Yoshiro KAKUDO

Estimation of Short Time Interval Snowfall Water Volume by Backward Stream Line Analysis Using Radar Precipitation

Toshiro KUMAKURA

Snowfall has a significant impact on people's daily activities during the winter season in Niigata Prefecture. Knowing precipitation amounts at short time intervals and being able to predict the onset and end of falling snow would be very effective information for disaster prevention and mitigation. In this study, backward trajectory line analysis was used to estimate the amount of precipitation carried by the wind from the radar observation surface that observes the sky overhead at short time intervals. The usefulness of the backward streamline analysis is verified by comparing the precipitation using the backward trajectory analysis with ground-observed precipitation from two radar observations directly above the observation point, which are the ones that are usually used. The radar observations used were meteorological radar installed at Nagaoka University of Technology, and the ground-based precipitation observations were precipitation observed at the Research Center for Snow and Ice Disaster Prevention, National Research Institute for Earth Science and Disaster Prevention. In the backward trajectory analysis, snowflake particles with a falling velocity of 1 m/s were moved backward in time using wind speeds linearly interpolated from the three-dimensional wind field of the numerical forecast model for north-south, east-west, elevation, and time based on the ground altitude, latitude, and longitude of ground observation points, and repeated to analyze backward trajectory lines. The precipitation at the intersection of the backward trajectory line and the radar observation plane at several elevation angles was used as the analytical precipitation at each elevation angle. As a result, compared to the radar observation directly above the observation point, the trend of temporal increase/decrease of the backward trajectory line analysis precipitation approached that of the ground precipitation. In addition, the analytical precipitation values at elevation angles closer to the ground were closer to the ground-based precipitation values. In conclusion, the backward trajectory line analysis used in this study shows a time-series behavior that is closer to that of ground-based precipitation than the radar data directly above the observation points, which is usually used for precipitation estimation. The backward trajectory analysis also showed that it is possible to estimate precipitation in the future because it goes back to the past.