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EARTH SCIENCE - B B.Miller Chapter 6 RUNNING WATER & GROUND WATER 6.1 Running Water The Water cycle ◦ The unending circulation of Earth’s water ◦ Water moves through solid, liquid & gas ◦ Infiltration: Movement of water into rock or soil ◦ Transpiration: Water released from plants during photosynthesis The Water Cycle Earth’s Water Balance This means, that overall precipitation equals the overall evaporation globally Streamflow Stream velocities range from 1-30 km/hr. Gradient: Slope or steepness of a stream gradient = velocity= erosion Channel Characteristics The shape, size and roughness of a stream channel can also affect the rate of flow. Discharge: The volume of water that passes by a certain point in a system Changes from Upstream to Downstream Streams are studied by their profiles Profile is a cross-sectional view from its source (beginning) to its mouth (end) Gradient decreases from the headwaters to the mouth of a stream The amount of discharge increases along a river, because the number of tributaries increase along the way. Tributaries: are smaller streams that drain into a stream along its path Base Level Defined: The lowest point to which a stream can erode its channel ◦ Ultimate Base Level: Ocean surface, it the lowest point that any stream can erode to ◦ Temporary Base Level: When a stream erodes to the surface of a lake or resistant rock layers 6.2 The Work of Streams Erosion ◦ Streams generally erode their channels ◦ The water moves particles by abrasion, grinding and by dissolving soluble materials Sediment Transport ◦ Streams transport sediment in 3 ways: 1. In solution (dissolved load) 2. In suspension (suspended load) 3. Scooting and rolling along the bottom (bed load) Dissolved Load Usually dissolved rock Expressed in ppm (parts per million) Suspended Load Visible cloud of sediment suspended in water Velocity during flooding increases and more suspended load is carried Bed Load Large pieces that are rolled along the stream bottom Competence Measure of the largest particles that a stream can carry Capacity The amount of load that a stream can carry Deposition Occurs when a stream flow slows and sediment drops out ◦ Deltas Sediment dropped at the end of a stream into a lake or ocean The velocity slows when reaching a larger body of water and drops its load ◦ Natural Levees Parallel ridges to a stream, that build up from past floods The sediment naturally piles up and creates a barrier to future floods. Yellow River Delta- Satellite Levee formation Stream Valleys Narrow Valleys (Ex:Yellowstone River) ◦ Characterized by steep sides ◦ Not much meandering ◦ No oxbow lakes Wide Valleys (Ex: Mississippi) ◦ Flat floodplain area ◦ Lots of weaving and winding ◦ Oxbow lakes left after flooding Oxbow lakes Floods & Flood Control Floods are caused by rapid snow melt, storms and heavy rainfall Ways to control flooding include: ◦ Artificial levees ◦ Flood control dams ◦ Limiting development Drainage basin: an entire area that drains into a river or river system 6.3 Water Beneath the Surface The amount of water that ends up underground depends on: 1. 2. 3. 4. Steepness of slopes Nature of surface materials Intensity of rainfall Type of and amount of vegetation Distribution: (location) Most water seeps down into the soil until it reaches the zone of saturation The Zone of Saturation is an area in the soil where water fills all the pore spaces in between the particles Movement ◦ Storage or movement of water depends on subsurface materials Porosity - % of soil or rock that consists of pore spaces Permeability – ability to release a fluid, and depends on pore sizes of soil and rock Springs A spring is a flow of groundwater that emerges naturally at ground surface ◦ Hot springs Water warmer by 6˚-9˚C, than the mean annual air temp. More than 1000 in the U.S. Most in the Western states ◦ Geysers An intermittent hot spring or fountain that shoots up with great force Columns of water 30-60 meters Most famous is Old Faithful in Yellowstone Nat. park Wells A hole bored into the zone of saturation Mostly for irrigation, some industrial and lastly some home use Artesian Wells ◦ Push water out of the hole on their own. Pressure is created along an aquifer Environmental Problems associated with Groundwater Overuse & contaimination Treating water as NON renewable: ◦ Groundwater seems endless, but we know there is a finite