32nd Conference on Broadcast Meteorology/31st Conference on Radar Meteorology/Fifth Conference on Coastal Atmospheric and Oceanic Prediction and Processes

Thursday, 7 August 2003: 9:45 AM
Observations of fogs with a millimeter-wave Doppler radar
Akihisa Uematsu, Kyoto University, Uji, Kyoto, Japan; and H. Hashiguchi, M. Teshiba, K. Hirashima, T. Hayashi, A. Yamamoto, and S. Fukao
Poster PDF (592.3 kB)
We conducted fog observations with a millimeter-wave (Ka-band: 34.75GHz) scanning Doppler radar in the summer seasons of 1999-2002. We observed fog with drizzle in some cases of 1999 and 2000, and in each case cellular periodic structures of echo pattern having about -10 dBZ with the period of 1 km were observed. These patterns moved northward, i.e., from the sea to the land, and was good consistency between moving velocity of echo pattern and horizontal wind at the top of the fog layer at the height of about 500-600 m. We consider that there is a source of drizzle particles near the top of the fog layer, and each particle is falling with blown by background winds which determine the movement of the echo pattern. From Doppler velocity field, there existed a vertical shear of the horizontal wind at the height of 200 m. Structure of each cells were vertically standing above the shear line and leaning below that. Inclination of echo cells below the shear line seems to be determined by the ratio between vertical difference of horizontal wind velocity and vertical falling speed of fog and drizzle particles.

In the observations of 2001-2002, simultaneous observations were conducted with a Doppler sodar and the radar. We especially focus on vertical wind velocity when fog appeared, and analyzed sodar and radar data in a case of July 20, 2002. In developing stage, vertical cross section of fog and stratus with the radar reflectivity of -40--30 dBZ, was observed with the radar. There were two layers at first, one was fog layer with the thickness of about 70 m and another was stratus at the height of about 450-700 m. Then the top of the fog layer and the base of the stratus simultaneously ascended and descended, respectively, within 25 min. In this period vertical wind over the radar site was almost downdraft. After that, cellular structure of radar reflectivity of -10 dBZ appeared, which is similar to the cases mentioned above, and updraft and downdraft were periodically observed, which implies the existence of convection in the drizzling fog layer.

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