East Asia and Western Pacific METEOROLOGY AND CLIMATE

210
IMPACT OF HOURLY S-VISSR SATELLITE IMAGERY
ON OPERATIONAL FORECASTING IN HONG KONG
S.T. LAI, B.Y. LEE, and H.K. LAM
(Royal Observatory, Hong Kong)
1. INTRODUCTION
In 1977, Japan launched the first of a series of Geostatioary Meteorological
Satellite (GMS) into an orbit 35 800 kilometres over the equator
at longitude 140 deg E. Imageries in the visible (VS) and infrared
(IR) channels were available every three hours in analogue facsimile
form. The first GMS was replaced by GMS-2 in 1981 which was subsequently
substituted by GMS-3 in 1984. To cope with a change in the transmission
mode of the satellite from analogue facsimile form to
stretched-VISSR (Visible Infra-red Spin Scan Radiometer) digital data,
the original reception system at the Royal Observatory (Hong Kong) was
replaced and put into operation in November 1988.
Since then, satellite pictures became available every hour with additional
playback and enhancement capabilities. Considering the relatively
short time frame since the commissioning of the new GMS system in
Hong Kong, there is no doubt that its potential as a forecasting aid is
yet to be exploited to the full. However, there are already two immediate
visible advantages brought about by the hourly GMS imageries.
Firstly, the continuity of mesoscale weather systems, which have typical
time scales of hours and could easily go undetected on conventional
weather charts, can now be closely monitored. Section 2 describes such
a case during a rainy period in April 1989.
Secondly, the position and intensity of tropical cyclones can now be
monitored on a near real-time basis. Continuity and reliability have
also been improved by the usage of special enhancement techniques. As an
illustration, section 3 presents the life history of Typhoon Brenda
(16. - 21 May 1989).