amount of freshwater on Earth ◦ There are intense shortages in areas with high irrigation rates (plains) ◦ Subsidence (shrinking of the surface) is occurring in areas of California Contamination: ◦ Runoff from farms and industrial areas, can allow chemicals and fertilizers to contaminate the ground water supplies. ◦ This is not a case of water shortage, but of clean water shortage. Chapter 15 OCEAN WATER & OCEAN LIFE 15.1 Composition of Water Salinity: ◦ Salt, total amount of dissolved solids in water Sources of Sea Salts Chemical weathering of rocks on the continents From Earth’s interior, volcanoes released chlorine, bromine, sulfur and boron when the oceans were formed 4 billion yrs. Ago. Processes Affecting Salinity Surface salinity 3.3-3.8% Precipitation, runoff, melting iceburgs – decrease it Evaporation & freezing – increases salinity Ocean Temperature Variation The ocean’s surface water temperature varies with the amount of solar radiation Temp variation with depth ◦ Generally warmer near the surface ◦ Thermoclines: (thermo=heat, cline=slope) A layer of ocean water 300-1000 m deep of rapid temp. change This is a barrier to many marine organisms Ocean Density Variation Density = mass per unit Factors affecting seawater density: ◦ Increase salinity = increase density ◦ Increase temperature = decrease density Pycnoclines (pycno=density, cline=slope) ◦ A layer of ocean water 300-1000m deep with rapid density change Water Density Demo http://youtu.be/Ak9CBB1bTcc Ocean Layering Surface Zone Nearly uniform temps. Extends ~300m Makes up 2% of all ocean water Transition Zone Below the surface zone and above the deep ocean zone Includes thermoclines and pycnoclines 18% of all ocean water Deep Zone Sunlight never reaches this zone Temps are just above freezing Density is very high 80% of the ocean water 15.2 Diversity of the Ocean Classification of Marine Organisms 1. Plankton (planktos=wandering) All organisms that drift Ex: algae, animals, plants and bacteria 2. Nekton (nektos=swimming) All animals capable of moving on their own Ex: Adult fish, squid, marine mammals, marine reptiles 3. Benthos (benthos=bottom) All organisms that live on or near the bottom Can be shallow or deep Ex: angler fish, crabs, sea stars Marine Life Zones 3 factors that divide ocean into 3 distinct zones: 1. Availability of sunlight 2. Distance from shore 3. Water depth 8 Ocean zones 1. Photic Zone 2. Intertidal Zone Upper part of the ocean; sunlight penetrates Euphotic zone, where photosynthesis occurs Narrow strip between high and low tides 3. Neritic Zone From the low tide mark outward to sea Entirely within the Photic Zone Rich in Biomass and diversity Supports 90% of commercial fisheries 4. Oceanic Zone Beyond the continental shelf Great depths of open ocean Lower in nutrients; low biodiversity 5. Pelagic Zone Open ocean of any depth Home to phytoplankton, zooplankton and nekton 6. Benthic Zone Seafloor organisms exist here Ex. Giant kelp, sponges, crabs, sea anemones, etc. Abyssal Zone Deep-ocean floor Extremely high pressure Low temps No sunlight Sparse life Hydrothermal vents Along the mid ocean ridge Super heated water, some >than 100˚C Supports organisms that live no where else Organisms rely on chemosynthesis for survival 15.3 Ocean Productivity Primary Productivity ◦ The production of organic compounds from the inorganic substances through photosynthesis or chemosynthesis Photosynthesis – uses light energy to convert water and carbon dioxide into glucose Chemosynthesis – Microorganisms create organic molecules from inorganic nutrients/minerals 2 factors that influence photosynthetic productivity: 1. The availability of nutrients 2. The amount of solar radiation (sunlight) Polar Oceans productivity Peaks in May, mostly of phytoplankton (diatoms and algae) The availability of solar energy, is what limits photosynthetic productivity in polar areas Tropical Ocean Productivity Typically low in open tropical ocean Sunlight is available in high supply all year, but there is no mixing of deep nutrient rich water and surface waters This thermocline keeps production low because of a lack of nutrients Temperate Ocean Productivity Productivity is controlled by both limiting factors (sunlight & nutrients) ◦ Winter Low production; low sunlight ◦ Spring Phytoplankton blooms; low nutrients; low productivity ◦ Summer Nutrients get used, then run low quickly ◦ Fall A final phytoplankton bloom Oceanic