Chapter 15 Notes (from Power Point)
• Weather & Climate
• Water in the Air
• Weather = condition of the atmosphere at a certain time & place.
• Condition of the atmosphere is affected by the amount of water in the air.
• Water in the Air
• The Water Cycle = the movement of water between the atmosphere, the land, and the oceans.
• Condensation = water vapor changes from a gas to a liquid. Clouds form in the process.
• Precipitation = rain, snow, sleet, or hail that falls from clouds to earth’s surface.
• Runoff = water that flows over land & into rivers, streams, & eventually the ocean.
• Evaporation = liquid water changes into water vapor (gas).
• Water in the Air
• Humidity = the amount of water vapor in the air.
• Humidity depends on the rates of evaporation & condensation.
• Evaporation increases as temperature increases.
• Vapor pressure = part of the total atmospheric pressure that is caused by water vapor.
• Vapor pressure increase, then condensation increases.
• When evaporation = condensation rate = air is saturated with water molecules.
• Temperature at which this happens is called dew point.
• At temp below the dew point, liquid water droplets form on a surface or tiny particles in the air.
• Water in the Air
• Relative Humidity = the ration of the amount of water vapor in the air to the amount of vapor needed to reach saturation at a given temp.
• It’s a measure of how close the air is to the dew point.
• Formula: actual water vapor content (g/m^3)/ saturation water vapor content (g/m^3) x 100 = Relative Humidity (%).
• Water in the Air
• Measuring Relative Humidity:
• Measure with humidity sensor (with thin film polymer).
• Thin film polymer in sensor absorbs water vapor as the relative humidity in the air rises.
• Thin film polymer releases water vapor as relative humidity drops.
• As the amount of water on film changes, the electrical properties of the film change & is converted to a humidity reading.
• Other ways to measure: hair hygrometers, dew cells, & psychrometers.
• Water in the Air
• Condensation = the process by which a gas (such as water vapor) becomes a liquid.
• Dew point condensation:
• Example: cup of ice
• By conduction, the glass cup absorbs heat from the air.
• Result: the temp. of air next to the glass drops below the dew point.
• As condensation rate exceeds evaporation rate, water droplets form on the glass.
• Water in the Air
• Reaching the dew point:
• When air is nearly saturated, only a small temp drop is needed for air to reach its dew point.
• During night, various things (grass, leaves) loose heat.
• Air may cool below dew point when air touches these cold surfaces.
• Water droplets form, called dew.
• Water in the Air
• Clouds & Precipitation:
• Clouds form as air rises & cools.
• When the air cools below the dew point, water droplets or ice crystals form.
• Types of Clouds:
• Classified by their shape & their altitude.
• 3 types: stratus, cumulus, & cirrus clouds.
• 3 altitude groups: low clouds (0-2,000m), middle clouds (2,000-6,000m), and high clouds (above 6,000m).
• Water in the Air
• Precipitation:
• In clouds, when a water droplet reaches a certain size, it falls as precipitation.
• Precipitation = water, in any form, that falls to earth’s surface from the clouds.
• 4 types of precipitation: rain, sleet, & hail.
• Fronts & Weather
• Air mass= a large body of air that has similar temp & moisture content throughout.
• Fronts = when a warm air mass & a cold air mass meet, warm air generally rises.
• Front = an area in which 2 or more air masses meet.
• Cold fronts = where air moves under warm air.
• Warm air is less dense, the cold air pushes the warm air up.
• Warm fronts = when warm air moves over cold, denser air that is leaving the area.
• Bring drizzly rain.
• Followed by clear, warm weather.
• Fronts & Weather
• Occluded fronts = forms when a warm air mass is caught between 2 colder air masses.
• Cool temps
• Large amounts of rain & snow.
• Stationary fronts = forms when a cold air mass & a warm air mass move toward each other.
• Warm air mass is commonly forced over the cold air mass.
• Many days of cloudy, wet weather.
• Fronts & Weather
• Air Pressure & Weather:
• Differences of pressure cause changes in the weather.
• Cyclone = an area that has a lower air pressure than the areas around it.
• Air rises.
• As air in the center of a cyclone rises, air cools.
• Clouds form & may cause rainy & stormy weather.
• Areas of high pressure are called anti-cyclones.
• Are areas where air sinks.
• As air sinks, it gets warmer & relative humidity decreases.
• Result: sinking air brings dry, clear weather.
• Fronts & Weather
• Thunderstorms = an intense local storm that forms strong winds, heavy rain, lightning & thunder.
• Conditions to have thunderstorms: warm & moist air near earth’s surface & unstable atmosphere.
• Lightning = an electric charge that happens between a positively charged area & a negatively charged area.
• Thunder = sound caused by the fast expansion of air along the lightning strike.
• Tornadoes = a rapidly, spinning column of air with high wind speeds & low central pressure that touches the ground.
• Fronts & Weather
• Hurricanes = a large, rotating tropical weather system that has wind speeds at least 120km/hour.
• Most powerful storms on earth.
• Where hurricanes form:
• Usually over warm, tropical oceans.
• At higher latitudes, the water is too cold for hurricanes to form.
• Fronts & Weather
• How hurricanes Form:
• Gets energy from evaporation & condensation of water vapor.
• Once formed, hurricanes are fueled through contact with warm ocean water.
• Heat formation causes ocean water to evaporate.
• Evaporation adds moisture of the warm air.
• As warm, moist air rises, the water vapor condenses & releases large amounts of energy.
• Fronts & Weather
• Effects of severe weather:
• Hail, lightning, high winds, tornadoes, & flash floods area all part of severe weather.
• Storms cause crop & car damage, break windows.
