The Naming of Tropical Cyclones

Photograph: HMAS "Arrow" lies wrecked in Darwin Harbour following tropical cyclone "Tracy" in December 1974. Image: Wikipedia Commons - click to enlarge

Whilst many of the famous tropical cyclones in Australia’s history are instantly recognised by the names they were given, such as Tracy, Althea and Trixie, some of our most intense cyclones were never named at all.

The reason for this is tied up in the history of the naming of cyclones in Australia, which is an interesting story in itself. Clement Wragge, the rather eccentric Queensland Government Meteorologist from 1887 to 1902, is thought to have been the first person in the world to name tropical cyclones.

He called them after letters from the Greek alphabet, figures from Greek and Roman mythology, feminine names and also the names of some of the politicians of the day, including Drake, Barton and Deakin. Wragge considered that both politicians and tropical cyclones were national disasters.

In 1902, the Member for Werriwa was the Honourable Mr. A.H.Conroy, who somehow had incurred Wragge’s displeasure because he featured in several cyclone warnings. These included “Conroy, looking nasty, is coming along the coast” and “Conroy, black and treacherous, is likely to cross the Southern District…”. Justifiably miffed, Conroy dismissed Wragge as “an advertising scientist”.

After Wragge had left the meteorological scene in 1908, the naming of tropical cyclones lapsed and was not resumed by the Bureau of Meteorology in Australia until 1963. Then only feminine names were employed, but after complaints that this practice was discriminatory, both male and female names were used from 1975 onwards.

As a result of all this, cyclones that occurred between 1908 and 1963 were generally not given a name and these included some major storms that created massive damage and considerable loss of life. A powerful cyclone devastated Mackay in January 1918, killing 30 people and destroying some 30% of the housing in the area. And in 1954 a cyclone struck the Gold Coast of Queensland with 26 people perishing and hundreds of houses destroyed in the general area. Neither of these cyclones was named.

Tropical cyclone "Ingrid" threatened the Queensland coastline during March 2005.

(NASA image) - click to enlarge

Today, the names of tropical cyclones come from a list maintained and updated by the Bureau of Meteorology according to quite a strict protocol.

This contains five main guidelines that are called the “Tropical cyclone naming policy” and these are:

* Tropical cyclone names in each list are alternate male and female

* Names of cyclones that have already significantly affected the Australian region cannot be used again – for example “Tracy”.

* If two or more cyclones are occurring simultaneously, similar sounding names (for example June & Jane) are avoided to minimise confusion

* Names should not be capable of being construed to subject the Bureau to criticism or ridicule (for example naming a sequence of cyclones after politicians)

* Lists of names are coordinated with neighbouring meteorological services to avoid duplication

These guidelines, together with the current list of names being used, can be found at

http://www.bom.gov.au/cyclone/about/names.shtml

Tropical revolving storms – that we call tropical cyclones in Australia - are referred to as “hurricanes” in the USA and “typhoons” in much of Asia.

Hurricane derives from the South American Carib word “Hurican” meaning God of Evil, and typhoon originates from the Chinese “tai’fung” meaning Great Wind.

Reference: Australia’s Natural Disasters, Richard Whitaker (New Holland Publishers) 2005.

Heatwaves in Australia

There is no universally accepted definition of a “heatwave” so to a certain extent we can make up our own. A simple and easy to remember definition is the 5/5 rule – that is five days in a row where the maximum temperature is five or more degrees Celsius above average.

But academic definitions aside, one thing is eminently clear – heat waves are lethal happenings – in fact the most deadly of all meteorological extremes. Perhaps surprisingly, heat waves kill many more people each year than tropical cyclones, bushfires, thunderstorms and floods. Whenever there is a heat wave there is an immediate spike in community mortality, and from analysing the nature of the “spike” experts can estimate the associated death toll.

