Midterm 2 Flashcards
Air Pressure
- air molecules produce pressure
- exerted on all surfaces that air contacts
- sea level atmospheric average is 1 kg/cm^2
Air Pressure: Gravity & Altitude
- gravity makes air denser at surface
- air pressure decreases with altitude
Measurements of Air Pressure
- barometer
- mercury: tube counterbalanced by mass of air around it
- exerts equivalent pressure on mercury in vessel
- normal sea level is 1013.2 millibars
Air Pressure & Density
- pressure and density DECREASE with altitude
- low density, molecules are further apart, less collisions there lower pressure
Air Pressure and Temperature
- air is heated, activity increases and temp increases
- increased activity, increased space between molecules
- density LOWER, pressure LOWER
- warmer air is LESS DENSE and exerts LESS PRESSURE
Wind: General
-horizontal motion of air across Earth’s surface
Vertical Wind
- updrafts
- downdrafts
- micro- and macro-bursts of air turbulence
Wind: How?
-differences in air pressure from one location to another
Wind Speed Measurement
- anemometer
- km/h, mph, m/s, knots
- knot is nautical Mph, covers 1 minute of Earth’s arc in an hour
Wind Direction Measurement
- wind vane
- 10 m from ground
- determined from source direction
Isobar
line denoting equal pressure
Isobaric Maps
show weight of atmosphere
help predict aridity and precipitation
Pressure Gradient Force
air moves from areas of high to low pressure
Pressure of North America in January
- low pressure over ocean (Pacific & Atlantic)
- high pressure over land
- extreme low temperatures
Pressure of North America in July
- pressure switch locations
- low pressure over land
- W coast, less precipitation
- E coast, summer showers and high humidity
- land heats rapidly due to low heat capacity
- high pressure over water
Coriolis Force
- spinning of Earth deflects path of objects
- different latitudes, different speeds
- equator: 1 675 km/h, poles: 0 km/h
Coriolis Force: Increased Speed
-faster objects create greater deflection
Coriolis Force: Wind and Ocean
- causes deflection to right in Northern Hemisphere
- causes deflection to left in Southern Hemisphere
High Pressure Area
Diverging
Descending
Low Pressure Area
Ascending
Converging
Close Isobars
- steep PGF
- strong wind, high speeds
Spaced Isobars
- gentle PGF
- gentle breeze, slow wind speed
Equatorial Low Pressure Trough
- low pressure band around equator
- lots of energy from the Sun
- warm, light, less dense, ascending & converging
- ITCZ
Heating and Converging Air
- forces air up
- air is moist & full of latent heat energy
Subtropical High Pressure Zone
- hot, dry air
- diverging and descending air at outer end of Hadley cells
- deflected POLE-WARD by Coriolis force
- cloudless, desert regions
- creates ocean gyres
Ocean Gyres: Directions
- CW in the Northern Hemisphere
- CCW in the Southern Hemisphere
Divergence of High Pressure Cells
-creates trade winds (easterlies )and westerlies
Easterlies and Westerlies
Easterlies
-easterly direction, create ocean currents
Westerlies
-westerly direction, create ocean currents i.e. gulf stream
Sub-polar Lows
- Polar Front: cold and dry conditions
- migrating centers of low p, brings precipitation
- winter, there is a shift to the South, rain in mid.latitude
Aleutian Low and Icelandic Low
- migratory pressure cells
- SUMMER: high latitudes, bring rain to Pacific NW
- WINTER: lower latitudes, cases cyclonic storms on the West coast of North America and Europe
Isobaric Maps: Ridges and Troughs
Ridges are areas of high pressure
Troughs are areas of low pressure
Wind near Maximum Speed
accelerates
diverges
Rossby Waves
westerly geostrophic winds
-develop along flow axis of a jet stream
Jet stream
irregular band of very strong wind
-occurs in specific locations
Land and Ocean Breezes in Day
- land heats faster than ocean
- warm air is less dense
- flow of cool onshore marine air
Land and Ocean Breezes at Night
- land cools faster than the ocean
- cool air on land flows offshore
- water remains warmer, warm air is lifted
