ENG-1960 — Page 293

COMMUNICATIONS

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There aircrews are briefed and weather information is issued to aircraft in flight and other weather centres.

In addition to providing weather bulletins for shipping and fishermen a close liaison is kept with merchant shipping by making visits to ships, checking barometers and supplying daily weather charts and reports. The Hong Kong voluntary observing fleet normally totals sixty to seventy ships and their reports are par- ticularly valuable.

One of the most important functions of the Observatory is to issue warnings of tropical cyclones. Whenever a tropical depres- sion, tropical storm or typhoon is located within the region bounded by the latitudes 10° and 30° North and the longitudes 105° and 125° East, six-hourly and often three-hourly bulletins are issued. These include information on the storm's intensity and expected development, the position and movement of its centre and the forecast position for 24 hours ahead. Reliable reports from ships and storm reconnaissance aircraft help to locate storms ac- curately. When the Colony itself is threatened, the local storm warning system is brought into use and warnings are widely distrib- uted by means of visual signals, telephone, radio and Rediffusion. Time Service and Seismology. Time signals originating at the Observatory are broadcast over Radio Hong Kong for the public, the VPS broadcast for shipping and the Hong Kong VOLMET broadcast to aircraft. A visual time signal is flashed from the Obser- vatory's signal mast and various signals are provided for time marking seismograms and other purposes.

The Observatory operates six'seismometers, three of which are on loan from the Lamont Geological Observatory. A weekly air- letter giving arrival times of significant earthquake waves is sent to the United States Coast and Geodetic Survey, and detailed analyses made later are published and sent to other scientific institutions. The results are included in the two international bulletins, the International Seismological Summary and the bulletin of the Inter- national Union of Geology and Geophysics. Normally one or two slight earthquake shocks are felt each year in Hong Kong, and on 10th July 1960 an earthquake whose epicentre was about 80 miles north-northeast of the Colony was felt by several local residents. The extremely violent and destructive Chilean earthquake in May gave rise to tsunami waves which reached Hong Kong on the