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

MEASUREMENT OF TURBULENCE IN TERRAIN-DISRUPTED AIRFLOW AT THE HONG KONG INTERNATIONAL AIRPORT USING A DOPPLER LIDAR

The Doppler LIDAR of the Hong Kong Observatory was used to measure eddy dissipation rate (EDR) directly for the first time at the Hong Kong International Airport in an experiment in 2004. EDR is a measure of turbulence intensity adopted by the International Civil Aviation Organization. The laser beam of the LIDAR stared in a direction parallel to the runways and radial velocity data were obtained at a range resolution of 60 m. The velocity structure function was computed based on two different estimates of the velocity fluctuation (viz. temporal and spatial methods) and EDR was then calculated by fitting the structure function with the von Kármán model. The two estimates of velocity fluctuation were found to give comparable EDR values. The LIDAR-derived EDR also turned out to have good correlation with EDR obtained from runway anemometers and a boundary-layer wind profiler. In a case of terrain-disrupted airflow during the experiment, the LIDAR-derived EDR showed that turbulence was present near the centre of a micro-scale vortex to the west of the airport

MEASUREMENT OF TURBULENCE IN TERRAIN-DISRUPTED AIRFLOW AT THE HONG KONG INTERNATIONAL AIRPORT USING A DOPPLER LIDAR

The Doppler LIDAR of the Hong Kong Observatory was used to measure eddy dissipation rate (EDR) directly for the first time at the Hong Kong International Airport in an experiment in 2004. EDR is a measure of turbulence intensity adopted by the International Civil Aviation Organization. The laser beam of the LIDAR stared in a direction parallel to the runways and radial velocity data were obtained at a range resolution of 60 m. The velocity structure function was computed based on two different estimates of the velocity fluctuation (viz. temporal and spatial methods) and EDR was then calculated by fitting the structure function with the von Kármán model. The two estimates of velocity fluctuation were found to give comparable EDR values. The LIDAR-derived EDR also turned out to have good correlation with EDR obtained from runway anemometers and a boundary-layer wind profiler. In a case of terrain-disrupted airflow during the experiment, the LIDAR-derived EDR showed that turbulence was present near the centre of a micro-scale vortex to the west of the airport

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

NUMERICAL SIMULATION OF VORTEX SHEDDING OBSERVED AT THE HONG KONG INTERNATIONAL AIRPORT USING A SHALLOW MODEL

The Hong Kong International Airport is situated in an area of hilly terrain, with a number of hills to its northeast and on the mountainous Lautau Island to the south. In a stably stratified boundary layer, vortices shed by these hills arc sometimes observed by the Terminal Doppler Weather Radar (TDWR) and the Doppler Light Detection and Ranging (LIDAR) System operated by the Hong Kong Observatory. They have a length scale of at least several hundred metres and occur with a shedding period of 15 to 45 minutes. This paper uses a single-layer shallow water model to simulate the vortex shedding events observed in two wind regimes, namely, an easterly wind case on 19 January 2005 and a northeasterly wind case on 27 January 2002. The model wind field (resolved along the measurement radials of TDWR and LIDAR) and the vortex shedding periods in the simulations were found to be largely consistent with the TDWR and LIDAR observations. Though the dynamical equations are simplified and there is a single layer only, the shallow water model appears to grasp the basic dynamics of the observed shedding events

Disordered Boson Systems: A Perturbative Study

A hard-core disordered boson system is mapped onto a quantum spin 1/2 XY-model with transverse random fields. It is then generalized to a system of spins with an arbitrary magnitude S and studied through a 1/S expansion. The first order 1/S expansion corresponds to a spin-wave theory. The effect of weak disorder is studied perturbatively within such a first order 1/S scheme. We compute the reduction of the speed of sound and the life time of the Bloch phonons in the regime of weak disorder. Generalizations of the present study to the strong disordered regime are discussed.Comment: 27 pages, revte

Cutaneous manifestations of hospitalized coronavirus disease 2019 patients: a report of six cases with clinicopathologic features and viral RNA in situ hybridization

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/163863/1/jdv16741.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/163863/2/jdv16741_am.pd

Improvement of Aerosol Optical Depth Retrieval over Hong Kong from a Geostationary Meteorological Satellite Using Critical Reflectance with Background Optical Depth Correction

Despite continuous efforts to retrieve aerosol optical depth (AOD) using a conventional 5-channelmeteorological imager in geostationary orbit, the accuracy in urban areas has been poorer than other areas primarily due to complex urban surface properties and mixed aerosol types from different emission sources. The two largest error sources in aerosol retrieval have been aerosol type selection and surface reflectance. In selecting the aerosol type from a single visible channel, the season-dependent aerosol optical properties were adopted from longterm measurements of Aerosol Robotic Network (AERONET) sun-photometers. With the aerosol optical properties obtained fromthe AERONET inversion data, look-up tableswere calculated by using a radiative transfer code: the Second Simulation of the Satellite Signal in the Solar Spectrum (6S). Surface reflectance was estimated using the clear sky composite method, awidely used technique for geostationary retrievals. Over East Asia, the AOD retrieved from the Meteorological Imager showed good agreement, although the values were affected by cloud contamination errors. However, the conventional retrieval of the AOD over Hong Kong was largely underestimated due to the lack of information on the aerosol type and surface properties. To detect spatial and temporal variation of aerosol type over the area, the critical reflectance method, a technique to retrieve single scattering albedo (SSA), was applied. Additionally, the background aerosol effect was corrected to improve the accuracy of the surface reflectance over Hong Kong. The AOD retrieved froma modified algorithmwas compared to the collocated data measured by AERONET in Hong Kong. The comparison showed that the new aerosol type selection using the critical reflectance and the corrected surface reflectance significantly improved the accuracy of AODs in Hong Kong areas,with a correlation coefficient increase from0.65 to 0.76 and a regression line change from MI [basic algorithm] = 0.41AERONET + 0.16 to MI [new algorithm] = 0.70AERONET + 0.01