Weather

Introduction

The sun is everything.  Its light, heat, and energy keep us and every other living thing on earth alive.  It makes our planet livable. 

The sun makes energy through nuclear processes.  It converts hydrogen into helium through nuclear fusion, and as the particles of hydrogen fuse together to make the helium, enormous amounts of energy are released. The sun converts more than 700 million tons of hydrogen into more than 600 million tonss of helium energy every second.  This sun-created radiant energy provides the earth with heat and light.

The weather and climate of the earth depend upon the sun.  Weather is what happens in the atmosphere around us every day. Climate is a pattern of weather that repeats itself over a long period of time. The heat energy of the sun causes changes in the density of the atmosphere. When air is warmed by the sun, it expands.  The molecules in warm air move faster than the molecules in cold air.  The molecules in warm air are also farther apart and more spread out and so they occupy more space which makes warm air less dense.  Cold air is denser than warm air.  Its molecules are closer together and take up less space.  Air always flows from high density to low density.  In other words, colder, densely packed molecules always flow to areas where the molecules are further apart and less crowded like the air rushing out of a balloon. Changes in the density of air and water are key factors in weather.

The sun does not heat the earth evenly. Because of the tilt of the earth, the sun’s rays shine more directly around the equator, and so it is warmer.  The extreme northern and southern parts of the earth near the poles receive the rays of the sun at a slant which makes them much colder.  The heat energy of the sun makes warm air rise because it is less dense, and then cooler, denser air rushes in to take its place. This movement of air is wind.  The heat energy from the sun is the driving force of the water cycle.  Heat energy from the sun causes water in oceans, lakes, and rivers to evaporate, and it becomes water vapor.  As the water vapor rises, it cools and condenses which turns it back into liquid water in the form of water droplets.  These droplets form clouds and eventually fall as rain because of the pull of gravity. The cycle then begins again.

The earth’s atmosphere is important to the overall functions of the earth’s cycles of life.  It’s a good regulator.  It prevents too much sunlight from reaching the ground; it lets in just the right amount of sunlight to keep life on earth flourishing.  When sunlight (heat energy) heats the different surfaces of the earth, some of that heat then bounces back into the atmosphere.  The greenhouse gases in the atmosphere absorb some of that heat and prevent most of it from floating back into space; these gases keep just enough heat to provide a good balance for the earth.  This is called the greenhouse effect, and it is beneficial to life on earth.  The greenhouse gases include water vapor, methane, nitrous oxide, ozone, and carbon dioxide.  Carbon dioxide does most of the work in the greenhouse effect and makes sure that the earth has the right amount of heat to create the necessary climates to support life.