ENG-1988 — Page 383

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THE ENVIRONMENT

short-term rainfall estimates at selected places. A lightning detection system located cloud-to-ground lightning within a range of about 130 kilometres and a spheric recorder was used to register thunderstorm activity within about 100 kilometres.

Besides land-based observations, upper-air atmospheric conditions were measured by radiosondes carried by balloons launched at King's Park Meteorological Station. For a hemispheric overview of weather systems, three-hourly high resolution satellite cloud pictures were received in Hong Kong from the Japanese Geostationary Meteorological Satellite (GMS). A new system to receive and process digitised signals from the GMS was installed during the year. The availability of hourly imageries greatly facilitated the monitoring of weather systems, especially when they are in close range.

For the real-time monitoring of floods in the North-west New Territories, water-level and rainfall information at Kam Tin were relayed directly to the observatory headquarters beginning in mid-1988. For operational warning of sea flooding in Hong Kong, tide data were collected from nine gauges in the territory and wave data were measured at Waglan Island. For safety of aviation, wind conditions at the airport and its vicinity were moni- tored continuously by a network of anemometers and a doppler acoustic radar at Lei Yue Mun on the southeastern approach to the airport.

Weather prediction requires constant meteorological data exchange with other countries through the dedicated international meteorological telecommunication circuit. The Hong Kong-Bangkok circuit, one of the three major links, was upgraded in 1988. The observa- tory computer system handled messages of about three million characters of coded weather data each day of the year through various links. In 1988, the computerisation of weather chart plotting as well as dissemination of warnings and forecasts became fully operational. In recent years, the vagaries of the weather were better understood through experience gained in analysing and interpreting numerical weather prediction models run at major meteorological and research centres. Previously, 24-hour forecasts had probably been the limit for reasonable accuracy. Recently, however, with the use of numerical model outputs, useful weather outlooks beyond the first day were issued whenever possible, and they were in the main satisfactory.

Geophysical, Oceanographic and other Services

The Royal Observatory carried out geophysical and oceanographic studies to provide the technical details required by engineering consultants undertaking major civil or coastal development projects.

During the year, forecasts of waves and swells in Hong Kong waters continued to be made. Microprocessor-based data logging systems were fabricated to store tidal informa- tion at various stations. Tide levels recorded at all tide stations were being analysed with a view to refining tidal predictions in Hong Kong.

To monitor earthquakes and seismicity, a network of three short-period seismometers was operational at Cheung Chau, High Island and Tsim Bei Tsui. Long-period seismo- graphs recorded tremors from all over the world. Strong-motion accelerographs were operated at two locations with different soil properties. On average, about 150 earthquakes were detected annually with epicentres within 320 kilometres of Hong Kong; more than four of these were felt by residents in Hong Kong.

The observatory operated a caesium beam atomic clock, which provided time signals accurate to fractions of a microsecond a day. A six-pip signal was broadcast on 95 MHz every quarter hour and was also relayed to Radio Television Hong Kong for broadcast.