Articles

Directing Bidston

Graham Alcock, 21 October 2016

I joined Bidston in 1972 and took early retirement in 2000, having survived five name changes (Institute of Coastal Oceanography and Tides, Institute of Oceanographic Sciences, Proudman Oceanographic Laboratory, Centre for Coastal and Marine Science and back to the Proudman Oceanographic Laboratory). Here are anecdotes about some of the Directors during that time.

I only met ICOT’s Director, Jack Rossiter, when he was chair of my interview panel in May 1972, because unfortunately he died before I was appointed. The subsequent ICOT Acting Director, Geoff Lennon, had a turn of phrase – “it occurs to me” – and that was used in my letter of appointment, suggesting that I might like to join a scientific cruise in September 1972, pre-dating my actual appointment date of 1 October. What Geoff omitted to say was that the cruise was on the RRS John Murray, an ex-fishing trawler rumoured to have been bought by NERC for £1, which had such a nasty rolling motion in anything higher than a Force 2 breeze that it was always difficult to encourage Bidston staff to go on it. That was my introduction to “wet” oceanography – subsequently I always preferred the “dry” oceanography remotely carried out by land-based radar and space-borne satellites.

The first of the frequent reorganisations of NERC’s marine science occurred in 1973, when Bidston became part of IOS, together with what had been the National Institute of Oceanography at Wormley and the Unit of Coastal Sedimentation at Taunton. Scientific rationalisation brought the Tides staff at Wormley to Bidston and David Cartwright was appointed as IOS Assistant Director.

David was a world-class researcher and an elected Fellow of the Royal Society; but as he said on his interview for The British Library’s “Voices of Science”, he “wasn’t temperamentally suited to getting too much involved with administration”. I remember attending an IOS meeting at Wormley to allocate funding for the year (in my capacity as responsible for contracted and commissioned research at Bidston), when David left early to catch his train back to Birkenhead before Bidston finances had been fully discussed and agreed. James Crease said: “I suppose we had better allocate some funds to Bidston”.

I worked on a number of projects for David and although he was the senior author of our joint papers he used the format of listing the authors in alphabetical order. For the George Deacon 70th Birthday commemorative volume of “Deep Sea Research”, we wrote a paper on our analysis and interpretation of telephone cable voltages across the English Channel to provide information on the ocean current flow. The DSR Editor knew of David but not me, and on his assumption that the first named author was the senior author, his acceptance letter (no emails then) to us was addressed to Professor Alcock; much to our amusement.

Another project that I worked on with David was the analysis of data from SEASAT – the first satellite dedicated to oceanography. In the 1970s, our visit to Venice for a SEASAT Workshop enabled David to indulge in two of his passions: railways (Liverpool – London – Calais – Venice is some train ride) and wine (his wife was French). A very good bottle consumed by us on the return rail journey was paid for using a pile of Italian Lire left over when we had discovered that our Hotel accommodation had been paid by the Workshop organisers.

After our successful campaign in the late 1980s against Bidston’s closure and transfer to Wormley, Bidston became autonomous and was renamed the Proudman Oceanographic Laboratory. (The IOS Taunton site was closed and staff transferred to Bidston or Wormley.) Brian McCartney was appointed POL Director and, in my opinion, the next eight years were Bidston’s halcyon days: we reported directly to NERC HQ, without an intervening level of bureaucracy of IOS or later CCMS or NOC.

Brian always let Group and Project leaders have a full say at the Management Committee; especially at the annual allocation meeting (consequently it sometimes went on for two days); so I felt that if you inevitably didn’t get all the money or equipment that you had bid for, you still accepted his final decisions because you had had a fair hearing. Brian was also careful to include all “Prime-movers” (the researchers) in the vision and major decisions that directed our strategy. In those ways, I believe that he made sure that all staff felt that they had had some input in formulating the strategy that POL took under his Directorship, with ensuing collective responsibility and underpinning the Bidston “family” atmosphere that John Huthnance mentions in his article.

Brian had been Head of the Engineering Group at Wormley, so it was not surprising that technology development at Bidston thrived during his Directorship. Bidston became one of the few European laboratories with the capability of developing and deploying oceanographic instruments in the coastal zone, shallow or deep water. Together with our expertise in the analysis and interpretation of the data and the world-class hind-casting and fore-casting modelling expertise developed under Norman Heaps’ leadership, Bidston’s scientists and engineers were in great demand for European Community/Union oceanography projects. Not bad for an organisation later accused of scientific isolation because it was on a hill five miles away from Liverpool University.

Under Brian’s leadership, POL became the host laboratory for the North Sea Project, the first large “Community Research Project”, involving many other research institutes and university research departments. We developed a strategy of funding all our Laboratory Science and Technology Projects from a triple combination of Commissioned Research (mainly from the DoE, MAFF and MoD), EC/EU Programmes and the NERC Science Budget; giving us some financial stability.

Happy days!

With the movement of IOS Wormley to Southampton University in the 1990s, NERC carried out yet another reorganisation of its marine science, lumping its remaining oceanographic laboratories at Bidston, Oban and Plymouth, into a “Centre” for Coastal and Marine Science. Jackie McGlade was appointed to what I always considered was a poisoned chalice of a job as the CCMS Director. (CCMS was disbanded in 2000, the then NERC Chief Executive admitting that the CCMS experiment had failed.) Jackie faced a fair degree of hostility from some senior staff, particularly at Plymouth where her office was situated, as staff at the three previously autonomous laboratories tried to work out what exactly was the purpose of the “Centre”.

I worked closely with Jackie on aspects of commissioned research and scientific applications across CCMS and got on well with her. She tended to be quite open about what she felt (perhaps that’s what some senior CCMS staff didn’t like) and because of this I was probably the first Bidston staff member to find out about the proposed closure of Bidston and transfer to Liverpool; a decision that had been taken by the then Bidston Director, without, as far as I know, any consultation with Bidston staff (the Management Committee had been an early casualty of his appointment.) Jackie and I were travelling on the London Underground, back from a meeting with an Intellectual Property lawyer, when Jackie asked me what I thought about the plan to close Bidston and move everyone to Liverpool University. I was non-committal.

Frank Field, MP for Birkenhead, had been a main factor in NERC’s decision not to close Bidston in the 1980’s and I informed him of the decision. I was summoned to the Bidston Director’s office and told, in no uncertain terms, that he was the Director and made the decisions, which I had to obey as a member of his staff without discussion. I demurred. I took early retirement in 2000, having thoroughly enjoyed most of the time at Bidston and working for most of the Directors.

(The British Libraries’ “Voices of Science” is at http://www.bl.uk/voices-of-science/interviewees. As well as David Cartwright, other oceanographers interviewed are James Cease, Anthony Laughton, John Woods and Philip Woodworth.)

Bidston recollections

John Huthnance, 7 Oct 2016.

I joined IOS Bidston (as it was then) in October 1977. The validity of my appointment could be questioned as the appointment letter came from DB Crowder (the Bidston administrator) who left before I arrived.

It was a good time to join. There were about 80 staff in total, few enough to give a “family” atmosphere with the feeling that everyone knew everyone else. Several colleagues had been taken on during the early 1970s but it was still a time of expansion rather than otherwise.   Scientists like myself had a fairly free hand to pursue promising lines of research within a fairly broad remit. I enjoyed a feeling of support from fellow scientists to do just this. Much of the funding came through a consortium of several government departments with an interest in our research. The negotiations were at some distance from most of the scientists who did not have to spend much time writing proposals, yet it was good to know of “user” interest in our work, always a characteristic of Bidston science. It was still possible to be “the” expert in a topic, a rarity today. I was lucky.

