Ch 15Atmospheric Circulation and Weather Systems — Class 11 Geography, concept-first.

The story of this chapter begins where the previous one ended. Chapter 8 showed you that the sun does not heat the earth evenly — some regions get far more energy than others.

We live at the bottom of an ocean of air, and that air presses on everything — including our bodies — all the time.

In the lower atmosphere, pressure does not stay constant as you go up — it falls off quickly with height.

The atmosphere presses down on everything with a force we call pressure, but that pressure is not the same everywhere.

The pressure we feel at the surface is not uniform across the globe. If you could strip away the effect of altitude and look at pressure at sea level everywhere, you would find a pattern of alternatin…

The air is set in motion because of differences in atmospheric pressure, and that moving air is what we call wind. Wind blows from regions of high pressure to regions of low pressure.

The atmosphere is not a uniform blanket of air. Pressure varies from place to place, and wherever it varies, the atmosphere tries to correct that imbalance.

Friction is the force that resists the motion of air as it moves across the Earth's surface. Its most direct effect is on wind speed — it slows the wind down.

The Earth’s rotation is the hidden hand behind the wind’s path. Air does not move in a straight line from high pressure to low pressure; it is bent sideways by a force that exists only because the pla…

The wind you feel at the surface is the net result of several forces acting together. Its velocity and direction depend on which forces dominate.

The general circulation of the atmosphere is the grand, planet-wide pattern of winds that results from a few fundamental controls.

The general circulation of the atmosphere is not a fixed, permanent machine. It responds to the changing position of the Sun, which shifts the belts of maximum heating, pressure, and wind throughout t…

Local winds are born out of the everyday or seasonal differences in how the Earth's surface heats and cools.

An air mass is simply a very large volume of air that has taken on the character of the place where it has been sitting.

When two different air masses meet, they do not mix readily. Instead, the boundary zone between them is called a front. The process by which fronts form is known as frontogenesis.

The systems that develop in the mid and high latitudes, beyond the tropics, are called middle latitude or extra tropical cyclones.

Tropical cyclones are among the most violent and destructive weather systems on Earth. They are born over warm tropical oceans, travel toward coasts, and unleash their fury through ferocious winds, to…

Thunderstorms and tornadoes belong to a family of severe local storms — short-lived, confined to small areas, yet intensely violent.