Moving Cellular Structure of Fog Echoes Obtained with a Millimeter-Wave Scanning Doppler Radar at Kushiro, Japan

Abstract

Observations of fogs with a millimeter-wave scanning Doppler radar were conducted at Kushiro in Hokkaido, Japan, in the summer seasons of 1999 and 2000. Three typical types of plan position indicator (PPI) displays were observed: cellular echoes with high radar reflectivity factors (??10 dBZ), uniformly distributed echoes with high reflectivities (??10 dBZ), and uniformly distributed echoes with low reflectivities (??30 dBZ). The authors focused on advection fog with cellular echoes observed on 5 August 1999 and 31 July 2000. Echoes showed structures of cells with a reflectivity of ?10 dBZ and with intervals of about 1 km. This echo pattern moved northward (i.e., from the sea to the land). There was a vertical shear of the horizontal wind at a height around 200 m in both cases, and structures of each cell were upright above the shear line and were leaning below it. The direction and the speed of the echo pattern in both PPI and range?height indicator (RHI) displays agreed well with that of the horizontal wind at heights above the shear (200 m). In the echo cells, existence of drizzle drops is implied.