Everyone was expected to go to sea at least once. My first experience was a long trip in October 1978 on RRS Discovery from South Shields to Recife (Brasil)! We had calm across the Bay of Biscay but gradually increasing seas as time progressed. Green terminal screens on board added to my discomfort. It also got hot enough to affect some of the electronics and the salinometer bath struggled to maintain any standard temperature. My struggles with the latter resulted in being one of many co-authors on a paper about steric height around the equator – as I discovered when the paper was published.

My next research “cruise” was less exotic, to the North Sea on RRS John Murray. The picture shows the arrangement for under-way surface sampling – a CTD (device for measuring the conductivity and temperature of sea water at a known depth) in a bucket lashed to the side.

Arrangement for under-way surface sampling
Arrangement for under-way surface sampling

I have seen some changes in the “style” of research – some for the better! In the 1980s John Bowman (Chief Executive of NERC) told us that if we wanted students, we should get a university job. Now student supervision is encouraged (and helped by being in Liverpool). When I started, current meter data processing typically involved printing out all the recorded values. Models were semi-analytic or had reduced dimension or coarse resolution. My thesis compared a few tidal harmonic constants between measurements and a simple model. Now we have millions of observed values, billions of model output values, and we need computer programs to translate these to something viewable. In the end, science wants to compare two independent numbers for the same quantity. With the “Big Data” that modern science generates, is it harder to think what we are aiming at?

 

North Sea Project - monthly surveys
North Sea Project – monthly surveys

Another change is towards “inter-disciplinary science”. I have been a believer in this owing to early good experience: a seminar at Bidston by John Allen (University of Reading) about sand transport gave me an idea for how sand banks might grow (I had already published about the character of tidal flow around the Norfolk sand banks). The “flip” side to inter-disciplinarity is the overhead of communication with a wider group of scientists. Anyway, Bidston (now Proudman Oceanographic Laboratory – POL) saw this in a big way in NERC’s first “Community Project”, the North Sea Project (formally 1987-1992). John Howarth and I were respectively coordinators of the monthly “surveys” (see figure) and intervening “process studies” for 15 months in 1988-89. I recall a “spat” with Philip Radford (PML) at the concluding 1993 Royal Society Discussion meeting. I showed a diagram characterised by physics-ecosystem. Philip countered with physics-ecosystem. These are of course quite compatible, differing only by which part is under the microscope.

The North Sea Project was followed by the “Land-Ocean Interaction Study” LOIS in the 1990s with POL at the centre of coastal, shelf-edge and modelling studies. Such large-scale projects with many participants involved a Steering group and many rail trips to London. At the same time (and possibly inspired by NERC) the EU Marine Science and Technology Programme (MAST) began. My main involvement was in “Processes in Regions of Freshwater Influence” (PROFILE; two phases), “Ocean Margin Exchange” (OMEX; two phases) – both inter-disciplinary – and “Monitoring Atlantic Inflow to the Arctic” (MAIA) which somehow managed to be only physics. MAST projects had several European partners; the beaten track became the M56 for Manchester airport and flights to partners’ laboratories, EU Brussels and MAST gatherings in rather nice places (e.g. Sorrento, Vigo, . . ).

After formation of Southampton Oceanography Centre SOC, there was an April 1st announcement setting up the “Centre for Coastal Marine Science” CCMS in the mid-1990s as a counterpart to SOC. CCMS incorporated PML, POL and SAMS and resulted in more trekking, to Plymouth and Oban. This was good for inter-lab communications but management went awry, especially regarding finances, and POL became “independent” again (within NERC) in 2001. 2001 was also the year of design for the new building for POL in Liverpool (pictured). There were several reasons for unhappiness about this; building down to a price, inevitable open-plan offices (being cheaper and set by Swindon precedent), more time and expense of commuting for most staff. I had the “joy” being project “sponsor”. In building procurement this does not mean having the money but rather liaison between the “owner” (NERC with the money) and the design team. I was in the architect’s Birmingham offices on “9/11”.

POL's new building in Liverpool
POL’s new building in Liverpool

After more than a year’s delay on completing the Liverpool building, we finally left Bidston at the beginning of December 2004.

A brief history of Bidston Observatory

Bidston Observatory was built in 1866, when the expansion of Waterloo Dock forced Liverpool Observatory to re-locate to Bidston Hill. It was built alongside Bidston Lighthouse and Signals Station, on land owned by the Mersey Docks and Harbour Board. George Fosbery Lyster was the architect.

George Fosbery Lyster
George Fosbery Lyster

John Hartnup, astronomer and Assistant Secretary to the Royal Astronomical Society, had been the Director of Liverpool Observatory since it was built in 1843. Amongst his achievements was the calculation of the longitude of Liverpool, which was important for navigation and the development of the port. He presided over the move to Bidston Hill, and continued as director of Bidston Observatory until his retirement in 1885, when he was succeeded by his son. The second director, John Hartnup Jr  died on 21 April 1892, when he fell from the roof of the Observatory while making meteorological observations.

Bidston Observatory and Lighthouse, postmarked 1907
Bidston Observatory and Lighthouse, postmarked 1907

Over the years, the emphasis of the Observatory’s work shifted from astronomy to other things, but always in the tradition of Time and Tide, so important to the port of Liverpool.

Of Time. The progression from observations of the stars, to the determination of longitude, to the calibration of chronometers was a natural one. The Observatory’s two levels of cellars and other features made it especially suited for calibrating chronometers under controlled conditions of temperature and seismic vibrations. Mariners sent their chronometers from all over the empire for calibration at Bidston. The One-O-Clock gun at Morpeth Dock was signalled from Bidston Observatory.

Of Tide. Ever since Liverpool’s harbour-master William Hutchinson (the same fellow who pioneered the use of parabolic reflectors in lighthouses on Bidston Hill) took the first extended series of tidal measurements over a period of nearly thirty years, Liverpool had led the world in tidal studies. This work became centred at Bidston Observatory when the Liverpool Tidal Institute was set up there under Joseph Proudman’s direction after World War I. Arthur Doodson’s work with mechanical computers for tide prediction happened here. One of his machines was used to predict the tides for the D-Day landings.

Observatory staff by the original one-o-clock gun, after its removal to Bidston Hill from Morpeth Dock.
Observatory staff by the original one-o-clock gun, after its removal to Bidston Hill from Morpeth Dock.

In 1969, the Natural Environment Research Council (NERC) took over responsibility for the Observatory. Oceanographic research continued to expand under their auspices. During the 1970’s, the Joseph Proudman Building was constructed in the former kitchen gardens of Bidston Lighthouse.

In 1989, the Observatory, Lighthouse and the perimeter wall enclosing them became Grade-II listed buildings.

In 2004, the Proudman Oceanographic Laboratory moved from Bidston Hill to a new building at the University of Liverpool. Their oceanographic research is still continuing today, but now in the guise of the National Oceanography Centre.

