ENG-1984 — Page 365

THE ENVIRONMENT

283

Upper-air atmospheric conditions are measured by radiosondes carried by balloons. launched at King's Park Meteorological Station. Signals transmitted by the radiosondes are processed by a minicomputer on the ground. A tethered balloon and radiosonde system is also used at selected locations to obtain data up to a few hundred metres above the ground.

A digital radar system which employs a minicomputer to process radar signals supplies information on rain distribution to forecasters at the Central Forecasting Office and the Airport Meteorological Office. The system also produces objective short-term rainfall estimates at selected locations.

High resolution satellite cloud pictures from the Japanese Geostationary Meteorological Satellite continued to be received in Hong Kong. The pictures, recorded in digital form, are processed by microprocessors to give special displays for such a purpose as estimating maximum winds in a tropical cyclone. In 1984, satellite pictures transmitted by polar- orbiting meteorological satellites were also received, supplementing information from the geostationary satellite.

In order to monitor local earthquakes, a network of three short-period seismometers at Cheung Chau, High Island and Tsim Bei Tsui is operated by the Royal Observatory. Long-period seismographs record tremors from all over the world. Strong motion accelerographs are installed at three locations with different soil properties. While on average only two or three earthquakes are felt by the public each year, hundreds are detected by the seismometer network. In recent years, about 150 earthquakes have been detected annually within 320 kilometres of Hong Kong.

Measurements of Beta and Gamma radioactivity in airborne dust and rain-water are made at King's Park. The observatory co-operates with the UK Atomic Energy Research Establishment and the International Atomic Energy Agency in making these measure- ments. During 1984, the obsolete radioactivity measuring equipment was replaced. The new system incorporates a microprocessor-based multi-channel analyser.

The observatory operates a caesium beam atomic clock which provides time signals accurate to about one micro-second. A six-pip signal is broadcast on 95 mHz every quarter hour and is also relayed to Radio Television Hong Kong for broadcast to the public.

Research

The Royal Observatory carries out investigations on weather systems affecting Hong Kong with a view to improving the standard of weather services. During 1984, an objective method of evaluating the potential of tropical cyclone development was formulated and put into use. The performance of existing objective methods of forecasting tropical cyclone movement was assessed and new methods were introduced. Several recent severe rain- storms were analysed in detail in the search for precursors which could guide weather forecasters in the issuing of appropriate warnings.

Research is also directed at meeting the demand for meteorological analyses by industry and for engineering projects. Other projects during the year included work on design wind and rainfall parameters and modelling of sea waves and tides by using computers. The analysis of meteorological data collected in Junk Bay as part of a study to investigate local conditions which might affect new developments was completed. Similar micro- meteorological studies for western Victoria Harbour and Tin Shui Wai were conducted.