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Hailstone Shape
Name: Tim
Status: educator
Grade: 9-12
Country: South Africa
Date: Fall 2011
Question:
My question relates to a Hailstorm in Somerset West, near Cape Town, South Africa, on Sunday 13 November 2011. Many of the hailstones were about 1 cm in diameter. The shape was interesting. In cross section, try to imagine a parachutist descending - dome shape on top and pointed at the bottom. I have never seen any reference to this shape of hailstone before. I wondered if the hailstones started falling as spheres and as they fell, friction sharpened the underside to a point. I always thought that hailstones tumbled on their way down but it seems as if I might be wrong. I should be interested in your comments
Replies:
Tim
Hailstones normally form in concentric spheres as rain accumulates and
freezes on the frozen hail stone.
What you MIGHT be seeing is:
Liquid rain at upper levels fall through a layer of freezing air, freezing
into your domed shaped hailstones before they fall to the ground.
Sincere regards,
Mike Stewart
Hail stones form from multiple falling and rising in turbulent air. If the
air is very turbulent and
Strong enough that there are many cycles, hail stones can be large and even
jagged.
I would guess a parachute shape could occur if either "up" or "down" differed
greatly in
The number of cycles.
Vince Calder
Tim,
The shape you describe is unusual!
It seems possible that round hailstones were falling through warm air
and melting on the bottom, resulting in the point, but this would
also imply that they were not tumbling as they fell. So perhaps they
were somewhat pointed when they first started falling and therefore
were somewhat aerodynamic, preferentially falling with the point down.
That is my educated guess.
David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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Update: June 2012
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