The departure of the Proudman Oceanographic Laboratory from Bidston Hill began a 12-year limbo. NERC’s original plan to sell the site to a developer aroused opposition from local pressure groups, and the spectre of an eleven-story high-rise residential development was averted. In 2012, NERC applied for and obtained planning permission and listed buildings consent (now lapsed) to convert the Observatory into four residential apartments. Later that year, the Joseph Proudman Building was demolished. Having put the Observatory to the market on several occasions, NERC finally sold it in 2015 to a developer (Bidston Observatory Developments Limited), who had outbid a community-led consortium. This was the lowest point in the Observatory’s history. A period of systematic neglect saw a rapid deterioration of the fabric of the building and the appearance of the grounds, exacerbated by water ingress, unpaid bills and a winter with no heating, and the Observatory was nominated to the Victorian Society’s list of the top ten endangered buildings of 2016.

Fortunately, the Observatory was sold again in September of 2016. The new owners have announced their intentions to operate the Observatory as a not-for-profit artists’ research centre and to incorporate an exhibition celebrating the Observatory’s scientific heritage.

 

 

 

Tidal Curiosities – The Whirlpool of Corryvreckan

Judith Wolf, 1 Sep 2016.

Most people know that the tide rises and falls periodically at the coast but not everyone is as aware of the periodic flood and ebb of tidal currents. These are of particular importance for mariners and need to be taken into account for navigation. Where currents become particularly strong, they can become known as a ‘tidal race’, which can be unnavigable at certain states of the tide.

Around the coast of the British Isles are many locations where a tidal race forms, usually in a constricted channel between two islands or an island and the mainland. In Scotland, between the islands of Jura and Scarba is the famous ‘Whirlpool of Corryvreckan’ – possibly the third largest whirlpool in the world (after Saltstraumen and Moskstraumen, off the coast of Norway). The Gulf of Corryvreckan, also called the Strait of Corryvreckan, is a narrow strait between the islands of Jura and Scarba, in Argyll and Bute, off the west coast of mainland Scotland.

Corryvreckan, between the islands of Jura and Scarba
Corryvreckan, between the islands of Jura and Scarba

The name ‘Corryvreckan’ probably derives from two words ‘Coire’ which in Irish means cauldron and ‘Breccán’ or ‘Breacan’, which may be a proper noun i.e. the name of an individual called Breccán, although this has also been translated as ‘speckled’ from the adjective brecc ‘spotted, speckled’ etc. combined with the suffix of place – an.

There is an Old Irish text known as Cormac’s Glossary written by the King and Bishop of Cashel, Cormac mac Cuilennáin who died in the year 908. The text is written in the form of a dictionary combined with an encyclopaedia. In it are various attempts at providing explanations, meanings and the significances of various words. At entry 323 it provides probably the fullest description of the Coire Breccáin of the early Irish material:

‘a great whirlpool which is between Ireland and Scotland to the north, in the meeting of various seas, viz., the sea which encompasses Ireland at the north-west, and the sea which encompasses Scotland at the north-east, and the sea to the south between Ireland and Scotland. They whirl around like moulding compasses, each of them taking the place of the other, like the paddles… of a millwheel, until they are sucked into the depths so that the cauldron remains with its mouth wide open; and it would suck even the whole of Ireland into its yawning gullet. It vomits iterum {again & again} that draught up, so that its thunderous eructation and its bursting and its roaring are heard among the clouds, like the steam boiling of a cauldron of fire.’

Corryvreckan Whirlpool, photo by Russ Baum, CC BY-SA 2.0
Corryvreckan Whirlpool, photo by Russ Baum, CC BY-SA 2.0.
https://commons.wikimedia.org/w/index.php?curid=2720206
Corryvreckan Whirlpool, photo by Walter Baxter
Corryvreckan Whirlpool, photo by Walter Baxter, CC BY-SA 2.0.
https://commons.wikimedia.org/w/index.php?curid=33579199

Corryvreckan is also very close to the island of Iona, famous for St Columba, and some of the tales about the whirlpool relate to this saint and his companions, praying to be spared from falling into it, while sailing from Ireland. In one story St Columba is supposed to have encountered and recognised the bones of one Brecan, supposed to have drowned in the whirlpool with his ship and crew, years before. However, there is some dispute as to whether the location of this event was off Scotland or in another whirlpool off northern Ireland.

More recently, in mid-August 1947, the author George Orwell nearly drowned in the Corryvreckan whirlpool. Orwell had fled the distractions of London in April 1947 and taken up temporary residence to write on the isolated island of Jura. On the return leg of a boating daytrip, Orwell seems to have misread the local tide tables and steered into rough seas that drove his boat near to the whirlpool. When the boat’s small engine suddenly sheared off from its mounts and dropped into the sea, Orwell’s party resorted to oars and was saved from drowning only when the whirlpool began to recede and the group managed to paddle to a rocky outcrop about a mile off the Jura coastline. The boat capsized as the group tried to disembark, leaving Orwell, his two companions, and his three-year-old son stranded on the uninhabited outcrop with no supplies or means of escape. They were rescued only when passing lobstermen noticed a fire the party had lit in an effort to keep warm. Orwell’s one-legged brother-in-law Bill Dunn was reputedly the first person to swim across the 300ft deep, mile-wide channel. Nowadays there are regular boat trips and diving trips for tourists.

As the flood tide enters the narrow area between the islands of Jura and Scarba it speeds up to 8.5 knots (>4m/s) and meets a variety of underwater seabed features including a deep hole and a pyramid-shaped basalt pinnacle that rises from depths of 70 m to 29 m at its rounded top. These features combine to create eddies, standing waves and a variety of other surface effects. Flood tides and inflow from the Firth of Lorne to the west can drive the waters of Corryvreckan into waves of more than 30 feet, and the roar of the resulting whirlpool can be heard ten miles away.

Image from Hebridean Wild website
Image from Hebridean Wild website.
http://www.hebridean-wild.co.uk/about.html

Although dangerous when the flood or ebb tide is running and particularly when the wind is blowing ‘against the tide’ (when choppy seas make it very dangerous), it can be safely crossed at slack water when the weather is calm. This is where accurate tidal predictions come into their own, to identify the safe passage times of slack water, although detailed modelling of these areas of complex bathymetry is still a challenge.

Tide and Storm Surge Modelling at Bidston Observatory

Philip L. Woodworth, 4 August 2016.

One of the main objectives of the research at Bidston Observatory was to understand more about the dynamics of the ocean tides, that is to say, the physical reasons for why the tide propagates through the ocean as it is observed to do. Before the advent of digital computers, the only way to approach these questions was from basic mathematical perspectives, in which eminent scientists such as Pierre-Simon Laplace in France excelled in the 19th century, and in which Joseph Proudman at Bidston was an acknowledged expert in the 20th century.

Similarly, there has always been considerable interest in the reasons for large non-tidal changes in sea level, including in particular those which occur due to the ‘storm surges’ generated by strong winds and low air pressures in winter. For example, following the Thames floods of January 1928, Arthur Doodson at Bidston chaired a committee for London County Council that undertook a detailed study of the reasons for the storm surge that caused the flooding, and made recommendations for protecting the city in the future.

These areas of research were revolutionised in the mid-20th century, stimulated by public concerns following the major floods and loss of life in East Anglia in 1953 (Figure 1c,d), and finally made possible by the availability of modern computers in the 1960s. An important person in using computers in this work at Bidston was Norman Heaps, who joined the staff in 1962 and was eventually joined by a group of ‘modellers’ and ‘student modellers’ including Roger Flather, Judith Wolf, Eric Jones, David Prandle and Roger Proctor.

