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the atmosphere
the atmosphere
tripled at last glacial maximum
the hydrosphere & cryosphere
temperature
structure of the atmosphere
temperature vs. height
in the troposphere temperature decreases with height
the average lapse rate is about 5-9 degrees C per kilometer depending on the humidity
in the stratosphere temperature increases with height
in the stratosphere ozone absorbs incoming ultraviolet radiation
80% of the mass of Earth’s atmosphere is in the troposphere, we
all live in the troposphere
tropopause height varies with latitude
pressure vs. height
pressure at sea level is around 1000 millibars
pressure decreases with height exponentially
50% of the mass of Earth’s atmosphere is below an altitude
of 5-6 km (the 500 millibar height)
pressure is a force per unit area
daily mean daily range (max-min)
monthly mean
annual mean annual range
air temperature data
temperature
latitude
controls of temperature
sun angles at different latitudes
land & water
ocean currents
altitude
coasts
cloud cover
January
July
seasonal temperature differences
daily variations in air temperature
water’s changes of state
water
ice
humidity
humidity
relative humidity
changes with added moisture
changes with temperature
relative humidity
saturation mixing-ratio
Which has more Moisture? Which has higher Relative Humidity?
Higher Temperature Lower Relative Humidity with MORE Moisture!
Lower Temperature Higher Relative Humidity
with LESS moisture!
diurnal changes in relative humidity
atmospheric pressure
pressure is a force per unit area exerted by the weight of air above
-- about 1 kg/cm2 or 14.7 lb/in2 at the surface of Earth (equivalent to a 10 meter column of water)
units of pressure are N/m2
where N = Newton = force required to accelerate a 1 kg mass 1 m/s2
The SI unit for pressure is the Pascal (Pa) 1 Pa = 1 N/m2
a standard atmosphere (and average typical of a mid latitude location) exerts a pressure of 101,325 Pa at sea level
the unit adopted by the National Weather Service is the millibar (mb) 1 mb = 100 Pa
--> standard sea level pressure = 1013.25 mb
factors affecting atmospheric pressure
• gas molecules are able to fill space available
• gas molecules bounce off one another when they collide (and off the wall if in a container)
• the atmosphere is bounded above (gravity) and below (ground)
Air pressure is the force per unit area exerted against a surface by continuous collision of gas molecules
pressure is partly determined by temperature
consider a change in temperature while holding density (volume) constant
Temperature increase --> speed of molecules increases
(force increases, higher pressure)
pressure is partly determined by density
Density (# molecules/volume) increase --> increase in # of collisions (higher pressure)
consider a change in density (volume) while holding temperature constant
ideal gas lawBoyle's Law - at constant temperature, the volume of gas varies inversely with pressure
p1V1 = p2V2
Charles' Law - at constant pressure, the volume of a given mass is directly proportional to absolute temperature--> increase in temperature results in increase in volume
V1 / V2 = T1 / T2
Combine these two laws to obtain ideal gas law, or equation of state
p = ρ R T
where p = pressure, ρ = density, R = gas constant, and T = temperature
sea level pressure on Earth
pressure changes with altitude
pressure vs. altitude
pressure at sea level is around 1000 millibars
pressure decreases with height exponentially
50% of the mass of Earth’s atmosphere is below an altitude
of 5-6 km (the 500 millibar height)
pressure is a force per unit area
pressure changes with temperature
reducing pressure to sea level
isobars and wind barbs