Australia has experienced numerous recorded heatwaves and some of the main events are listed here together with the estimated number of deaths recorded nationally:

* January 1908 - 246
* February 1921 - 147
* January 1927 - 130
* January 1939 - 438
* February 1959 - 105
* January 1973 - 26
* February 1981 - 15
* February 1993 - 17
* February 2004 - 12
* February 2009 - 374



The temperature profile of the Melbourne heatwave of January and February 2009. Note the three consecutive days over 43C in late January, followed by a record 46.4C on February 7. It is believed that 374 people died as a result. Melbourne's average maximum temperature for this time of the year is 26C.
Image: Wikipedia Commons.
(Click on image to enlarge)

These mortality numbers cannot be used to directly gauge the severity of heatwaves as the population and social habits of the day also play a role. The larger number or people around today will obviously produce a proportionate increase in mortality compared to the situation of say fifty years ago.

But on the other hand, people today have far more access to fans and air conditioning than their earlier counterparts. Direct comparisons are therefore difficult.

Australia’s southern capitals are all subject to heatwaves, including Perth, Adelaide, Melbourne, Canberra and Sydney, and these events are often accompanied by severe bushfires.

An interesting article appeared in the Melbourne Argus on Friday 19th January 1934 that contained some recollections of severe heatwaves in Melbourne over the years. The temperatures quoted are of course in the old Fahrenheit scale – 100 degrees Fahrenheit is approximately 38 degrees Celsius.

“A very good idea of the intense heat of Thursday (January 25th 1875) may be gathered from the fact that a gentleman of Soldiers Hill who thought it unnecessary to have a fire in the house to provide himself a meal utilised the suns rays to cook an omelette and the feat was successfully performed. He placed a school slate for a while out of doors then spread some butter upon it and breaking an egg thereon in a few minutes the egg was, perfectly cooked, as if done in the orthodox pan over a fire.

The Weather Bureau record on that day was 110.4 degrees, compared with 102.5 degrees yesterday. There were bush fires all over Victoria then; there were four days of intense heat in Melbourne, and it was reported that a stack of firewood had been ignited by the heat of the sun’s rays. As usual in a heat wave in those days the Yan Yean supply failed in most of the suburbs and water was carted in drays to Emerald Hill (South Melbourne) Richmond and
Kew.

In 1883 the Hon. Ivo Bligh's cricket team was visiting Melbourne, on three days the temperature exceeded 100 degrees - twice it exceeded 104 degrees. Correspondents wrote to the newspapers of the odour of the filthy Elizabeth street drain-and the Yan Yean failed. For the next heat wave, in 1898, there was also an English team present and "Observer" wrote in his introduction to the account of the match, ' On every hand there were heard weary sighings for rain - rain by the inch even though Australia lost the cricket match because of it!” Almost the whole of Gippsland was ablaze. In Melbourne the horses of the Fire Brigade were exhausted and none could be found strong enough to take their places. Elms, planes, oaks, and willow trees withered in the parks in the first days of February.

In 1905 some persons walked through the streets of the city in bathing suits when 108.5 degrees was registered on two days in January - but bathing suits then were different. Amusements were postponed and labourers were forced to cease work.

The record heat wave in Melbourne, however, was in 1908 from January 15 to January 20, six days of “centuries" with a maximum of 109.1 degrees. There were many sudden deaths from heat-stroke; the heat hastened the deaths of many sick persons; there was a constant stream of ambulance wagons to the Melbourne Hospital, and the number of deaths was so abnormal that the Melbourne General Cemetery management was unable to keep pace with the demand for burials. The Yan Yean failed again though not so seriously. The heat was so intense in the Newport railway workshops that portions of it were closed. Schools postponed their opening after the Christmas holidays, stock and poultry died. Thousands of suburban residents left their homes and carried mattresses into the public parks. The tram and train services could not cope with the crowds who went to the beaches, and thousands were left stranded at St Kilda and Brighton beaches unable to obtain a foothold on the last trams and trains to their homes.

In February 1912 when there appeared the first report of a man and his wife having driven to the beach wearing bathing suits in a “motor landaulette”. Birds, beasts and even fish in the lakes dropped dead. Since then the heat and its effects have been more mild. A constable collapsed on Flinders Street station in 1922. In 1927 the most serious effect of 104.5 degrees in the shade after a run of hot weather, was that potatoes suffered from sunburn; two years ago a temperature of 108.9 degrees was registered at the Weather Bureau, and many persons suffered from heat-stroke”.

Even in modern Australian society with its air conditioning, fast communications and advanced medical practices, heat waves remain a summer menace, and with the experts predicting an increasing frequency, this is a menace that will probably get worse rather than better.

