Week six - start here for final

Question 1

Air masses

Answer 1

Large bodies of air with fairly uniform temperature and moisture characteristics

Question 2

We define air masses based on

Answer 2

• Latitude (temperature) - Tropical, Polar, Artic / Antarctic,

Equatorial: empty air mass (tropical and maritime)

• Surface type (moisture) - marine, continental

Question 3

Fronts

Answer 3

• Fronts are the boundaries that separate the air masses with differing temperature and other characteristics.
• Most often the boundary represents the boundary between polar and tropical air
• Cold air typically more dense than warm air, the two bodies not mix well together. Instead the denser air remains near the surface and forces the warm air up.

Warm air is unstable

Question 4

Frontal Lifting (q card for visual)

Answer 4

• When boundaries between air of unlike temperatures (fronts) migrate, warmer air is pushed aloft (frontal lifting)
• This results in adiabatic cooling and cloud formation
• Cold fronts: cold air advances towards warm air and warm air is displaced vertically by cooler air
• Warm fronts: warm air advances towards cold air and gently rises on it

Question 5

Cold fronts

Answer 5

• The cold air mass forces the warm air mass aloft, often forming a line of clouds or thunderstorms (a squall line)>

Think about cloud types and precipitation characteristics (intensity and duration)

Cloud type are cumuliform clouds that are characterized by intense, but short precipitation events. Intense thunderstorms can develop along the front.

Question 6

Warm fronts

Answer 6

The warm air rides up and over the cold
air, causing stratus formation and precipitation.

Think about cloud types and precipitation
characteristics (intensity and duration.

* Warm fronts generally slower than cold fronts

• Since warm air gently overrides the cold air, stratiform
  clouds form
• As the warm air raises along the front a sequence of
  higher clouds develops: nimbostratus, altostratus, cirrostratus and cirrus
• Precipitation along warm fronts is generally less
  intense, but of longer duration than in the case of a cold front.
• Since the precipitation particles are falling through a cold air mass, sleet and freezing rain are often observed in connection with warm fronts during the
  winter time

Question 7

Occluded fronts (A faster moving cold front overtakes a warm front,
leading to precipitation)

Answer 7

• The term occluded front or occlusion refers to closure – the
  cutting off of the warm air from the surface by the meeting of two fronts
• It happens when a fast moving cold front catches up to the
  slower moving warm front.
• The warm air is still present, but it is aloft, pinched off from the surface and therefore not reflect in surface measurements.
• Due to the strong lifting, occluded fronts can be associated with significant precipitation

Question 8

Travelling cyclones and anticyclones

Answer 8

The movement of air into cyclones (low pressure) and outward from anticyclones (high pressure) which travel
across the surface are responsible for changing weather conditions.

Question 9

Three general types of cyclones:

Answer 9

• “Wave” or “mid-latitude” cyclones
• Tropical cyclones
• Tornadoes

Question 10

Stages of a mid-latitude cyclone

Answer 10

1. Early stage or Cyclogenesis – convergence of cold, polar air and warm, subtropical air wand war air masses
2. Open Stage – warm air moves north along advancing front, cold air moves south
3. Occluded stage – cold front overtakes warm front, forcing
   warm air aloft and causing Precipitation
4. Dissolving stage – lifting of warm air ceases so cyclone
   loses source of energy and moisture