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New uptake in Event: Meteotsunami

by on July 11, 2011

A small tsunami that struck the south coast of England on 27 June was most likely caused by weather conditions and not a submarine landslide or earthquake, according to the British Geological Survey (BGS).

The tsunami occurred in South West England, between Penzance and Portsmouth, along approximately 200 miles of coastline. It struck the Yealm (see below video) at about 10.30 on 27 June; wave heights were 0.5–0.8 metres.  Tide data indicates an east to west progression of the wave, confirmed by observations at St Michael’s Mount, where the water built up on the east side of the causeway (20 cm higher than on the west) before it was overtopped.

According to the Tidal Gauge Anomaly measure, which records the difference between the forecast tide and actual tide, the wave was higher by 20 cm in Newlyn, 30 cm in Plymouth and 40 cm in Portsmouth. The water levels dropped and withdrew from the coast before the wave came in (Marazion, Cornwall). Video evidence shows the wave as a bore in the Yealm Estuary. At St Michael’s Mount there were reports of ‘hair standing on end’ before the wave struck.

It says: “Our conclusion is that the tsunami was not geological in origin. It was probably caused by a meteorological effect, such as a squall over the ocean developed during summer storms; these events are called meteotsunami. These types of waves are common all over the world and are known by their local names, such as: rissaga (Spain), milghuba (Malta), marrobbio (Italy), and abiki (Japan).

In explaining the unlikely occurnace of an earthquake or submarine landslide, the BGS said: “From the available data the tsunami wave progressed and decreased in height from east to west, indicating a source in the eastern English Channel: this rules out a source to the west.

“Hair Raising Event”

One aspect of the June 27 event that is considered novel, and may bear on the answer, is the ‘hair standing on end’ before the tsunami that was reported from St Michael’s Mount, that suggests an atmospheric source, as it is known that this phenomena can take place in association with lightning.  According to the BGS: “We know that there were storms in the south-east of England on 27 June. At Wimbledon, play was restricted to the covered Centre Court on Monday afternoon, and there was thunder and lightning.”.

“Monitoring Stations”

Meanwhile, a network of coastal tidal and wave monitoring stations maintained by Southampton, UK-based EMU Limited recorded the progress of the waves caused by the  minor tsunami.

EMU Limited’s Principal MetOcean Scientist, Mr Robin Newman, initially thought there was a malfunction with the oceanographic instruments, installed by EMU for the Southeast and Southwest Regional Coastal Monitoring Programmes, due to the unusual data patterns recorded by the Etrometa Step Gauges and Rosemount WaveRex Radars.

“There was a significant amount of variation in the observed data against what would be expected so I checked at multiple sites and they were all consistent with some sort of movement from east to west,” Mr Newman said. “We subsequently realised we had recorded what appears to be a minor tsunami.”

“While 0.8 metres waves may not sound like much, it could have caused flooding events if combined with high tides,” he said. “Tsunamis are not expected to affect the UK so this is a very rare event. But from this week’s experience, clearly they can, but also clearly we can now say we have an operational system which can detect these unusual events.”

EMU Limited will monitor the continuing wave movements as these may be a form of standing-wave oscillation, or seiching, in the Channel.

UK Meteotsunami History

On 18 August 1892 tsunamis hit the  Yealm (Devon) and Fowey estuaries (Cornwall), following thunderstorms in the region. The Times reported the event in the River Yealm as well as stating that ‘there was a rapid rise in the River Fowey as a great tidal wave, but this immediately subsided’.

A large tsunami-like wave struck the Kent and Sussex coasts, busy with tourists, and drowned two people, at Folkestone (Kent) and Brighton (Sussex) on 20 July 1929. At Brighton and Worthing the wave was accompanied by sudden downpours of rain and high winds, but at Folkestone and Hastings, where one person drowned at each, the weather was clear and the unexpected wave was estimated to be between 3.5 m and 6 m high, respectively. Later analysis of the event suggested the wave was caused by a squall-line travelling up the English Channel, coincident with thunderstorms, and so may be referred to as a meteotsunami.