Feeding Relationships Main oceanic producer: Algae, plants, bacteria-like organisms ◦ Trophic Levels: Algae Zooplankton carnivores ◦ Transfer Efficiency The energy transfer from trophic level is very inefficient The majority (90%) of the energy is lost as heat to the environment Food chains and Food Webs Food Chain Sequence of organisms through which energy is transferred A B C D Food Web Shows all the possible food chains in an environment D C B A Ch 16 (sec. 1 only) THE DYNAMIC OCEAN 16.1 Ocean Circulation Surface Circulation ◦ Ocean Currents: masses of ocean water that flow from one place to another ◦ Surface Currents: Develop from friction between wind that blows across its surface ◦ Gyres: (gyres=circle) 5 main gyers.. 1. 2. 3. 4. 5. North Pacific South Pacific North Atlantic South Atlantic Indian ocean 5 main Gyres Gyres are huge circular moving current systems Wind influences most of these, but the spinning of the Earth causes deflection of some called Coriolis Effect Coriolis Effect Coriolis effect Ocean Currents and Climate When currents from low-latitude regions move into higher latitudes, they transfer heat from warmer to cooler areas Cold water currents travel toward the equator and help moderate the temperatures of land areas Upwelling Vertical water movements Rising of cold water from deep layers to replace warmer surface waters Driven by winds across the surface Brings dissolved nutrients up to the organisms in the shallower waters. Deep Ocean Circulation Density Currents ◦ Vertical currents of ocean water that result from density differences ◦ Dense water sinks and spreads ◦ Cooler water is more dense and tends to sink High Latitudes (toward the poles) ◦ High latitudes are colder and thus water is heavier and ultimately sinks ◦ This tends to slow the “conveyor belt” movements from the North to South Evaporation ◦ The evaporation allows water to evaporate away, leaving the salt behind. Salt water is more dense and therefore sinks The Conveyor Belt ◦ A global system of water continuously moving based on changing density and temperature. Ch 17 THE ATMOSPHERE: STRUCTURE & TEMPERATURE 17.1 Atmosphere characteristics Climate Vs. Weather ◦ Weather: Is constantly changing, and it refers to the state of the atmosphere at any given time and place. ◦ Climate: Is based on weather observations collected over many years. ◦ Most measureable properties of weather and climate include: Temp, humidity, type & amount of precip, air pressure, and direction and speed of wind Composition of the Atmosphere It has changed drastically over 4.6 billion years. Gases originated from volcanic eruptions Oxygen accumulated beginning ~2.5 billion yrs ago Major components: ◦ 99%= nitrogen and oxygen ◦ 1% = carbon dioxide and argon Variable components ◦ Water vapor - cloud formation & precip. ◦ Dust – allows vapor to condense ◦ Ozone – filters UV radiation Human Influence Air pollutants are airborne particles and some gases in large amounts can endanger the health of organisms Primary pollutants: Emitted directly from identifiable sources Ex: emissions from transportation Secondary pollutants: Not emitted directly into the air. Become dangerous when they react with another substance Ex: Sulfurs in exhaust mix with water vapor to create acidic precipitation Photochemical Reactions: The sun causes a chemical reaction to convert Nitrogen oxides into smog Height & Structure of the Atmosphere The atmosphere thins as you travel away from Earth ◦ Pressure changes: Atmospheric pressure is caused from the weight of the air above us At sea level = 1 kg/cm2, and decreases as you move up through the atmosphere ◦ Temperature changes: There are 4 vertical layers The thickness of these layers varies in different places on Earth Thermosphere ~50-90 miles Temp. increases Mesosphere ~30-50 miles Temp. decreases Stratosphere ~8-30 miles Temp. increases Troposphere ~0-8 miles from the Temp. decreases surface Earth-Sun Relationships Nearly all of the energy that drives Earth’s weather comes from the sun. Solar energy is not distributed evenly over Earth’s surface. Lower latitudes, closer to the equator get more direct rays than area toward the poles Earth’s Motions Rotation ◦ The spinning of Earth on its axis ◦ One rotation every 24 hours Revolution ◦ Movement of Earth in its orbit ◦ 113,000 km/hr ◦ One revolution per year Earth’s Orientation Seasonal changes occur because Earth’s position relative to the sun