2009 - The Year That Was

2009 turned out to be a year of amazing weather extremes - hot and cold, wet and dry with many records being set along the way. Here are some of the weather highlights for 2009 with great photographs supplied by viewers of The Weather Channel.

* During January and February, widespread heavy rain fell across north-western Queensland, producing extensive flooding around the Mt. Isa and Cloncurry areas. Flood-waters travelled southwards into Lake Eyre over the following weeks.

The Copperfield River, Queensland, in flood. Photo by Cindy and Damien (click to enlarge)

* A record-breaking heat- wave began building across south-eastern Australia during January and early February. During this time many temperature records were broken in South Australia, Victoria, Tasmania and southern NSW.

Tasmania recorded its highest ever temperature on 30th January (Scamander 42.2C).

On 7th February Victoria’s highest ever temperature was registered at Hopetoun at 48.8C and Melbourne’s new temperature record was raised to 46.4C on the same day.

Numerous deaths attributed to the heat were reported and morgues in Melbourne and Adelaide were filled to capacity because of the spike in heat related deaths. In Melbourne alone it’s estimated that more that 350 people died as a direct result of the heat during the scorching days of the 28th, 29th and 30th January, when maximum temperatures climbed above 43C on each day.

* Disastrous bushfires erupted across parts of central Victoria on Saturday 7th February – the Black Saturday fires - with 173 lives lost and more than 1800 houses razed. These were the worst fires in Australian history.


Black Saturday fires rage across Victoria. Photograph from Wikipedia Commons. (Daniel Cleavely)
(Click to enlarge)

* An east coast low dumped heavy rain along the NSW coastal areas between Kempsey and Newcastle on Tuesday 17th February, generating further floods across the already saturated Bellinger River catchment. The town of Bellingen was totally isolated over the next 24-hour period.

* On Tuesday March 31st, phenomenal rain from a nest of slow moving thunderstorms produced major flooding around Coffs Harbour. Some locations experienced more than 400 mm in a six hour period. The flooding produced major damage as well as numerous evacuations around the area.


Raging floods in Coffs Harbour. Photo by Steve Canute

* Heavy snow fell across the NSW and Victorian ski fields during Sunday 26th and Monday 27th April, allowing Mount Buller in Victoria, to open for business on Saturday 2nd May – the earliest start to the ski season in 45 years.

* Heavy rain set in across south-eastern Queensland on the night of Tuesday 19th May and continued through Wednesday. 48 hour totals in excess of 300 mm produced massive flooding across Brisbane and the Gold Coast with the inundation being compared in extent to the floods of 1974. Massive infrastructure damage unfolded with roads cut, power-lines down and waterways overtopping their banks. South-eastern Queensland was declared a natural disaster area by the Premier as the damage bill continued to rise. Queensland dams rose to 73 % by the end of the week – an increase in 13% in less than 1 week.

* The eastern rainfall focus then turned to the northern coastal areas of NSW on Thursday and Friday 21st and 22nd May with very heavy falls triggering widespread flooding across the NSW Northern Rivers and Mid North coast. Flood warnings eventually spread to 10 major river systems in the area.

* On Monday 15th June, rain began ramping up along the NSW coastline, in particular the Mid North Coast and northern Rivers areas. A succession of wet days followed with three day totals in excess of 200 mm accumulating in some areas, and a minor flood warning was issued on Saturday 10th for the Orara River – a tributary of the Clarence River.

* Heavy rainfall across eastern Tasmania, produced by a low over eastern Victoria, generated big rain gauge totals during Wednesday and Thursday, 12th and 13th August, with substantial flooding resulting over the South Esk and Macquarie River basins.

* Very warm to hot weather developed over central and eastern Australia during the week of 9th to 16th August, in north-westerly winds ahead of the fronts, as they moved eastward. Alice Springs experienced 6 days in a row where the temperature reached or exceeded 30C, which is the first time this has happened in August in at least 60 years.

* On Tuesday 22nd September a major dust storm spread across inland NSW, affecting Broken Hill, Tibooburra, and the ACT. The dust hit Sydney early on Wed 23rd, producing the most intense dust storm across the city in living memory. The dust then extended north over the next 48 hours, affecting Brisbane and then cities further north over inland and coastal areas of Queensland.


