3D Wind Field Estimation with Higher Spatial Resolution Using Multi Compact X-Band Weather Radars

Introduction

Strong wind in a local area causes serious damage on transport systems such as highways, railways and airports. In order to prevent such a disaster, real-time observation of wind field is very important. Especially the Dual polarimetric X-band Doppler weather radar with high spatial resolution and temporal resolution gives us the most effective solution. The high resolution observation of wind field prevents the threat of wind shear so that safe commuting and traveling can be realized.

Case study

This study shows one interesting case study of 4 April 2016 when rain came in Osaka-Bay area, the Japan. Three radars, a compact Dual polarimetric X-band Doppler weather radar, have been deployed in the Osaka-Bay area in Japan. Each distance among these radars is approximately 10 km. At 6:00 LST, low pressure and cold front came from west and hit Osaka-Bay area.

Analysis results

The observed data by three radars were processed by Triple-Doppler analysis. By deploying the three radars within 10 km range, horizontal wind field and vertical velocity of raindrops can be directly estimated by the Triple-Doppler analysis. As a result, horizontal wind and vertical speed of raindrop were obtained for each altitude. In this case, the radar observed every 1 minute and the elevation angle was 0 to 90 degrees.

On the other hand, the reference data was acquired by VAD analysis in each radar. The VAD analysis made it possible to estimate the horizontal wind and the vertical drop velocity at each altitude. The analysis was compared with Triple-Doppler one. Each analysis was carried out at altitudes from 500 m to 4000 m by 500 m step.

The wind field by Triple-Doppler analysis and one by VAD analysis were compared during 1 hour from 6:00 to 7:00 LST. As a result, tendencies of wind direction and wind speed were in good agreement as can be seen in Figure 1 and Figure 2. The maximum error of wind direction was 9.0 deg, maximum error of wind speed was 2.5 m/s and maximum error of vertical drop speed was 3.1 m/s. The averaged RMSE (Root Mean Squared Error) at each altitude was 5.4 deg in wind direction, 1.1 m/s in wind speed, and 1.7 m/s in vertical drop speed. Figure 2 shows that there was a significant point where the wind speed changed around 1500 m to 2000 m. This result suggests that vertical shear was observed by Triple-Doppler analysis.

Conclusions

This study shows one case study of 4 April 2016. Wide area rain is observed by three polarimetric weather radars. The result of Triple-Doppler analysis and VAD analysis are compared. The analysis using a compact Dual polarimetric X-band Doppler weather radar indicates the possibility for understanding the horizontal wind field, vertical drop speed. This technology contributes to safe operations in urban transportation systems and support safe takeoffs and landings at airports during strong wind weather and severe storm.