1. Air Masses

2. Introduction Video Weather and Climate
Watch the Video and Fill In the Guided Viewing Sheet

3. Weather vs. Climate
Weather: Physical conditions in the troposphere at any given moment (temperature, pressure, humidity, precipitation, sunshine, cloud cover and wind speed and direction.
Climate: A regions general pattern of weather over a long period

4. WEATHER INSTRUMENTS

5. Measurable properties include: Temperature Pressure Moisture content
WEATHER INSTRUMENTS
Different tools are used to measure a number of the atmosphere’s physical properties.
Measurable properties include:
Temperature
Pressure
Moisture content
Wind speed
Wind direction

6. WEATHER INSTRUMENTS Temperature is measured with a thermometer.
Temperature is measured in degrees.
Non-metric Units: Fahrenheit (°F)
Metric Units: Celsius (°C), Kelvin (K)
Temperature measures the amount of heat an object has, or the amount of molecular movement.
At absolute zero (0 K or °C), molecules don’t move.

7. THERMOMETERS

8. WEATHER INSTRUMENTS Humidity is measured with a hygrometer.
Absolute humidity tells you the mass of water per volume of air (in g/m3)
Also known as vapor pressure
Relative humidity tells you how saturated the atmosphere is (as a percentage).
It’s the ratio of absolute humidity to the maximum amount of water the air can hold at a given temperature
The dew point tells you at what temperature the atmosphere would be saturated.

9. HYGROMETER

10. WEATHER INSTRUMENTS Atmospheric pressure is measured with a barometer.
Pressure units:
Inches of Mercury: non-metric
Pascals (Pa), bars (b): metric
Most commonly expressed in hectopascals (hPa) and millibars (mb)
Mean sea level pressure = 29.92”, mb (or hPa), Pa
If pressure is rising, it usually means improving weather conditions.
If pressure is falling, it usually means deteriorating weather conditions.
Deteriorating = getting cloudy, rainy, stormy

11. BAROMETERS

12. They measure the pressure of different values.
BAROMETERS HYGROMETER
They measure the pressure of different values.
A barometer measures the atmospheric pressure of the air above you… the “weight” of the air where you are.
Hygrometer measures the water vapor content of the atmosphere where you are.

13. ANEMOMETERS
An instrument for measuring the speed of the wind, or of any current of gas.

14. WEATHER INSTRUMENTS Wind direction is measured with a wind vane.
Wind direction is expressed as a compass direction (north, south, east, west, or a combination of those: north- northwest, east-southeast, etc.)
The wind direction is the direction that the wind is blowing from.
In other words, if you turn so that the wind is blowing in your face, the direction you are looking is the wind direction.

15. WIND VANES

16. WHAT’S THE WEATHER?

17. What Creates Weather/Climate?
Air Masses Produce Weather/Climate
Air mass – a large region of air (thousands of square miles) having similar temperature, pressure, and moisture characteristics
Air masses move and strongly influence the changing of the weather, making them very important to understand

18. Formation of Air Masses
Air masses attain their characteristics from the part of earth’s surface over which they exist
Simple Examples
- air sitting over tropical ocean becomes warm and
moist
- air sitting over a desert will be warm and dry

19. Formation of Air Masses
Source region – an area of earth where air masses form
- Source regions are very large
- Source regions occur at high and low latitudes
(mid-latitudes are too variable)

20. Air Masses
Air masses are classified according to their temperature and moisture characteristics:
1) Based on moisture – continental (dry) or maritime
(moist)
2) Based on temperature – tropical (warm), polar (cold), or arctic (very cold)

21. There are 5 different types of air mass:
Air Masses
There are 5 different types of air mass:
1) Continental arctic (A) or (cA)
2) Continental polar (cP)
3) Continental tropical (cT)
4) Maritime polar (mP)
5) Maritime tropical (mT)

23. AIR MASSES: 5 TYPES Maritime Tropical (mT) Continental Tropical (cT)
a warm & humid air mass originating in the Gulf of Mexico, Caribbean Sea, Atlantic near the Bahamas, or off Mexico’s Pacific Coast
Continental Tropical (cT)
a hot & dry air mass originating in/near the deserts of the southwestern U.S. or northern Mexico, or the High Plains