Source British Geological SurveyIrish Weather

A most remarkable feature in the sea level signals observed in Malta consists of a band of high frequency signals with periods ranging from several hours to as low as a few minutes. These non-tidal short period sea level fluctuations are an expression of a coastal seiche, known by local fishermen as the ‘milghuba’ . This phenomenon has now been observed to occur all along the northern coast of the Maltese archipelago and manifests itself with very short resonating periods of the order of 20 minutes…

Analysis shows that weak seiching is present uninterrupted and appears as a background ‘noise’ on the tidal records. During random sporadic events the seiche oscillations can however become greatly enhanced. The maximum range measured in Mellieha Bay reached 1.1m. The seiche is often big enough to mask completely the small astronomical tide.These large-amplitude sea level oscillations are accompanied by remarkable currents that are triggered by the sloshing water masses. These currents are comparable in size to those generated in coastal areas characterised by tidal forcing.

While these seiche induced currents can be an important means for the flushing of coastal inlets and harbours, they can on the other hand be dangerous to navigation. Source Physical Oceanography Institut Malta Related Everythingselectric Forum

Malta Meteotsunami

Sudden flooding a phenomenon called meteo-tsunami, March 25th 2011

PANAJI: The unusual flooding of Morjim and Baga beaches showed signs of respite on Thursday, but a tsunami expert said it may have been caused by a meteo-tsunami on the lines of a similar phenomenon in Kerala during the past decade. “There were no strange meteorological disturbances seen on the state’s coastline,” the source said. There was no depression in atmospheric pressure nor was the wind abnormally strong, though it blew in gusts and may have contributed partly to the flooding.

“It appears that a wave from a storm far in the sea travelled a long distance to the state’s coast,” the source said. A similar phenomenon, which local people in Kerala mistakenly thought was a tsunami, had hit the southern state’s Poonthura coast in May 2005, April 2007 and February 2008. The impact of flooding is more intense when it occurs on supermoon spring tides. “The case of Baga and Morjim was one such, and it was caused by wave set up” the source said. The sea water level rise showed signs of receding in Baga on Thursday.

The water level rose seven metres on Tuesday, five metres on Wednesday but only three metres on Thursday,” shack owner Mario D’Souza said. “We had never seen anything like this earlier,” Morjim shack owner Jenny Madeira told TOI.

“The event in Baga and Morjim, unlike Kerala, may be a new event,” the source said. The flooding events and detailed accounts of meteotsunamis in the world has been provided by NIO scientist Anthony Joseph in his book, “Tsunamis: Detection, monitoring and early-warning technologies”, published in February 2011. Huge sea waves on the coast or meteorological tsunamis are caused by atmospheric gravity waves, atmospheric pressure jumps, wind waves and other factors, but may result in less impact.

“Other mechanisms that may result in a meteo-tsunami include tide-generated internal waves, wave superposition, wind-current interaction, wave-current interaction and atmospheric shockwaves (say, from volcanic activity),” the source added. The atmospherically generated ocean waves, whose origin remains shrouded in mystery, have been observed in recent sea-level records from coasts, among others, of the Adriatic Sea, English Channel, and Washington (USA) and notoriously in several locations in the Mediterranean Sea. Source Times of India

A meteotsunami or meteorological tsunami is a tsunami-like wave phenomenon of meteorological origin. Tsunamis and meteotsunamis propagate in the water in the same way and have the same coastal dynamics. In other words, for an observer on the coast where it strikes the two types would look the same. The difference is in their source only. One definition of a meteotsunami is as an atmospherically generated large amplitude seiche oscillation.

The principal source of these tsunami-like ocean waves are travelling air pressure disturbances, including those associated with atmospheric gravity waves, roll clouds, pressure jumps, frontal passages, and squalls, which normally generate barotropic ocean waves in the open ocean and amplify them near the coast through specific resonance mechanisms. In contrast to “ordinary” impulse-type tsunami sources, a travelling atmospheric disturbance normally interacts with the ocean over a limited period of time (from several minutes to several hours).

Source Meteotsunami

Related

Climate anomalies – One source for air pressure anomalies: There is also scientific evidence that suggests the extreme northern winters are linked to climate change – as the Arctic sea warms, air pressure increases and pushes cold air south. Source Oxfam

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