Red dust blankets Sydney on Wednesday 23rd September.
Image from Wikipedia Commons
(Merbabu)
(Click to enlarge)

* Heavy rain over the Mid North Coast area during Monday 26th October produced further minor to moderate flooding in the Bellinger, Nambucca and Orara river valleys during Tuesday 27th and Wednesday 28th October. This was the fourth time that the area has flooded in the last 9 months and the districts were declared a natural disaster area later in the week.

* Tropical Cyclone “Laurence” formed off the Kimberley coastline on Sunday 13th December, and after an irregular movement, proceeded to track across the central inland of Australia. The remnants of “Laurence” then produced widespread flooding rains across large areas of NSW and southern Queensland during the last week of 2009.

The Severe Weather Season in Australia

The period from November to April each year is often a time of considerable atmospheric turmoil across Australia. Heatwaves, bushfires, tropical cyclones and severe thunderstorms are frequent visitors, producing massive damage bills and on occasion, even loss of life.

This is the severe weather season for Australia and a great deal of effort is invested in providing timely warnings to minimise the impact these events produce on the Australian public.

Bushfires:
During this period, south-eastern Australia frequently experiences bursts of strong, hot, low humidity winds, and this, coupled with an abundance of often tinder dry eucalypt forest, can produce large and uncontrollable bushfires.

The aftermath of the Black Saturday Bushfires in Victoria, February 2009. Image - Peter Campbell, Wikipedia Commons. (Click on image to enlarge)

Three of the worst examples in recent history are:

Black Friday: Victoria
Friday 13th January 1939
71 deaths, 1300 homes destroyed

Ash Wednesday: Victoria and South Australia
Wednesday 16th February 1983
75 deaths, 2500 homes destroyed

Black Saturday: Victoria
Saturday 7th February 2009
171 deaths, 1800 homes destroyed

Severe thunderstorms:
This weather phenomenon has produced many trails of major damage across Australia in the past, with some of the most financially damaging events affecting the capital cities of Brisbane and Sydney.

Both these cities are located in an environment suitable for severe thunderstorms that are produced when warm, moist sub-tropical air interacts with cold upper atmospheric air that moves up from the higher latitudes. On occasion both cities have been blasted by large hail and strong winds, producing many millions of dollars damage.

Severe thunderstorms remain one of the main forecasting challenges because of their rapid periods of evolution and the small warning lead-time available. A severe thunderstorm can evolve from “no cloud” to a fully-fledged storm in less than an hour, leaving little time to issue weather warnings.

Developing thunderstorm towers high into the atmosphere. Image - Bidgee, Wikipedia Commons (Click on image to enlarge)

They can also produce an astonishing amount of damage in a very short period, particularly when giant hail is involved. Hail larger than golf ball size can smash roof tiles and pulverize cars, producing multi million dollar headaches for insurance companies.

Severe thunderstorms can also generate damaging wind gusts, flash flooding and in extreme cases, tornadoes, that are amongst the most destructive of all weather phenomena.

Tropical cyclones:
The tropical northern coastline of Australia is an area highly prone to tropical cyclone activity, with these often massive storm systems posing a constant threat to the area, particularly between the months of November and April – that is the cyclone season.

Tropical cyclone "Faye" off the coast of Western Australia in March 2004. NASA image - click to enlarge.

The north coasts of Western Australia and Queensland are included in this “strike zone” as is virtually the entire coastline of the Northern Territory. There have been numerous “direct hits” on these coastal areas over the years producing occasional massive destruction and loss of life when a major system collides with one of the larger tropical cities.

Heat waves:
Prolonged spells of hot weather, typically where the daytime temperatures remain five degrees or more above average, are called heat waves, and are amongst the most lethal of all weather patterns.

Mortality rates always show a pronounced peak during heat waves, with many thousands of people around the world succumbing to heat stroke or other related conditions each year.

In Australia it is believed that heat waves kill more people than any other meteorological phenomenon, and estimations indicate that more than 4000 Australians have died as a result between 1803 and 1992.

Heat waves also result in massive increases in power demand, particularly through the use of domestic air conditioning systems and swimming pool filters.

