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Science in Focus: Shedding Light: Highlights

Workshop 8

rotational motion and forces | air pressure | global warming | how raindrops are formed

Rotational Motion and Forces

This basic convection cycle of equator-to-pole-to-equator is affected by the constant rotation of Earth. The rotating solid Earth slides under the gaseous atmosphere as the air moves between the poles and equator. When looking down on the north pole, the Earth rotates counterclockwise and the air appears to curve in a clockwise direction. When looking down on the south pole, the Earth rotates clockwise and the air appears to curve in a counterclockwise direction. This is known as the Coriolis Effect after Gaspard G. de Coriolis (1792-1843), French mathematician. This is the second major factor affecting winds.

Air Pressure

Warm air moves away from the Earth. Rising warm air creates a low atmospheric pressure area on the Earth's surface. Cool air sinks toward the Earth creating a high atmospheric pressure area. These pressure differences or "pressure gradients" drive wind. The greater the pressure difference the greater the wind speed.


Global Warming

Since the late 1700's, the beginning of the industrial revolution, the burning of fossil fuels has increased the concentration of carbon dioxide in the atmosphere by about 30 percent. Green plants and the oceans can remove some carbon dioxide. Carbon dioxide and other greenhouse gases absorb some of the radiation from the Earth that would otherwise be radiated to space, resulting in global warming. In the past 120 years, most scientists agree that the Earth's mean temperature has increased 0.6 degrees Celsius.

Global warming from the greenhouse effect causes the atmosphere to carry more moisture, leading to an enhanced water cycle with more severe storms. More moisture in the air causes increased global warming since water vapor (like carbon dioxide) is a "greenhouse" gas.

Although there is no doubt that humans influence the Earth, details of the extent of that influence on the Earth's climate are fiercely debated by researchers and politicians. However there is little doubt that climate change is happening now and more will occur in the future.

How Raindrops are Formed

There is still some disagreement over the mechanism that forms raindrops. We do know that a cloud is composed of millions of tiny droplets of water and it has been estimated that one raindrop is the result of about one million of these tiny droplets uniting. How do the tiny droplets unite? To cause the tiny droplets to unite, it is thought that clouds contain some larger droplets. As these larger cloud droplets swirl around within the cloud, they collide with and capture the tiny droplets, growing in size until a raindrop is formed. Where do the larger cloud droplets come from? One suggestion is that larger cloud droplets form when water vapor condenses around particles in the air such as salt crystals. (Salt crystals enter the air when sea-spray evaporates). Another mechanism might be that the tiny cloud droplets condense on ice crystals in the tops of tall thick clouds. As the crystals grow they descend, melt, and form the larger cloud droplets from which a raindrop forms.

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