Research has begun to elucidate the mechanism of the "linear rain zone" that causes heavy rain disasters in various places by observing with aircraft.
On the 5th of this month, which was a record heavy rainfall in Shikoku, a large amount of water vapor inflow called "atmospheric river" that led to the occurrence of a linear precipitation zone was observed from the sky for the first time in Japan.
As a result, it was found that there was a characteristic that water vapor was concentrated especially near the low sea level.
I will explain in detail.
Causes of "Linear Rainfall Zone" What is an "Atmospheric River"?
This research is being conducted by a group of Professor Kazuhisa Tsuboki of Nagoya University.
The "atmospheric river" was confirmed in the heavy rains that led to the flooding of the Kuma River in Kumamoto Prefecture (2020) and the heavy rains in the Kanto and Tohoku regions in 2015, and has been regarded as one of the factors leading to the linear precipitation zone.
However, it does not necessarily generate a linear precipitation zone, and it is not known in detail under what conditions heavy rainfall is caused.
In addition, since it occurs in the sea area where there is no observation equipment, detailed observations necessary for elucidating the mechanism have not been made.
In fact, it is difficult to predict the linear precipitation zone, and although the linear precipitation zone was confirmed in Kochi Prefecture on the 5th of this month, the forecast information of the Japan Meteorological Agency was not announced in advance.
For these reasons, we tried to clarify the mechanism by directly observing the relationship between the "atmospheric river" and the occurrence of the linear precipitation zone from the sky.
What is the first observation of the "atmospheric river" from the sky?
The observation was made on the 5th of this month when Typhoon No. 4 approached western Japan.
Due to the effects of typhoons and extratropical cyclones, linear precipitation zones were confirmed in Kochi Prefecture, resulting in heavy rainfall in various parts of western and northern Japan.
At this time, Professor Tsuboki himself boarded the aircraft and made observations while moving over the Pacific Ocean off the coast of Okinawa from western Japan.
Professor Tsuboki noticed that even before the approach of the typhoon, a large amount of water vapor flowed into the Japanese archipelago from the Pacific Ocean and the East China Sea in the form of a huge band.
This phenomenon is also called "atmospheric river".
This time, we were able to observe directly from the sky for the first time in Japan.
Since the "atmospheric river" is water vapor, it cannot be seen directly with the naked eye.
(The image is an image)
Directly drop the observation equipment
This time, the research group used a cylindrical device called a dropsonde for observation from the sky.
While moving over the sky by aircraft, we dropped this device directly into the "river of the atmosphere" and observed data such as the amount of water vapor, the wind direction, and the wind speed from about 13,000 meters above the sea surface.
As a result, we can see some characteristics of this "atmospheric river".
Analyzing the data off the Kii Peninsula,
・ While there was relatively little water vapor in the area
above 1000 meters above sea level, ・ a large amount of water vapor was concentrated in the relatively low area from the sea level to 1000 meters above sea level. ..
The amount is said to be about twice the amount of water vapor contained in the average air when there is no "atmospheric river".
Professor Tsuboki believes that the distribution of the amount of water vapor differs depending on the height from the sea surface, which makes the atmospheric condition unstable and the weather conditions are such that linear precipitation zones are likely to occur.
However, there are many things that are still unknown, and the research group hopes to further analyze data such as the speed and direction of the wind carrying water vapor, and to continue observations to elucidate the mechanism that causes the linear precipitation zone. increase.
Professor Tsuboki "I want to contribute to improving prediction accuracy"
Professor Tsuboki, who made the observations, stated his determination, "Global warming is progressing and heavy rains that cause disasters are increasing. We will continue to make observations and contribute to improving prediction accuracy based on the data." rice field.
In addition, even after the heavy rain on the 5th of this month, heavy rains due to linear precipitation zones have continued in various places due to the inflow of a large amount of water vapor.
Regarding this, Professor Tsuboki said, "Recently, the weather has changed drastically, such as heavy rains like the rainy season after the intense heat this month. It is still difficult to accurately predict the linear precipitation zone, but after this I want you to prepare for the typhoon season and the heavy rain that you have never experienced. "