Chapter 12 Notes
- Winds
occur on all scales, but small scale winds are driven by pressure gradient
force and are slowed by the effects of friction.
- Viscosity
is the friction in a fluid, such as air.
Higher viscosity means higher friction.
- Molecular
Viscosity- friction at the smallest scales when molecules bump into each
other, occurs near boundaries
- Eddy
Viscosity- friction that arises through Eddies, which are
human-sized swirls of air that interact with the larger-scale wind and
help slow it down. Eddies arise
when wind blows over obstacles such as trees or buildings, or through
daytime heating from the sun, or from the atmosphere itself.
- Turbulence
is the irregular, almost random, pattern of wind.
Small Scale Winds going from East to West Across
the US
- A
Coastal Front is the boundary between two air masses along a coastline
that acts as a smaller-scale version of a stationary front. Common in Northeast
US.
- Cold
Air Damming is the stubborn entrenchment of cold air that in pinned
against high mountains. Classic
case of shallow, cold air.
- Gravity
Waves are atmospheric waves with an alternating small scale pattern of
high and low pressure maintained by the help of gravity. They are sometimes visible when the
rising air in the crests in the waves becomes saturated and forms parallel lines of clouds.
Midwest
- Lakes Breezes
are winds that blow onshore during the day around the Great
Lakes. They are
similar to sea breezes with cool water with high pressure at the surface
and warmer land with low pressure at the surface forming a slope of
pressure gradient force from the water to the land.
- A
Derecho is an hours long windstorm associated
with a line of severe thunderstorms that can leave significant
damage. It is a result of straight
line winds. A thunderstorm’s cold
downdrafts can drag down high speed air from aloft.
- A Bow
Echo can result form a derecho when high winds push the thunderstorms
outward, causing it to bend or “bow”.
- Derechos
are generally confined to the eastern two thirds of the US.
- A Blue
Norther is the fierce north wind behind a fast racing cold front in west Texas. It can also be called a Norte or a Buran
in other parts of the world.
- Dust
Storms are weather conditions characterized by strong winds and dust
filled air over and extensive area.
- A
Heatburst is when the temperature rises drastically throughout the night
and conditions becomes very dry with winds
howling. It can be explained by
adiabatic warming and static stability.
They are most common in late spring and early summer in the Great Plains.
- Microbursts
are similar to heatbursts in how the air splashes against the ground and
rapidly pushes outward. A
microburst is a strong, localized downdraft less than 4 km in diameter
that sometimes develops underneath a thunderstorm as a result of
evaporative cooling.
- A
Chinook is a dry, warm wind in western North America on the lee side of
the Rocky Mountains. The Chinook speeds the melting and
evaporation of snow.
West
- Valley
Breeze- Develops during the day when the thin air above the high mountainsides
warms quickly and the warm air rises and creates local low pressure along
the slopes. Air from the lower
valley moves in to replace it, creating an upslope breeze that becomes
strongest around noon.
- Mountain
Breeze- Develops at night when the high mountain slopes cool very quickly
and this cold, dense air forms a local high-pressure area. The pressure gradient then drives a
gentle breeze down the slope into the valley that is strongest just before
sunrise.
- Mountain
and Valley Breezes are generally very gentle.
- Katabatic
Winds are more violent relatives of mountain breezes and occur all over
the world with gusts sometimes exceeding 100 mph.
- Boulder
Windstorms are downslope winds associated with mountain gravity waves that
can be very strong.
- Dust
Devils are thin, rotating columns of air in the desert Southwest
that develop from intense daytime heating.
- Lenticular
Clouds are clouds in the shape of a lends that
sometimes resemble spaceships.
Usually form downwind.
- Santa
Ana Winds form when the pressure gradient caused by an anticyclone (high
pressure) over the Rockies, in combination with friction, forces already
dry air from the mountainous West down the Coast Range of northern
California or down the San Gabriel mountains in southern California and
all the way down out into the ocean.
Can cause roaring fires.