continually changes as it travels along its orbit The Earth is tilted 23.5˚ from perpendicular. This changes how directly solar rays strike the surface of the planet Seasons Summer solstice: ◦ June 21/22 ◦ Sun passes at highest point in the sky because of Earth’s potion ◦ Longest day of the year Winter solstice: ◦ ◦ ◦ ◦ Dec 21/22 1st day of winter Shortest day of the year Sun is at lowest point in the sky Autumnal Equinox: ◦ ◦ ◦ ◦ Sept 22/23 ½ way between seasons Day and night are equal in length Sun is mid-way between high and low positions in the sky Spring Equinox ◦ March 21/22 ◦ Sun is mid-way btwn high & low points ◦ Day and night are equal in length 17.2 Heating the Atmosphere 3 mechanisms of heat energy transfer: ◦ 1. Conduction: Transfer of heat through matter by molecular activity Ex. Hot handle of a pot cooking on the stove ◦ 2. Convection: Transfer of heat in the atmosphere by movement or circulation (mixing) Ex. Convection currents that move warm water from the bottom of a heating pan toward the top. ◦ 3. Radiation Radiation travels out in all directions from an object Ex. Electromagnetic waves; how the sun’s energy warms surfaces here on Earth Radiant energy does not need a medium to travel through. It can travel in a vacuum where no atoms or molecules exist. Convection, Conduction, Radiation 4 laws of Radiation 1. 2. 3. 4. All objects emit radiation Hotter objects emit more than cool ones Hotter radiating bodies produce the shortest wavelengths of energy Objects that are good absorbers of radiation, are also good emitters of radiation. What happens to Solar Radiation? When radiation strikes an object, there are 3 possible results: 1. Energy is absorbed 2. Energy is transmitted thru the object 3. Energy will bounce off, without being absorbed. Reflection ◦ Radiation bounces off an object ◦ The reflected energy is equal in intensity as the original radiation Scattering ◦ Reflects many weaker rays than the original ray. Absorption ~50% of the solar energy that strikes the top of the atmosphere and reaches Earth’s surface is absorbed Most is radiated skyward Carbon Dioxide and water vapor allow Earth to hold on to some of the sun’s energy. ◦ This is what allow us to live on this planet ◦ GREENHOUSE EFFECT Photosynthesis Some energy from the sun is absorbed by plants (chlorophyll) This energy is converted into carbohydrates and is the base of most food chains. 17.3 Temperature controls Why does temperature vary? ◦ ◦ ◦ ◦ ◦ ◦ ◦ Latitude Heating of land Heating of water Altitude Geographic position Cloud cover Ocean currents Land and Water ◦ Land heats more rapidly and heats to higher temperatures than water ◦ Land also cools faster than water ◦ So therefore, temperature changes occur very quickly over land Geographic position: ◦ Coastal vs. inland: Large nearby bodies of water can influence temperature changes ◦ Urban vs. rural: Cities tend to heat to higher temps and remain warm longer than rural places Altitude: ◦ Within the same latitude, the temps are lower as the altitude increases ◦ So it gets colder as you get higher from sea level. Cloud cover & Albedo: ◦ Albedo is the fraction of radiation reflected by any surface ◦ Clouds reflect some of the sun’s radiation ◦ Ex: darker objects reflect very little light, and therefore have low albedo, compared to light objects. Isotherms Lines that connect points that have the same temperature across a map Allows us to study temperature ranges across the globe. Ch. 18 MOISTURE, CLOUDS & PRECIPITATION 18.1Water in the Atmosphere Precipitation ◦ Any form of water that falls from a cloud Water vapor – is the most important gas in the atmosphere Water Changes States ◦ Water changes states throughout the water cycle ◦ All water in the cycle must pass through the atmosphere as vapor 3 state changes Solid to liquid ◦ Melting ◦ Heat is absorbed Liquid to gas ◦ Evaporation ◦ Heat is absorbed Solid to gas ◦ Sublimation ◦ Heat is absorbed Energy transfer between states Humidity Defined: the amount of water vapor in the air ◦ Saturation: When the number of molecules of water returning to the surface equals the number leaving ◦ Relative Humidity: The ratio of the air’s actual water vapor content compared with the amount of water vapor air can hold at that temperature and pressure Increase temp = decrease relative humidity Decrease temp = increase relative humidity Dew Point: ◦ The temperature at which if cooled any further, the