10,000km 6214mi Exosphere 600km 372mi Air Pressure In the atmosphere air molecules have weight Scientists measure air pressure with a tool called a barometer Areas with more molecules have denser or heavier air We call them high pressure areas Air with fewer less dense molecules is a Thermosphere Shuttle low pressure area Aurora 62mi 100km Kármán line 60 85km 37 53mi Mesosphere Meteors On a weather map L represents a low pressure area while H represents a high pressure area 15 50km 9 31mi Stratosphere Hot Air Balloon 0-15km 0 9mi The Atmosphere The atmosphere is the layer of gases that surrounds Earth The atmosphere is primarily nitrogen 78 percent and oxygen 21 percent The atmosphere contains small amounts of other gases such as carbon dioxide and water vapor The atmosphere reaches about 372 miles 600 kilometers from the Earth's surface The layers closest to the surface are where weather happens that we experience Troposphere Mount Everest The atmosphere is divided into five basic layers
Wind You cannot see it but you can feel it Air moves from high pressure areas toward low pressure areas The greater the difference in pressure the faster the air moves People describe wind by its direction and speed Wind direction is the direction from which the wind blows Winds also have different speeds The Beaufort Scale divides wind speeds into 12 different categories Calm winds move less than 1 mile per hour 1 6 kilometers per hour Hurricane force winds travel more than 73 miles per hour 118 kilometers per hour Moderate Breeze 1 1 3 mph 2 4 7 mph 3 8 12 mph 4 13 18 mph Gale Force 5 19 24 mph 7 32 38 mph 6 25 31 mph Storm Force 8 39 46 mph Hurricane Force 9 47 54 mph 10 55 63 mph 11 64 72 mph 12 73 mph Sir Francis Beaufort of England designed the Beaufort Scale in 1805 after observing the effects of wind
Clouds As wind blows into low pressure areas it forces air to move upward When warm air that contains water vapor rises it cools The cooling water vapor turns into tiny water droplets The water is not large or heavy enough to fall to Earth These droplets combine with particles of dust in the atmosphere to form clouds Sometimes a cloud turns gray or black This happens because the cloud becomes so dense that sunlight cannot pass through it The Rain Cycle cooling water vapor forms clouds precipitation warm air rises
Precipitation When the water in clouds becomes too heavy it falls to the Earth as precipitation Precipitation can be rain snow sleet or hail Rain is liquid water that falls from clouds On the way down tiny raindrops collect more water and grow larger until they splat on the Earth's surface Sometimes liquid rain freezes as it falls and becomes sleet When the air temperature is cold snow falls Snow forms when cold air makes water vapor turn directly from a gas into solid ice particles Hail forms in thunderstorm clouds Hailstones grow larger as drops of cold water hit them and freeze When the icy balls become too heavy they fall to the Earth as hailstones Hail Formation Hail too large for cloud to hold falls to Earth causing strong cold downdraft Hail growing in circulating convection currents Freezing Level Did You Know Raindrops being sucked into the updraft The largest recorded hailstone weighed more than 1 5 pounds 0 7 kilograms A faster updraft will cause hailstones to grow larger