Line of air conditioning units outside a university.
Image: Ildar Sagdejev - Wikipedia Commons. (Click to enlarge)

Weather and the Melbourne Cup

An iconic moment in Australian sporting history - Phar Lap wins the 1930 Melbourne Cup. Judging by the dress of the crowd and their shadows, the weather was fine and cool during race time that day.
Image - Wikipedia Commons
(Click to enlarge)

Rain is a surprisingly frequent visitor to Melbourne on Cup Day, with about one in three race-days affected by rain of some sort.

However rain during the race itself is far less frequent – in fact only about once in every nine years. But there were only two occasions since the Cups beginning in 1861 where the race was actually postponed because of rain and these were the years 1870 and 1916, when the track was so waterlogged that it was deemed unsafe to ride.

Some of the wetter years are described here from contemporary newspaper articles:

1870 - Melbourne Cup is postponed one week due to rain
Eventually won by Nimblefoot

1892 – “The Cup was run in pouring rain”
Won by Glenloth

1899 – “The Melbourne Cup was run in a heavy shower, and the course at the time was fetlock-deep in water and slush”.
Won by Merriwee

1912 – “Wintry Day at Flemington – Rain Mars Attendance”
Won by Piastre

1913 – “A Vast Attendance - Racing in the Rain”.
Won by Posinatus

1916 - Rain postpones the Cup by 5 days – “The track was of the consistency of porridge”.
Eventually won by Sasanof

1924 – “Rain adversely affected the meeting”
Won by Backwood

1934 – “Rain Mars Pleasure of 90,000 people”
Won by Peter Pan

1941 – “No Sectional Times in Cup” – Owing to rain, visibility was so poor when the Melbourne Cup was being run that sectional times could not be obtained.
Won by Skipton

1976 - Rain throughout the race

Won by Van Der Hum

1992 – Rain all through the race
Won by Subzero

A wonderful reminiscence that appeared in The Argus on Saturday 16th August 1939 was written by a lady (who called herself "La Femme") recalling her first visit to the Melbourne Cup as a young lady in 1892 – when it rained heavily throughout the day.

Women's Woe - When it Rains
My first Melbourne Cup was in 1892, and I shall never forget it. I was supposed to be much too young (17) to go to the races, but one of my aunts who had been going became ill, and rather than waste the ticket they let me go. I was very thrilled and excited. I wore a white muslin dress and a scarlet hat trimmed with velvet geraniums. I also had a scarlet sunshade (borrowed).

Getting to Kensington in good time, we got a seat on the grandstand without trouble. We had taken sandwiches and cake, but had to do without tea at lunch, as thermos flasks were unknown then.

We were no sooner seated than it started to rain - as it can in Melbourne. It poured. Everybody looked dejected and miserable, but the races went on just the same. The Cup was also run in pouring rain. Glenloth won - a rank outsider. I heard someone say it was a milkman's horse, and well it might have been, for milkmen's horses are used to being out in all weathers. |

On the platform while waiting for the train back to Melbourne two women came along somewhat "under the influence." One was dressed in a lace frock and what had been a tulle hat with red poppies on it, but the rain had ruined the tulle, which was hanging round her face, and on top of her golden hair was perched a large bunch of wet poppies.

The other was dressed in amber - coloured satin. Her hat must have been beautiful when she started out for the races, but now it was just a bedraggled lot of ostrich feathers. She had only one shoe on, the - other one must have got stuck in the mud, and she had not bothered to put it on again. When the train pulled into the station she took off the remaining shoe and threw it at the engine.

My white muslin dress was a sorry sight, too. To protect my nice hat from the rain I had opened the red sunshade, but the dye ran and made dreadful splashes all over my dress. The dye later proved to be indelible.

I don't think I have since seen so many dejected people coming from the races. We had a miserable trip home in the train. Uncle was so cross. He must have lost a lot of money. Thank goodness we don't often have Cup Days like that.

Extreme Temperatures on Melbourne Cup Day:

Highest maximum temperatures: 35.1C in 1902

Lowest maximum temperature: 11.0C in 1913

Horse Names

As well as weather affecting the race itself, several - but surprisingly few - winners have had weather related names, including the most famous of them all – Phar Lap - which is Thai for lightning.


The mighty Phar Lap - winner of the 1930 Melbourne Cup.