air would reach saturation Measuring Humidity: ◦ A hygrometer, which is made of 2 thermometers. Specifically called a phychrometer 18.2 Cloud Formation Air compression & Expansion ◦ When air is compressed, it warms ◦ When air is expanded, it cools ◦ Adiabatic temp. change: The concept that temp. changes can happen because of a change in pressure Increase pressure = increase temperature Decrease pressure = decrease temperature Clouds form when the temp of the atmosphere reaches a point where the vapor condenses (dew point) and turns to droplets Processes That Lift Air Orographic lifting Frontal wedging Convergence Localized convective lifting This is just a list, and each will be explained on the following slides Orographic lifting: Mountains or barriers cause air to lift up Frontal Wedging: ◦ Warm air fronts meet cold, and the warm, less dense mass moves upward Convergence: ◦ 2 air fronts converging have no where to go accept upward Localized convective lifting: ◦ Isolated pockets of warmed air move upward Stability A pocket of air that is cooler than its surroundings, tends to remain STABLE. ◦ Density differences: Warmer, less dense air is not stable and wants to rise (ex: A hot air balloon) ◦ Stability Measurments: Measure temp. differences with altitude changes Temperature Inversion Occurs when the ground air cools faster than the upper atmosphere. ◦ This traps air at the surface ◦ This can act as a bubble over cities with smog, and prevent the smog from lifting. Degrees of Stability Air is stable when the temp. changes gradually with altitude changes Stable conditions produce very few clouds in the sky The shape and location of clouds can explain the level of stability in the air masses (used to predict weather) Condensation Occurs when water vapor in the air changes to a liquid ◦ Dew, Fog or clouds result Water vapor is invisible, you only see clouds because they are condensed water molecules Fog, dew and clouds can only form when: ◦ Air is cooled and ◦ Air is saturated with moisture Generally water vapor needs a surface to condense on, however in the atmosphere dust, smoke, and salt particles act as nuclei for water to condense around 18.3 – Cloud Type & Precipitation Cloud Types: ◦ Clouds are classified on the basics of their form and height 3 Basic clouds: ◦ Cirrus ◦ Cumulus ◦ Stratus Cirrus = “curl of hair” ◦ High, thin & white ◦ Feathery appearance ◦ Wispy fibers Cumulus = “a pile” Rounded masses Usually flat base Rising towers or dome shapes Stratus = “Layer” Sheets or layers covering most of the sky Large & Blanketing Clouds By location High clouds: ◦ Cirrus, Cirrostratus, Cirrocumulus Middle clouds: ◦ Altocumulus, Altostratus Low clouds: ◦ Stratus, stratocumulus, nimbostratus Clouds of vertical development Some clouds form and extend through all 3 levels of the atmosphere They are related to unstable air Ex: Cumulonimbus – which may produce rain showers and thunder storms Fog Cloud with its base at or near the ground ◦ Caused by: ◦ 1. Cooling- When the air near the ground cools and reaches the dew point ◦ 2. Evaporation – when warm water evaporates to form a cloud above its surface. How Precipitation Forms Cloud droplets must grow in volume by roughly one million times ◦ Cold cloud precipitation: Bergeron Process = the growth of ice crystals, until they are large enough to fall Ex: snow, sleet, hail ◦ Supercooled = below freezing but not frozen yet ◦ Supersaturated = holding more water than it should be able to (unstable) Slight temp change can cause condensation & rain Chapter 19 AIR PRESSURE & WIND 19.1 – Understanding Air Pressure Air pressure is one of the basic weather elements and is an important factor in weather forecasting. ◦ Air Pressure Defined = The pressure exerted by the weight of air above. Air pressure is exerted in all directions (up, down and sideways) Average sea level air pressure is 1Kg/cm3 Measuring Air Pressure Barometer (bar=pressure, metron=measure) ◦ Invented in 1643 by a student of Galileo’s named Torricelli ◦ Measured in millibars ◦ “inches of mercury” was an old phrase used to refer to atmospheric pressure ◦ Increase Pressure = rise in mercury ◦ Still used today Barometer diagram Factors Affecting Wind Wind is the result of horizontal differences in air pressure Air flows from high pressure to low pressure areas The unequal heating of Earth’s surface generates the pressure differences Therefore, SOLAR RADIATION is the ultimate