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EVSC 1300
Earth’s Weather and Climate
Scales of Motion
Scales of Motion
Increasing
size
Increasing
duration
Scales of Motion
Mercury Barometer
Aneroid Barometer
Barograph or Recording Barometer
Barograph Trace
Charlottesville
Jan. 5–10, 2009
Time of frontal passage
(4–6 p.m., Jan. 7)
Surface Map; Jan. 7, 2009; 7 a.m. EST
Surface Map; Jan. 7, 2009; 7 p.m. EST
Sea-level pressure
variations
Station
vs.
Sea-level
Pressure
correction factor for elevation
resulting map of sea-level
pressure variations
(surface map)
station pressure—barometer measurement
Sea-level Pressure
Map
Influence of topography
(elevation) on pressure
has been removed
Change of Air Pressure and Density with Height
Earth’s atmosphere is thin relative to the size of the planet.
Change of Air Pressure with Height
10% of
atmosphere’s
mass above
100 mb
100 mb
90% of
atmosphere’s
mass below
100 mb
500 mb Map
Upper air map showing winds and other variables at the “mid-point” of the atmosphere.
air molecules
Number of air
molecules determine
surface pressure
(Note: Unrealistic
example...constant
density and fixed top)
Air Column
D
E
N
S
E
TWO BAROMETERS
SAME
TEMPERATURE
High Pressure
Barometer
Air Column
L
E
S
S
D
E
N
S
E
Low Pressure
Barometer
At same temperature, dense air has higher pressure than less dense air
Impact of Heating and Cooling on Pressure
Reference Level
Warming or cooling air can induce pressure changes.
Pressure change can produce air motion—wind!
Pressure and Density
Same temperature at both locations
Denser air produces higher surface pressure
(Chap. 8; pp. 199–206)
Wind Direction (16-point compass)
Wind is defined based on the direction from which it is coming.
Cyclones and Anticyclones
Surface Low = CYCLONE
(counter-clockwise winds)
Surface High = ANTICYCLONE
(clockwise winds)
(N. Hemisphere)
Cold vs. Warm Air Parcels
Cold air is denser that warm air (at the same pressure)
Surface Air
Temperature
Variations
Composition of Atmosphere
Permanent
Variable
N2
O2
SOURCE
(to atmosphere)
SINK
(removal from atmosphere)
•Denitrification by anaerobic
bacteria in wet soil
•Fixed by (incorporated into) soil
bacteria
•Fixed by ocean phytoplankton
•Lightning
•Ocean phytoplankton
•Photosynthesis
6 CO2 + 6 H2O
CO2
•Aerobic bacterial processes
•Combustion
•Respiration (oxidation: food to energy)
•Respiration
•Combustion
Vis. light
C6H12O6 + 6 O2
•Photosynthesis
•Fixation by ocean phytoplankton
•Dissolved directly into ocean surface
STORAGE: limestone sediments, marine shells, fossil fuels
SOURCE
(to atmosphere)
CH4
N2O
O3
SINK
(removal from atmosphere)
•Anaerobic processes
(wetlands, rice paddies)
•Bovine flatulence
•Termites
•Biomass burning
•Bacteria in soils/oceans
(nitrification)
•Combustion (cars, biomass)
•Fertilizers
O2 + O
O3
•Interaction with hydroxyl in atmosphere
•Soils
CH4 + OH
CH3 + H2O
•Stratospheric photochemistry
(converted to NOx)
O3 + uv
O2 + O
Also chlorine, bromine, NOx
H2O
•Evaporation from open water
•Sublimation (from ice)
•Transpiration (through plants)
•Condensation onto surfaces
•Precipitation
•Deposition
Average
vertical
temperature
structure
of atmosphere
(Chap. 1)
Variation of Tropopause Height by Latitude
Tropopause is higher over equator and lower over poles