Sciency Thoughts: Kantō Region

Showing posts with label Kantō Region. Show all posts

Thursday, 2 July 2020

Fireball meteor over the Kanto Region of Japan.

Witnesses across the Kanto Region of Japan have reported observing a bright fireball at about 2.30 am local time on Thursday 2 July 2020 (about 5.30 pm on Wednesday 1 July, GMT). The fireball is described as having moved from east to west, and as having been brighter than the Full Moon, as well as having made an audible boom which caused windows to rattle. A fireball is defined as a meteor (shooting star) brighter than the planet Venus. These are typically caused by pieces of rock burning up in the atmosphere, but can be the result of man-made space-junk burning up on re-entry.

Series of still images from a video of a fireball meteor observed from Tokyo on 2 July 2020. Kyodo News.

Objects of this size probably enter the Earth's atmosphere several times a year, though unless they do so over populated areas they are unlikely to be noticed. They are officially described as fireballs if they produce a light brighter than the planet Venus. The brightness of a meteor is caused by friction with the Earth's atmosphere, which is typically far greater than that caused by simple falling, due to the initial trajectory of the object. Such objects typically eventually explode in an airburst called by the friction, causing them to vanish as an luminous object. However this is not the end of the story as such explosions result in the production of a number of smaller objects, which fall to the ground under the influence of gravity (which does not cause the luminescence associated with friction-induced heating).

These 'dark objects' do not continue along the path of the original bolide, but neither do they fall directly to the ground, but rather follow a course determined by the atmospheric currents (winds) through which the objects pass. Scientists are able to calculate potential trajectories for hypothetical dark objects derived from meteors using data from weather monitoring services.

Tuesday, 15 October 2019

Typhoon Hagibis kills at least 73 people in Japan.

A total of 73 people have now been confirmed dead after Typhoon Hagibis made landfall in Japan's densely populated Kantō Region on 12 October 2019. The storm had been a Category 5 (a storm with sustained winds in excess of 254 km per hour) between 7 and 10 October, but then began to subside and was only a Category 2 storm (storm with sustained winds of between 154 and 176 km per hour) when it made landfall on the Izu Peninsula, still the most severe storm to hit the region since 1958. In addition to the known casualties at least 12 more people are missing and more than 200 injured. Low lying areas of the Kantō Region have suffered extensive flooding, more that 270 000 households have been left without power, around 110 000 without water and about 30 000 people have been unable to return to their homes due to flooding and damage.

Flooding near the Chikuma River, which burst its banks as Typhoon Hagibis battered the Kantō Region of Japan on 12 October 2019. Reuters.

Tropical storms are caused by the warming effect of the Sun over tropical seas. As the air warms it expands, causing a drop in air pressure, and rises, causing air from outside the area to rush in to replace it. If this happens over a sufficiently wide area then the inrushing winds will be affected by centrifugal forces caused by the Earth's rotation (the Coriolis effect). This means that winds will be deflected clockwise in the northern hemisphere and anti-clockwise in the southern hemisphere, eventually creating a large, rotating Tropical Storm. They have different names in different parts of the world, with those in the northwest Pacific being referred to as typhoons.

Flooding close to the Isuzu River in Ise, central Japan, after heavy rainfall caused by Typhoon Hagibis. Reuters/Kyodo News.

Despite the obvious danger of winds of this speed, which can physically blow people, and other large objects, away as well as damaging buildings and uprooting trees, the real danger from these storms comes from the flooding they bring. Each drop millibar drop in air-pressure leads to an approximate 1 cm rise in sea level, with big tropical storms capable of causing a storm surge of several meters. This is always accompanied by heavy rainfall, since warm air over the ocean leads to evaporation of sea water, which is then carried with the storm. These combined often lead to catastrophic flooding in areas hit by tropical storms.

Cleanup opperations following Typhoon Hagibis in Japan. Getty Images.

Monday, 5 May 2014

Tokyo shaken by Magnitude 6.2 Earthquake.

The Japan Meteorological Agency recorded a Magnitude 6.2 Earthquake at a depth of 160 km, off the south coast of the Kantō Region of Honshu Island, slightly before 5.20 am Japan Standard Time on Sunday 4 May 2014 (slightly before 8.20 pm on Monday 5 May, GMT). This is a large quake, though at a great depth (shock waves from Earthquakes lose energy as they pass through rock in any direction, including up), and it was felt across the Kantō Region, as well as adjacent areas of easter Chūbu Region and southern Tōhoku Region. There are no reports of any serious damage following this event, however seventeen people were reportedly injured, and delays were experienced on the train network.

The approximate location of the 4 May 2014 Kantō Earthquake. Google Maps.

Japan has a complex tectonic situation, with parts of the country on four different tectonic plates. The eastern Honshu area lies on the boundary between the Okhotsk, Eurasian and Philipine Plates, where the Okhotsk Plate is passing beneath the Eurasian and Philipine Plates as it is subducted into the Earth, and, beneath the Kantō Region, the Pacific Plate being subducted beneath the Philipine plate. This is not a smooth process; the rocks of the two plates constantly stick together, only to break apart again as the pressure builds up, causing Earthquakes in the process.

The movement of the Pacific and Philippine Plates beneath eastern Honshu. Laurent Jolivet/Institut des Sciences de la Terre d'Orléans/Sciences de la Terre et de l'Environnement.