(As a digression, we may also mention the attempted simulation in this period of storm surges using electronic circuits, in effect analogue computers, by Shizuo Ishiguro, the father of the novelist Kazuo Ishiguro, at the Institute of Oceanographic Science at Wormley in Surrey. These devices were made redundant by digital computers. Ishiguro’s equipment can be seen at the Science Museum in London.)

Computer modelling of the tides has many similarities to the modelling of storm surges. In both cases, there are external forces involved: gravitational due to the Moon and Sun in the case of the tides, and meteorological (winds and air pressure changes) in the case of storm surges. These forces are exerted on the water surface inducing currents and redistributing volumes of water.

So the first thing a modeller has to know is how much the forces are. These are provided from astronomy in the case of the tides, and from meteorology for storm surges (e.g. information from the Met Office). In the case of the 1953 storm surge, the effect of the wind can be appreciated from Figure 1(a) which shows a deep depression crossing from west to east and strong winds from the north pushing water into the southern part of the North Sea. The winds are especially important in this case: their force is determined by the ‘wind stress’, which is proportional to the square of the wind speed, and the dynamics are such that a greater surge occurs when wind stress divided by water depth is maximum. In other words, bigger surges occur in shallower waters, such as those of the southern North Sea or the German Bight.

Figure 1. Images from the 1953 North Sea storm surge that resulted in over 2500 fatalities, mostly in the Netherlands and eastern England. (a) Meteorological chart for 1 February 1953 (0 hr GMT) with the track of the storm centre shown by black dots in 12-hour steps from 30 January (0 hr) to 1 February (0 hr); (b) maximum computed surge throughout the area (cm); (c) flooding at Sea Palling on the Norfolk coast of England; (d) the Thames Barrier, an example of the considerable investment in coastal protection in the United Kingdom and Netherlands following the 1953 storm. For image credits, see Pugh and Woodworth (2014).
Figure 1. Images from the 1953 North Sea storm surge that resulted in over 2500 fatalities, mostly in the Netherlands and eastern England. (a) Meteorological chart for 1 February 1953 (0 hr GMT) with the track of the storm centre shown by black dots in 12-hour steps from 30 January (0 hr) to 1 February (0 hr); (b) maximum computed surge throughout the area (cm); (c) flooding at Sea Palling on the Norfolk coast of England; (d) the Thames Barrier, an example of the considerable investment in coastal protection in the United Kingdom and Netherlands following the 1953 storm. For image credits, see Pugh and Woodworth (2014).

The next problem is to determine what the impact of these forces is, and for that the computer solves sets of mathematical equations at each point on a grid distributed across the ocean (e.g. Figure 2); these equations are in fact the same ones that Proudman and others used but could not be applied in this way at the time. The output of the models consists of long records of sea level changes and of currents at all points in the grid: as an example, Figure 1(b) provides a map of the maximum resulting surge during the 1953 storm surge event. Layers of ‘nested models’ enable very detailed information to be provided to coastal users in particular localities.

Figure 2. The grid used for the numerical surge model employed in the current UK operational surge forecasting system. Only a section of the grid is shown to give an impression of model resolution and matching of a finite-difference grid to a coastline. The complete grid covers the entire northwest European continental shelf from 40° to 63° N and eastwards of 20° W. The model is forced by winds and air pressures covering the entire North Atlantic and Europe on a 0.11° grid indicated by dots. From Pugh and Woodworth (2014).
Figure 2. The grid used for the numerical surge model employed in the current UK operational surge forecasting system. Only a section of the grid is shown to give an impression of model resolution and matching of a finite-difference grid to a coastline. The complete grid covers the entire northwest European continental shelf from 40° to 63° N and eastwards of 20° W. The model is forced by winds and air pressures covering the entire North Atlantic and Europe on a 0.11° grid indicated by dots. From Pugh and Woodworth (2014).

As Figure 1 demonstrates, surge modelling is particularly important to people who live at the coast. The Met Office can provide data sets of winds and air pressures up to 5 days ahead, which can be used to force the computer models. And, because the models can thankfully run faster than ‘real-time’, they can provide forecasts of what the likely magnitudes of storm surges will be several days ahead, enabling flood warnings to be issued. In the case of London, the operational warnings can be used to decide whether or not to close the Thames Barrier (Figure 1d).

These forecast techniques, developed at Bidston by Norman Heaps, Roger Flather and others, were first used operationally at the Met Office in 1978, and successor models, which are conceptually the same, are still used there, providing warnings to the Environment Agency. Similar schemes have been adopted by other agencies around the world. Storm surge models developed at Bidston have also been applied to areas such as the Bay of Bengal where surges can be considerably larger than around the UK and where there has been a large loss of life on many occasions.

Modelling at Bidston later developed into studying the 3-dimensional changes in the ocean that result in the transport of sediments or pollutants (‘water quality modelling’) or that have impacts on ecosystems. Modelling has also been applied to topics such as the safety of offshore structures and renewable energy. The same sort of computer modelling is now used throughout environmental science. For example, the models that the Met Office uses for weather forecasting, or the Hadley Centre uses to predict future climate use the same principle of solving physical equations on a grid.

But every modeller knows that their model provides only an approximate representation of the real world, and to help the model along there is sometimes a need to include real measurements into the model scheme, in order to constrain the mathematical solutions on the grid. These are called ‘assimilation models’, of which forecast weather models are the most obvious examples.

This enables us to return to tide modelling. Scientists at Bidston developed many regional models of the ocean tide for engineering applications as well as scientific research. These models tended to have ‘open boundaries’ where the region of the model grid meets the wider ocean. In these cases, it is normal to prescribe ‘boundary conditions’ which specify the tide at the boundary, and which are in effect a form of data assimilation. However, if one wants to make a tide model for a large region or for the whole ocean, with no boundaries, it was found that there were problems with obtaining acceptable results, as the assumptions which go into the computer codes were not universally applicable or missed some aspects of the tidal dynamics. Assimilation of sea level measurements by tide gauges and from space by radar satellites provided a solution to these problems.

In the last decade, a number of excellent parameterisations of the global ocean tide have become available. Some of these parameterisations are based purely on measurements from space (e.g. Figure 3), others are based on computer tide models that make use of only the known dynamics, and others are hybrid models that employ data assimilation. The two latter schemes provide information on tidal currents as well as tidal elevations. All three techniques are in agreement to within 1-2 cm which is a superb achievement. Proudman could never have dreamed of knowing the tide around the world so well, and it is thanks to him and others at Bidston leading the way that we now have an understanding of why the tide is so complicated.

Figure 3. Co-tidal chart of the M2 ocean tide: global map of lines joining places where high tides for M2 occur simultaneously, and places with equal tidal range. The lines indicate Greenwich phase lag every 30°, a lag of zero degrees being shown by the bold line, and the arrows showing the direction of propagation. The colours show amplitudes. Map provided by Richard Ray (Goddard Space Flight Center) for Pugh and Woodworth (2014).
Figure 3. Co-tidal chart of the M2 ocean tide: global map of lines joining places where high tides for M2 occur simultaneously, and places with equal tidal range. The lines indicate Greenwich phase lag every 30°, a lag of zero degrees being shown by the bold line, and the arrows showing the direction of propagation. The colours show amplitudes. Map provided by Richard Ray (Goddard Space Flight Center) for Pugh and Woodworth (2014).

