Wind

What is “wind”?

• “Moving air”

What are the 2 types of wind based on geographical locations?

• Mediterranean = Mistral

• Rocky Mountain = Chinook

Why is wind important to aviation?

• Takeoff, en-route, landing

• Navigation

• Fuel management

• Flight safety purpose

What are the 2 causes of wind?

• Atmospheric pressure

• Temperature variations

What are the 2 types of wind motions?

1. Vertical

• Ascending current

• Descending current

1. Horizontal

True or false: “wind direction is measured according to whichever direction the wind is blowing from”

True!

What are some instruments used to determine “wind direction”?

• Wind vane

• Wind sock

• Wind sleeve

• Wind tee

What is “wind speed”? What are the 3 standard units for wind speed?

• The rate of wind movement in distance per unit of time

Units:

• Knots (KT)

• Kilometers per hour (kph)

• Meters per second (mps)

What are some instruments used to measure “wind speed”?

• Anemometer

• Aerovane

Describe “general circulation”

• The observed patterns of winds & pressure which continue throughout the year

What is the key driver of atmospheric circulation?

• The uneven heating of the earth’s surface by the sun

True or false: “the equator region is colder than the polar region”

False! (The most direct rays strike the earth near the equator, heating equatorial regions much more than polar regions)

What is the name of the circulation if the earth didn’t rotate? (Hint: … cell)

“Single cell”

Explain wind circulation if the earth did not rotate

• The wind simply flow back-and-forth between the poles and the equator.

• At the poles = cold air sink, move toward the equator

• At the equator = warm air rises, move toward the poles

As the earth rotates, the single cell breaks up into how many cells? What are they?

3 cells!

• Hadley cell

• Ferrel cell

• Polar cell

Explain “Hadley cell”

• Movement = counterclockwise

• The air rises at the equator

• Flows toward the poles aloft

• Reaching only about 30 degrees latitude

• Cool down and sink

Explain “Ferrel cell”

• Movement = clockwise

• Between 30-60 degrees latitude

• Air move poleward until 60 degrees latitude

• Meet cooler air from the pole

• Acting as a "gear" between the Hadley and Polar cells

Explain “Polar cell”

• Movement = counterclockwise

• Between 60 degree latitude and the poles

• Cooler air sink to 60 degrees latitude

• Then move upward

What are the 6 forces and winds?

Forces:

• Pressure Gradient Force (PGF)

• Coriolis Force (CF)

• Centrifugal Force

• Friction

Winds:

• Geostrophic Wind

• Gradient Wind

Explain “pressure gradient force”

• Different pressure create the force to drive the wind

• Develops from the poles to the equator

• Always flow from H → L!!!

• If the earth did not rotate, PGF = the only force acting on the world

How does different PGF affect the wind?

• Weak/loosely aligned PGF = light wind

• Strong/tightly packed PGF = strong wind

Explain “Coriolis force”

• A defective force resulting from the earth’s rotation and the law of inertia

• Northern hemisphere = acts to the right of wind direction

• Southern hemisphere = acts to the left of wind direction

• Vary with wind speed and latitude, zero at equator, max at the poles

Explain “Geostrophic wind”

• A steady horizontal air motion along straight, parallel isobars

• Perpendicular to that in which the CF and the PGF are acting equally and oppositely

• Layer of frictionless

Explain “Centrifugal force”

• Cause a rotating body to be propelled away from the center of rotation

Explain “Gradient wind”

• Steady horizontal and frictionless

• Wind blows parallel to curved isobars

• CFF, CF, and PGF are balanced.

• PGF = CF + CFF

True or false: “gradient wind occurs at the earth’s surface”

False! (It doesn’t occur at the earth’s surface due to friction)

What will happen when PGF is stronger than CF

• PGF = CF + CFF

• Wind flow counterclockwise around low in the Northern hemisphere

What will happen when CF is stronger than PGF

• CF = PGF + CFF

• Wind flow clockwise around high in the Northern hemisphere

Explain “friction”

• Surface friction slows down air movement

• Reduction in wind speed by friction = reduced CF

• Disrupt the balance between CF and PGF

What are the 2 types of circulations that result from friction? Simply elaborate

• Cyclonic = into a low pressure cell in the Northern Hemisphere

• Anticyclonic = out of a high pressure cell in the Northern hemisphere

True or false: “geographical characteristics create local pressure and wind systems”

True!

• Land

• Water

• Mountains

• Valleys

What are the 5 different types of local wind?

• Land breeze

• Sea breeze

• Mountain wind

• Valley wind

• Katabatic wind

Explain “sea breeze”

• Occurs during the day

• Land heats up more quickly → hotter than the sea

• Wind blows from sea (H) → land (L)

Explain “land breeze”

• Occurs at night

• Land releases heat faster than the sea

• The wind reverses and blow from cool land to warmer water

• Land (H) → Sea (L)

Explain “valley wind”

• Occurs during the day

• “Anabatic wind”

• Air near the slope of the mountain receives radiation from the sun and is heated by the contact with the ground

• Ground (H) → top of mountain (L)

Explain “mountain wind”

• Occurs at night

• “Katabatic wind”

• The air in contact with the mountain slope is cooled down by terrestrial radiation → becomes heavier than the surrounding air → sinks

• Air sinking → mountain wind (stronger than valley wind, especially in winter)

• Top of the mountain (H) → ground (L)

Explain “Katabatic wind”

• Any wind blowing down an incline (e.g. mountain breeze)

What are the 2 types of Katabatic wind?

• Foehn wind = warm downslope wind

• Fall/gravity wind = cold downslope wind

What are the 2 Foehn wind called?

• Chinook = located along the Eastern slopes of the Rockies

• Santa Ana = descends from the Sierra Nevada mountain into the Santa Ana valley

What are the 3 gravity wind called?

• Bora = Northeast wind blowing in the upper Adriatic Sea

• Mistral = blows through the Rhône valley into the Mediterranean

• Taku = Southeast Alaska

True or false: “L = counterclockwise, H = clockwise”

True!

What determines good/bad weather?

• Bad weather = low pressure & troughs

• Good weather = high pressure & ridges