Physical Geography Exam 2 – Flashcards
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Air Pressure
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the measured weight of air as it exerts pressure on Earth's surface decreases with increasing altitude Air density is greatest near the Earth's surface
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Air pressure is influenced by air temperature:
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Warm air results in lower air pressure Cooler air results in higher air pressure
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Measuring Air Pressure:
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Barometer
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Mapping Air Pressure:
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Air pressure changes with altitude Average air pressure at sea level = 1013.25 mb
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High-pressure system
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A circulating body of air that exerts relatively high pressure as air sinks toward the surface Air flow diverges
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Low-pressure system
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A circulating body of air where relatively less pressure is created as air rises away from the surface Air flow converges
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Pressure systems
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create large-scale circulatory systems that are interconnected by airflow
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Advection
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the process by which air flows horizontally from high-pressure to low-pressure
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Map of Atmospheric Pressure:
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Isobars indicate the geographic patterns of pressure systems Red arrows illustrate the path of airflow relative to pressure systems
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Wind Direction
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Winds are named for the direction in which they originate
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Convection
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causes motion in the atmosphere
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Pressure gradient
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The greater the difference in pressure, the steeper the gradient The steeper the gradient, the faster the airflow
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Coriolis Force
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Due to Earth's rotation Deflects objects traveling in the atmosphere Earth's eastward rotation below Northern Hemisphere, deflection is to the right Southern Hemisphere, deflection is to the left
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Frictional Forces
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Occurs at ground level Strongest at surface, diminishing at about 1500 m (5000 ft) Causes wind to slow down and move in irregular ways
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Convection loops
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spiraling descending and rising air are linked horizontally by advection
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Hadley Cell
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the tropical convection loop Air at tropics is warmed by year-round direct sunlight
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Intertropical Convergence Zone (ITCZ)
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Warming creates a zone of low pressure at Equator as air rises into the atmosphere Winds converge into ITCZ by advection
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Subtropical High Pressure System (STH)
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Air rising from ITCZ eventually sinks at subtropics creating zones of high pressure Dry and warm winds diverge from STH
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Ferrel Cell
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the circulatory loop that mixes cool polar air with warm tropical air
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Polar Front
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the line of contact between contrasting air masses at about 60 N/S
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Polar Jet Stream
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formed by high-altitude winds that are formed with the temperature/pressure gradient
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Rossby Waves
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develop as undulations in the Polar Front and moderate significant temperature difference on either side
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Polar Cell
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the circulatory loop in the polar regions
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Polar High-Pressure System
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Air flowing northward from midlatitudes sinks, producing a weak high-pressure system Consists of masses of rotating, descending dry air that flows toward the Polar Front
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Circulatory Loops and Wind Patterns
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Trade Winds ITCZ STH Westerlies and Trade Winds Westerlies and Polar Easterlies Polar Front Polar High Polar Easterlies
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Monsoonal Winds
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Seasonal shift of the ITCZ and prevailing wind direction in the subtropics
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Asian monsoons
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Winter: ITCZ in south Cold air, high pressure Summer: ITCZ in north Warm air, low pressure
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Sea Breeze
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Breeze blows from high- pressure sea to low- pressure land
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Land Breeze
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Breeze blows from high- pressure land to low- pressure sea
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Valley Breeze
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Breeze blows upslope as mountain slopes heat up
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Mountain Breeze
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Breeze blows downslope as mountain slopes cool off
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Katabatic Winds
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Extremely cold, dense air flows downslope under force of gravity Flow at great speeds
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Chinook Wind
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Occurs when a steep pressure gradient develops in mountainous regions high pressure on windward side low pressure on leeward side
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Currents and Gyres
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Surface currents are driven by winds as energy transfers by friction
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Gyres
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form as continents block the movement of water
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Oceanic Conveyor Belt
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Slow vertical mix of water between layers of the ocean
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Downwelling currents
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caused by high-density water that is cooler and saltier
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Upwelling currents
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caused by low-density water that warms in tropical regions
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El Niño
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Reversal of "normal" flow of currents and winds in tropical Pacific Occurs every 3-8 years Affects climate Changes ocean surface temperature Changes patterns of precipitation
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Wind farms
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Collection of turbines used to harness wind power Conversion to clean usable energy
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Hydrogen Bonding
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Attraction between the hydrogen atoms of water molecules Explains water's physical states
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Hydrologic Cycle
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Movement of water between various storage locations Amount of water is finite Total amount evaporated equals the total precipitated globally Yet, local and regional imbalances occur
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Humidity
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refers to the concentration of water vapor in the air
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Maximum Humidity
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Maximum amount of water vapor that a body of air can hold Subject to air temperature Warm air can hold more water vapor than cold air
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Saturation
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the point where the air cannot hold any more water vapor at its current temperature
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Specific Humidity
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How much water vapor is actually in the air
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Relative Humidity
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Ratio of specific humidity to maximum humidity How close the air is to saturation, at its current temperature
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Lower latitudes
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Specific humidity is low Relative humidity is high
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Higher latitudes
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Specific humidity is high Relative humidity is low
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Diurnal cycle
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Maximum humidity increases with warming Specific humidity is constant Relative humidity gradually decreases
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Dew-Point Temperature
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Temperature at which a mass of air is saturated Related to changes in relative or specific humidity