The tide and surge models we have described above are usually operated in 2-dimensional mode (i.e. with the currents at each point in the grid taken as averages through the water column), and such model codes are relatively straightforward to construct and fast to run. A big change since the early days of the 1960s that first saw their construction is that modellers nowadays tend not to write their own codes, but instead adapt sophisticated modelling code packages written by others. This enables them to construct the 3-dimensional models of much greater complexity that are now used in research.

Numerical computer modellers now comprise one of the largest groups of scientists in oceanography laboratories such as the National Oceanography Centre in Liverpool (the successor of Bidston Observatory). Their models provide a way to make maximum use of oceanographic measurements from ships, satellites and robotic instruments in the ocean (and the ocean is a big place and there are never enough measurements) and a way to forecast how conditions in the ocean might evolve. It is inevitable that oceanography and many other aspects of science will rely on modelling more in the future.

 

Some References for More Information

  • Cartwright, D.E. 1999. Tides: a scientific history. Cambridge University Press: Cambridge. 292pp.
  • Heaps, N.S. 1967. Storm surges. In, Volume 5, Oceanography and Marine Biology: an Annual Review, edited by H.Barnes, Allen & Unwin, London, pp.11-47.
  • Murty, T. S., Flather, R. A. and Henry, R. F. 1986. The storm surge problem in the Bay of Bengal. Progress in Oceanography, 16, 195–233, doi:10.1016/0079-6611(86)90039-X.
  • Pugh, D.T. and Woodworth, P.L. 2014. Sea-level science: Understanding tides, surges, tsunamis and mean sea-level changes. Cambridge: Cambridge University Press. ISBN 9781107028197. 408pp.
  • Stammer, D. and 26 others. 2014. Accuracy assessment of global barotropic ocean tide models. Reviews of Geophysics, 52, 243-282, doi:10.1002/2014RG000450.
  • Wolf, J. and Flather, R.A. 2005. Modelling waves and surges during the 1953 storm. Philosophical Transactions of the Royal Society, A, 363, 1359–1375, doi:10.1098/rsta.2005.1572.

Tide Gauges and Bidston Observatory

Philip L. Woodworth, 4 August 2016.

Everyone knows that the level of the sea goes up and down. Most of these changes in level are due to the ocean tide (at Liverpool the level changes due to the tide by more than 8 metres at ‘spring tides’), but changes of several metres can also occur due to ‘storm surges’ that occur during bad weather, while slow changes in level can take place due to climate change and because of the geology of the adjacent land.

Changes in sea level are measured by devices called ‘tide gauges’: the more suitable name of ‘sea level recorders’ has never been widely adopted in the UK although Americans often call them ‘water level recorders’. There are as many types of tide gauge such as:

Vertical scales fixed to a jetty or dock entrance.

These were simple ‘rulers’ (sometimes called ‘tide poles’ or ‘tide boards’), by means of which the sea level could be measured by eye. An example is shown in Figure 1.

Figure 1. A simple ‘tide pole’ or ‘tide board’ installed vertically in the water by means of which the water level can be estimated by eye.
Figure 1. A simple ‘tide pole’ or ‘tide board’ installed vertically in the water by means of which the water level can be estimated by eye.
Float and stilling well gauges.

This way of measuring sea level was first proposed by Sir Robert Moray in the mid-17th century. However, over a century went by before the first practical systems were introduced at locations in the Thames during the 1830s. They quickly become the standard way of measuring sea level and by the end of the 19th century they had spread to major ports around the world.

A stilling well is a vertical tube with a hole at its base through which sea water can flow. The level inside will be, in principle, the same as that of the open sea outside, but energetic wave motion will be damped (or ‘stilled‘) inside due to the hole acting as a ‘mechanical filter’. In the well is a float which rises and falls with the water level, and is attached via a wire over pulleys to a chart recorder driven by an accurate clock. The rise and fall of the water level is thereby recorded as a line traced by a pen on paper charts that are regularly replaced, the charts finding their way to a laboratory such as that at Bidston Observatory, where an operator ‘digitises’ the pen trace and so provides the measurements of sea level.

Figure 2(a) demonstrates how the level of the float is recorded on the paper chart, while Figure 2(b) is a photograph of the tide gauge station at Holyhead where there are two exceptionally large stilling wells.

Figure 2a. An example of a float and stilling well tide gauge. In modern gauges of this type, the recording drum and the paper charts are replaced by digital shaft encoders and electronic data loggers.
Figure 2a. An example of a float and stilling well tide gauge. In modern gauges of this type, the recording drum and the paper charts are replaced by digital shaft encoders and electronic data loggers.
Figure 2b. Two large stilling wells at Holyhead in North Wales.
Figure 2b. Two large stilling wells at Holyhead in North Wales.

This type of gauge is of historical importance as they were used for almost two centuries (although with modern improvements such as replacing the paper charts with modern electronic data loggers) and so data from them make up the data sets of sea level change that are nowadays archived at the Permanent Service for Mean Sea Level (PSMSL) in Liverpool and used for studies into long-term climate change. During the 19th century, most of these gauges were operated in the UK by the major ports, and even by the railway companies which operated ferries. Bidston Observatory operated one at Alfred Dock in Birkenhead for many years. A number of countries still operate float and stilling well gauges although most in the UK have been replaced with other types.

Pressure gauges.

These gauges measure sea level by recording water pressure with the use of a pressure sensor that is installed well below the lowest likely level of the water. The recorded pressure will be the sum of two forces pressing on the sensor: the pressure due to the water above it (which will be the sea level times the water density and acceleration due to gravity) and the pressure of the atmosphere pressing down on the sea surface. In practice, the latter can be removed from the pressure measurement using what is called a ‘differential’ sensor, thereby, after some calculation, providing a measurement of the sea level.

We mention two types of pressure sensor below, which were both developed at Bidston. One type (the bubbler pressure gauge) has been used at 45 locations around the UK for several decades and remains the main technology for sea level measurements in this country. Until recently (mid-2016), this large network was operated for the Environment Agency by a group at Bidston called the Tide Gauge Inspectorate, and then, following relocation, at the National Oceanography Centre in Liverpool.

Ranging tide gauges.

These devices consist of a transducer that is installed over the sea so that it can transmit a pulse down to the water, where the pulse is reflected back and recorded by the transducer, so measuring the time taken to travel down and back. If one knows what the speed of the pulse is, then one can readily compute the height of the transducer above the sea, and so measure sea level. The transmitted pulse can be either an acoustic one (sound), or electromagnetic (radar) or optical (light). During the last decades of the 20th century, acoustic systems became very popular and replaced float gauges, and even replaced pressure gauges in some countries. However, they have since been largely replaced in their turn by radar gauges for several reasons. One simple reason is relative cost. However, radar gauges are potentially more accurate than acoustic systems owing to the speed of a radar pulse, unlike sound, being independent of air temperature. Optical ranging gauges use lasers to transit the pulses but, to my knowledge, are used in only two countries (Canada and South Korea).

Bidston Observatory had expertise in all of these types of tide gauge, but three can be mentioned in which Bidston scientists took a special lead.

Bubbler pressure gauges.

