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Earth Science Chapter 16 and 17 Weather and Climate Goal Prediction z Old way – Groundhog – Color of the sky z Modern way – satellites – instruments – computers z Weather Factors Studied by meteorologists z Several factors influence the weather z Heat energy z air pressure z winds z moisture z Heat Energy Almost all the earth’s energy comes from the sun z Visible and invisible waves – Infrared and ultraviolet z As light hits the earth – some is reflected back into space by dust particles and water droplets – Some is absorbed in the atmosphere, in the ozone layer z Heat Energy Ozone layer protects us from dangerous ultraviolet radiation. z The energy that does hit the earth is converted to heat energy. z Heat is then spread through the atmosphere – Conduction – Convection – Radiation z Conduction Direct transfer of heat z From one molecule to the next z Air above the pavement is slightly hotter. z Not a big effect on the atmosphere z Convection Transfer of heat in a fluid z Heated air is less dense, it rises z Cooler air is more dense, it sinks z Makes convection currents in the atmosphere z Circular movement of air caused by uneven heating. z Big impact on the atmosphere z Radiation Transfer by waves z Energy transferred by infrared waves. z Infrared waves get trapped by carbon dioxide and other gases in the atmosphere z Called the greenhouse effect. z If there is too much carbon dioxide, the earth will warm up z affect the world’s weather z Variations of temperature Why are the tropics hot, and the poles cold? z The angle of the sun’s rays. z Near 90° at the equator z Becomes smaller as you get farther from equator closer to the poles z Measuring temperature Device is called a thermometer z As the temperature rises, liquid inside the bulb expands and rises up the thin tube. z Units are called degrees z Scientist use the Celsius scale z Water boils at 100 °C z Water freezes at 0 °C z Body temperature is 37 °C z Air Pressure Caused by air molecules hitting you. z We are at the bottom of a “sea” of air z We can feel the pressure of all that air above us z Dense air has more mass, so it causes a higher pressure z Three factors that influence air density and air pressure z Temperature Air expands as it is heated. z Higher temperature z lower density z less pressure z Water Vapor Water molecules have less mass than air molecules. z More water vapor z less mass z lower density z Less pressure z Moist air has lower pressure than dense air z Elevation Higher elevations air is thinner z fewer air molecules above z less dense z lower pressure. z We need to set a standard z Measure 1 atmosphere at 0°C at sea level z Barometer zAt one atmosphere pressure a column of mercury 760 mm high. Column of Mercury Dish of Mercury Another barometer An aneroid barometer z Airtight metal container z When the pressure changes, it expands or contracts and moves a needle. z Wind The movement of air z Caused by warm air rising, less dense, lower pressure z Cooler air sinking, more dense, higher pressure z Cooler air moves under warmer air. z Two types of winds – local – global z Local Wind Blow from any direction, over short distances z Sea breeze z During the day, land heats up faster z Warm air over land rises. z Cool air from over ocean or lake replaces z Air blows from the sea, called a sea breeze z Land Breeze During night z Land cools off faster z Warmer air over sea rises z Cooler air from the land replaces it z Wind is from land, called a land breeze z Winds are named by the direction they come from. z A northern wind comes from the north z Monsoon A major land or sea breeze z a seasonal wind z One part of the year the wind blows from the continent to the ocean z The rest of the year it blows from the ocean to the continent. z Makes for two seasons, rainy and dry z Global Winds Caused by unequal heating z Near the equator air is hot z At the poles it is cold z Air moves from the poles to the equator z Not directly north or south, because the earth rotates. z Coriolis Effect Apparent shift (or curve) in movement caused by the rotation of the earth z In the Northern Hemisphere they curve to the right z In the Southern Hemisphere they curve to the left. z Global Winds Doldrumsz At the equator the winds are calm z Caused by rising, low pressure, warm air z Problem for sailors z Horse latitudes- at 30° Latitude air from the equator cools and sinks z air is calm here z Horse Latitudes Doldrums Global Winds Trade winds z Some sinking air moves towards the equator z Makes steady winds from the east in the Northern hemisphere z From the east in the Southern Hemisphere z Usually weak winds z Global Winds Trade Winds Trade Winds Global winds Sinking air moves toward pole 40° to 60° z Bends to right in Northern Hemisphere z goes east z Prevailing Westerlies z Why our weather moves to east z Bends to left in Southern Hemisphere z goes east z Global Winds z Used by sailors to the New World and back Global Winds North and south of 60° the air flows from the poles then rises. z Turn right in the Northern Hemisphere z Polar Easterlies z Turn left in the Southern Hemisphere z Cold weak winds z Local winds may be different than global winds z Jet Streams Not Discovered until the 1940’s z High Pressure belts of air high in the atmosphere z Move