Causes of Weather PDF

12/23/2024 Chapter 12 Section 1 & 2 What is the difference between weather and climate? 1  12/23/2024 How d...

12/23/2024 Chapter 12 Section 1 & 2 What is the difference between weather and climate? 1  12/23/2024 How do high- and low-pressure systems differ? What is meteorology? Meteorology is the study of atmospheric phenomena. The root word of meteorology is the Greek word meteoros, which means high in the air. Copyright © McGraw-Hill Education The Causes of Weather 2  12/23/2024 What is meteorology? Weather versus climate Short-term variations in atmospheric phenomena that interact and affect the environment and life on Earth are called weather. Climate is the long-term average of variations in weather for a particular area. Copyright © McGraw-Hill Education The Causes of Weather Heating Earth’s Surface Imbalanced heating One reason that temperatures may vary from location to location at a certain time of year is that Earth’s axis of rotation is tilted relative to the plane of Earth’s orbit. Copyright © McGraw-Hill Education The Causes of Weather 3  12/23/2024 Heating Earth’s Surface Imbalanced heating Solar radiation is unequal partly due to the changing angle of incidence of the sunlight. The greater the area covered by solar radiation, the smaller the amount of heat per unit of area. Copyright © McGraw-Hill Education The Causes of Weather Heating Earth’s Surface Thermal energy redistribution The constant movement of air redistributes thermal energy around the world. Weather—from thunderstorms to large-scale weather systems—is part of the constant redistribution of Earth’s thermal energy. Copyright © McGraw-Hill Education The Causes of Weather 4  12/23/2024 Air Masses An air mass is a large volume of air that has the same characteristics, such as humidity and temperature, as its source region. A source region is the area over which an air mass forms. Copyright © McGraw-Hill Education The Causes of Weather Air Masses Types of air masses The origins of maritime tropical air are tropical bodies of water. The southwestern United States and Mexico are the source regions of continental tropical air, which is hot and dry, especially in summer. Copyright © McGraw-Hill Education The Causes of Weather 5  12/23/2024 Air Masses Types of air masses Maritime polar air masses form over the cold waters of the North Atlantic and North Pacific. Continental polar air masses form over the interior of Canada and Alaska, and carry frigid air southward in the winter. Earth’s ice- and snow-covered surfaces above 60° N latitude in Siberia and the Arctic Basin are the source regions of arctic air masses. Copyright © McGraw-Hill Education The Causes of Weather Air Masses Air mass modification When an air mass travels over land or water that has characteristics different from those of its source region, the air mass can acquire some of the characteristics of that land or water and undergo modification. Copyright © McGraw-Hill Education The Causes of Weather 6 12/23/2024 7  12/23/2024 Air Masses Air mass modification As the cold, continental polar air moves over the warmer Great Lakes, the air gains thermal energy and moisture. This modified air cools as it is uplifted and produces lake-effect snows. Copyright © McGraw-Hill Education The Causes of Weather Global Wind Systems The directions of Earth’s winds are influenced by Earth’s rotation. This Coriolis effect results in fluids and objects moving in an apparent curved path rather than a straight line. Copyright © McGraw-Hill Education Weather Systems 8  12/23/2024 Global Wind Systems The directions of Earth’s wind systems, such as the polar easterlies and the trade winds, vary with the latitudes in which they occur. Copyright © McGraw-Hill Education Weather Systems Global Wind Systems Polar easterlies The polar easterlies are the wind zones between 60° N latitude and the north pole, and 60° S latitude and the south pole. Copyright © McGraw-Hill Education Weather Systems 9  12/23/2024 Global Wind Systems Prevailing westerlies The prevailing westerlies are the wind systems on Earth located between latitudes 30° N and 60° N, and 30° S and 60° S. Copyright © McGraw-Hill Education Weather Systems Global Wind Systems Trade winds Between latitudes 30° N and 30° S are two circulation belts of wind known as the trade winds. Near latitudes 30° N and 30° S, the sinking air associated with the trade winds creates an area of high pressure. This results in a belt of weak surface winds called the horse latitudes. Copyright © McGraw-Hill Education Weather Systems 10  12/23/2024 Global Wind Systems Trade winds Trade winds from the North and the South meet and join near the equator. The air is forced upward, which creates an area of low pressure. This process, called convergence, can occur on a small or large scale. Near the equator, it occurs over a large area called the intertropical convergence zone (ITCZ). Copyright © McGraw-Hill Education Weather Systems Jet Streams A large temperature gradient in upper-level air combined with the Coriolis effect results in strong westerly winds called jet streams. A jet stream is a narrow band of fast, high-altitude, westerly wind. Copyright © McGraw-Hill Education Weather Systems 11  12/23/2024 Jet Streams Weather in the middle latitudes is strongly influenced by fast-moving, high- altitude jet streams. Copyright © McGraw-Hill Education Weather Systems Jet Streams Types of jet streams The major jet streams, called the polar jet streams, separate the polar easterlies from the prevailing westerlies. The minor jet streams are the subtropical jet streams. They occur where the trade winds meet the prevailing westerlies. Copyright © McGraw-Hill Education Weather Systems 12  12/23/2024 Jet Streams Jet streams and weather systems Storms form along jet streams and can generate large-scale weather systems. Jet streams affect the intensity of weather systems by moving air of different temperatures from one region of Earth to another. Copyright © McGraw-Hill Education Weather Systems Fronts A collision of two air masses forms a front—a narrow region between two air masses of different densities. Copyright © McGraw-Hill Education Weather Systems 13  12/23/2024 Fronts Cold front When cold, dense air displaces warm air, it forces the warm air, which is less dense, up along a steep slope. This type of collision is called a cold front. Copyright © McGraw-Hill Education Weather Systems 14  12/23/2024 Fronts Warm front Advancing warm air displaces cold air along a warm front. A warm front develops a gradual boundary slope. Copyright © McGraw-Hill Education Weather Systems Fronts Stationary front When two air masses meet but neither advances, the boundary between them stalls. This stationary front frequently occurs between two modified air masses that have small temperature and pressure gradients between them. Copyright © McGraw-Hill Education Weather Systems 15  12/23/2024 Fronts Occluded front Sometimes, a cold air mass moves so rapidly that it overtakes a warm front and forces the warm air upward. As the warm air is lifted, the advancing cold air mass collides with another cold air mass that was in front of the warm air. This is called an occluded front. Copyright © McGraw-Hill Education Weather Systems Pressure Systems Sinking or rising air, combined with the Coriolis effect, results in the formation of rotating high- and low-pressure systems in the atmosphere. Copyright © McGraw-Hill Education Weather Systems 16  12/23/2024 Pressure Systems Low-pressure systems In surface low-pressure systems, air rises. When air from outside the system replaces the rising air, this air spirals inward toward the center and then upward. Copyright © McGraw-Hill Education Weather Systems Pressure Systems High-pressure systems In a surface high-pressure system, sinking air moves away from the system’s center when it reaches Earth’s surface. Copyright © McGraw-Hill Education Weather Systems 17  12/23/2024 Pressure Systems In the northern hemisphere, winds move counterclockwise around a low- pressure center, and clockwise around a high-pressure center. Low-pressure center High-pressure center Copyright © McGraw-Hill Education Weather Systems Down and away Part one – Watch and Describe the video – Fill out worksheet Part two – Groups of 2 – Graph and answer the question 18