In the late 1970s, the Institute of Oceanographic Sciences (IOS, as Bidston Observatory was then known) was encouraged by the government to see if the new types of tide gauge then becoming available would be suitable for replacing the float and stilling well gauges then standard in the UK. This led to a programme of research by David Pugh and others into the use of different types of pressure gauge, including the bubbler gauge, and the curiously-named ‘non-bubbling bubbler gauge’ which we shall not explain.

Bubbler gauges were not invented at Bidston but they were developed there into practical instruments. They offered advantages over other pressure sensor systems in which the sensors themselves are installed in the water. In a bubbler system, the only equipment in the water is a tube through which gas flows at a rate sufficient to keep the tube free of water, such that the pressure in the tube is the same as that of the water head above the ‘pressure point’ at the end of the tube (Figure 3). The pressure sensor itself is located safely at the ‘dry land’ end of the tube, so there are no expensive electronic components that could be damaged in the water. If the tube is damaged it is simple and cheap to replace. The only drawback is that a diver is needed to install the tube, although the same need for a diver applies to all other pressure systems.

Figure 3. A outline of the bubbler pressure gauge system. (From Pugh and Woodworth, 2014).
Figure 3. A outline of the bubbler pressure gauge system. (From Pugh and Woodworth, 2014).

Comparisons of the old (float and stilling well) and new (bubbler) gauges were made at various locations, including at the important tide gauge station at Newlyn in Cornwall. In addition, the way that they measure sea level was thoroughly understood from both theoretical and experimental perspectives. The conclusion of the research was that bubbler pressure gauges could be reliably installed across the network. Bubblers are now standard in the UK and Ireland although they have since been replaced in countries such as the USA by other systems.

‘B’ gauges (where B stands for Bidston).

These gauges were developed in the 1990s by Bob Spencer, Peter Foden, Dave Smith, Ian Vassie and Phil Woodworth for the measurement of sea level at locations in the South Atlantic. They are rather complicated to explain in this short note, but the gist of the technique is that it uses three pressure sensors to measure sea water pressure (as in a bubbler gauge) and also maintain the datum (measurement stability) of the data in the record. ‘B gauges’ are probably the most accurate and stable types of tide gauge ever invented, but they are expensive (because of the requirement for three sensors) and were never developed commercially. Nevertheless, the principle of the ‘B technique’ was eventually incorporated into the way the bubblers were operated in the UK network, which remains the situation today.

Radar tide gauges.

Bidston Observatory cannot claim to have invented radar tide gauges; these radar transducers were developed first for the measurement of liquids and solids in giant industrial tanks, and were then applied to the measurement of river levels. However, Bidston can claim to have been one of the first laboratories to have used radar gauges for measuring sea level, a one year comparison of radar and bubbler data from Liverpool having shown that radar was a suitable technique for a tide gauge (Figure 4). Radar gauges have since fallen in price, are even more accurate than they were, can be readily interfaced to any kind of computer, and consume less power (an important feature in remote locations where gauges have to be powered from solar panels). They have become the standard technique for measuring sea level around the world and look like remaining so in the future.

Figure 4. A radar tide gauge at Gladstone Dock in Liverpool. The gold-coloured radar transducer transmits pulses down to the water and so measures sea level. The grey box on the wall is a satellite transmitter that sends the data to the laboratory.
Figure 4. A radar tide gauge at Gladstone Dock in Liverpool. The gold-coloured radar transducer transmits pulses down to the water and so measures sea level. The grey box on the wall is a satellite transmitter that sends the data to the laboratory.

Some References for More Information

  • Bradshaw, E., Woodworth, P.L., Hibbert, A., Bradley, L.J., Pugh, D.T., Fane, C. and Bingley, R.M. 2016. A century of sea level measurements at Newlyn, SW England. Marine Geodesy, 39(2), 115-140, doi:10.1080/01490419.2015.1121175.
  • IOC. 2015. Manual on Sea Level Measurement and Interpretation. Manuals and Guides 14. Intergovernmental Oceanographic Commission. Volumes I-V may be obtained from http://www.psmsl.org/train_and_info/training/manuals/.
  • Pugh, D.T. and Woodworth, P.L. 2014. Sea-level science: Understanding tides, surges, tsunamis and mean sea-level changes. Cambridge: Cambridge University Press. ISBN 9781107028197. 408pp.
  • Woodworth, P.L., Vassie, J.M., Spencer, R. and Smith, D.E. 1996. Precise datum control for pressure tide gauges. Marine Geodesy, 19(1), 1-20.

Hartnup moves in

This article appeared in the Liverpool Mercury on 20th December 1866, two days before Liverpool’s astronomer, John Hartnup, took possession of Liverpool’s shiny new observatory on Bidston Hill. It makes fascinating reading 150 years later.

The New Liverpool Observatory

Bidston-hill has hitherto been chiefly noted for its picnic parties, and for entertainments in which ham and eggs were the principal ingredients. It will now acquire a wider celebrity as the site of one of the most complete observatories at present in existence – one which is certain to make the Dock Board spoken of with respect by men of science, and to render Mr. Hartnup’s position, as astronomer of Liverpool, an object of something like envy to his professional brethren. For the interests both of the port and of science, it was certainly a good thing that the space which the old observatory has occupied during the last 22 years, on the Prince’s Pierhead, was required for docks. Close to the river on one side, and the murkiest part of the town on the other, Mr. Hartnup was often in a fog, not by any means intellectually, but materially, and still more frequently had his nicest observations interfered with by the smoky canopy which overhung his post of observation. Obliged to cast about for a new site, the dock board selected Bidston-hill as the most eligible situation to be found in the neighbourhood for an observatory. The design and erection of the building were left to Mr. Lyster, the dock engineer, and he and his staff have produced a work of which they have no reason to be ashamed. Commenced in 1864, it has been gradually growing up by the side of the old lighthouse, which formerly was the sole occupant of the height, and now with its two domes and picturesque outline, stands out as a prominent feature in the landscape. The transfer of instruments from the old observatory has been for some time in progress, and at the beginning of next year Mr. Hartnup will probably be able to resume his labours – made still more important by this change – under conditions more favourable than he has yet enjoyed.

Externally, the new observatory has a bold and massive appearance, which accords with the position in which it is placed. A building perched alone at the summit of a hill is in danger of looking insignificant from one or other points of view, but Mr. Lyster has so well arranged the different fronts that from all aspects an effective grouping is presented. Two domes, springing from octagonal towers at the east and west extremities of the south front, are prominent features of the building. Beneath one is the “equatorial”, for making astronomical observations, and beneath the other an instrument called the transit. The domes enclosing these instruments have apertures at several points, and are made to revolve, so that observations can be taken in any part of the heavens. The substantial character of the whole building strikes the observer at once. It is founded upon a rock, and if the waves as well as the winds could come to Bidston-hill, Mr. Hartnup’s castle would not be likely to fall. Strength and solidity are characteristics of Dock Board work, but there are special reasons for making an observatory, from foundation to summit, firm and secure as builders’ skill can contrive. Some of the operations carried on are so delicate that the variation of almost a hair’s breadth would seriously affect the results, and hence the utmost precautions have been taken to avoid the vibration to which all but the most substantial buildings are liable. A deep foundation excavated out of the solid rock and thick stone walls to form the superstructure were not considered sufficient to secure perfect immovability, and to prevent all possibility of vibration from anything short of an earthquake the building has been insulated from the surrounding rock to the depth of 12 or 14 feet by a trench about 18 inches wide. Even this has not been deemed a sufficently stable basis for the transit. That instrument is located immediately beneath the dome at the south-east angle of the building. It is used for taking the time, fixing the latitude, and determining the declination of the stars. These operations require the utmost accuracy of observation, and consequently the most perfect steadiness of position. To support the instrument a huge pillar, nine feet in diameter, has been carried up from the solid rock to the floor immediately beneath the dome, and this pillar, though passing through several floors, and apparently in contact with them, actually touches the building at no part. In other respects, the thorough adaptability of the building to the purpose for which it is intended has been studied. In many of the processes uniformity of temperature is very necessary, and towards securing this lofty cellars have been excavated in the basement, where an efficient heating apparatus, communicating with all the apartments in the building, is situated. The other internal arrangements are in a corresponding style of completeness. There is a fine chronometer room 36 feet long by 21 feet abroad; an anemometer room and a library, each 18 feet by 21 feet; a computation room; and, in short, every provision for carrying on efficiently the work belonging to an observatory. The northern portion of the building forms the private residence of Mr. Hartnup, and in reference to the arrangements of which it need only be said that the comfort and convenience of its occupant have been consulted in every particular.

