線せん状じょう降水こうすい帯たい予測よそくに向むけ 気象庁きしょうちょう 航空こうくう機きで海上かいじょう水蒸気すいじょうきを直接ちょくせつ観測かんそくへ

The Meteorological Research Institute of the Japan Meteorological Agency, together with universities, will start directly observing water vapor over the sea using aircraft from next month, in order to study linear rainbands—which, as seen with the Noto Peninsula heavy rain, cause major damage almost every year.

The Japan Meteorological Agency makes predictions about linear precipitation zones about half a day in advance, but the low accuracy rate is an issue, and they hope to clarify the mechanisms and improve prediction accuracy.

The Japan Meteorological Agency issues information calling for caution about linear precipitation zones—where cumulonimbus clouds form one after another and line up in bands over the same area—about half a day in advance if their occurrence is predicted.

However, last year, more than 60% of cases were missed, such as being unable to predict the heavy rain in the Noto Peninsula in September, and the accuracy rate remained at about 10%.

In order to understand the situation where a large amount of water vapor flows from the sea toward the land, observations have so far been conducted using ships. However, according to those involved, it has been revealed that the Meteorological Research Institute of the Japan Meteorological Agency will begin efforts to observe from the sky using aircraft.

Observations are scheduled to be conducted several times from next month through September this year. If the seasonal rain front is expected to become more active or if a strong flow of warm, moist air is anticipated, flights will be made over the seas from Tokai to Okinawa, and observation instruments called dropsondes will be released from an altitude of about 13,000 meters.

A dropsonde observes and transmits data such as atmospheric pressure, humidity, and wind speed as it falls.

Observations from the sky using aircraft have so far been mainly conducted by research groups such as Nagoya University, focusing on typhoons. This time, the Meteorological Research Institute will carry out the observations jointly with university research groups.

We want to closely understand the situation in which cumulonimbus clouds rapidly develop, and ultimately use this knowledge to improve forecasting accuracy in the future.

Expert: If we can predict accurately, we can reduce lost lives to zero. Professor Kazuhisa Tsuboki of Nagoya University and Yokohama National University, who is well-versed in the mechanisms of heavy rain and has continued aircraft observations of typhoons, points out that aircraft observations are essential to improve the accuracy of linear rain band forecasts.

According to Professor Tsuboki, whenever a linear rainband has formed, a phenomenon known as an atmospheric river, in which a large amount of water vapor flows into the sky in a band-like shape, has been observed.

To predict linear precipitation zones, it is important to closely monitor the distribution of water vapor in atmospheric rivers over the ocean and the degree of atmospheric instability. However, since atmospheric rivers can disappear in a short period of time, it is considered extremely important to collect data from multiple locations using aircraft.

Professor Tsuboki will also participate in the observations at the Meteorological Research Institute starting next month.

Professor Tsuboki said, We believe we will be able to obtain data on the detailed structure of the atmospheric river, which is necessary to accurately predict linear precipitation bands.

If we can accurately predict when, where, and how much it will rain half a day in advance, I believe we can reduce the number of lives lost due to linear rainbands to zero, and this observation is the first step toward that goal.

I think long-term continuous observation is essential, he said.