EPOD - a service of USRA

The Earth Science Picture of the Day (EPOD) highlights the diverse processes and phenomena which shape our planet and our lives. EPOD will collect and archive photos, imagery, graphics, and artwork with short explanatory
captions and links exemplifying features within the Earth system. The
community is invited to contribute digital imagery, short captions and
relevant links.


Different Ice Patterns Inside a Hailstone

January 19, 2023

Mario-Freitas-Nov23-2022

Photographer: Mario Freitas

Summary Author: Mario Freitas

The photo above was taken just after a violent spring storm in
Curitiba, Brazil. The collected 1-inch diameter (2.54 cm)
hailstone fragment shows a milky nucleus surrounded by alternating
rings of transparent and translucent ice.

Hail can be formed when thunderstorm drafts carry up raindrops into
higher freezing layers of the atmosphere. A hailstone grows inside
a cloud each time it collides with water drops making them freeze onto
its surface, until an upper limit is reached when the updraft can no
longer support its weight, causing it to fall and impacting the
ground. Microphysical processes determine density, structure, and
sizes of hailstones. At very high altitudes, temperature can be so
low that few liquid water drops remain, so hailstones don’t reach
significative sizes.

The structure of a cloudy ice layer scatters light in all
directions because specific temperature conditions cause
supercooled liquid water to freeze instantaneously on hailstone
surfaces, resulting in cracked ice with trapped air bubbles ( dry
growth). Light is otherwise refracted leading to the hailstones'
transparency if the water freezes slowly enough, permitting penetration
into the gaps before freezing and thus allowing air bubbles to escape
( wet growth). Photo taken on November 23, 2022.


Curitiba, Brazil Coordinates: -25.4372, -49.2700


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More...

Severe Weather Links

* World Severe Weather Information Center
* Enhanced Fujita Scale
* A Lightning Primer
* More About Thunderstorms
* Staying Safe Outdoors in Severe Weather
* NOAA Storm Prediction Center
* Patterns of Lightning Activity
* US National Weather Service

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