1. Unit 4 – Atmospheric Processes

2. Winds… Earth’s atmospheric circulation is an important transfer mechanism for both energy and mass The imbalance between equatorial energy surpluses and polar energy deficits is partly resolved Wind – the horizontal motion of air across Earth’s surface Differences in air pressure (density) between one location and another produce wind Names for the direction from which they originate

3. Driving Forces within the Atmosphere Gravitational force Pressure gradient force Coriolis force Frictional force

4. Earth’s Gravitational Force Earth’s gravitational force on the atmosphere is practically uniform, equally compressing the atmosphere near the ground worldwide Density decreases as altitude increases

5. Pressure Gradient Force High- and low-pressure areas exist in the atmosphere because of uneven heating of the Earth’s surface A pressure gradient is the difference in atmospheric pressure between areas of higher pressure and lower pressure A steep gradient causes faster air movement from a high- pressure area to a low-pressure area. High and low pressure areas are caused by differences in surface heating and cooling. Land versus water. Different albedos and energy absorbing abilities of land, vegetation and human built surfaces

7. Isobars Isobars are lines of equal atmospheric pressure drawn on a map. Widely spaced isobars display a gradual pressure gradient. Gradual pressure gradients imply light winds. Closely spaced isobars display a steep pressure gradient. Steep pressure gradients imply strong winds.

8. Coriolis Force Deflects from a straight path any object that flies or flows across Earth’s surface Wind, airplane, ocean currents Deflection to the right in the Northern Hemisphere; to the left in Southern Hemisphere The strength of the Coriolis force strengthens with an increase in latitude.

10. Friction Force Drags on the wind as it moves across surfaces; up to 500m Varies with surface texture, wind speed, time or day and year, and atmospheric conditions Since surface friction decreases wind speed, it reduces the effect of the Coriolis force Anticyclone Winds in the Northern Hemisphere spiral out from a high- pressure area clockwise Cyclone Spiral into a low-pressure area counterclockwise In the Southern Hemisphere these circulation patterns are reversed

12. When the “forces” combine… When the gravitational force, pressure gradient force, Coriolis force and frictional force combine we see the development of ‘predictable’ global wind patterns.

13. Air Masses Air masses are bodies of air that develop over large areas of the Earth’s surface Two conditions needed: 1. Air must stay over the source region for a long period of time so that it can take on the characteristics of that region 2. Air must be stable Usually form where air is descending back to Earth These high-pressure cells line up roughly over the polar circles and the Tropics

14. Your task Look at the defining characteristics of the 6 major air masses. This will be done by completing the “Characteristics of Air Masses” chart You will then look at cloud formation along fronts Complete the “cloud development in fronts” diagram and associated questions on handout Additional questions: 1. Explain a mid-latitude storm. 2. Why are storms more common in the mid-latitudes than elsewhere? 3. Explain the differences between continental and maritime air masses. 4. Explain the role of convections currents and the rotation of the Earth in the development of a storm. 5. Explain how studying jet streams could help long-range weather forecasting. All info is found in Chapter 16, pages 262-268