Question:
I teach preschool and would like to be able to answer
these questions for future weather units. In a recent storm I
noticed that the hailstones were tear drop or triangular shaped. I
don't remember seeing such a shape before. Can you tell me about the
shape? Why it is different?
Replies:
Hi Tina
In upper regions of clouds, air temperatures are below 32 degrees Fahrenheit
and water freezes.
The shape the water freezes in forms the shape of hailstones.
So irregular shaped hailstones are more the rule than the exception.
And then as they fall to earth, and sometimes get sucked back up into the
cloud by uplifting winds, they may add more layers of ice adding to the
irregular shapes.
Sincere regards,
Mike Stewart
Tina,
How the hail is oriented/tumbles as it falls and
the forces of the wind upon it determine its
final shape. Teardrop shapes are common, as are
half spheres with one side (the side that is up
while it falls) "scooped out". Hail can form
a tear drop shape when it falls without being
tumbled or blown sideways by wind (in still air).
Air moving past the hail stone as it falls causes
water that is encountered to move upwards along
the hail (water streams out from the top), resulting
in a tear drop shape.
The triangular shape may be just an oddity of how
the wind spun the hail around as it was falling.
David R. Cook
Meteorologist
Climate Research Section
Environmental Science Division
Argonne National Laboratory
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