ENG-1979 — Page 281

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THE ENVIRONMENT

larly important during tropical cyclone alerts and is also used in connection with engineering projects. The observatory co-operates with the University of Hong Kong in operating anemometers at Cape D'Aguilar to record the vertical structure of winds, especially in relation to wind stress on buildings. As the majority of these instruments are unique in Hong Kong, all repairs, calibration and maintenance are done by observatory staff.

Special meteorological instruments, including transmissometers used to measure runway visual range, are operated at Hong Kong International Airport, where the safety of aircraft depends on reliable and accurate meteorological measurements. In 1979, a new system of five anemometers to identify low-level wind shear along the airport approaches began operating. Based on information obtained from this system, warnings on significant varia- tions in winds occurring during the critical periods of take-off and landing are provided to pilots.

The seismology section operates six seismographs in a specially-constructed cellar at the observatory's Tsim Sha Tsui headquarters. On average, tremors from about 800 earthquakes all over the world are detected and analysed each year. Other tremors, such as those from underground nuclear explosions, storm microseisms, local blasting or piling, are also recorded. Hong Kong lies just outside the circum-Pacific seismic belt and has not suffered significant earthquake damage since 1918. However, an average of two to three minor tremors are felt each year by residents.

A telemetry network of three modern short-period seismographs was established during 1979 at Tsim Bei Tsui, Chi Ma Wan and Yuen Ng Fan. A microprocessor-based data acquisition system, based on a mini-computer, is being set up to process the data collected. The seismology section also operates three strong-motion accelerographs installed on bedrock, decomposed granite and reclaimed land. Data from these instruments is used to study the response of different geological structures to seismic waves.

The observatory prepares bulletins on all earthquake tremors recorded, and participates in the Tsunami Warning System for the Pacific region. Tsunamis are abnormal sea waves caused by earthquakes. Whenever an intense earthquake is recorded with an epicentre in the Pacific Ocean or the South China Sea, a tsunami warning message is sent to Tokyo, Bangkok and Honolulu.

Geomagnetic measurements are made at the geomagnetic station at Tate's Cairn in a joint project with the University of Hong Kong. The observatory also monitors radio- activity. Regular measurements of beta and gamma activity in the atmosphere, in rainfall and in tap water, have been made since 1961 at the King's Park Meteorological Station. The general level of atmospheric radioactivity during 1979 was low.

The concentrations of particulates and sulphur dioxide in the atmosphere are measured daily at the Tsim Sha Tsui headquarters and at King's Park. A derivative spectrometer at King's Park also provides a continuous record of sulphur dioxide concentrations in the atmosphere. This air pollution data is processed by computer and monthly summaries of the results are produced. The information is needed for a scientific study of the effects of local weather on the concentration of pollutants.

Research

Apart from research in applied meteorology and geophysics, considerable effort is devoted to meet the demand for meteorological analyses required by industry and also various engineering projects. Consultative services are also rendered from time to time to government departments and to local and overseas organisations in relation to various weather-sensitive activities.