from west to east at 180 to 350 kilometers per hour z Wander as they circulate z Can move weather systems z Measuring wind Use wind vane to measure direction z An anemometer to measure wind speed. z Rotating cups z Faster rotation, higher wind speed z Moisture Water vapor in the atmosphere is called humidity, z Comes from evaporation from oceans, lakes, rivers, soil, plants, animals z Varies from place to place z Higher temperature air can hold more moisture z Relative Humidity Comparing how much water vapor there is in the atmosphere to how much it could possibly hold. z Given as a percentage. z At 100% the air is saturated z As warm air is cooled, it can hold less, so it condenses out. z The temperature that water condenses out is called the dew point. z Clouds Form when moisture condenses on small particles of dust. z Clouds are tiny water droplets. z Categorized two ways z Shape z Altitude z Shape Cumulus - puffy, flat bottom good weather z Can turn into cumulonimbus clouds which produce thunderstorms. z Stratus- layer clouds, grey, light rain z Close to ground called fog z Turn into Nimbostratus which bring rain or snow z Shape Cirrus- Feather clouds at high altitudes z Ice crystals z Appear when the weather is clear but often are followed by rain or snow z Altitiude Stratus- Low level <2.5 km z Cumulus- Mid level 2-6 km z Cirrus- high level Higher than 6-12 km z Cumulonimbus clouds can rise to heights of 13 km z Cirrus Cirrostratus Cirrocumulus Altocumulus Stratus Stratocumulus Cumulus Cumulonimbus Precipitation Caused by water condensing in the clouds and falling to earth z Water droplets must get bigger to fall z Combine with other droplets z Raindrops are 1 million times bigger than cloud droplets z Gravity pulls them to earth z Sleet- rain freezes as it falls to earth z Other types Snow- moisture forms ice crystals as it condenses z Hail- chunks of ice formed in an updraft – Ice crystals form – falls through moisture – Wind blows it back up – Freezes and falls again – Repeats – Layers, up to 5 inches across z Measuring Precipitation Use a rain gauge z Straight sided, flat bottom container that fills up with water z Weather Patterns Weather is caused by large air masses z Areas with the same temperature and humidity z Continental- dry - low humidity z Maritime - wet - high humidity z Polar- cold z Tropical- hot z Four possibilities z Maritime Polar Forms over cold water z Causes fog in California z Maritime Tropical Forms over warm water z Hot humid days z Continental tropical Forms over Mexico z Dry hot air to Southwest z Continental Polar Forms over Canada z Very cold winter days z Fronts Where two air masses meet z Cold front when cold air replaces warm air z Warm front when warm air replaces cold air z Occluded front- when a cold front catches up with a warm front z Stationary front- no movement occurs when cold and warm air meet. z Cold Front Warm air rising cause violent thunderstorms z Clear cool days follow z Cold Air Warm Air Warm Front Warm Air Cold Air Warm Front Rain and showers are caused by warm fronts z Followed by hot humid days z Occluded Front Warm Air Cold Air Cold Air Occluded Front z Less violent weather than a cold front. Stationary Front Cold air meets warm air and no movement occurs z Rain can fall in the same place for days z Symbols Warm Front Cold Front Occluded Front Stationary Front Weather from Fronts Warm fronts form nimbostratus clouds z Cause steady rainfall that lasts for hours z or snow z Cold fronts can form cumulonimbus z Produce thunderstorms and hail z Cyclones An area of low pressure. z Warm air is rising z Wind spins around counter clockwise in the Southern Hemisphere z Cause stormy rainy weather z Anticyclones High pressure area z cold air sinks and spirals outward z Move in a clockwise direction in the Northern Hemisphere z Usually bring clear dry weather z Reading Maps Reading Maps Clear Cloudy Partly Cloudy West Wind East Wind Hurricanes A powerful cyclone z Forms over tropical oceans z Late summer or early fall z Warm moist air rises z Starts to spin, then spins faster z Forms a cylinder of strong winds around the center, which is calm z Called the eye z Hurricanes Wind speeds reach 120 to 320 km/hr z Lose energy when they hit land, but heavy rains and large waves cause damage z This year expect 21 named storms z 1 or 2 major z Tornadoes Whirling funnel shaped cloud z Develops inn cumulonimbus clouds z In the center of the funnel there is low pressure, which acts like a vacuum cleaner z Tornadoes over water are called water spouts z Winds can reach speeds of 350 km/hr z Predicting Weather Allows people to plan their days z Warns people of severe weather z Meteorologists interpret weather information from a variety of sources – observers – balloons – satellites – weather stations around the world z Predicting Weather Draw a weather map z use the symbols we have studied z Add curved lines called isotherms which connect areas with the same temperature z Other curved lines called isobars connect areas with the same pressure z Controlling the Weather Could save money and lives z Only success has come from “seeding” clouds z Sprinkling dry ice to condense moisture z or silver iodide to cool clouds enough to form crystals z Used to remove fog around airports z Or tried to increase the snow pack in the Sierras z
