Climates on Earth
5 major climate types
tropical, desert, mid-latitude (2 kinds), polar
Classifications based on temperature and humidity
Basic Climate Patterns
Tropical (wet and dry) (0-15o N & S)
Deserts (evaporation is greater than precipitation)
Often classified as less than 9 in of rain a year
Average for W. OR is ~45in/year
Mid-latitude
Climate varies based on location
Polar (warmest month < 50o F)
Why does the earth have the climates at the locations it does?
Air masses moving around on the Earth control the weather patterns and climates
Why does air move around the globe?
Tropics: most solar energy
Poles: least solar energy
Air rises and moves to poles from the equator
High heat at equator
Wet air masses
Air sinks and moves to equator from the poles
Low heat at poles
Dryer air masses
Earth’s Complications with this Basic Model
Friction
Coriolis effect
Secondary ocean current influences
Differential heating effects
Radiant heat from different materials
Seasonal variations
All of these variations create small circulation cells in the atmosphere with more complex patterns at mid latitudes
Hadley, Ferrel and Polar Cells
These air masses rising and falling create high and low pressure system at
particular latitudes.
Equatorial Low
Rising air mass
Subtropical High
Sinking air mass
Subpolar low
Rising air mass
Polar High
Sinking air mass
Winds
Coriolis effect and where wind comes from determines where they go
Often named for direction they come from
Jet Streams
High altitude and high velocity winds
Creates continuous migration of W to E air masses
Affected by seasonal temperatures
Often polar jet stream affects Oregon
Why do we get global climates we do?
Rising air masses & Sinking air masses
How does this affect temperature and humidity of these air masses?
Humidity and rain
Absolute humidity: Actual amount of water present in an air mass.
Water Vapor capacity: the amount of water an air mass can hold at any given t
temperature
Relative humidity: a percent of how much water is in an air mass relative to what that
air mass can hold. (Absolute hum/capacity) x 100
If an air mass has a temperature of 50oF, what is the H2O vapor capacity of the air mass?
If the air mass has 3 grams of water vapor in it what is the relative humidity
If the relative humidity of an air mass is 56% and the temperature of the air mass is 50oF, how much water is actually in the air mass (what is its absolute humidity?)
What is the Dew point of an air mass?
Dew point is the point where the amount of water the air mass is holding is the most
it can hold…
100% relative humidityà clouds, rain, fog, snow, etc…
Expressed as the temperature at which 100% relative humidity is reached.
Ex// if an air mass has 14 g of H2O per kg of air, what would it’s dew point be?
Water Vapor + Lower Temperature = Dewpoint
The formation of clouds, fog and dew
Clouds form at high altitudes and often during the heat of the day…Why?
Why do air masses rise?
Density differences
Orographic lifting
Frontal wedging
Convergence
Why does an air mass cool as it moves upward?
Adiabatic pressure changes create temperature changes
Air expanding cools down
Air contracting warms up
Rate of adiabatic cooling depends on dew point
Dry adiabatic rate 1oC /100m (10oC/1000 m)
Wet adiabatic rate 0.5oC/100m (9o to 5oC/1000 m)
Why is the wet rate different than the dry?
Why does the wet adiabatic rate vary?
Environmental lapse rate (ELR)
Rate of temperature change for atmosphere with change in altitude
Can vary depending on conditions
ex// an environmental lapse rate of 5oC/1000m means that if we start at sea
level with a temperature of 25oC then at 1000m the temperature would be
20oC; at 2000 meters t=15oC
DON’T CONFUSE WITH ADIABATIC RATE
ELR vs adiabatic rate
Environmental lapse rate says how the surrounding air is changing
Adiabatic rate says how a particular air mass is changing
Adiabatic rate is usually 10oC/1000m (dry) or 9o to 5oC/1000 m (wet)
ELR can vary to any rate
Stability of an air mass
Combine ELR and adiabatic rate
Stable air masses occur when temperature of surrounding air is greater than air
mass
Absolute unstable air masses occur when temperature of surrounding air is less
than air mass
Conditional unstable air masses--> dry air is stable, saturated is not
Exercise #2
Determine if an air mass with a temperature of 20oC at sea level is stable or unstable
at an ELR 0f 5oC/1000 meters. The dew point for the air mass is 0oC.
Determine if an air mass with a temperature of 20oC at sea level is stable or unstable
at an ELR of 13oC/1000 meters. The dew point for the air mass is 7oC
For the air mass in the above question, at what elevation does it reach it’s dew point?
An air mass is 30oC and has a relative humidity of 26.4%
what is the dew point for this air mass
if the ELR is 12oC/1000m is this a stable or unstable air mass