Monsoon Drivers
- size and location of Asian landmass
- proximity to Indian Ocean
- changing ITCZ
Gyres: definition and strength
- west gyres stronger than east
- trade winds drive ocean west in a channel
- water piles at the equator, spills north and south
Upwelling Definition and Causes
- surface water swept from coast
- Coriolis , surface divergence, or offshore winds
- cool water, nutrient rich, rises from depth
Upwelling Locations
- Pacific Coasts of North and South America
- Subtropical and mid latitude west African coast
Four Downwelling Regions
- Labrador Sea
- Icelandic Sea
- margins of Antarctica
Downwelling: What
- thermohaline currents generated from downwelling
- travel extents of ocean basins, carrying heat and salinity
Downwelling: How
- cold, salty water sinks in North Atlantic
- full loop takes 1000 to 2000 years
Antarctic Downwelling
-very deep, flows north in Atlantic basin, UNDER other downwelling currents
Global Warming and Downwelling
- effect distribution of heat throughout ocean
- could increase warming
Humidity: General
- water vapor content of air
- changes with temperature of air and temperature of water vapor
Relative Humidity
-percentage amount of water ACTUALLY in air (content) and the maximum water vapor possible at a given temperature (capacity)
Saturated Air
-contains all water vapor possible at given temperature
Condensation
- occurs when further addition of water to saturated air
- occurs when temperature of saturated air decreases
dew point temperature
-temperature a given mass of air becomes saturated
Daily Air Temperature Trend
- at dawn, water vapor fills to near saturation
- during the day, lower relative humidity because air temperature decreases and specific humidity increases
Stability of Air Parcels
- tendency of a parcel to either:
- stay as it is
- change initial position by lifting or falling
Stable Air
- if it resists displacement
- returns to initial position
Unstable Air
-parcel rises to altitude where surrounding air is similar to its own
Two Main Forces acting on Air
- buoyancy force
- gravitational force
Warm Air Parcels
- less dense
- parcels rise (buoyancy force wins)
Cool Air Parcels
- more dense
- parcels sink (gravitational force wins)
Buoyancy, Density, Temperature
- dependent on density, which is dependent on temperature
- therefore, buoyancy is dependent on temperature
Air Mass temperature higher/less dense than surrounding
- rise vertically
- begin to expand due to decreasing pressure
- rise until parcel matches surrounding temperature and density
Air Mass Cool
- gravity pulls it down
- parcel compresses
Normal Lapse Rate
- average temperature decrease in altitude increase
- 6.4 degrees Celsius per 1 000 m
- for still, calm air
Environmental Lapse Rate
-rate for specific areas and weather
Adiabatic
-occurs without loss/gain of heat to surroundings
Diabatic
-occurs with exchange of heat
Dry Adiabatic Lapse Rate (DAR)
- rate that dry air cools by expansion or heats by compression
- dry air is LESS THAN saturated
- relative humidity is less than 100%
- 10 degrees Celsius per 1 000 m
Moist Adiabatic Rate (MAR)
- average rate which moist air heats/cools by compression/expansion
- 6 degrees Celsius per 1 000 m
- can vary from 4 to 10 degrees Celsius per 1 000 m
DAR and MAR in Cold Air
-similar, MAR can be the same as DAR
Unstable Weather
- atmosphere dominated by warm air
- warm air absorbs moisture available and reaches level of saturation
- parcels may rise vertically, cool, condense, and precipitate
Stable Weather
- no vertical movement of air
- atmosphere remains cool and dry
Clouds
- made up of moisture droplets
- 1 million moisture droplets = one rain drop
Cloud Formation: Unstable Condition
- air parcel rises to saturation
- further cooling produces condensation
Facilitation of Condensation
- condensation nuclei
- come from volcanic ash, dust, combustion
Clouds: Above Freezing
- collision coalescence is dominate in clouds
- large drops combine with small ones as falling
- become too heavy for the could to hold (rain!)
