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GEOGRAPHY AND CLIMATE
the intensity of rainfall and provides valuable information for the preparation of local thunderstorm and heavy rain warnings as well as for local hydrological purposes.
The Observatory is also responsible for the Colony's time service. Six pip signals obtained 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 the various radio and television stations.
The Observatory operates 12 seismometers, prepares bulletins of all earthquake tremors recorded, and participates in the Pacific Tidal-wave Warning Service. Hong Kong lies just outside the circum-Pacific seismic belt and has not suffered serious earthquake damage since 1918. However a few tremors are felt each year by residents in favourable locations such as on balconies of high buildings. One tremor occurred on July 6, 1969 and the intensity was five in the modified Mercalli Scale.
The general level of atmospheric radio activity in the Colony is monitored at King's Park, where routine measurements of Beta and Gamma activities of fallout, airborne particles near the ground, rainfall and ordinary tap water are carried out.
The Observatory acts in an advisory capacity in the planning of a great many projects that may be affected by meteorological conditions. Technical notes and other publications are prepared to provide detailed information on various aspects of the climate of Hong Kong and a wide variety of related subjects.
RESEARCH
Many investigations and analyses were carried out during the year on meteorological problems for numerous shipping and airline com- panies, for commercial and industrial firms and for other government departments. Efforts were made to improve the techniques used to forecast seasonal and five-day rainfall for the planning of water supply and the control of reservoirs. Radar time-lapse pictures of rainstorms which affected the Colony were analysed.
Revised mean maps showing the air flow at the various standard upper levels up to 12 km were prepared for use in aviational planning and weather forecasting. Several investigations on the summer and
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