuquerque (1964), Boulder? (1980), Thessaloniki (1984), L'Aquila (1996), Sapporo (2000). (See also Dobson, Applied Optics, 387-405, vol. 7 no 3, 1968.)

The framed original of the signed group photograph hangs in the Dobson Room, Atmospheric, Oceanic and Planetary Physics, Department of Physics, Clarendon Laboratory, Oxford University.