MONITORING AND OBSERVATION OF FÖHN WIND IN HONG KONG USING A MULTI-CHANNEL, GROUND-BASED MICROWAVE RADIOMETER

The performance and application of a multi-channel, ground-based microwave radiometer in the monitoring of Föhn wind was studied in an experiment conducted in Hong Kong in 2004. Three scanning modes (zenith, elevation and 15-degree elevation) were tried out for the radiometer to monitor the low-level temperature inversions upwind of the hills. Thermodynamic profiles retrieved from the zenith mode compared the best with the radiosonde measurements. For inversions associated with low clouds, an empirical method based on saturation temperature appeared to improve temperature retrieval. When placed downwind of the hills, the radiometer captured very well the warming and drying of the boundary layer as a result of Föhn wind. The frequency spectrum of the brightness temperature from the radiometer was found to follow a -5/3 law. A quantity derived from the spectrum turned out to vary in a manner similar to the intensity of air turbulence in a strong Föhn wind case