source for most winds 3 factors that control wind 1. Pressure differences 2. Coriolis Effect 3. Friction Pressure differences Indicated by Isobars on a map Isobars= ◦ Lines that connect places of the same pressure A steep pressure gradient is indicated by very close lines, and a weak or very gradual gradient is indicated by lines with more space between them. Coriolis Effect Describes how Earth’s rotation affects moving objects. All free-moving objects, fluids, & winds are deflected to the right of their path in the Northern Hemisphere In the South they are deflected Left Friction Wind speeds are affected by the obstructions near the surface of Earth (12 km) High above the friction layers, are the jet streams Jet streams move at 120-240 km/hr. 19.2 Pressure Centers & Wind Highs and Lows Low pressure centers = cyclones High pressure centers = anticyclones Cyclonic & Anticyclonic winds The 2 most significant factors that affect wind are: ◦ 1. pressure gradients ◦ 2. the Coriolis Effect In the northern hemisphere winds blow: ◦ Counter clockwise around a Low ◦ Clockwise around a High Cyclones & Anticyclones Global Winds Air is constantly being rotated from the poles to the equator in huge conveyorlike convection currents. This helps regulate the overall global temperatures ◦ Non-rotating Earth Model: The conveyor belts of air would move from Equator to poles and back ◦ Rotating Earth Model: There are additional cells of rotation caused from the movement of trade winds and westerlies Influence of Continents As you already know, the continents heat and cool faster than the oceans. This disrupts the global wind patterns These seasonal disruptions can cause monsoons, which are usually associated with very raining seasons. 19.3 Regional Wind Systems Local Winds ◦ Caused by topographic effects, or variations in surface materials (land or water) ◦ Sea Breezes: As warm land warms the air, it rises, pulling cooler air from above the water toward the shoreline This gives a consistent afternoon cool sea breeze. ◦ Valley & Mountain Breezes: As the land heats up in the day time, warm air begins to creep up the sides of mountains & valleys. At night the cool air sinks, so air is usually always moving up or down along hills, valleys and mountain sides. How Wind is Measured Direction: ◦ determined by a wind vane ◦ Designed to turn toward the direction of oncoming winds Speed ◦ An anemometer helps us determine how fast air is moving. ◦ Usually by allowing a device to spin, which is then calculated into MPH. El Niño and La Niña El Niño: ◦ Warm counter currents become strong at regular intervals of every 3 to 7 yrs ◦ They slow the normal upwelling processes that bring nutrients to the ocean organisms along the equator. ◦ Small fish starve, and the entire food chain suffers La Niña: ◦ The opposite of El Niño. ◦ This event brings in cooler than normal water temperatures, and in turn affects weather patterns. ◦ Increases the occurrence of Hurricanes in the U.S. ◦ Can increase snowfall rates along the Eastern coast of the U.S. Global Distribution of Precipitation We know that tropical regions experience the bulk of Earth’s precipitation And the reasons for this are tied up in the complex patterns that we have discussed throughout this chapter. Weather Patterns & Severe Storms Chapter 20 20.1 Air Masses Many of the common weather masses we are familiar with (thunderstorms, tornadoes, hurricanes) are the result of moving air masses. AIR MASSES: immense body of air that is characterized by similar temperatures and amounts of moisture. As Air Masses move, the characteristics of the air mass can change, and so does the weather in the area over which the air mass moves. Classifying Air Masses (P) = Polar: Form at high latitudes; cold (T) = Tropical: Form at low latitudes; warm (c) =Continental: Over land; dry (m)=Maritime: over water; moist (cP) = Continental/Polar (cT) = Continental/Tropical (mP) = Maritime/Polar (mT) = Maritime/Tropical Weather in North America Most weather in North America is influenced by (cP) continental/polar and (mT) maritime/Tropical air masses Continental/Polar Cold & Dry in winter Cool &Dry in summer Not associated with heavy precipitation, HOWEVER when they pass over the Great Lakes region, they can bring several inches of snow! What causes Lake Effect Snow? The cold, dry continental air mass moves over a relatively warm lake, and picks up large amounts of moisture. It then