Weather & Climate
What is the weather?
Weather – present state of the atmosphere
- Includes
o Air pressure (mB)
o Wind
o Temp
o Humidity
- water cycle is the basis of weather
- sun
o causes heat
o evaporates water
o heats air and creates wind
- 3 components
o Air
o Sun
o Water
What is climate?
Climate – the pattern of weather that occurs in an area over many years
- determined by averaging weather over an area for 30 years or more
- scientists average:
o temperature
o precipitation
o air pressure
o humidity
o days of sunshine
- other factors that affect climate:
o latitude
o landforms
o location of lakes and oceans
o availability of moisture
o global wind patterns
o ocean currents
o location of air masses
Zones based on Latitude
Tropics – latitudes 23.5 degrees N and 23.5 degrees S
- receive the most solar radiation
- close to equator
Polar – latitudes 66.5 degrees N and S to the poles
- solar energy hits area at an angle
- reduces absorption of land & water
- waves bounce off back into space
- winter, axis tilts pole away from sun entirely
- no radiation during winter
- remains cold and partly frozen year round
Temperate – inbetween tropics and polar regions
- moderate temps
- moderate rainfall
- US is in this zone
Other Factors
- natural feature:
o mountains
 radiation that is reflected upward hits fewer molecules in the air to
hold the heat
 windward side
 air rises, cools and drops moisture
 leeward side
 air descends, heats up, and dries out the land
 forms deserts
o large bodies of water
 heat up slower and cool down slower
 coastal regions are warmer in winter and cooler in summer
 winds from sea carry more moisture therefore create a wetter
environment
 currents
 warm currents warm the area they pass
 cool currents cool the area they pass
- anthropogenic changes (man-made)
o inhabited areas (ex. cities)
 solar radiation is absorbed by paved areas
 sidewalks, streets, etc.
 heat up and radiate energy into the atmosphere
 engine exhaust traps heat
 temperature increases in big cities
 skyscrapers act as mountains
 affect wind and precipitation patterns
o agriculture
 farmland – constant plowing and clearing creates more erosion
Energy from the Sun
Sun – source of all energy in our atmosphere
- Earth reflects some energy, absorbs some energy
- Radiation – the transfer of energy by electromagnetic waves
- Heat – energy that flows from an object with a higher temp to an object with a
lower temp
Conduction vs. Convection
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Conduction – the transfer of energy that occurs when molecules bump into
on another
o By contact
o Faster moving particles to slower moving particles
Convection – the transfer of heat by the flow of a heated material
o Molecules move apart when heated, less volume or density so it rises
o Molecules come closer together when cooled, more volume or density
so it sinks
o Air masses move this way
Weather Patterns
Air mass – large body of air that has the same properties as Earth’s surface where it develops
- over land is dry compared to over water
Pressure systems
- 2 types:
o High pressure
 Lots of molecules sinking
 Makes it difficult for clouds to form
 Sign of fair weather
o Low pressure
 Lots of room for molecules to rise and collect
 Cloudy weather
- Amount of air molecules that push down from above
- Determined by 3 things
o Temp
o Density
o Water vapor
Fronts – boundaries where cold and warm air masses meet
- storms & precipitation are typical
- low pressure systems evident
- air masses move from high to low
o warm to cold
- air doesn’t mix when they meet
o colder air moves under warmer air
o warm air rises
o winds form (from high to low pressure)
- 4 types of fronts:
o Warm
 Warm ari rises over cold air
 Precipitation occurs over a wide area
o Cold
 Cold air pushes under warm air up steeply
 Narrow band of strong storms
 Move at 2x the speed of warm fronts
o Occluded
 Faster moving cold front over takes a slower moving warm front
 Warm air is forced up
 Strong winds
 Heavy precipitation
o Stationary
 Pressure differences cause the warm and cold front to stop moving
 Light wind & precipitation
 Can cause flooding
Water cycle
http://www.mbgnet.net/fresh/cycle/cycle.htm
Evaporation:
Transpiration:
Condensation:
Precipitation:
Groundwater infiltration:
Runoff:
Severe weather
Thunderstorms – warm, moist air masses and fronts
- cumulonimbus clouds form
- heavy droplets fall creating downdrafts
- strong winds associated with these types of storms
Lightning – rapid uplift of air builds electric charges in clouds
- positive and negative charges attract forming lightning
- can leap from cloud to cloud or from Earth to cloud
- thunder results from rapid heating of air due to lightning
o 30,000 C
o 5x + the surface of the sun
