Handout (1.4 MB)
1. Introduction
Wind shear in a localized region usually causes a big damage on transport systems such as highways, railways and airports. Real-time observation of wind field with high spatial and temporal resolution using dual polarimetric Doppler weather radar gives us the most effective solution for preventing the threat of wind shear so that safe commuting and traveling can be realized.
The Multi-Radar System has been developed and deployed around the Osaka-Bay, in which three Doppler radars are connected through the Internet. A case study for estimation of 3D wind field using the triple-Doppler analysis is presented here.
2. Triple-Doppler Analysis
In conventional dual-Doppler analysis, vertical wind field was indirectly estimated using the equation of continuity. In Furuno's Multi-Radar System, the wind field around the Osaka-Bay is observed in real time on a regular basis. By deploying the three radars within 10 km range, vertical wind field can be directly estimated by the triple-Doppler analysis.
Fig 1 indicates the probable error of a vertical wind field based on a simulation. Given that horizontal wind is 0-50 m/s and upward flow is 10 m/s. Random errors of 1 m/s are added to Doppler velocity and averaged possible errors are estimated and drawn in colors. As can be seen from the Fig 1, the accuracy of a vertical wind field can be optimized in the region which is more than 2 km altitude and surrounded by these three radars.
Each dataset of Doppler-velocity from all the radar sites is collected and converted into 3D dataset of grid-point-value via Cressman interpolation and it is input into the triple-Doppler analysis to estimate 3D wind field.
Fig 1: The probable error of a vertical wind field based on a simulation.
Given that horizontal wind is 0-50 m/s and upward flow is 10 m/s. Random errors of 1 m/s are added to Doppler velocity and an averaged possible error is estimated and drawn in colors.
3. Results
(1) The wind field at 600 m altitude
The interesting case study of 12th November 2014 is presented when a cold front has passed through the Osaka Prefecture. Fig 2 indicates the horizontal and vertical wind field at 600 m altitude. The horizontal wind field is indicated with arrows and vertical one is shaded by colors. The estimated horizontal wind field within 10-20 km range is precise and reliable. But horizontal and vertical wind vectors out of 20 km range were too large and they were not reliable quantitatively.
Fig 2: Horizontal and vertical wind field at 600 m altitude.
The horizontal wind field is indicated with arrows and vertical one is shaded by colors, where warm colors indicate updrafts and cold colors indicate down drafts.
(2) The comparison between radar observation and anemometer
The horizontal wind vectors at 750 m altitude within 10-20 km range are averaged, and compared with the observed wind vector obtained from an anemometer locating at Kobe Airport. Fig 3 indicates the wind field at 750 m altitude at 19:20. A position of Kobe Airport is also marked. The results of the comparison are as follows.
- The averaged wind field estimated by three radars at 750 m altitude;
7.9 m/s, 216 deg, from west or west-southwest
- The observed wind field at Kobe Airport at 0 m altitude approx.;
6.1-8.7 m/s, from west or west-southwest
The estimated horizontal wind field from radar observation is reliable compared with the one observed by anemometer.
Fig 3: The comparison between radar observation and anemometer.
The averaged horizontal wind vector at 750 m altitude is compared with the observed wind vector at Kobe Airport.
(3) A shear line associated with the cold front
Fig 4 indicates horizontal and vertical wind field at 1500 m altitude. The meanings of arrows and colors are same as Fig 2. As can be seen from Fig 4, a remarkable shear line is observed at 1500 m altitude. In addition updrafts are observed in the south side and downdrafts are observed in the north side. It supports the fact that the shear line is associated with the cold front.
Fig 4: Horizontal and vertical wind field at 1500 m altitude.
A remarkable shear line associated with the cold front is observed.
4. Conclusions
The Multi-Radar System has been developed and deployed around the Osaka-Bay. Three Doppler radars are connected through the Internet and the wind field around the Osaka-Bay is observed in real time on a regular basis. By deploying the three radars within 10 km range, vertical wind field can be directly estimated by the triple-Doppler analysis.
The interesting case study of 12th November 2014 is presented. The estimated horizontal wind field within 10-20 km range is precise and reliable, but horizontal and vertical wind field beyond 20 km were not. A remarkable shear line observed at 1500 m altitude is associated with the cold front.
5. Acknowledgement
This research is supported by Adaptable and Seamless Technology Transfer Program through target-driven R&D, JST.
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