Phar Lap is Thai for lightning.
Image - Wikipedia Commons
(Click to enlarge)

Phar Lap won in 1930, and second place that year was Second Wind, another “weather” name. The 1930 Cup is the only one where horses with meteorological titles came first and second.

You can see a movie of this famous event here:
http://www.youtube.com/watch?v=CkppKT4-yI8

The 1992 Cup was the only race in which a horse with a “weather” name - Subzero - won whilst it was actually raining.

Only one horse with a "weather" name has won twice - Rain Lover in 1968 and 1969.

Melbourne Cup Winners with “weather” names

1925 Windbag

1930 Phar Lap

1945 Rainbird

1968 Rain Lover

1969 Rain Lover

1992 Subzero

Recent publications by the author: 

From Gods to Gigabytes – a Brief History of Weather Forecasting 

Firewise, Firesafe - How to Survive a Bushfire

For information about either publication you can contact the author at 

weathersmart047@gmail.com

Tsunami Disaster in Japan

On the afternoon of March 11th 2011 a massive tsunami was generated by an estimated 8.9 intensity earthquake that occurred out to sea about 380 km to the northeast of Tokyo. Chains of giant waves up to 10 metres high swept across the adjacent shoreline of Japan around Sendai during the afternoon, producing widespread damage and an unknown loss of life.

This is shaping up to one of the worst natural disasters of modern times.

The tsunamis struck Hawaii overnight, producing only minor damage, but some 12 hours later reached the US west coastal area of Crescent City, near Oregon, where extensive damage resulted in the local harbour.

This event was probably as severe as the infamous Boxing Day tsunami that raced across the Indian Ocean on December 26 2004.

This Indian Ocean event was one of the worst ever natural disasters in recorded history, killing more than a quarter of a million people over eleven countries and this event in Japan is also a major tsunami disaster.

In September 2009 another deadly tsunami created devastation on a smaller scale around the Pacific Island nation of Samoa.

Once again the terrible phenomenon of a tsunami has captured the worlds headlines.

What is a tsunami?

Tsunami is a Japanese word meaning “harbour wave”. A tsunami is a wave or series of waves generated in the ocean by such phenomena as earthquakes, undersea land-slides, volcanic eruptions and meteor impacts. It should not be confused with ocean swell waves, which are generated by the action of wind on the surface of the sea, or tides, which are produced by gravitational effects of the Sun and Moon.

Undersea earthquakes, as we have just seen off the coast of Japan, are common around the so called Pacific Ring of Fire, a geologically unstable region that extends from New Zealand, across the Tongan region, Papua New Guinea, Indonesia and then northwards to Japan. It then travels east across the northern Pacific and moves down the west coast of both North and south America.



The Pacific Ring of Fire
(Image from Wikipedia Commons - click to enlarge)

This zone is largely generated by the movement of the Pacific tectonic plates against other adjacent plates. It has been unusually active this year, also producing the devastating earthquake across Christchurch.


Tsunamis are sometimes referred to as “tidal waves” or “seismic waves” but both of these terms are inaccurate descriptions.

Above - The Pacific tectonic plate runs close to Japan.
(Image from Wikipedia Commons - click to enlarge)

Tsunamis have produced tremendous devastation throughout history, causing massive damage along shorelines, wrecking many coastal townships and killing untold thousands of people through drowning.

The tsunami as a shallow water wave

When an earthquake occurs near or under the ocean, a tsunami can be generated, and the characteristics of this type of wave are markedly different to the “normal” waves we are used to seeing down at the beach. These waves may break on the shore say every 10 or 12 seconds (called the “wave period”), and have a distance of around 100 to 120 metres between wave crests (called the “wavelength”).

But tsunamis may have a period of up to an hour and a wavelength of around 100km, with the second and third waves still maintaining massive power. This wavelength is very much greater than the depth of the ocean through which the wave is travelling, which for the Pacific Ocean can be around 3000 to 4000 metres.

