Wednesday April 27, 2011

1. WednesdayApril 27, 2011 (Cyclones and Anticyclones; Complete Lab; Video - Twister) Period 2 Only

2. The Launch Pad Wednesday, 4/27/11 Explain the three controls of wind.

3. Announcements Please check your yearly average in this class. If you are below 70 for the year, please come and see me ASAP! There are only two more grades remaining!

5. Cyclones and Anticyclones A cyclone is a center of low pressure where the pressure decreases even more toward the center. The winds associated with a cyclone in the Northern Hemisphere circle inward (called a convergence) with a counterclockwise rotation. In the Southern Hemisphere, cyclone winds circle inward (convergence) with a clockwise rotation.

6. Cyclones and Anticyclones A cyclone is associated with rising air, and often bring clouds and precipitation. An anticyclone is a center of high pressure, with the pressure increasing toward the center.

7. Cyclones and Anticyclones

8. Cyclones and Anticyclones Winds associated with an anticyclone In the Northern Hemisphere swirl outward (a divergence) in a clockwise direction. Winds associated with an anticyclone In the Southern Hemisphere swirl outward (a divergence) in a counterclockwise direction. Anticyclones are associated with subsiding air and usually bring “fair” weather.

9. Cyclonic and Anticyclonic Winds in the Northern Hemisphere Figure 18.11

10. Airflow Associated with Surface Cyclones and Anticyclones Figure 18.13

11. The underlying cause of Earth’s wind is unequal surface heating by the Sun. Idealized Global Circulation At the surface, airflow is outward from the subtropical high. Air traveling equatorward from the subtropical high produces the trade winds. Air traveling poleward from the subtropical high produces the westerly winds (westerlies On the rotating Earth, there are three pairs of atmospheric cells that redistribute heat. The center of this zone of subsiding air is the subtropical high pressure zone, which encircles the globe near 30 degrees latitude, north and south. As the westerlies move poleward, they encounter the cool easterlies in the region of the subpolar low pressure zone. The interaction of these warm and cool winds prodcuces the stormy belt known as the polar front. The source region for the variable polar easterlies is the polar high pressure zone. Here, cold polar air is subsiding and spreading equatorward. As the upper-level flow from the equatorial low reaches 20-30 degrees latitude, north or south, it sinks back toward the surface. This produces hot, arid conditions. Near the equator, the rising air is associated with the pressure zone known as the equatorial low pressure zone, a region marked by abundant precipitation.

12. Complete Lab Air Masses, the Middle-Latitude Cyclone, and Weather Maps

13. Video Twister