There are a good many people in Liverpool, we dare say, who have a very shadowy notion of the objects of an observatory, and the labours which Mr. Hartnup has to perform. Quoting from his last report, we will let the astronomer tell in his own words what are the merely routine duties of the observatory :-

Observations are regularly taken with the transit instrument, for the purpose of ascertaining the local time. From the local time so obtained, the Greenwich mean time is deduced and communicated to the port daily by the dropping of the time-balls at the Observatory and at the Victoria Tower. The clocks at the Victoria Tower and Town Hall, and also the seconds clock seen from the Exchange flags, are controlled from the Observatory. The other public clocks on the dock estate are regulated twice each week, and a record is preserved showing their errors at the time they were regulated. The velocity and direction of the wind, and the fall of rain, as derived from the self-registering anemometer and rain-gauge, are tabulated for each hour of the day, and hourly readings are taken from the tracing produced by the self-registering barometer. The results thus obtained are tabulated, and the mean reading at each hour of the day is taken at the end of every month. The ordinary meteorological observations obtained by means of the standard barometer, thermometers, hygrometers, &c., are taken at eight and nine a.m., and at one, three, and nine p.m. daily. A telegram containing the corrected readings of the barometer, wet and dry thermometers, strength and direction of the wind, and general state of the weather for the proceeding 24 hours, is forwarded daily at eight a.m. to the Meteorological Department of the Board of Trade. Weekly meteorological observations are forwarded to the Mersey Docks and Harbour Board, and to the medical officers of health for Liverpool and Birkenhead. Monthly and weekly meteorological observations are forwarded to the Registrar-General of Births, Deaths and Marriages; and a tracing of the record produced by the self-registering barometer, together with an account of the hourly strength of the wind, &c., are supplied daily to the Liverpool Underwriters’ Association.

The value of the observatory in keeping an exact record of time is shown by the fact that in Liverpool there are, on an average, upwards of 2000 chronometers dependent on the time disseminated from the observatory for their errors on Greenwich mean time, and of their daily rates obtained while the ships to which they belong remain in port. Now that the observatory has been removed to Bidston, it is possible that the time-balls will give place to a time-gun, which is found to possess several advantages over the ball. With regard to meteorological observations, their importance is every year becoming more largely recognised, and during the last 20 years Mr. Hartnup has contributed not a little to the advance which this department of science has made by his carefully compiled tables of results.

In a more direct and immediate manner, the observatory at Bidston will be of immeasurable value to Liverpool by reason of the facilities it affords for testing nautical instruments. The seaman is chiefly dependent for a knowledge of his chronomoter, compass, sextant, &c. Errors in these have, times out of number, led to the destruction of noble ships, and the loss of many lives and the importance of efficiently testing nautical instruments has long been present to the mind of the astronomer. At the old observatory, chronometers only could be tested. Its nearness to the docks, the possible proximity of iron ships, and other disturbing influences, rendered the testing of compasses out of the question. At Bidston, all these difficulties will be removed, and it is proposed to erect a wooden house specially for the testing of compasses. If this be done, it is to be hoped nautical men will take advantage of the opportunity afforded them of ascertaining that their compasses act properly. It will also be possible at Bidston to test sextants; and if arrangements are made for that purpose, the Liverpool Observatory will be, with the single exception of Kew, the only place in the kingdom at which these instruments are tested. The practical advantage of subjecting instruments to a systematic test has already been exemplified in the case of chronometers. It is often that three or four voyages elapse before a captain ascertains the exact rate of his chronometer, whereas the testing process at the observatory puts him in possession of the information at once. This is the mode of testing chronometers –

All chronometers received at the Observatory are compared daily with the normal clock, which is kept as nearly as possible to Greenwich mean time. From subsequent astronomical observations, the daily errors of this clock, at the times of its comparison with the chronometer, are deduced, and the correction for each day, thus obtained, is applied to the daily comparisons of all the chronometers. In this way the error of each timekeeper is found daily, with as much accuracy as it is well possible to attain. The temperature in a glazed chamber is kept, by artifical means, between 50′ and 85′, and changed weekly 10′ or 15′, in order to show the change of rate that may be expected on going from a temperate to a tropical climate. The record supplied to the captain or owner of each chronometer, contains its error on Greenwich mean time for each of the first few days; and subsequently it is given at the end of each week, together with the mean daily rate, the temperature to which the instrument has been exposed, and the greatest variation of rate between any two days in each week. The corrections for imperfect adjustment are sometimes found to be so large or so irregular as to render it troublesome or difficult to apply them all efficiently, and in such cases the record becomes a serviceable guide to the maker, as it directs his attention to the peculiar fault, and often enables him to make the necessary adjustment at once.

It is rather puzzling to be told that the wind is made to register its own velocity, force, and direction; that the quantity of rain which falls is measured and recorded without human interference; and that the atmosphere marks its own variations on a sheet of paper. Yet all this is done by means of the anemometer, rain-gauge, and barograph – contrivances as ingenious as they are effective. Any one who has been in the neighbourhood of the observatory must have observed on the roof a sort of horizontal windmill, consisting of four hemispherical cups. These serve the double purpose of keeping a four-feet pressure plate facing the wind and turning the shaft which runs through into the room where the anemometer is situated. This shaft, by an ingenious contrivance, regulates the motions of a pencil placed in contact with a sheet of paper stretched round a slowly revolving cylinder. The sheets of paper which receive the record made by the pencil are divided by vertical lines into spaces equal to the hourly motion of the cylinder, and by horizontal lines into other spaces, representing the pressure of wind per square foot. The barograph, or self-registering barometer, has been in use about three years, and the Liverpool Observatory is the only institution which possesses an instrument of this character. It was invented by Mr. Alfred King, of this town, and shows great ingenuity of construction. In the ordinary barometer the variations in the atmospheric pressure are indicated by the varying height of a column of mercury within a tube; in the floating barometer these variations are made evident by the movements of the tube itself, and its changes of position are recorded in a somewhat similar manner to that adopted in connection with the anemometer. There are various other interesting features connected with the observatory, but we must bring this notice to a close. In many respects, the establishment of the new observatory is an important event, and there can be no question that Mr. Hartnup will turn to good account the increased advantages he will possess for carrying on his useful labours in the fine institution placed under his charge.

