Ch 35- Weather BIG IDEA: Weather has 6 elements: atmospheric pressure, temperature, wind, humidity, clouds, and precipitation

35.1 The Atmosphere Earth’s atmosphere= mix of gases (78% N. 21% O) and aerosols including dust, ash, pollen, pollution (~1%) Atmosphere provides gases required by living things, and an insulating blanket to protect us

Climate= general weather pattern of an area “Weather”= atmospheric pressure, temperature, wind, precipitation, cloudiness, and humidity Climate= general weather pattern of an area Air has weight, combined weight= atmospheric pressure The reason we don’t feel the crushing weight of the atmosphere is our bodies are used to it, and the pressure inside our bodies is equal to that of the surrounding air

Air pressure and air density decrease w/ increasing altitude

35.2 Structure of the Atmosphere 4 Atmospheric layers: 1. Troposphere: - lowest, where we live, where weather occurs. - In troposphere temp decreases w/ increasing altitude 2. Stratosphere: Next layer, contains ozone (O3), which absorbs UV rays to protect us. Temp increases w/ increasing altitude

3. Mesosphere: Gases don’t absorb much, cold layer 4. Thermosphere: Highest layer, absorbs lots of solar radiation, so very hot. Ionosphere= upper mesosphere + lower thermosphere containing ions (charged electrons) Ions+solar energy= aurora borealis (Northern lights)

Heating the Atmosphere Solar radiation: electromagnetic heat energy, given off by Sun On electromagnetic spectrum shorter wavelengths=higher frequency= more energy

Sun= ultimate source of energy Terrestrial radiation: solar radiation absorbed by ground to heat Earth’s surface, much is reflected back into atmosphere Greenhouse effect= Energy trapped in the atmosphere where greenhouse gases absorb and reemit solar energy many times before escaping into space. This build up causes increased temperatures The re-radiated energy bounced off by the ground has less energy than when it was incoming. The greenhouse effect is named after a florist’s greenhouse. Without the greenhouse effect life on Earth would be frigid. However, when too many greenhouse gases build up in the atmosphere Earth’s temperature rapidly increases, causing global warming.

35.3 Temperature Depends on Latitude Latitude (runs East West) + Longitude (runs North  South) determine location 0° latitude= prime meridian, 0° longitude= equator B/c of Earth’s shape the highest temps are @ the equator, which gets the most direct sunlight.

35.4 Why are there Seasons? Earth’s axis tilting toward/ away from Sun through the course of a year causes seasons * Whichever hemisphere is towards Sun =more direct sunlight, longer days, summer Summer in N, winter in S Summer in S, winter in N

35.5 Flow of Atmosphere-Wind Air moves from high pressure to low pressure Wind is air that flows horizontally from high to low pressure Bigger differences in air pressure= stronger, faster winds

35.6 Some Winds are local-others are global Local winds= pressure differences in small, short distances Global winds= Huge pattern of air circulation around the globe that go in the same direction * Global winds are produced by planet-scale pressure differences that occur b/c of unequal heating of Earth at the equator and poles

Unequal pressure of wind rising and sinking causes patterns called wind belts, which move air in predictable patterns Jet streams are narrow belts of high-speed wind that blow in the upper troposphere and lower stratosphere. * They don’t follow consistent paths, move fast, and their altitude and latitude vary

Coriolis effect The Coriolis effect is the tendency of moving bodies (like air and water) to move to the right in the Northern hemisphere and to the left in the Southern hemisphere. It is caused by Earth’s rotation on its axis

35.7 Ocean currents distribute heat Surface currents occur at the top of a body of water , and are created by global winds pushing water in certain directions -The patterns created by surface currents along w/ the Coriolis effect cause circular flow patterns called gyres Surface currents redistribute heat by taking water far from it’s source

Gulf stream warms the eastern coast of U. S Gulf stream warms the eastern coast of U.S. by bringing water from Mexico up along in a Northeast pattern

35.8 Water in the Atmosphere Water vapor in the atmosphere produces humidity, clouds, and precipitation Humidity- amount of water vapor in the air Amount depends on temp. (more w/ hot weather, less w/ cold)

Water vapor: High in atmosphere=clouds Condenses near ground= fog Condensing on surface when dew point is reached= dew Dew point is @ or below freezing= frost

Clouds are visible collections of billions of tiny water droplets or ice crystals Solid particles like smoke or dust need to be present for the droplets/crystals to condense on

3 types: Cirrus- thin/wispy, high elevation, indicate rain or snow coming Cumulus- “fair weather”, fluffy. Cumulonimbus are tall/dark, produce thunderstorms Stratus- flat, low altitude, may produce drizzle of rain

Precipitation is water in liquid or solid phase that returns to Earth’s surface from the atmosphere -Rain: most common, water falling @ above freezing temps -Snow: water vapor goes to solid state @ below freezing temps, produce 6 sided crystals called snowflakes! -Hail: forms in cumulonimbus clouds, forms from frozen water droplets condensing for a long time, until large hailstones are produced. Can be very damaging

35.9 Changing weather- Air masses, fronts, and cyclones Air mass- a large pool of air w/ similar temp and characteristics throughout. Have characteristics of where they were formed, but move by global winds Tropical=warm, polar= cold, continental=land, maritime=water Fronts- A boundary between air masses - Dense, cool air sinks, warm air rises

Whichever air mass displaces the other determine what type of front (cold front vs. warm front) Stationary front= neither air mass is moving

Cyclones: a low pressure weather system, associated w/ rough weather Cyclones: a low pressure weather system, associated w/ rough weather. Wind moves counterclockwise Anticyclone: high pressure, moves clockwise. Generally fair skies and no precipitation