Global and Local Winds

Review of Air Air Movement Air Pressure Wind is the movement of air caused by differences in air pressure The greater the difference, the faster the wind moves Air Pressure Differences in air pressure are caused by the uneven heating of Earth Uneven heating produces pressure belts which occur every 30° latitude

Winds Differences in air pressure produce winds. Pressure difference between a high pressure area and a low pressure area determines the strength of the wind. ( larger pressure differences  stronger winds) Difference in air temperature also lead to pressure differences that produce winds.

Pressure Belts AT EQUATOR AT POLES 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 AT POLES At the poles, cold air sinks and moves towards the equator Around 60° north and south, the air begins to heat up and rise

Coriolis Effect Once air has been set in motion by the pressure belts it is deflected from its path by the Earth’s rotation. This deflection is called the "Coriolis Force" In the northern hemisphere, air moving from high to low pressure is deflected to the RIGHT. Cyclonic wind pattern around L pressure area In the southern hemisphere, air moving from high to low pressure is deflected to the LEFT. Anticyclonic wind pattern around H- pressure area

Coriolis Effect

Jet Stream The jet streams are narrow belts of high speed winds that blow in the upper troposphere and lower stratosphere Jet stream is a narrow ribbon of moving air caused by temperature differences between the earth’s equator and the poles. Separates warm air from cold air The term "jet stream" is often used to refer to the rivers of wind high in the atmosphere - above about 20,000 feet - that steer storms. They also help determine locations of areas of high and low air pressure at the Earth's surface.

Jet Stream Narrow belts of strong wind - Jet streams form between areas of low pressure and high pressure Polar jet stream forms at the boundary of cold, dry air to the north anf warmer, more moist air to the south. Jet streams move faster in the winter because of differences between cold air and warm air is greater. The JET STREAM moves storms across the country. Jet pilots take advantage of jet streams moving east but fly at different altitudes moving west !

Global Winds Each hemisphere has three wind belts Each hemisphere contains three looping patterns of air flow called convection cells Each of convection cells correlates to an area of Earth’s surface , called a wind belt. These winds are called prevailing winds and curve because of the Coriolis Effect.

Global Winds The combination of pressure belts and the Coriolis Effect cause GLOBAL WINDS Some examples of global winds are polar easterlies, westerlies, and trade winds Remember! Northern Hemisphere deflects right. Southern hemisphere defects left.

Global Winds - Polar Easterlies Prevailing Winds that blow from east to west Wind belts that extend from the poles ( 90 ) to 60° latitude Formed from cold sinking air moving from the poles creating cold temperatures

Global Winds - Westerlies Prevailing Winds that blow from west to east Wind belts found between 30° and 60° latitude Flow towards the poles from west to east carrying moist air over the United States

Global Winds - Trade Winds Prevailing Winds that blow from east to west Winds that blow from 30° almost to the equator Called the trade winds because of their use by early sailors

Global Winds - Doldrums Trade wind systems of Northern and Southern Hemisphere meet at the equator in a narrow zone called the doldrums. Located along the equator where no winds blow because the warm rising air creates an area of low pressure. Surface winds are weak.

Global Winds - Horse Latitudes Sub-tropical high pressure zones Occur at about 30° north and south of the equator where the winds are very weak Most deserts on the Earth are located here because of the dry air

Global Winds

Local Winds On a scale much smaller that a global scale; not part of global wind belts. Generally move short distances ( <100 km. )and can blow in any direction Caused by geographic features that produce temperature differences Called breezes.

Local Winds - 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 sea breeze See a satellite animation at http://atmo.tamu.edu/class/atmo203/tut/seabr/sea18.html

Sea Breezes A sea breeze, is created during the day because solar radiation warms the land more than the water. Air over the land is heated by conduction. Heated air is less dense and has lower pressure. Cooler, denser air over the water has higher pressure and flows toward the warmer, less dense air. Convection current results and wind blows from the sea toward the land.

Local Winds - Land Breezes Low pressure occurs over the ocean during the night and high pressure over land due to the uneven heating of earth This causes wind to move from the land to the ocean creating a land breeze

Land Breezes At night, land cools much more quickly than ocean water. Air over the land becomes cooler than air over the ocean. Cooler, denser air above the land moves over the water, as the warm air over the water rises. Movements of air toward the water from the land is called a land breeze.

Local Winds - Animation Go to http://www.classzone.com/books/earth_science/terc/content/visualizations/es1903/es1903page01.cfm?chapter_no=visualization and view the animation of land breeze and sea breeze. Sketch the a land breeze and a sea breeze in your notes.