WIND Pages 527-537

What is Wind? Wind is the horizontal movement of air flowing from areas of higher pressure to lower pressure. The greater the difference in pressure, the higher the wind speed.

What causes wind? All wind results from uneven heating of the atmosphere. The sun heats up the earth, which heats up the air over it.   The hotter air is less dense and begins to rise leaving a low pressure void over the earth.   But the temperature doesn’t rise as high over areas like oceans that can absorb more of the sun’s heat.   This creates the opposite situation, i.e. high atmospheric pressure over the oceans.   So the air flows from high pressure over the ocean to the lower pressure areas over land.  

Pressure and Wind Closely spaced isobars indicate a steep pressure gradient and strong winds, widely space isobars indicate a weak pressure gradient and light winds.

From what direction would the wind be blowing at point C?

From what direction would the wind be blowing at point C? From North East C

Where would winds be strong? Weak? C

Wind Direction and Isobars Winds flow roughly parallel to the isobars.

Air Pressure and Weather p523 Cyclones are swirling centers of low pressure air (L on weather map), where winds spiral inward  Clouds and precipitation form. Anticyclones are swirling centers of high pressure air (H on weather map),winds spiral out.  produce clear, dry weather.

Uneven Heating: Day and Night p 527 Water reflects most solar radiation that reaches its surface back to the atmosphere. Since land absorbs more solar radiation the land surface retains more heat as do the vegetation for energy. Thus, land surfaces warm more quickly than water  Sea Breeze

Daytime: Sea breeze

Daytime: Sea Breeze During the day: Wind will blow from the higher pressure over the water to lower pressure over the land causing the sea breeze.

Night time: Land breeze

Night time: Land Breeze At night: The land cools more quickly than the ocean, cooling the air above it. The warmer air above the water continues to rise, and cooler air from over the land replaces it, creating a Land Breeze.

The Coriolis Effect p528 The Coriolis Effect causes freely moving objects to appear to move right in the Northern Hemisphere and to the left in the Southern Hemisphere https://www.khanacademy.org/partner- content/nova/clouds/v/hurricanes

Coriolis Effect p528 Earth rotation causes fluids to move in a slightly curved direction. Earth’s round shape causes equator to spin more slowly than the poles As air moves away from the mid-latitudes toward the poles and toward the equator, it doesn't move in a straight line relative to the earth's surface. Coriolis demo, 3min: https://www.youtube.com/watch?v=mPsLanVS1Q8

Coriolis Effect p528 Prevents winds from blowing directly from high to low pressure. Winds in Norther turns right (clockwise) Winds in the South turn left (counterclockwise)

Measuring Wind Weather Vane, wind sock – measures wind direction Anemometer – measures wind speed Wind direction is reported as the direction from which the wind blows, not the direction toward which the wind moves. A north wind blows from the north toward the south.

Wind Barbs Wind Barbs indicate wind speed and direction. Point in the direction "from" which the wind is blowing.

Wind Barbs From which direction is this wind coming from?

Wind Barbs From which direction is this wind coming from? the winds are out of the northeast, or northeasterly

Wind speed is measured in "knots“ (knt) A "Knot" is a nautical mile per hour. 1 Knot = 1.15 Miles Per Hour (MPH) 1 Knot = 1.9 Kilometers Per Hour (KM/HR)

Wind Speed Short barb = 5 knots, Long barb = 10 knots. Pennants = 50 knots. No barb = winds are calm.

Practice Topic Questions #6-10 p530

Global Wind Patterns trade winds, prevailing westerlies, polar easterlies, and the jet streams—flow around the world and cause most of the Earth’s weather patterns.

Circulation Cell - Convection Earth is warmer at the equator. Rising air splits into two currents: one North, one South. Coriolis turns them. By 30 latitude, both winds are travelling due East. Here the air cools, sinks to zone of high pressure at the surface at 30° latitude. Air at surface flows from high pressure at 30° lat to low pressure at the equator

Circulation Cells Hadley Cell: from equator to 30º Ferrel cell: between 60º  and 30º . Polar cell:

Global Wind Belts Global wind belts are enormous, relatively steady winds

Pressure Belts p532 Pressure belts are horizontal distributions of air pressure across the latitudes. These regions of pressure cells are called belts as they run around the earth as would a belt around one's waist.

Pressure Belts p532 Doldrums – low pressure belt at equator to about 22.5°. Horse Latitudes – high pressure belts at 30° Polar – low pressure belts.

Global Winds p533 Trade Winds Polar Easterlies: From 60-90 ° Prevailing Westerlies: From 30-60 °

Trade Winds p533 Trade winds are warm, steady prevailing patterns of wind from the east to west (easterly) found in the tropics, within the lower portion of the Earth's atmosphere, near the Earth's equator. between 30°N and 30°S https://www.youtube.com/watch?v =crSJsDX1yHY

Jet Streams The highest winds are the jet streams. They are formed where the other wind systems meet. The jet streams flow far above the Earth where there is nothing to block their paths. These fast moving “rivers of air” pull air around the planet, from west to east, carrying weather systems with them. These global winds—trade winds, prevailing westerlies, polar easterlies, and the jet streams—flow around the world and cause most of the Earth’s weather patterns.

Monsoon Effect of continents on wind

Weather Station Symbols