Wind and Air Circulation Wind is the horizontal movement of air parallel to Earth’s surface.

An anemometer is an instrument that measures wind speed. Wind is caused by differences in air pressure – which in turn is caused by changes in atmospheric conditions (Ex: water vapor, temperature, etc…) Air pressure gradient is the difference in air pressure over a specific distance. An isobaric map illustrates the pressure gradient of an area. When the air pressure gradient is steep, the isobars are close together. HIGH WINDS When the air pressure gradient is gentle, the isobars are further apart. LOW WINDS or NO WINDS

Wind Direction Winds moves from areas of high pressure to areas of low pressure. Due to the Coriolis Effect, the wind direction is deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. A weather vane (wind vane) is an instrument that determines the direction of wind. The weather vane will point in the direction that the wind is coming from. The wind is coming from the northwest and is blowing to the southeast.

Convection Cells The atmosphere is heated by insolation. Due to the changes in intensity and duration of insolation, unequal heating leads to difference in air pressure. This will lead to the creation of convection cells – the rising of warm/less dense air and the descending of cool/more dense air. Regions where air comes together to form a vertical current is called convergence. Regions where air spreads away from a vertical current is called divergence. convergence divergence

RT = Pg. 14 A jet stream is a strong, easterly flowing wind found in the upper troposphere. Jet streams influence the formation and direction of weather patterns. Jet Stream Jet streams help to steer air masses and fronts.

Planetary Winds and Pressure Belts How do the winds seem to blow? Winds blow towards low pressure. Winds blow away from high pressure. L H

Planetary Winds and Pressure Belts High Pressure Low Pressure Due to the Coriolis Effect, winds that move away from a high pressure belts are deflected to the right in the Northern Hemisphere. These winds would be deflected to the left in the Southern Hemisphere. These are known as planetary winds. Pressure Belts Planetary Winds

Planetary Winds and Pressure Belts The position of Earth’s pressure belts and the planetray winds that are created will change as different points of the Earth are exposed to direct insolation during Earth’s revolution around the Sun. As a result, different locations on Earth’s surface will experience seasonal shifts in weather patterns. Northern part of the United States Pierre experiences cold weather conditions in the winter due to a northerly prevailing wind Pierre experiences warm weather conditions in the summer due to a southwesterly prevailing wind Pierre experiences warm weather conditions in the summer due to a southwesterly prevailing wind

Weather Movement in the United States Generally speaking, weather patterns move from the southwest to the northeast in the US due to the southwest prevailing winds.

Surface Ocean Currents RT = Pg. 4 Surface ocean currents are caused by wind blowing over the oceans thus transferring energy to it. The direction of movement of these ocean currents is a reflection of the Coriolis Effect (clockwise in Northern Hemisphere and counterclockwise in Southern Hemisphere) and the landmasses surrounding the oceans. As is true of prevailing winds, the positions of surface ocean currents will change seasonally due to different areas of Earth’s surface receiving maximum insolation as Earth revolves around the Sun.

Weather Station Model Wind Direction The wind blows along the shaft. The wind originates from the southwest and has a speed of 15 knots at this location. Wind Speed Whole feather = 10 knots Half Feather = 5 knots 1 knot = 1.15 mi/hr