No. 808: A new approach to the prediction of torrential rainfall (November 20, 2013)

Technology:

A Doppler radar

A research team led by Director Hiromu Seko of Meteorological Research Institute developed a new approach to increase the prediction accuracy of regional torrential rainfall. The new approach determines the increase and decrease trend of water vapor content with the help of radio waves that reflect off obstacles like transmission line tower and return to the observation radar of Japan Meteorological Agency, and take them into consideration for the calculation of precipitation and the region subject to rainfall. 

Because the Doppler radar cannot get data without raindrops, it cannot measure water vapor content before it rains. The research team calculated the refractive index of air using the conditions of radio waves returning from transmission line towers and confirmed that the increase and decrease trend can be determined from the time change the refractive index. They put the trend together with such data as temperature and wind in the calculation model and reproduced the lightening storm that hit the Tokyo Metropolitan area on August 4, 2008 and found that the experimental data agreed with the actual rainfall. The research results are scheduled to be presented in the autumn meeting of Meteorological Society of Japan on November 21. 

The torrential rainfall that hit Tochigi Prefecture

in the Kanto district on July 27, 2013