Waves with this characteristic are called shallow water waves, which is somewhat confusing because here we are talking about the deep ocean. But “shallow” in this case is only a relative term, meaning the ocean depth (~3000m) is shallow compared with the wavelength (~100km or 100, 000m)

It can be demonstrated through the physics of wave theory that shallow water waves move at a speed which is directly proportional to the depth of the water through which they are moving, and in a water depth of 3000 m, this translates to a wave velocity of ~ 170 m/s or over 600 kph. If a wave of this type is encountered by a ship at sea, it may be barely noticed, as the wave is spread out through the entire depth of the ocean and may only form a slight disturbance on the surface, although moving at great speed.

Another characteristic of shallow water waves is that they lose energy at a rate that is inversely proportional to the wavelength – meaning the longer the wavelength the further the wave can travel. The extremely long wavelengths of tsunamis means that they can travel extended distances, in the order of thousands of kilometers, or, in other words, across entire oceans.

Tsunamis approaching the shoreline

Whilst tsunamis are markedly different from ocean waves in all the ways described, the normal physics of wave motion still applies. All waves contain a certain amount of energy that is dependant on the mass of water being displaced (which is closely related to the height of the wave), and the velocity of the wave. This energy is largely conserved, apart from a slight dissipation over time.

A tsunami surging into shallow water
(Image from Wikipedia Commons - click to enlarge)

When the wave approaches a shoreline and the water becomes shallower, the wave begins to slow as a result of friction with the ocean bed. But the overall energy of the wave stays much the same, so to compensate for the slower speed, the height of the wave ramps up.


A tsunami approaching the shore will "arc up" sometimes to great heights
Image: Wikipedia Commons
(Click on image to enlarge)
This means that a tsunami, whilst barely noticeable at sea, quickly grows in height, and cases of waves reaching heights of 30 metres are known. An entire tsunami event may consist of several waves, called a wave train, each of which can carry a major destructive punch.

The final height and shape of the wave are largely determined by the topography of the ocean bed near the shoreline. As well as the celebrated wall of water towering over the beach as is often portrayed in the movies, the wave can also present as a rapidly rising tide moving a long way inland with unstoppable force, destroying everything in its path.

A tsunami train approaching shallow water will "bunch up" but increase in height. (Image from Wikipedia Commons - click to enlarge)

A sign that a tsunami is approaching is a lengthy retreat, or “drawdown” of the ocean along the shoreline, and the water level can retreat more than 300 metres seawards of its normal position when this happens.


Immense drawback of the ocean just before the onslaught of a tsunami wave at Kata Noi Beach, Thailand on December 26th 2004. Image: Wikipedia Commons. (Click on image to enlarge)

Destruction generated by tsunamis

Tsunamis can reach the coast with tremendous amounts of energy. They can create significant shoreline erosion, stripping beaches of sand that may have taken years to accumulate and uprooting trees and other coastal vegetation. Capable of inundating, or flooding, kilometers inland past the typical high-water level, the fast-moving water associated with the breaking tsunami can easily crush homes and disrupt coastal infrastructure such as powerlines and roadways.

As we have seen with the Japanese disaster, after crossing a built up area, tsunamis carry a massive volume of debris with them, and this acts as a colossal "grinder", scouring existing structures away, which then becomes part of the moving debris mountain.


A devastated town on the coast of Sumatra, seen just after the Boxing Day tsunami 2004, graphically illustrates the enormous power of a tsunami. Image: Wikipedia Commons. (Click on image to enlarge)

Tsunami prone areas and warning systems

Throughout history, tsunamis have been recorded in most of the oceans of the world. However because of inherently unstable geological conditions, the Pacific Ocean is particularly notorious, with frequent earthquakes occurring around the Pacific Rim.

No formal warning system was in place until 1960, when the devastation caused by a massive tsunami in Chile during May of that year led to the formation of the Pacific Tsunami Warning System (PTWS) located in Hawaii. This group organises and monitors a network of earthquake detectors and tide gauges which determine where earthquakes occur and whether or not a tsunami may have been generated.

After a major earthquake in Alaska in 1964, the PTWS concept was extended and the International Tsunami Warning System (ITWS) was created. Following the disastrous Boxing Day tsunami of 2004, this system was extended to cover the Indian Ocean.

As soon as an earthquake is detected, it is evaluated as to its location and intensity, and if it is thought that a tsunami may have been generated, calculations are made which estimate the speed of propagation of the wave, based on the depth of the ocean. Warnings are then issued to all countries in the affected area, and depending on the lead-time available, emergency preparations are begun.