o Air expands rapidly then cools quickly
o Condenses and contracts creating a sound wave
Tornados – violent, whirling wind storms
- SW to NE travels
- Most form along a front
- Wind shear
o Difference in wind direction & speed
o Occurs @ different heights
o Strong updraft tilts wind shear & cause rotation in clouds
o Funnel cloud may apprear
o Not all reach/touch Earth’s surface
o Center has an updraft
o Don’t usually exceed 200m width
o Lasts only a few minutes (typically)
o Most occur in US (~700 per year)
 Texas, Oklahoma, Kansas
- NEXRAD and Doppler
o Next Generation Weather Radar
 Nationwide system of radar stations
 Use doppler
o Doppler
 Sends out radio waves continuously
 Tracks storm movement by way it bounces radio waves
 Higher frequency – storm is moving towards radar
 Lower frequency – storm is moving away from radar
 Use colors to indicate frequency fluctuations
 Green – closer
 Red – away
 The two close together indicates rotation
Hurricanes – large, swirling, low-pressure system that forms over tropical oceans
- most powerful storms
- winds must reach up to 120km/hr to be categorized as a hurricane
- can travel on land
- rotates counter-clockwise in N. hemisphere
Movement of Air
Air pressure – differences in pressure causes wind
- wind is created from high pressure moving to low pressure
Heated air – temp differences on Earth
- spherical shape and tilt allows for varied amounts of solar radiation
- heated air rises – has low density because it is spread out
- cooler air sinks – has high density because molecules are close together
Coriolis Effect
- rotation of Earth creates this effect
- surface of Earth rotates and rubs against atmosphere
- causes the air in the northern hemisphere to move westward
- help create wind patterns on Earth
o affects ships sail
o affects planes flights
Wind systems
- surface winds – affected by convection currents
 where solar radiation affects the air
o doldrums
 windless areas located right near the equator
 air moves straight up
o trade winds
 wind travels from NE to SW in northern hemisphere
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-
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 SE to NW in southern hemisphere
 Used for “trade” routes of ship sailing
o prevailing westerlies
 opposite directions from trade winds
 SW to NE in northern hemisphere
 Weather patterns travel over US with their help
 NW to SE in southern hemisphere
o polar easterlies
 NE to SW near north pole
 SE to NW near south pole
high altitude winds
o jet streams
 near top of the troposphere
 move west to east in both hemispheres
 near the prevailing westerlies
 speeds range 97 to 185 km/hr
 major effect on weather
daily and seasonal winds
o sea breezes
 during the day
 land heats up faster than sea
 air moves up and cooler air over sea moves in its place
o land breezes
 during the night
 land cools more quickly than sea
 air moves towards sea due to warm air rising over water
mountains and valley have cycle as well
Monsoons – warm moist air moves over land bringing rain in warmer season
Climatic Changes
Seasons
- Temperate zones
- Earth’s tilt and revolution around Sun
- Amount of solar radiation fluctuates
- short term periods of climate change caused by regular differences:
o daylight
o temperature
o weather patterns
Latitudes
- Middle latitudes have temperate zones
- Tropics – latitudes near equator do not fluctuate much in temp and precipitation
- Poles – extremes of daylight hours
o Summer 24 hours of daylight
o Winter 24 hours of darkness
o Opposite at opposite poles
El Nino
-
climatic event that starts in the tropical pacific ocean
occurs every 3 to 7 years
pacific waters warm
trade winds from E to W weaken and may reverse
allows warmer waters to hit S. America
creates more stormy weather
jet stream may split
o changes atmospheric pressure
o changes wind and precipitation patterns around world
- may cause droughts in eastern hemisphere
Climate change
- geologic records shows us fluctuation in temps on Earth
- fossils of organisms from that would live in tropic regions are found at polar regions
- glacial erosion and deposition shows glaciers covered surface for long periods of
time
- ice cores show changes in climate
Climatic theories
- meteorite collisions
- volcanic eruptions
- plate tectonics
- Earth’s position in space
Climatic changes today
- greenhouse effect
o natural heating caused when gases in our atmosphere trap heat
o life could not survive on Earth w/o the greenhouse effect
o CO2 is major greenhouse gas
- global warming
o global temps rising
o due to increase amounts of greenhouse gases
o deforestation
o ice caps will melt
o rise in sea levels will occur
Anthropogenic (human influence)
- burning fossil fuels
- deforestation
- need to be more energy conscious