All language subtitles for What is dust devil？

What is dust devil?

A dust devil is a strong, well-formed, and
relatively short-lived whirlwind.

The primary vertical motion is upward.

Dust devils are usually harmless, but can
on rare occasions grow large enough to pose

a threat to both people and property.

Many dust devils are usually small and weak,
often less than 3 feet or 0.9 m in diameter

and a few meters tall with maximum winds averaging
about 45 miles per hour (72 km/h), and they

often dissipate less than a minute after forming.

On rare occasions, a dust devil can grow very
large and intense, sometimes reaching a diameter

of up to 300 feet (90 m) and 1000 meters tall
with winds in excess of 60 mph (97 km/h) and

can last for upwards of 20 minutes before
dissipating.

They are comparable to tornadoes in that both
are a weather phenomenon involving a vertically

oriented rotating column of wind.

Most tornadoes are associated with a larger
parent circulation, the mesocyclone on the

back of a supercell thunderstorm.

Dust devils form as a swirling updraft under
sunny conditions during fair weather, rarely

coming close to the intensity of a tornado.

In Australia, a dust devil is also known as
"Willy-willy".

In Ireland, dust devils are known as "Shee-gaoithe"
or "Fairy wind".

Formation

The sun heats the ground.

A pocket of hot air near the surface rises
quickly through cooler air above it, forming

an updraft.

It creates an area of low pressure.

If conditions are just right, the updraft
may begin to rotate.

Air rushes in to fill the low pressure area,
the circulation stretches vertically and speeds up.

As more hot air rushes in toward the developing
vortex to replace the air that is rising,

the circulation effect becomes further intensified
and self-sustaining., sucking up dirt and debris.

As available hot air near the surface is channeled
up the dust devil, eventually surrounding

cooler air will be sucked in.

Once this occurs, the effect is dramatic,
and the dust devil dissipates in seconds.

Usually this occurs when the dust devil is
not moving fast enough (depletion) or begins

to enter a terrain where the surface temperatures
are cooler.

Certain conditions increase the likelihood
of dust devil formation.

First condition is flat barren terrain, desert
or tarmac.

Flat conditions increase the likelihood of
the hot-air "fuel" being a near constant.

Dusty or sandy conditions will cause particles
to become caught up in the vortex, making

the dust devil easily visible, but are not
necessary for the formation of the vortex.

Second condition is clear skies or lightly
cloudy conditions.

The surface needs to absorb significant amounts
of solar energy to heat the air near the surface

and create ideal dust devil conditions.

Last condition is light or no wind and cool
atmospheric temperature.

The underlying factor for sustainability of
a dust devil is the extreme difference in

temperature between the near-surface air and
the atmosphere.

Windy conditions will destabilize the spinning
effect of a dust devil.

Hopefully you have learned something from
the dust devil.