What is hail?
Hail is precipitation in solid form. It can vary in size from
smaller than peas to larger than golfballs!
Ice is formed when condensation in the sky freezes solid, and this
turns to hail when it starts falling but gets pushed back upwards by warmer
air. This cycle continues multiple times, each time adding a layer of ice to
the hailstone, until it falls to the ground. “If you cut a hailstone in half, you would see alternating concentric layers
inside it.” (http://weather.about.com/od/h/g/hail.htm)
Holding the very large hailstone that fell in her garden:
Sources used:
(Zoe)
So if there are concentric layers of ice forming one after another to make a hail stone bigger and bigger, how long does it stay in the sky for??? Doesn't gravity affect hail stones??!!
ReplyDeleteI am looking forward to cutting some hail stones open to see...
In relation to Duncan's question, I read somewhere that hailstones are carried upwards by a force (assuming up-thrust?) before gravity affects them'would be really interesting if you could find out if that is true Zoe, and why they eventually fall as hailstones...
DeleteThanks, Emma
To answer both of your questions:
ReplyDeleteHailstones are kept in the sky not by upthrust exactly, but by updrafts (strong winds in the cloud). The hail falls and is pushed back up through the cloud by updrafts, and the cold temperatures freeze more water around the hailstone, adding another layer, and the hailstone falls again.
Whether the hailstone falls to the ground at this stage depends on the strength of the updrafts in the cloud, so if there are very strong updrafts, the cycle of hail rising and falling will most likely occur many times, and consequently the resulting hail will be very large. If the updrafts are weak, then the hail falling is likely to be small. This is also where gravity comes in, as gravity will pull the hailstone to the ground if the updrafts are not strong enough to push the hail back up through the cloud.
Therefore a hailstone stays in the sky for as long as the updrafts can keep it there!
I found this site useful to answer these questions:
http://www.azcentral.com/business/articles/2011/09/30/20110930science-of-hail-arizona-storm.html
Zoe.