is rather unstable, and can deliver many inches of precipitation in the form of snow over the coastal region of Michigan Maritime/Tropical Air Masses Play a large role in North American weather Warm, moist and unstable These air masses are where the Eastern portion of the U.S. gets the majority of their precipitation. Associated with High temperatures, and high humidity. Maritime/Polar Air Masses The maritime/polar air masses that affect North American weather come from the North Pacific region, often from Siberia Associated with low clouds and heavy rain or snow. Continental/Tropical Air Masses These air masses rarely affect weather outside of their regions. Associated with mild calm conditions Cause “indian summer” conditions in the Great Lakes region 20.2 Fronts When 2 air masses meet, they form a front. A Front: is a boundary that separates 2 air masses. Fronts are often associated with some form of precipitation Most of 15-200 km (8-111 miles) wide Types of Fronts ◦ 1.Warm, 2.Cold, 3.Stationary, 4.Occluded Warm front: ◦ Forms when warm air moves into an area formerly covered by cooler air Cold front: ◦ When cold, dense air moves into a region occupied by warmer air Stationary front: ◦ Air flow goes around the air mass and at least one side of the air mass does not move. Occluded fronts: ◦ When a cold front overtakes a warm front Middle-Latitude Cyclones Large centers of low pressure that generally travel from west to east and cause stormy weather. Air moves in a counterclockwise direction How do Cyclones form? As a warm and cool front slide horizontally past each other, a slight swirl begins to develop. As the dense cool mass drops down, it gives an effect very similar to water going down a drain in a bathtub (see step by step diagrams pg. 569) 20.3 Severe Storms Thunderstorms: ◦ Generates lightening and thunder, gusty winds, heavy rain and often hail ◦ One cumulonimbus cloud can cause a thunder storm, or clusters of cumulonimbus clouds ◦ The fronts can be miles wide Thunder Storm Occurrences At any given time there are ~2000 thunder storms in progress on Earth. The U.S. has ~100,000 per year, with Florida having the most. Most common where there is moist warm air (tropical and sub tropical regions) Thunderstorm Development T-storms form when warm, humid air rises in an unstable environment. ◦ Cumulus stage: warm, moist air is supplied to the cloud ◦ Mature stage: heavy precipitation falls ◦ Dissipating stage: cloud begins to evaporate and the precipitation slows Tornadoes Violent windstorms that rotate (vortex). This vortex extends down from the cumulonimbus cloud all the way to the ground May be a single vortex, but many stronger tornadoes will have smaller vortexes inside of the larger one. Most form in and around thunderstorms Tornado Intensity Low pressures inside of a tornado cause nearby air to be pulled into it. The lower the pressure the greater the force pulling inward. Intensity is measured from F0 – F5 Intensity is based on recorded wind speeds and the type of damage done to structures (pg 574) Hurricanes Whirling tropical cyclones that produce sustained winds of at least 119 kph (66mph) They are also called typhoons, cyclones, and tropical cyclones, depending on the part of the world it occurs. THE most powerful storms on Earth As more people live in coastal areas, the dangers of hurricanes are increasing Occurrences of Hurricanes Most occur between 5-20 degrees north and south latitude The North Pacific averages 20 per year Many tropical disturbances occur, but only those reaching wind speeds of 119 kph / 66mph are given hurricane status. Development of Hurricanes Develop most often in late summer when water temps are warm enough to provide the heat and moisture to the air. They begin as tropical disturbances, cloud formations, and thunder storms If they continue to develop, then the possibility of the funnel activity may begin, which leads to the spinning of a hurricane Hurricane Intensity Saffir-Simpson scale measures intensity based on wind speeds, and storm surge height Storm surge is the dome of water that rises up, due to the pressure change around and within the hurricane. A hurricane weakens if it moves over cooler water, or over land Climate Chapter 21 21.1: 6 Factors that Affect Climate 1. 2. 3. 4. 5. 6. Latitude Elevation Topography Water Bodies Atmospheric Circulation Vegatation 1. Latitude Distance North or South of equator As latitude increases, the average intensity of solar energy decreases. 