Weather Phenomena - Official First Day Cover 2014-03-27 [Hongkong Post]
Situated in the subtropical zone, Hong Kong has a humid climate with fog and drizzle in spring. Summer, also a typhoon season, is hot with occasional showers and thunderstorms. Autumn normally brings pleasant breezes, plenty of sunshine and comfortable temperatures. Winter becomes cloudier, with occasional cold fronts crossing the territory, bringing frost at times. In collaboration with the Hong Kong Observatory, Hongkong Post introduces seven common weather phenomena in Hong Kong under the theme of "Weather phenomena" to help the public understand the changes in our weather.
$ 1.7 Rainbow
It is an optical phenomenon.The stamp illustrates a double rainbow in the sky over the urban area of Hong Kong. When sunlight passes trough water droplets and gets reflected twice, two rainbows are developed.
$2.2 Frost
It forms when water vapor freezes into ice crystals. The stamp portrays frost formed on the surface of a plant in cold weather in Hong Kong
$2.9 Cloud
It is formed when water vapor rises through the atmosphere and cools. The stamp shows lenticular clouds in the sky over an urban area of Hong Kong. As air rises on the lee side of a mountain, water vapor condenses into water droplets, which accumulate and develop into lenticular clouds, taking the shape of a lens
$3.1 Lightning
It is an atmospheric electric discharge phenomenon. In an unstable and moist atmosphere, water droplets and ice pellets in clouds will become electrically charged in a convective motion. When the building up of charges reaches a certain threshold, discharges take place between clouds or between clouds and the earth's surface.
$3.7 Fog
It refers to tiny suspended water droplets near the ground. Under light wind, stable and humid conditions, when the air near the ground cools down sufficiently, the water vapor in the air condenses into tiny water droplets and fog is formed.
$5 Rain
It is a natural phenomenon of precipitation. Water droplets in the clouds will come down as rain when they accumulate to a certain weight. The stamp features Chek Lap Kok Airport in the rain.
Source: Back of envelop
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