VIRTUAL TOUR OF THE WEATHER STATION

EVAPORATION

For a long time the station determined evaporation amounts by observing the changing level of water in an evaporation pan using a Hook gauge. However, the impracticalities of using this method in cold weather owing to ice, variations due to the effect of wind and the need to maintain water levels within a fixed range led to the station abandoning this method in favour of a Piché evaporimeter (pictured inset). The principle of determining changing water levels is the same, but the Piché evaporimeter is hung inside the Stevenson screen and water allowed to evaporate from a filter disk fitted to the base of a graduated tube. Evaporation amounts are determined daily. When the water inside the tube is frozen, the abbreviation 'fr' is given in the record.

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