• Lightning starts forest fires & can kill/injure people/animals each year.
• Winds/tornadoes can uproot trees & destroy homes.
• Floods = millions $$ property damage.
• Storm surge = rise in sea level that forms in the ocean during a storm- crashes onto shore, endangering lives, & property damage.
• Fronts & Weather
• Severe Weather safety:
• During severe weather, listening to local radio or TV stations are important.
• Safe to stay indoors & way from windows.
• In some situations, you need to evacuate.
• During a flood warning, you need to move to higher ground.
• What is Climate?
• Climate vs. Weather:
• Weather = the condition of the atmosphere at a certain time.
• Conditions change from day to day.
• Climate = describes average weather conditions in an area over a long period of time.
• Described by 2 factors: temp & amount of precipitation.
• What is Climate?
• Factors that affect climate:
• Climate is determined by temperature & precipitation.
• Factors that affect temp & precipitation:
• Latitude, wind patterns, locations of mountains & large bodies of water & nearness to ocean currents.
• Solar energy & latitude:
• Latitude = the distance north or south from the equator.
• The sun’s rays strike the earth’s surface at different angles because earth’s surface is curved.
• At equator, more direct sunlight & warmer temperatures.
• What is Climate?
• Global Circulation & Wind:
• Uneven heating of earth’s surface – differences in air pressure – wind blows from area of high to low pressure.
• Winds affect precipitation that a region receives.
• Winds may carry evaporated water away from ocean surface.
• The water vapor that is carried to other places where it may condense & fall as precipitation.
• What is Climate?
• Topography = the sizes & shapes of the land surface features of a region.
• Elevation = the height of surface landforms above sea level.
• High elevations = temperature of air is lower.
• As elevation increases, temperature decreases.
• Rain-shadow effect = as air rises to pass over a mountain, the air cools. As a result: clouds form & precipitation may fall.
• What is Climate?
• Proximity to large bodies of water:
• Large bodies of water (such as the ocean) can influence an area’s climate.
• Water absorbs & releases heat more slowly than land does.
• Ocean currents:
• Surface currents = are stream-like movements of water at or near the surface of the ocean.
• The surface temperature of the water affects the temperature above it.
• Ie: warm currents heat the surrounding air & cause warmer air temperatures.
• What is Climate?
• Climates of the world:
• Plants & animals that area adapted to 1 climate would not be able to live in another climate.
• Climate & zones:
• 3 zones: tropical, temperate, & polar.
• Zones based on latitude.
• Tropical = high temp & located in equatorial region.
• Temperate = lower temp than the tropical zone.
• Polar zone = coldest climate zone.
• Various climates in each zone due to differences in: topography, winds, ocean currents, & geography.
• Changes in Climate
• Ice Ages:
• Ice Age = period during which ice forms in high latitudes & moves toward lower latitudes.
• During ice age, there are periods of cold & periods of warmth.
• Called glacial & interglacial periods.
• Glacial periods = large sheets of ice advance – they get bigger & cover a larger area – large amount of ocean water is frozen – sea level drops.
• Changes in Climate
• Causes of climate change:
• Changes in earth’s orbit
• Tilt of axis.
• Movement of tectonic plates
• Suns cycle
• Asteroid impacts
• Human activity
• Volcanic eruptions
• Changes in Climate
• Changes in earth’s orbit & tilt:
• During ice age- temperature alternates between cold & warm.
• 3 factors change or intensity of solar radiation received by earth (orbit, tilt, wobble).
• As a result, these factors affect climate.
• Changes in Climate
• Plate Tectonics:
• A continent’s location relative to the equator & poles determines how much solar radiation the continent receives.
• A continents location deflect ocean currents & winds influence climate.
• When continents move, the flow or air & moisture around the globe changes – this causes changes in climate.
• The Sun’s Cycle:
• Variations in the amount of energy cause slight changes in earth’s climates.
• Sun produces low percentage, high energy radiation or low energy radiation.
• Changes in Climate
• Asteroid Impacts:
• Asteroid = small, rocky object that orbits the sun.
• Rock slams into earth – debris (dust & smaller rocks) shoots into the atmosphere.
• Debris blocks sunlight reaching earth’s surface – lowers temps – change climate.
• Reduced light for plants.
• Volcanic eruptions: send out large amounts of dust, ash, & smoke –covers the sun- solar energy cannot reach earth’s surface.
• Changes in Climate
• Human Activity:
• Global warming = a gradual increase in the average global temperatures.
• Caused by increases in carbon dioxide.
• Burning fossil fuels & trees increases carbon dioxide in atmosphere.
• Plants use CO2 to make food: removing plants also increases CO2 in air.
• Changes in Climate
• Global Warming:
• Greenhouse effect = earth’s natural heating process, in which gasses in the atmosphere absorb thermal energy.
• Suns rays radiating through your car window. Car seats & surfaces absorb radiation (sun’s energy) & reradiate that energy as heat. Car windows stop most of the heat from escaping – inside gets hot.
• The greenhouse effect on earth:
• Earth (instead of car glass) stops heat from escaping & gasses (such as CO2) absorb the heat. Result: heat stays in the atmosphere & keeps earth warm.
• Changes in Climate
• Consequences of global warming:
• Global temps rise – icecaps melt- raises sea level – flood low lying areas (coasts).
• Places will receive little rain (deserts) because of increased evaporation.
• Changes in weather patterns could harm crops & in some areas & improve farming in other areas.
• What humans can do:
• Industrial practices being monitored.
• Community projects to rainforest areas.
• People can help reduce CO2 in atmosphere caused by pollution.
• Use less electricity, use vehicles less so less burning of fossil fuels.