Clouds & Particles

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1. What happens in clouds?

1. Observtion of convection currents in wax candles

Find a candle with a diameter of at least 3-4 cm, light it and let it burn until there is a small pool of melted wax around the wick. Closely watch the small particles of wick and of unmelted wax that moves around in the "pool".

Can you see convection currents? How do these currents appear?
 

2. Convection currents in the field

Insects are lifted and birds and gliders can soar in the rising air beneath cumulus clouds.

The air may rise at a speed of about 1 m/s under a fair-weather cumulus, maybe 4 or 5 m/s under a cumulus congestus cloud. Air can rise at 10 m/s or more beneath and inside vigorous cumulonimbus clouds.

What does it feel like to ascend at

a) 1 m/s
b) 10 m/s?

Relate to the speed a lift ascends. To work out the speed, divide the height the lift rises when it goes from one floor to another by the time taken to travel that height.

c) Is it safe for birds, gliders or, indeed, any other aircraft to be caught in the upcurrents of cumulonimbus clouds?

Authors: Ellen K. Henriksen and Camilla Schreiner - University of Oslo - Norway. Scientific reviewer: Justine Gourdeau - LaMP Clermont ferrand - France - 2004-01-13. Last update: 2004-03-27.