Ice Crystals in Clouds
- ice crystal + super cooled water drops create rain
- super-cooled drops evaporate faster near ice crystals
- ice crystals grow and fall as rain/snow
Basic Cloud Form and Classification
- classified by shape and altitude
- puffy, wispy, flat
- 4 classes, 10 types
- in troposphere
Stratiform
- horizontal, flat, layered
- low level
Cumuliform
-vertical, puffy, globular
Cirriform
- wispy, composed of ice crystals
- High altitude
Cloud Indications
- atmospheric temperature
- atmospheric pressure
- relative humidity/moisture leve
Atmospheric Temp (indicated by clouds)
-shown by altitude clouds form
Low Elevation Clouds
- stratus, cumulus
- indicate cool atmosphere
- can lead to precipitation
Vertical Clouds
- cumulus, cumulonimbus
- suggest moist air
Fog
- cloud in contact with the ground
- dew point temperature and ground temperature is nearly identical
- visibility reduced to max 1 km
Advection Fog
-air migrates to a saturated area
Steam Fog
-water molecules evaporate from surface into cold overlying air
Radiation Fog
-radiate cooling of surface chills air layer above to dew point
Source Regions and Air
-air masses reflect characteristics of source regions
Great Lakes Effect
- warm great lakes heat up air
- moisten it
- causes heavy snow fall
Adiabatic Lifting
- air cools adiabatically
- reaches dew point and saturates
- condense and forms clouds
- possibly precipitates
Convergent Lifting
- occurs along ITCZ
- air flows from high to low pressure
- high, vertical, cumulonimbus clouds
Convectional Lifting
- stimulated by local surface heating
- and difference between land and water temperature
Orographic LIfting
-air masses forced over physical barrier
Front
-leading edge of air mass
Frontal Lifting
- air masses of different temperature and humidity
- interact by jet stream
- cold front displaces warm air (forcing up)
- warm front slides over cool air, forced to rise
Cold Front
- denoted by triangles
- life warm/moist air abruptly
Warm Front
- denoted by semi circles
- leading edge cannot displace cold air
- pushes cooler air underneath
Orographic Precipitation: Stable and Unstable Air
- stable forced up, may create stratiform
- unstable produces cumulonumbus
Windward Slode
-wetter, air masses passing above mountain absorb moisture
Leeward Side
- dry side of mountain
- air masses heated by compression
- hot and dry
Cyclonic Storms
- migrating, low pressure center
- converging, ascending
- spiraling
- draws surrounding air in
- born on polar front
Cyclonic Storms: Cyclogenesis
- disturbance at polar front
- warm are converges and rises
- > instability
Cyclonic Storms: Open stage
- counter clockwise (N. Hemisphere) flow
- pulls warm, most air
- from South into Low Pressure center
Cyclonic Storms: Occluded stage
- faster moving cold front overtakes warm front
- wedges, creating occluded front
- warm air forced upward
- precipitation occurs
Cyclonic Storms: Dissolving Stage
-dissolves when cold air mass cuts off warm air from energy and moisture
Thunderstorms
- tremendous energy release
- violent updrafts and downdrafts
- heavy rain, lightning, thunder, hail, blustery winds
- can cause tornado
Lightning
- enormous electrical discharge
- ignites air (15 000 to 30 000 degree Celsius
- violent expansion of abruptly heated air
- shock waves through atmosphere
Lightning: Relation to Thunder
-shock waves create sonic bangs, which is thunder
Lightning Build Up
- electrical energy between areas within cumulonimbus cloud
- electrical energy buildup between cloud and ground
- 3 seconds/km (time for distance between seeing lightning and hearing thunder)
Mesocyclone Formation
- body of air pushes faster at higher altitude than at surface
- creates horizontal rotation
Mesocyclone: Diameter, encountering updrafts
- strong updrafts create vertical rotation
- range diameter of 10 km
Mesocyclone: extending vertically and compressing horizontally
- speeds mesocyclone up
- inward vortex created
Mesocyclones Produce:
-heavy rain, hail, winds, lightning
Rain Routes: Interception
-rain striking ground cover/vegetation
Rain Routes: Throughfall
- rain that falls directly to ground
- rain that drips to ground from vegetation
Rain Routes: Stem Flow
-rain and drains across plant leaves and down stems
Rain Route Reaching the Soil
- reaches subsurface through infiltration
- permeates soil.rock through percolation
Potential Evotranspiration (PET)
- amount of moisture that WOULD evaporate and transpire if the moisture were available
- moisture demand
- correspond to temperature and humidity
PET Approximation
- mean month air temperature
- day length
Soil Moisture Storage (S)
- amount of water stored in soil and accessible to plants
- held against gravity
Water Budget
- comparing Precipitation P with PET
- by month determines if there is a net supply (+) or net demand (-) for water
