Preliminary observations of small scale wakes generated by complex terrain using a portable X-band radar

The purpose of this paper is to discuss close range and high resolution radar observations of wakes generated by complex terrain. The observations described herein were obtained using a portable X-band radar, currently developed by Mitsubishi Electric Tokki Systems Corporation. An important aspect of this radar is its portability. In mountainous regions, radar observations are usually affected by beam blockage, which makes it nearly impossible to interpret the wake structures. The radar can deploy close to ridges and observe modification of the airflow and precipitation pattern by the topography. The fine-scale data of wakes obtained with the portable radar are important as they provide unique reflectivity information, which can be used to help to understand the fine structures of wakes and verify the theory of mountain airflow disturbances. On 1 March, 2005, widespread snow occurred over the western side of the central mountain range of Japan associated with a cold westerly monsoon. Numerous fine-scale wake structures are revealed in the reflectivity fields from this radar. Associated with wakes, it is evident that elongated strong reflectivity regions with sharp edges. Usually, wake length exceeded 15 km. Near the ridges, 1km-scale cells occurred at intervals of 2 minutes and were carried downstream by the ambient flow. It is suggested that positive and negative vortices had formed behind the ridge and were shed downstream quasi-periodically. The results of this study suggest that the radar would be particularly useful for documenting sub-km-scale reflectivity fields near the ridge with fine special and temporal resolution. Further studies using the radar with Doppler capability, currently under developed, will permit single -Doppler study of wakes.