3 main global zones: ◦ ◦ ◦ Polar (66.5° to the poles) Temperate (23.5° – 66.5°) Tropics (equator – 23.5°) 2. Elevation Height above sea level The higher the elevation, the colder the climate 3. Topography Features such as mountains play an important role in the amount of precipitation that falls over an area 4. Water Bodies Large bodies of water such as lakes and oceans have an important effect on the temperature of an area The temperature of the water body influences the temperature of the air above it. 5. Atmospheric Circulation Global winds influence climate because they distribute heat and moisture around the Earth 6.Vegetation Different types of plants grow in different parts of the world because of the climate differences (ex: cactus) Vegetation can also affect the actual temperature and precipitation patters in an area Vegetation influences how much solar energy is absorbed, whereas transpiration can increase the local air moisture levels. 21.2 World Climates What is the Koppen Climate Classification System? System that uses mean monthly and annual values of temperature and precipitation to classify climates 5 principal groups: ◦ Humid tropical, dry climates, humid midlatitude, polar climates and highland climates What are humid tropical climates? Climates without winters Every month the mean temperature is above 18 °C (64 ° F). The amount of precipitation exceeds 200 cm per year Humid Subtropical locations Different types of humid midlatitude climates Humid Mid-Latitude with MILD WINTERS: ◦ Humid subtropical climates: Btwn 25° -40° N and S latitude Eastern sides of continents Hot, humid summers, mild but frosty winters Ex: Southeastern U.S. ◦ Marine West Coast climates: Btwn 40 ° – 65 ° N and S latitude Mild winters, cool summers Ample rainfall Ex: northern California to southern Alaska HML with Mild Winters cont. ◦ Dry-summer subtropical climates: 30 ° – 45 ° latitude Unique because of the large amount of winter precipitation Ex: only parts of California in the U.S. Humid Mid-Latitude with Severe Winters: ◦ Humid Continental Climates: Absent in Southern Hemisphere Winters are severe, but summers are very warm 40 ° -50 ° N latitude ◦ Subarctic Climates: North of humid continental and South of the tundra Expansive region that stretches from Western Alaska to Newfoundland, and from Norway to the Pacific coast of Russia Dry Climates Dry climates are identified as regions where the evaporation rates are greater than the precipitation rates. 2 Types: ◦ Arid or Desert: Driest of the dry climates ◦ Semi-arid or Steppe: Slightly more moisture than arid/desert regions Arid climate Semi arid climate Polar Climates Climates where the mean temperature of the warmest month is below 10 °C (50 °F) Polar winters are periods of complete darkness Very little precipitation treeless Highland Climates Cooler and wetter than nearby areas at lower elevations All mountainous regions 21.3 Climate Changes Natural processes that change climate: 1. 2. 3. 4. 5. Plate Tectonics Earth’s orbital motions Ocean circulation Solar activity Volcanic eruptions 1. Plate Tectonics Geographic changes in Earth’s land and oceans due to plate tectonics cause changes in climate over very long time scales. ◦ Oceans open and close, changing the currents ◦ Himalaya mountain range formed from plates colliding, creating this topographic barrier to weather. 2. Earth’s Orbital Motions Earth travels on an elliptical path around the sun, and it is tilted on its axis. The tilt of earths axis is not always the same, and it wobbles like a slowing top One complete revolution of this cycle takes 26,000 years This effects the severity of the seasons, and changes how directly the sun strikes the surface. 3. Ocean circulation Short term climate fluctuations by ocean changes El Niño and La Niña 4. Solar Activity The amount of energy given off from the sun has increased over the course of its existence. Sunspots increase the amount of energy we get from the sun and correspond to warm periods on Earth Fewer sunspots correlates with cooler periods in Earths history 5.Volcanic Eruptions Volcanic ash, dust, and sulfur-based aerosols in the air increase the amount of solar radiation that is reflected back into space. This causes Earth’s lower atmosphere to cool Over long periods of time, volcanic eruptions may increase the greenhouse effect by adding carbon dioxide.
