How much force does the wind exert?

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How much force does the wind exert?

• Wind Forcewind pressure x area
• v2 (ft/sec) x 0.0024 x area (ft2)
• The wind produces how much force on an 8 x 6 foot
  fence panel during a weak hurricane (60mph)?
• Force0.0024 x (88ft/sec)2 X 48ft2 890 lbs
• Katrina (130mph189ft/sec)4110 lbs!
• This principle affects everything from building
  design to car fuel efficiency aerodynamic lift
  in aircraft

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Wind and Exposed Soil
Microscale winds bounce and skip sand grains,
expose desert pavement, erode patterns into
rocks, and shape sand dunes with ripples
revealing wind direction.
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Wind and Snow Surfaces
. Turbulent eddies of wind can trigger rolling of
moist snow to create cylindrical snow
rollers. Snow fences are used to accumulate snow
so that it does not drift over roads
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Wind and Vegetation
Wind speeds increase with elevation above earth's
frictional surface, where stronger winds sculpt
and denude the branches of trees. Shelter belts
may protect downwind property, but may also
create unwanted turbulent eddies.
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Wind and Waves
-Water waves are generated by surface friction
and eddies that force winds and water upward and
downward. -Wave height increases with wind speed,
wind duration, and fetch (the length) of open
water.
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Wind Direction and Origin
-Wind direction is typically given as the origin
from which it blows, such as "westerlies" coming
out of the west. -Counter-examples use the
adverbs 'on' and 'up' to indicate direction, such
as 'onshore wind', and "upslope wind" for wind
moving uphill.
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Charting Prevailing Winds
-Winds shift in direction, noted by degrees or
compass direction, and knowledge of prevailing
wind directions are useful in planning. -A wind
rose of likely directions might be used to orient
runways and pollution sources
.
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Wind Rose

• Monthly or annual average speed and directions
  represented graphically

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Wind Measurements
-Pilot balloons observed with theodolites, and
rawinsondes are useful ways to detect winds in
the lower atmosphere. -Doppler radar detects
changes in wind speed. Also very helpful in
identifying developing storms and tornadoes.
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Thermal Wind Circulations
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Thermal Circulations
-Solar heating and radiational cooling of earth's
surface generates cold-core thermal highs and
warm-core thermal lows. -Winds can circulate
between these two systems.
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Thermal Winds
Changes in air temperature causing warm air to
rise and cool air to sink can also generate
horizontal winds. Rising warm air creates a
surface low and upper level high. Sinking cool
air creates a surface high and upper level low.
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Land/Sea Breeze

• Forms when large scale pressure differences are
  small (large scale winds are weak), or when large
  scale winds are blowing in direction of breeze
  development.
• There must be strong temperature differences
  between land and water.
• Leading edge of the sea breeze front frequently
  will cause lifting and trigger thunderstorms.

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Sea/Land Breezes

• Land heats more quickly than water, creating
  land-water temperature differences along a
  coastline.
• - During the day the land's warm-core thermal low
  draws a sea breeze, while at night, the warmer
  sea draws a land breeze.

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Sea and Land Breezes
Opposing breezes may converge on an isthmus of
land, and this rising moist unstable air will
trigger thunderstorms. The leading edge of
land-water breezes can bring rapid changes in
humidity or pollutants.
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Sea Breeze Animation
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Asian Monsoon
Seasonal reversal of monsoon winds in southern
Asia is explained by continental temperature
shifts. Summer monsoon depressions of low
pressure and rains are enhanced by solar
insolation, latent heat of condensation, and jet
stream patterns. El Nino-Southern Oscillation
is also known to affect monsoon intensity.
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Southwest US Monsoon
Monsoon-like winds develop in July across the
southwestern U.S. region. As the continental
interior heats and rises, humid Gulf air sweeps
in creating instability and thunderstorms
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Mountain and Valley Winds
-Solar heating of hill slopes creates air that is
warmer and less dense than air at the same
elevation over the valley, and generates rising
valley breezes. -Nighttime radiational cooling of
the mountain slope creates relatively denser air
that sinks as a mountain breeze, or gravity wind.
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Mountain and Valley Breezes
Daily warming of mountain slopes that trigger
valley breezes of moist air may result in cumulus
clouds above mountain summits.
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Katabatic Wind

• Elevated plateaus with snow cover may foster
  development of a thin layer of high pressure cold
  air.
• Pressure gradient winds are triggered due to
  lower pressure above the adjacent valley, pushing
  cold air into the lower valleycan be as strong
  as 100 kts
• Common in Columbia River Gorge in Washington
  state in the former Yugoslavia, and France

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Chinook Winds

• Known as the snow eater, or Chinook winds
• Common in US Great Plains
• Strong westerly winds force air upslope
• Moisture condenses and precipitates when
  ascending high mountains
• The air is then warmed upon descent
• Air is much warmer and much drier on the lee side
  of the mountain

The drying/warming process happens any time the
air rises and then descends over high mountain
ranges, but Chinook winds form when upper level
winds are strong and perpendicular to the
mountain range
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Chinook Wall Cloud
Chinook wall clouds are an indicator of the
presence of Chinook conditions.
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ChinookRapid Temperature Changes
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Santa Ana Winds

Easterly winds that descend from southern
California's elevated desert plateau are heated
by compression and lowered in humidity.

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Santa Ana Story

• Named after Southern California's Santa Ana
  Canyon and a fixture of local legend and
  literature, the Santa Ana is a blustery, dry and
  warm (often hot) wind that blows out of the
  desert.
• In Raymond Chandler's story Red Wind, the title
  being one of the offshore wind's many nicknames,
  the Santa Anas were introduced as "those hot dry
  winds that come down through the mountain
  passes and curl your hair and make your nerves
  jump and your skin itch.
• On nights like that every party ends in a fight.
  Meek little wives feel the edge of the carving
  knife and study their husbands' necks. Anything
  can happen."

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Haboob Winds
Al Asad, Iraq
-Desert winds with dust and sand may form from
cold downdrafts along the leading edge of a
thunderstorm. -These winds are most commonly
found in the African Sudan and Arizona Sonora
deserts.
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Dust Devils
-Not a tornado -On a hot, dry day the sun
strongly heats the surface of the ground, causing
strong thermals.
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Dust Devils
-Winds near the surface can cause the thermal to
spin -The dust devil then creates a rising
column of dust and (light) debris.