TOKYO – The Tokyo Skytree, the world’s tallest freestanding tower, is more than one of the city’s top tourist attractions: It is also a science laboratory for lightning and other research and a disaster mitigation hub.
The 634m-tall structure – more than twice the height of Singapore’s tallest building, the 290m-high Guoco Tower – towers over the bustling Japanese capital and has welcomed more than 50 million visitors since it opened in May 2012.
The main role of the Tokyo Skytree is to transmit digital terrestrial broadcasting for the Greater Tokyo region. Since 2012, it has taken over the transmission role from the 333m-tall Tokyo Tower, which was completed in 1958 and was increasingly unable to provide complete coverage as it came to be surrounded by high-rise buildings.
The Tokyo Skytree’s height makes it a literal lightning rod, with at least 10 strikes a year – not a surprise considering the relatively flat terrain around it – effectively debunking the old saying that lightning never strikes the same place twice.
This makes the structure ripe for lightning research, and the world’s scientists are taking notice – no other lightning measuring devices are installed on buildings at such heights anywhere else in the world.
A view of Tokyo, as taken from an outdoor platform 497m above ground at the Tokyo Skytree.ST PHOTO: WALTER SIM
The Straits Times was among a few media outlets to recently get a look at the lightning research apparatus located outdoors at 497m above ground. This is higher than the 450m-high observation deck accessible to the public.
Getting there required donning a helmet and a safety vest, before taking the service lift and navigating a labyrinth of steep staircases and ladders while facing strong winds. Reporters had to secure their belongings, including smartphones, pens and notebooks, to their bodies with string so that nothing fell through the steel gratings or was blown off.
While it has been more than 270 years since Benjamin Franklin, one of the United States’ founding fathers, realised that lightning was a form of electricity, mysteries still persist over the natural phenomenon today.
Many contemporary lightning countermeasures being taken worldwide are based on data derived more than 50 years ago from measurements taken on a Swiss mountain.
This presents a knowledge gap that the Tokyo Skytree aims to bridge by offering an urban counterpoint, especially during severely humid Japanese summers, as climate change brings on more instances of what Japan calls “guerilla rainstorms” – short, localised deluges with more than 100mm of rain per hour.
“Many aspects of lightning are still unknown today, given how difficult it is to measure and study,” said senior researcher Mikihisa Saito of the Central Research Institute of Electric Power Industry (CRIEPI).
Other than lightning studies, the Tokyo Skytree also serves as a research laboratory for the heat island effect (where urban areas are warmer due to the absorption of heat by pavements, buildings or other surfaces), airborne PM2.5 particles and levels of greenhouse gases in the atmosphere.
For the lightning research, the structure’s operator, affiliated with railway giant Tobu, gave CRIEPI permission to install what are known as “Rogowski coils” to monitor strikes round the clock.
Senior researcher Mikihisa Saito of the Central Research Institute of Electric Power Industry showing the lightning measurement apparatus on an outdoor platform located 497m above ground at the Tokyo Skytree. ST PHOTO: WALTER SIM
Data – including the current and direction of the lightning strike – is fed to an indoor observation room located 300m above ground, and stored in a recording device.
Mr Saito’s team gets smartphone alerts every time the Tokyo Skytree is struck. While the observation is fully automated, his team manually collects data and inspects the coil for any damage.
Numerous studies have been published in scientific journals through the years, but Mr Saito said the data collected so far is not enough: “We obviously want to gather more data, but this is difficult since it depends on natural conditions.”
His team hopes to study different types of lightning, what kinds of conditions lead to them being induced and the amount of current produced, whether it is possible to create devices that can accurately pinpoint the location of lightning strikes, and if there are efficient ways of preventing lightning damage.
He hopes the work can benefit weather scientists and agencies, as well as utilities companies that oversee the maintenance of power cables and protection of high-rise buildings from lightning damage.
This is becoming increasingly urgent as Tokyo faces a surge in lightning strikes, which have been hypothesised to be due to more violent storms triggered by climate change. Tokyo registered 60,741 lightning strikes from July to September 2024, which was 3.9 times that of the same period in 2023.
Additionally, Japan is naturally prone to disasters such as earthquakes and typhoons, which makes it necessary for the Tokyo Skytree to continue its role as a broadcasting tower even during crises.
Structural engineer Atsuo Konishi from engineering firm Nikken Sekkei, who was involved in the construction of the 36,000-tonne tower, said two key features make the tower resilient to disasters.
An aerial shot of Tokyo Skytree.PHOTO: COURTESY OF TOKYO SKYTREE
The first is a central pillar, which is a reinforced concrete core column built in the centre of the Tokyo Skytree. This is separate from another steel-framed tower, which allows both components to vibrate at different frequencies, thus reducing vibrations by up to 50 per cent during earthquakes.
The structure was inspired by five-storey pagodas such as the Horyuji Temple in Nara Prefecture, which, at more than 1,600 years old, is among the oldest surviving wooden structures in the world. There are no records in Japan of such pagodas ever collapsing in a quake, and this is thought to be due to the existence of a central pillar.
The Tokyo Skytree, which towers 634m above ground, is the tallest freestanding tower in the world.ST PHOTO: WALTER SIM
The second feature is the Truss structure, which is formed by interconnecting triangles made with high-strength steel pipes. This allows the tower to withstand maximum instantaneous wind speeds of up to 110m per second.
“The tower has been built to withstand the strongest envisioned earthquake that may hit Tokyo, based on government research of all the fault lines and activity beneath the city,” Mr Konishi said, while wind velocity of such strengths is regarded as an at least once-in-2,000-year event.
One of two disaster monitoring cameras installed by the Sumida Ward Office at 260m above ground at the Tokyo Skytree.ST PHOTO: WALTER SIM
The Tokyo Skytree’s durability during disasters is why the local Sumida Ward is using it as a back-up disaster response headquarters if the ward office cannot be used. There are emergency rations as well as equipment such as monitors and microphones that can broadcast announcements to public speakers throughout the ward.
The ward office has also installed two disaster monitoring cameras at 260m above ground, with zoom functions of up to 100 times, providing a 360-degree bird’s eye view of the area for the monitoring of threats, from fires to flooding.
That the Tokyo Skytree was built to its full height of 634m just seven days after the Great East Japan Earthquake of March 11, 2011, was symbolic of Japan’s recovery and resilience, said Mr Kenichiro Iwamoto, a disaster prevention manager at Sumida Ward Office.
“Even 300 years ago, when Tokyo was called Edo, it was one of the largest cities in the world with more than one million people,” he said.
“Much like the fire watchtowers of the era that helped prevent fires from engulfing wooden homes of the time, the Tokyo Skytree plays a similar disaster prevention role today.”
- Walter Sim is Japan correspondent at The Straits Times. Based in Tokyo, he writes about political, economic and socio-cultural issues.
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