Wind and Rain 3/8/10

Wind  Wind – the horizontal movement of air from an area of high pressure to an area of lower pressure.  All winds are caused by differences in air pressure.

Measuring Wind  Anemometer – has 3 or 4 cups mounted at the ends of spokes that spin on an axle. The force of the wind spins the cups and a speedometer is connected to the cups to measure the wind speed.

Wind-Chill Factor  Wind blowing over your body cools your skin. The stronger the wind the cooler you feel.  Wind-Chill Factor – the increased cooling that a wind can cause.

Local Winds  Local winds – wind that blows over a short distance that are caused by unequal heating of the Earth’s surface within that small area.

Global Winds  Global Winds – winds that blow steadily from specific directions over long distances.

Coriolis Effect  Coriolis Effect – the way the Earth’s rotation makes winds curve. Coriolis was a French mathematician who studied and explained it in Coriolis was a French mathematician who studied and explained it in 1835.

Horse Latitudes  Horse Latitudes – at 30 o and 60 o the winds do not go up or down.

Wind Belts  The major global wind belts are: Trade winds Trade winds Prevailing Westerlies Prevailing Westerlies Polar Easterlies Polar Easterlies

Trade Winds  Trade winds – winds that blow from the horse latitudes towards the equator.

Prevailing Westerlies  Westerlies – winds that blow away form the horse latitudes. These winds blow southwest between 30 o and 60 o north.

Polar Easterlies  Polar Easterlies – cold air near the poles sinks and flows back down. The Coriolis effect shifts these winds to the west meeting at the 60 0

Clouds  Meteorologists have put clouds into three main groups: Cumulus Cumulus Stratus Stratus Cirrus Cirrus

Cumulus  Cumulus – heap or mass. These clouds are fluffy and look like cotton candy.  They are anywhere from 2-18 km off the ground.  A sign of good or fair weather.

Stratus  Stratus – spread out. These clouds have flat layers and cover most of the sky.  As they get thick they can produce rain or snow.

Cirrus  Cirrus – high feathery clouds that are made of ice crystals above 6 km.

Nimbus – rain Nimbus – rain (cumulonimbus is a storm cloud) (cumulonimbus is a storm cloud) Alto – high Alto – high (altostratus is a high, flat cloud) (altostratus is a high, flat cloud)

Cloud layers  The layers of clouds starting from the ground are: Fog Fog Cumulus Cumulus Stratus Stratus Nimbostratus Nimbostratus Cumulonimbus Cumulonimbus Altostratus Altostratus Altocumulus Altocumulus Cirrocumulus Cirrocumulus Cirrus Cirrus

The Water Cycle  Evaporation – liquid water escapes into the air as water vapor.  The water cycle is the movement of water between the atmosphere and the Earth.

Humidity  Humidity – a measure of the amount of water vapor in the air.  Humidity can be measured using a psychrometer.

How Clouds Form  Clouds form when water vapor in the air becomes liquid water or ice crystals which is called condensation.

How Clouds Form  Dew Point – the temperature at which condensation begins.  Precipitation – any form of water that falls from clouds and reaches Earth’s surface.

Rain  Most common form. Water drops must be at least 0.5 mm or larger in diameter in order to be rain.

Sleet  If the temperature of the air is below 0 o C then the rain will freeze. If it is less than 5 mm in diameter then it is considered sleet.

Freezing Rain  If the rain doesn’t freeze until it reaches the ground, then it is considered freezing rain and is very dangerous.

Hail  Round pellets of ice larger than 5 mm in diameter are called hail. Hail forms in cumulonimbus clouds during thunderstorms.

Snow  When water vapor changes directly into ice crystals. All snowflakes have exactly 6 sides or branches.

Droughts  Long periods of unusually low precipitation  Cloud seeding helps get rid of droughts when silver iodine is placed into clouds with airplanes.