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THE ENVIRONMENT
Close liaison is maintained with all ships visiting Hong Kong and about 45 selected vessels are provided with instruments by the observatory and encouraged to transmit weather reports. These are used to prepare forecasts and locate tropical cyclones. About 60 weather reports are received each day from ships, through two coastal radio stations in Hong Kong, and disseminated to other centres through the World Weather Watch telecommunication network. About 5,000 weather reports from land stations and ships are received each day from other countries together with aircraft reports and other data. They are decoded, plotted and analysed at the Royal Observatory. Special weather bulletins are broadcast for shipping and fisher- men, and all aircraft leaving Hong Kong are given briefings, written forecasts and weather charts.
One of the most important functions of the Royal Observatory is to issue warnings of tropical cyclones. Whenever a tropical cyclone is located within the region bounded by latitudes 10°-30° north and longitudes 105°-125° east, warnings for shipping are generally issued every three hours. These provide information on the maximum winds, the position and movement of the centre and the forecast position 24 hours ahead. Reports from ships and reconnaissance aircraft and cloud pictures received at the Royal Observatory direct from meteorological satellites together with radar observations are used to locate the centre and evaluate the intensity of the tropical cyclone.
When Hong Kong is threatened, warnings are widely distributed by visual signals, telephone, radio and television. Advice and recommended precautions are broadcast at frequent intervals whenever signals are displayed. Gale or storm signals 5, 6, 7 and 8 were renumbered as 8NW, 8SW, 8NE, 8SE from January 1, 1973. The Royal Observatory also issues strong monsoon, thunderstorm and/or-heavy rain, fire hazard, frost and low temperature warnings whenever necessary.
The observatory's weather radar station at Tate's Cairn is equipped with a 30-millimetre radar for detecting showers and local rainstorms and a 100-millimetre radar for locating larger tropical disturbances up to 240 nautical miles away. A new iso-echo device was fitted to the larger radar in 1973 to facilitate the real-time estima- tion of the intensity of rainfall. This equipment now provides valuable additional information for rainfall forecasting, as well as for hydrological applications.
The observatory is responsible for Hong Kong's Time Service. Six pip signals from a special crystal clock, accurate to 0.05 second, are broadcast every 15 minutes on a frequency of 95 MHz and are relayed by broadcasting and television stations. With effect from January 1, 1972, the time kept by the Hong Kong Time Standard was changed to Universal Co-ordinated Time (UTC). This new time system has been adopted by international agreement and is based on an atomic time standard which provides a more uniform time scale than that based upon astronomical standards. The UTC will never differ by more than 0.7 second from the astronomical time. To ensure this, step adjustments to UTC of one second were made on July 1, 1972 and January 1, 1973 in accordance with international agreement.
Twelve seismometers are operated by the observatory. The department prepares bulletins of all earthquake tremors recorded and participates in the Pacific Tsunami