Chapter 10 – Atmospheric Circulation and Weather Systems
- What is atmospheric pressure?
It’s the force exerted by the weight of air above a surface. Measured in millibars, it decreases with altitude and is crucial in determining wind patterns and weather. - How is atmospheric pressure measured?
Using a barometer. Standard sea-level pressure is 1013.25 mb. Mercury and aneroid barometers are commonly used instruments for measuring pressure changes. - What is wind?
Wind is the horizontal movement of air from high-pressure to low-pressure areas. It balances atmospheric pressure differences and plays a key role in weather formation. - What causes wind?
Winds are caused by pressure gradients, Earth’s rotation (Coriolis force), and friction. Solar heating creates pressure differences that initiate air movement. - What is the Coriolis force?
Due to Earth’s rotation, moving air deflects to the right in the Northern Hemisphere and to the left in the Southern Hemisphere, affecting wind direction. - What is the pressure gradient force?
It is the force that causes wind to blow from high-pressure to low-pressure areas. The steeper the gradient, the stronger the wind. - What are planetary winds?
Permanent winds like trade winds, westerlies, and polar easterlies that blow in specific directions throughout the year due to global pressure belts and Earth’s rotation. - What are trade winds?
Trade winds blow from the subtropical high-pressure belts towards the equator (tropical low), deflected westward due to the Coriolis force—northeast in the Northern Hemisphere. - What are westerlies?
Westerlies blow from the subtropical highs to subpolar lows. Found between 30° and 60° latitudes, they influence the weather of mid-latitudes. - What are polar easterlies?
Cold winds blowing from the polar highs towards the subpolar lows, deflected westward due to the Coriolis effect. They are dry and cold. - What are jet streams?
High-speed, narrow air currents found in the upper atmosphere. They influence weather patterns and are important for aircraft navigation. - What is the Inter-Tropical Convergence Zone (ITCZ)?
A low-pressure zone near the equator where trade winds from both hemispheres meet, causing heavy rainfall and thunderstorms due to rising moist air. - What is the monsoon?
A seasonal wind reversal caused by differential heating of land and sea. It brings heavy summer rains and dry winter winds, especially in South Asia. - What are local winds?
Winds that blow over small areas due to local pressure variations. Examples: land breeze, sea breeze, loo, chinook, and mistral. - What is a sea breeze?
During the day, land heats faster than sea. Air over land rises, and cooler sea air moves in to replace it—called a sea breeze. - What is a land breeze?
At night, land cools faster than the sea. Cooler air from land moves towards the warmer sea, forming a land breeze. - What is a cyclone?
A low-pressure system with inward-spiraling winds. In the Northern Hemisphere, they rotate counterclockwise; in the Southern Hemisphere, clockwise. They bring intense rainfall and storms. - What is an anticyclone?
A high-pressure system with outward-spiraling winds. They bring clear, dry weather and rotate clockwise in the Northern Hemisphere. - What are tropical cyclones?
Intense low-pressure systems over warm oceans. They bring heavy rain, strong winds, and storm surges. Known as hurricanes, typhoons, or cyclones depending on the region. - What are temperate cyclones?
Formed in mid-latitudes where warm and cold air masses meet. They are large systems affecting a wide area with rain, snow, and changing weather. - What are fronts?
Boundaries between two air masses of different temperatures and humidity. Types: cold front, warm front, stationary front, and occluded front. - What is a cold front?
A cold air mass pushes under a warm one, forcing it to rise rapidly, often causing thunderstorms, heavy rain, or snow. - What is a warm front?
A warm air mass gently rises over a retreating cold air mass, causing steady rain or drizzle over a wide area. - What is an occluded front?
Formed when a cold front overtakes a warm front, lifting the warm air completely. It brings complex weather patterns and precipitation. - What causes rainfall in a cyclone?
Warm, moist air rises in the low-pressure center, cools, condenses, and forms clouds and precipitation. Strong convection causes heavy rain and storms. - How do jet streams affect weather?
Jet streams steer weather systems, influence monsoons, and affect temperature changes by creating high and low-pressure zones. - What is the Hadley cell?
A tropical atmospheric circulation where warm air rises near the equator, moves poleward at high altitudes, descends at subtropical regions, and returns as trade winds. - What are Rossby waves?
Large-scale meandering of jet streams that influence weather by transporting warm and cold air masses over large distances. - What is the role of air pressure in weather systems?
Low pressure causes air to rise, leading to cloud formation and rain. High pressure leads to sinking air and clear skies. - Why is understanding atmospheric circulation important?
It explains weather systems, climate zones, wind patterns, and ocean currents, helping in forecasting, agriculture, aviation, and disaster preparedness.