Atmosphere Circulation
Winds
What Causes Winds? Difference in air pressure due to unequal heating of the atmosphere.
Temperatures vary according to the amount of sun it gets. Uneven heating of the Earth s atmosphere and surface Balance between warm and cool air is constantly changing, creating wind. The variation in angle at which the Sun's rays strike The amount of surface area over which the Sun's rays are distributed Some areas of Earth reflect more solar energy than others (Albedo)
Winds are created by. Heating the air, decreases pressure (warm air rises creating a low pressure) Cool air rushes into replace the warm air (cooler dense air, produces high pressure) As air goes from high to low pressure, winds form. The greater the difference, the faster the wind moves
HIGH & LOW PRESSURE AND WEATHER High pressure means sinking air. What kind of weather would you expect and why? Low pressure means rising air. What kind of weather would you expect and why?
Air Pressure Differences in air pressure are caused by the uneven heating of Earth Uneven heating produces pressure belts which occur every 30 latitude
Pressure Belts As warm air rises at the equator and moves toward the poles, it cools As it cools, some of the air sinks around 30 north and south of the equator
Pressure Belts At the poles, cold air sinks and moves towards the equator Around 60 north and south, the air begins to heat up and rise
There are 2 types of winds Global Winds and Local Winds
Types of Global Winds Doldrums Horse Latitude Trade Winds Prevailing Westerlies Polar Easterlies All caused by uneven heating
Global Winds The combination of pressure belts and the Coriolis Effect
Doldrums Named from their ability to quickly propel trading ships across the ocean Found between the equator and 5 latitude Steady and blow about 11 to 13 mph
Doldrums Located along the equator where winds are calm and weak, because the warm rising air creates and area of low pressure Warm air rises at the doldrums near the Equator high into the atmosphere. That air then flows north in the Northern Hemisphere and south in the Southern Hemisphere. When it gets to about 30 degrees north or south latitude, the air is cooled off and sinks.
Horse Latitude Subtropical latitudes between 30 and 38 degrees both north and south where Earth's atmosphere is dominated by the subtropical high, an area of high pressure, which suppresses precipitation and cloud formation. The horse latitudes are associated with the subtropical anticyclone and the large-scale descent of air from highaltitude currents moving toward the poles.
Trade Winds Strong winds One lying between 25 and 30 north of the equator and the other lying between 25 and 30 south of it In the Northern Hemisphere, the trade winds blow from the northeast and are known as the Northeast Trade Winds In the Southern Hemisphere, the winds blow from the southeast and are called the Southeast Trade Winds.
Prevailing Westerlies Has an impact on the US weather Cold, but weak winds Near the north and south poles US weather is influenced by these Cooling takes place between the 30-60 degree latitude as it approaches the poles
Prevailing Westerlies Flow towards the poles from west to east carrying moist air over the United States They tend to grow stronger during winter when there is low pressure over the poles, and weaker during the summer when there is high pressure over the poles.
Polar Easterlies Wind belts that extend from the poles to 60 latitude Formed from cold sinking air moving from the poles creating cold temperatures
Jet Stream The jet streams are narrow belts of high speed winds that blow in the upper troposphere and lower stratosphere Separates warm air from cold air Discovered in 1940 s Can be found in the upper troposphere Strong high speed and high pressure Moves west to east across the US, moving storms
Local Winds Generally move short distances and can blow in any direction Caused by geographic features that produce temperature differences
Types of Local Winds Sea Breezes- from sea to land Land Breezes from land to sea Mountain Breeze/Valley Breeze Monsoon- Seasonal changes in wind All caused by uneven heating
Sea Breezes High pressure is created over the ocean during the day and low pressure over land due to uneven heating Air moves from the ocean to the land creating a seas breeze
Land Breeze Low pressure occurs over the ocean during the night and high pressure over land due to the to uneven heating This causes wind to move from the land to the ocean creating a land breeze
Mountain Breeze/Valley Breeze Wind that travels down from a mountain to a valley A mountain breeze and a valley breeze are two related, localized winds that occur one after the other on a daily cycle
Monsoon Patterns of wind circulation that change with the season. Areas with monsoon generally have dry winters and wet summers.
Monsoon Winds
Atmospheric Convection Current
Atmospheric Convection Currents Air has four properties that determines its movement: Density - less dense air rises, denser air sinks Water vapor capacity - warm air has a higher capacity for water vapor than cold air Adiabatic heating or cooling - as air rises in the atmosphere its pressure decreases and the air expands; conversely, as air sinks, the pressure increases and the air decreases in volume Latent heat release - when water vapor in the atmosphere condenses into liquid water and energy is released
Formation of Convection Currents Atmospheric convection currents are global patterns of air movement that are initiated by the unequal heating of Earth. Hadley cells - the convection currents that cycle between the equator and 30 north and south. Intertropical convergence - the area of Earth that receives the most intense sunlight and where the ascending branches of the two Hadley cells converge. Polar cells - the convection currents that are formed by air that rises at 60 north and south and sinks at the poles (90 north and south)
Circulation Systems Produce Climate Patterns Convective currents contribute to climatic patterns Hadley cells = convective cells near the equator Surface air warms, rises, and expands Causing heavy rainfall near the equator Giving rise to tropical rainforests Currents heading north and south are dry Giving rise to deserts at 30 degrees
Circulation Systems Produce Climate Patterns Ferrell cells and Polar cells = lift air and create precipitation at 60 degrees latitude north and south Conditions at the poles are dry
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