ACTIVITY 8.1 The basic principles of air movement (Individual) 1. Refer to Figure 8.1b. Explain why low pressure is found at the equator and high pressure is found at the poles. 2. Identify 4 differences between a low pressure and a high pressure cell in the Southern hemisphere. 3. Describe how a low pressure cell in the Southern hemisphere will differ from one in the Northern hemisphere.

Below is one way to approach the answers for Activity 8.1 on the basic principles of air movement. Note that some wording may vary, but the key ideas below should guide your answers. ────────────────────────────── 1. Explain why low pressure is found at the equator and high pressure is found at the poles. • At the equator, the Sun’s rays are more direct, and solar heating is stronger. This heating warms the surface and the adjacent air, causing the air to become lighter (less dense) and to rise. As the upward moving air leaves behind less air near the surface, a region of relatively low pressure is created. • At the poles, the incoming solar energy is much weaker because of the lower sun angle and greater reflectivity from ice or snow. The cooler temperatures cause the air to become denser, and this denser, cold air sinks back toward the surface. This sinking creates a buildup of air and results in relatively high pressure. ────────────────────────────── 2. Identify 4 differences between a low pressure and a high pressure cell in the Southern hemisphere. • Circulation Direction:   – Low Pressure: In the Southern hemisphere, the air around a low pressure area circulates counterclockwise (cyclonic circulation).   – High Pressure: In contrast, the circulation around a high pressure area moves clockwise (anticyclonic circulation). • Surface Wind Flow:   – Low Pressure: Winds converge toward the center of the low, promoting upward motion.   – High Pressure: Winds diverge from the center of a high, which generally leads to sinking air. • Vertical Air Movement:   – Low Pressure: Air is rising. This rising motion can lead to cloud formation and precipitation.   – High Pressure: Air is descending. The downward motion tends to inhibit cloud formation, often resulting in clear skies. • Weather Conditions:   – Low Pressure: Associated with unsettled, stormy, or rainy weather due to the rising and cooling of moist air.   – High Pressure: Generally associated with more stable, dry, and clear conditions because the descending air suppresses cloud formation. ────────────────────────────── 3. Describe how a low pressure cell in the Southern hemisphere will differ from one in the Northern hemisphere. • Rotation (due to the Coriolis Effect):   – In the Southern hemisphere, the Coriolis effect causes the winds around a low pressure cell to be deflected to the left relative to their direction of motion. This means that the cyclonic (counterclockwise) circulation in the Southern hemisphere is the opposite of what is observed in the Northern hemisphere.   – In the Northern hemisphere, the deflection is to the right, resulting in a cyclonic (counterclockwise) circulation as well—but note that the mechanism of deflection operates with opposite handedness relative to the hemisphere, leading to mirror-image behaviors when comparing identical pressure systems in the two hemispheres. • Symmetry in Size and Intensity (Generally speaking):   – While the fundamental physics is the same (rising warm air at the center), low pressure cells can sometimes differ in their size, intensity, and the extent of associated weather systems due to differences in regional factors (e.g., land–sea contrasts). However, the most distinct difference between hemispheres is the direction of rotation that results directly from the Coriolis force. In summary, although both hemispheres feature low pressure cells that form where warm air rises, the Coriolis force causes them to rotate in mirror-image directions relative to each other (counterclockwise in both cases but with different deflection mechanisms), and their associated surface wind patterns reflect this difference. ────────────────────────────── These explanations and comparisons should help you answer Activity 8.1 by addressing the key physical processes: solar heating, air density changes (rising warm air versus sinking cold air), and the influence of the Coriolis force on wind patterns in different hemispheres.