 

Bidston Observatory and Its Tide Prediction Machines

This article originally appeared in the newsletter of the Friends of Bidston Hill in February 2016. It is reproduced here with the permission of the author.

The role of Bidston Observatory has changed several times through the years. In its early decades, following the decision in the 1860s by the Mersey Docks and Harbour Board to move the Liverpool Observatory from Waterloo Dock to Bidston Hill, the focus was on astronomical measurements. These were required in order, amongst other things, to determine accurately the latitude and longitude of the site. Famous names involved included John Hartnup and his son (also John) and W.E. Plummer. Other areas of science undertaken by the Observatory included meteorology and seismology. In addition, it provided several local services, such as the calibration of accurate chronometers for port users and precise timing via the “One O’Clock Gun”.

By the 1920s, the Observatory had become ‘moribund’ (to quote from the excellent book by David Cartwright) and, after the death of its then Director Plummer, the decision was made to combine its work with that of the University of Liverpool Tidal Institute, with both to be located at Bidston. The latter had been founded in 1919 on the university campus in Liverpool with Joseph Proudman as Director and Arthur Doodson as Secretary, with funding from several sources including the major Liverpool shipping companies. The formal amalgamation of the Observatory and the Tidal Institute took place in 1929.

Proudman is another famous name, with Bidston Observatory later becoming known as the Proudman Oceanographic Laboratory. However, it is Arthur Doodson who is more relevant to this article. In the first year of the Tidal Institute, Doodson and Proudman began work on the problem of predicting tides, especially in shallow waters. They also undertook an evaluation of the benefits of mechanical tide prediction machines, which had been invented in the late 19th century by Lord Kelvin (William Thomson) and later developed by Edward Roberts. In effect, they were ‘analogue computers’. By 1924 Doodson had taken delivery of a brand new tide machine, the so-called ‘Bidston Kelvin machine’ thanks to the generosity of Liverpool ship-owners. Then in 1929, with all staff now installed at Bidston, he acquired and refurbished the so-called ‘Roberts machine’ which had been constructed by Roberts in 1906. The Roberts family had used this machine as part of a business of providing tidal predictions to the government but, due to the death of Roberts’ son, were no longer able to continue.

The Bidston Kelvin Machine and (inset) Arthur Doodson (from Parker, 2011)
The Bidston Kelvin Machine and (inset) Arthur Doodson (from Parker, 2011)

The Roberts machine was in many ways superior to the Kelvin machine, being capable of predicting 40 ‘constituents’ of the tide instead of 29. Such machines can only have a decent stab at simulating the tide at all thanks to the fact that the tide is capable of being described as the sum of individual harmonic constituents. Constituents can be thought of as cosines with particular frequencies (or periods) that are known from astronomy. So, for example, two of the most important constituents are called M2 and S2. These come from the Moon and Sun respectively with periods of 12 hours 25 minutes for M2 and 12 hours exactly for S2. These two terms are responsible for the regular twice-daily tide we have at Liverpool. However, many more constituents than these two are required to do a decent job of simulating the real tide to the accuracy required, and a machine with as many constituents as possible is highly desirable.

The Roberts machine at an exhibition in Paris in 1908. This machine is now on display at the National Oceanography Centre in Liverpool.
The Roberts machine at an exhibition in Paris in 1908. This machine is now on display at the National Oceanography Centre in Liverpool.

These two machines were responsible for many important achievements in the Observatory’s history. Bidston had become the undoubted centre of excellence in tidal research, both from theoretical perspectives (primarily Proudman) and on more practical bases such as the provision of tidal predictions worldwide using these machines (primarily Doodson). Doodson was excellent at devising techniques for handling numbers within complicated scientific calculations that nowadays would be undertaken by digital computers. He also became an expert in the technical design and construction of the tide prediction machines.

Although important individual machines were constructed in Germany and the USA, the majority of the 33 ever made (24 machines) were designed and manufactured in the UK, in either London, Glasgow or Liverpool. The UK was the only country to export machines to other countries. The construction of the majority of the machines made after 1920 was supervised, one way or another, by Arthur Doodson. These included a series of machines made after World War II, of which one (called locally the “Doodson-Légé machine”) was to be found in the lobby of the main POL building for many years until the move of the laboratory to the Liverpool campus in 2004.

The Doodson-Légé machine in the 1990s in the reception area of the Proudman Oceanographic Laboratory. The machine is now on display at the National Oceanography Centre in Liverpool.
The Doodson-Légé machine in the 1990s in the reception area of the Proudman Oceanographic Laboratory. The machine is now on display at the National Oceanography Centre in Liverpool.

Two of the three machines at Bidston have an importance in a notable period in the Observatory’s history, in providing tidal predictions during World War II and, in particular, for the D-Day landings and in other military operations around the world. These were the Kelvin and Roberts machines, which were located in separate buildings at the Observatory during the 1940s in case of bomb damage. The Kelvin machine, Doodson’s first, is now to be found in good condition at the headquarters of the French Hydrographic Service in Brest. Its disposal by Bidston after the war was a financial requirement in order to obtain funding for the Doodson-Légé machine.

The Roberts and Doodson-Légé machines are still located in Liverpool and are now owned by the Liverpool Museum. Recently, they have both been refurbished excellently and are capable of working as well as they can in order to show how things were done at Bidston, before the advent of digital computers in the 1960s saw their demise as the Observatory’s main technical assets.

Both machines are now on long-term loan from the Museum to the National Oceanography Centre in Brownlow Street on the Liverpool University campus, NOC being the successor to POL and therefore the ‘spiritual home’ of the machines. They are available for viewing by the public but arrangements must be made beforehand with the NOC Administration.

For anyone interested in Bidston Observatory and these machines, there is more to read. For an excellent introduction to tidal science, see Cartwight (1999), while histories of the Observatory and the people who worked there are given by LOTI (1945), Jones (1999) and Scoffield (2006). Aspects of Doodson’s career have been described by Carlsson-Hislop (2015). An ‘inventory’ (or overview) of tide prediction machines can be obtained from me, while the story of the use of the Kelvin and Roberts machines in World War II is given by Parker (2011).

Philip L. Woodworth
National Oceanography Centre,
6 Brownlow Street,
Liverpool L3 5DA
December 2015

References

  • Carlsson-Hislop, A. 2015. Human computing practices and patronage: anti-aircraft ballistics and tidal calcuations in First World War Britain. Information and Culture: A Journal of History, 50, 70-109, doi:10.1353/lac.2015.0004.
  • Cartwright, D.E. Tides: a scientific history. Cambridge University Press: Cambridge, 1999. 292pp.
  • LOTI. 1945. Liverpool Observatory and Tidal Institute. Centenary Report and Annual Reports for 1944-5. Available from P.L. Woodworth.
  • Jones, J.E. (original date 1999) From astronomy to oceanography: a brief history of Bidston Observatory. http://noc.ac.uk/f/content/downloads/2011/proudman-history.pdf.
  • Parker, B. 2011. The tide predictions for D-Day. Physics Today, 64(9), 35-40, doi:10.1063/PT.3.1257. Available from http://scitation.aip.org/content/aip/magazine/physicstoday/article/64/9/10.1063/PT.3.1257.
  • Scoffield, J. 2006. Bidston Observatory: The place and the people. Merseyside: Countyvise Ltd. 344pp.