The Japanese tsunami was particularly well photographed, including some unique footage of the wave trains approaching the shoreline taken from helicopter. This vision will be closely analysed by experts in an attempt to learn more about these massive and lethal monsters of the deep.

Extraordinary footage showing the tsunami slamming through the port of Kamaishi, in northeastern Japan can be seen here:

http://www.guardian.co.uk/world/video/2011/mar/11/kamaishi-tsunami-earthquake-japan-video

An untested hypothesis

An interesting hypothesis has been advanced to explain the "disaster clusters" we sometimes see - this year we have seen severe flooding in Australia, the massive Christchurch earthquake and the the Japanese tsunami - could these be connected in some way?

During times of strong El Ninos and La Ninas sea levels rise for prolonged periods over either the western or eastern sides of the tropical Pacific Ocean. Could this colossal extra weight of water be enough to disturb the Pacific plate and trigger periods of high seismic activity? The strong La Nina we've experienced this year has produced record flooding across much of eastern Australia but could it have also triggered the Christchurch and Japanese disasters?

This hypothesis is totally untested but it could help explain the confluence of natural disasters we sometimes see.

References:

http://passingparade-2009.blogspot.com/2010/09/el-nino-and-la-nina.html

“Disasters, Events and Moments that Changed the World”, Richard Whitaker, New Holland Publishing, 2007

Duststorms in Australia

Between Monday 21st and Saturday 26th September 2009 two very large dust storms swept across eastern Australia and affected three major cities – Canberra, Sydney and Brisbane. The dust cloud that covered Sydney on the morning of Wednesday 23rd was one of the most severe in recent memory, with visibility dropping below 100 metres in some areas, and thousands of tonnes of dust settling across the Sydney basin.

Dust storms are common over inland areas of NSW and Queensland, but usually they are prevented from reaching Sydney by the massive wall of the Great Dividing Range that acts as a large shield, preventing the dust from moving to the coastal fringe.

However when a strong cold front is involved, the dust can be lifted, up to 3000 metres above the ground, and swept over the mountains and across the coastal fringe.

Cold fronts can lift dust up to 3000 m
above the ground (Click on image to enlarge)

The front also tends to produce an organised line of dust that can extend hundreds of kilometres north and south, a line that rolls steadily eastwards and can be readily identified from satellite photography.

In these cases the dust consists of very fine particles of topsoil that are highly penetrative – even houses that have been carefully closed up will have their interiors carpeted with a fine film of dust.

Dust storm lining up with a cold front, 25th September 2009

On occasion the dust cloud can carry across the Tasman Sea and drop across New Zealand, producing red snow on the New Zealand Alps. Much of the dust also falls into the Tasman Sea and sediments at the bottom of the ocean in this area reveal evidence of many similar events that have taken place in the past.



The dust storm of 23rd September was over 1500 km long and 200 km wide (NASA picture)














Another severe dust storm affected Sydney during the summer of 1944 as the following newspaper article recalls.

DUST STORMS AND FIRES IN NSW

SYDNEY, Sun 10th December 1944 – The Argus

Dense dust storms, accompanied by high temperatures, raged over most of New South Wales at the weekend. Bush fires in the Blue Mountains destroyed seven cottages, a dairy, a store, look- outs, and kiosks. Nineteen houses were destroyed in the Richmond district and four near Gosford.

A man and a woman aged 80 were burned to death in the fires. They were J. H. Barnes, who was burned in a paddock at Kurrajong, and . Miss Irene Cavanagh, who was trapped in a house at Oswald.

Some relief from the heat is forecast for tomorrow.

Sydney was swept by a violent westerly gale. The maximum wind velocity recorded at the Weather Bureau was 63 mph, but one gust at Richmond reached 76 mph.

The maximum temperature in Sydney today was 91deg, compared with 91.5deg yesterday. Clouds of dust carried by the wind from inland districts almost blotted out the sun at times.

Metropolitan fire brigades answered more than 150 calls. The task of extinguishing outbreaks was made more difficult by the gale.

One of the biggest dust storms to ever affect an Australian capital city occurred in February 1983, when a massive wall of dust swept across Melbourne, also carried along by a powerful cold front.