Classification of Air Masses

Based on 2 aspects
1) Latitude: indicates the general temperature conditions
3 class system
A (Arctic) – highest latitudes, coldest air masses
P (Polar) – Mid- to high latitudes, cold air masses
T (Tropical) – Low latitudes, warm air masses

2) Source Area Surface: Indicates humidity conditions
m (maritime) – oceans, seas or gulfs; Generally moist, humid air masses.
c (continental) – large land masses; Generally dry, arid air masses.

2 letter scheme, combining:
– small case Source designation
– upper case Latitude designation.
Examples: mA, cA, mP, cP, mT, cT

Climate

Long term average atmospheric conditions for a region.
Typically based on:
Global Climate: long term average atmospheric conditions for entire planet.

Temperature

Physical factors controlling temperature:

Precipitation

Physical factors controlling precipitation:

Climographs

Displays average temperature and precipitation for a specific location
Should contain following information:
Location name
Longitude and latitude
Elevation
Temperature line graph
Precipitation bar graph

Climate Classification

5 Major Groups of 13 Climate Types based on Temperature and Precipitation
Wladimir Köppen classification developed in 1900

Group A – Tropical Moist Climates

Winterless climates
All months have a mean temperature above 18°C
Annual precip. is >150 cm
ITC, Trade winds, Subtropical High Pressure Belt
cT and mT air masses

Group B - Dry Climates

Climates where evaporation exceeds precipitation; constant deficiency of water
cP, mP, cT, mT air masses
Subtropical High Pressure Belt, Polar Front, Wave Cyclones, Prevailing Westerlies

Group C – Moist Subtropical Mid-Latitude Climates

Mild winters; average temperature of coldest month is below 18°C, but above -3°C.
cP, mP, cT, mT air masses
Subtropical High Pressure Belt, Polar Front, Wave Cyclones, Prevailing Westerlies

Group D – Moist Continental Mid-Latitude Climates

Severe winters; average temperature of coldest month is below -3°C, and the warmest monthly mean is above 10°C.
cA, mA, cP, mP, cT, mT air masses
Polar Front, Wave Cyclones, Prevailing Westerlies

Group E – Polar Climates

Summerless climates; average temperature of the warmest month is below 10°C.
cA, mA, cP, mP air masses
Polar Front, Wave Cyclones, Polar Easterlies

H - Highland Climate

Occurs in higher elevation terrains
No common latitude
Temperature is generally lower than neighboring climates but varies widely
Precipitation can be very low to very high
Orographic precipitation / Rain shadow effects are common
Many local variations in climate - Microclimates

Microclimates

Small variations in the climate due to small changes in:

---