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Transpiration
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results in evaporation directly from leaf pores in plants into the atmosphere
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Evapotranspiration
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the combination of evaporation and transpiration
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Evapotranspiration rates depend on
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Net radiation which increases heating Air temperature which influences maximum humidity Relative humidity and moisture capacity of air
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Dry Adiabatic Lapse Rate
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Applies to unsaturated air Dry air cools or warms at 10C/1000 m or 5.5F/1000 ft
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Wet Adiabatic Lapse Rate
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Applies to air that reaches the level of condensation, or the altitude of saturation Rate varies with moisture content and temperature Average rate is about 10C/1000 m or 5.5F/1000 ft
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Clouds
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visible masses of suspended, minute water droplets or ice crystals
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Two necessary conditions for cloud formation
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Air must be saturated Either by cooling below the dew point or by adding water vapor to the air There must be a substantial quantity of small airborne particles for water vapor to collect Such particles are known as condensation nuclei
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Clouds are classified based on form and altitude
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Form Cirrus Cumulus Stratus Altitude High Middle Low
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Radiation fog
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develops at night when air cools to the dew point and is held below a temperature inversion, or an overlying body of warmer air
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Advection fog
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develops when warm air flows over a cooler surface, cooling it to the dew point
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Sea fog
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develops when cool marine air comes in direct contact with colder ocean water
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Windward side
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Air cools at DAR to dew point Forms clouds that cool at WAR and precipitation follows
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Leeward side
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Air descends downslope, warming at DAR Creates rain shadow of dry conditions
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Orographic Uplift
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Airflow interrupted by a mountain range
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Convectional Uplift
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Unequal heating of Earth's surfaces
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Stable Air
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little convection and no precipitation
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Unstable Air
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strong convection bubbles lift and create precipitation
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Air Mass
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a large body of the lower atmosphere with uniform conditions of temperature and moisture
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air mass source region
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any large body of land or water where air derives its characteristics
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Fronts
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Boundaries between differing air masses When one air mass advances in a front, frontal uplift causes clouds and/or precipitation
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Warm Front
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Warm air advances Warm air slowly lifted
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Cold Front
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Cold air advances Warm air rapidly lifted
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Midlatitude Cyclones:Interactions at the Polar Front
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A well-organized low-pressure system that migrates across a region while it spins
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Midlatitude Cyclones: Upper Air Flow
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500-mb upper air-pressure surface Occurs at a specific but varying altitude over any given place on Earth Vertically divides atmosphere in two, from surface to top Explains pressure changes associated with temperature change
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High-pressure ridges
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form when height of pressure surface is higher and anticyclones occur
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Low-pressure troughs
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form when height of pressure surface is lower and cyclones occur
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Cyclogenesis
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is the process that forms midlatitude cyclones Conditions in upper atmosphere and surface are significant Upper-level convergence sends air to the surface, creating high pressure Upper-level divergence allows air to rise, creating low pressure
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Evolution of Thunderstorms
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Cumulus Stage Begins with convection or advancing cold front into mT air Rapid rising air forms cumulus clouds Developing Stage Condensation releases latent heat Mature Stage Very unstable air with development of strong updrafts Intense precipitation brings cold air down to create downdrafts Dissipation Stage
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Lightning
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Collisions among ice crystals and rain droplets cause difference in electrical charge within clouds Ground has positive (+) charge Most lightning within clouds from positive (+) to negative (-) In strong storms, leader (-) from cloud meets streamer (+) from ground, creating "spark" as cloud-to-ground lightning
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Tornadoes
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Small, intense cyclone formed in supercell thunderstorms
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Mesocyclones
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are large rotating updrafts Form at high altitudes with strong updrafts and wind shear A horizontal vortex of air gets pulled vertically in updrafts
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Tropical Cyclones
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Develop in homogeneous air masses at low latitudes Fueled by abundant water vapor and latent heat Early Formation: Easterly Wave slow-moving trough migrates along tropical easterlies Upper air converges on windward side and diverges on leeward side, causing rapid uplift
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Hurricane
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Tropical storms in the Atlantic or eastern Pacific with very high winds Rare combination of environmental variables: Warm ocean surface High evaporation Favorable upper air winds High pressure aloft
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Anatomy of a hurricane:
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Around the eye, air flows inward and upward In the eye, air flows toward surface and warms
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Atlantic Hurricane Tracks
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Originate in West Africa driven by trade winds Intensify over warm tropical Atlantic Driven northeast by westerlies
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Weather
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the state of the atmosphere at a specific place and time on Earth's surface
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Climate
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the long-term average values of weather elements, such as temperature and precipitation
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Köppen Climate Classification
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Most widely used classification system Stems from the recognized relationship between major vegetation regions and regional climate characteristics System's description of world climates is based on Average monthly temperature Average monthly precipitation Total annual precipitation
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Tropical (A) Climates
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Surrounds the Equator from 25 N/S Consistently warm average temperatures Subcategories based on precipitation only Tropical rainforest (Af) Tropical monsoon (Am) Tropical savanna (Aw)
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Arid and Semi-Arid (B) Climates
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Poleward of A climates Subtropical high creates precipitation patterns Subcategories based on precipitation and temperature: Hot low-latitude desert (BWh) Cold midlatitude desert (BWk) Hot low-latitude steppe (BSh) Cold midlatitude steppe (BSk)
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Mesothermal (C) Climates
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20 to 60 N/S Distinct warm seasons and cold seasons Subcategories Humid Subtropical Hot-Summer (Cfa, Cwa) Mediterranean Dry-Summer (Csa, Csb) Marine West Coast (Cfb, Cfc)
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Microthermal (D) Climates
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35 to 60 N/S Longer cold seasons and limited warm seasons Subcategories: Humid Continental Hot-Summer (Dfa, Dwa) Humid Continental Mild-Summer (Dfb, Dwb) Subartctic (Dfc, Dwc, Dwd)
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Polar (E) Climates
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Nonmountainous areas poleward of 70 N/S Long, cold winters with little precipitation Subcategories Tundra (ET) Ice cap (EF)