24. AIR MASSES: 5 TYPES Maritime Polar (mP) Continental Polar (cP)
Cool and moist air mass that originates in the northern parts of the Pacific or Atlantic Oceans
Continental Polar (cP)
Cold and dry air mass that originates from the northern parts of North America (Alaska and northern Canada)
Arctic (A)
Very cold and dry air mass that originates from the Arctic Ocean or eastern Russia (Siberia)

25. Continental Polar Air Mass
Continental polar air masses are dry and cold
Form over high-latitude land surfaces (including ice)
In winter, very little solar radiation causes net cooling of air mass
Extremely dry since cold air cannot contain much water vapor
Typically clear and cloudless
Very stable (resists vertical motion)

26. Water Vapor in Cold Air

27. Continental Polar Air: Very Stable

28. Continental Arctic Air Masses
Continental arctic air masses are extremely dry, extremely cold versions of continental polar air masses
The only difference: Continental arctic air masses are shallower than continental polar air masses

29. Continental Arctic vs. Continental Polar

30. Maritime Polar Air Masses
Maritime polar air masses are moist and cool
Form over oceans (not ice) at high latitudes
Cool and moist due to contact with cold ocean water
Generally cloudy

31. Continental Tropical Air Masses
Continental tropical air masses are dry and warm
Form over low-latitude land surfaces
Hot and dry due to contact with hot land surfaces with little moisture
Generally cloud-free
Fairly unstable due to heating from below (but dryness inhibits cloud formation)

32. Maritime Tropical Air Masses
Maritime tropical air masses are moist and warm
Form over warm ocean (tropical) waters
Unstable conditions (moist warm air at surface)
Generally cloudy and partly cloudy
Responsible for daily showers/thunderstorms in the southeast U.S.

33. The Importance of Different Air Masses: The Pineapple Express
The Pineapple express – a weather phenomena that impacts the NW U.S.
Constant flow of maritime tropical air into the NW U.S.
Significant orographic (mountain-induced) rainfall
High freezing (and snow) levels
Causes destructive flooding

34. The Importance of Different Air Masses: The Pineapple Express

35. The Importance of Different Air Masses: The Pineapple Express

36. Summary of Air Masses

37. Air Mass Modification
Air masses can be modified as they move into new regions with different surface characteristics

38. Air Mass Modification
Air masses can be modified as they move into new regions with different surface characteristics
Example: Continental polar air moves southward

39. Air Mass Modification

40. Air Mass Modification

41. Air Mass Modification

42. CAUSES OF CLIMATE: TOPOGRAPHIC EFFECTS
Water heats up and cools down more slowly than land. Thus, large bodies of water affect the climates of coastal areas.
Temperatures in the lower atmosphere generally decrease with altitude. Thus, mountain climates are usually cooler than those at sea level.
The temperature of the atmosphere drops three degrees Fahrenheit for every 1000 feet in elevation rise.

43. CAUSES OF CLIMATE: TOPOGRAPHIC EFFECTS
Orographic lifting leads to rain on the windward side of a mountain. The leeward side is usually dry and warm
Leeward Side
- Less precipitation
Windward Side
- More precipitation

45. CAUSES OF CLIMATE: AIR MASSES
Air masses affect regional climates by transporting the temperature and humidity of their source regions.
Many times, air masses will modify (cool or warm, gain or lose moisture) as they move across the continent

46. KNOWLEDGE CHECK
During the summer, which air mass do you think has the biggest impact on Georgia’s weather? During the winter, which air mass do you think has the biggest impact on Georgia’s weather?

47. AIR MASSES AND FRONTAL BOUNDARIES
A front—regardless of its type (cold, warm, stationary, occluded)—is the boundary between two different airmasses.
The barbs (triangles) and pips (semi-circles) point the direction the airmass is moving.
The wind directions on either side of a front can clue you in on where the airmasses are moving from.
In North America, if the winds are from the northern half of a compass, its source is most likely polar or arctic.
If the winds are from the southern half of a compass, its source is most likely tropical.

48. AIR MASSES AND FRONTAL BOUNDARIES
Temperature gradient is the biggest clue as to whether an airmass is Arctic, Polar, or Tropical.
Moisture content can clue you in on if it’s continental or maritime.
If there is a strong moisture gradient—there’s a significant difference in dew points on either side of a boundary—hints at a difference between a maritime and continental airmass.
A change in wind direction will also clue you into a frontal boundary’s position.
Remember that the wind direction is where the wind is blowing from, so that should tell you something about the airmass’ source region.