CHAPTER ONE Elements of Weather Look out the window Is it sunny or cloudy hot or cold Every day people ask about weather Weather is how we describe the events in the atmosphere that happen each day The weather may be cloudy rainy or snowy Weather can change each hour day or season It may rain in the morning and then become sunny in the afternoon U S Winter Outlook Temperature Cooler 40 Cooler 33 33 40 50 Warmer 40 389 Emprar Protability Doc Jan Feb A weather map shows the likelihood of regions experiencing a colder or warmer season winter
The Sun does not heat the Earth evenly Areas where the Sun's rays are most direct like the equator become hot for most of the year Areas like the poles that receive more indirect rays are colder for most of the year The unequal heating from the Sun puts the Earth's atmosphere in motion Hot air is lighter and rises Cold air is heavier and sinks The air warms at the equator then rises and starts to move toward the poles At the poles the cooler dense air sinks and moves back toward the equator where it replaces the warm air and the cycle begins again This exchange of warm and cold air affects weather
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
