Air Masses and Fronts

Question 1

What is an air mass?

Answer 1

A large volume of air that has uniform:

• Horizontal temperature
• Relative Humidity
• Environmental Lapse Rate

Question 2

What is a front?

Answer 2

A narrow boundary of transition between air masses of different temperatures

Question 3

What are source regions?

Answer 3

When air masses remain in a particular area for a lengthy period and the regional surface conditions are relatively uniform, the air mass will acquire the characteristics of that area.

Question 4

What classifications of air masses are used in Australia?

Answer 4

• Pm (Polar Maritime)
• Tc (Tropical Continental)
• Tm (Tropical Maritime)

Question 5

What is an airstream?

Answer 5

A moving air mass

Question 6

What occurs if an air mass moves towards the equator?

Answer 6

Destabilizes and increases the ELR

Question 7

What occurs if an air mass moves towards the pole?

Answer 7

Stabilizes and decreases the ELR.

Question 8

What front moves faster, cold or warm?

Answer 8

Cold fronts move faster.

Question 9

Are warms fronts more common in Australia or NZ?

Answer 9

NZ

Question 10

What is the approach of a warm front characterized by?

Answer 10

• Direction and speed of approach are generally towards the east at less than 20 kts
• Clouds develop well ahead of the front, thicking and cloud base lowering as the front approaches
• Wind from north to northeast
• Barometric pressure falling
• Rain at about 150 NM ahead of the surface position.

Question 11

What is the passage of a warm front characterized by?

Answer 11

• Wind backs to west to northwest
• Rain easing and eventually stopping
• Cloud clearing to the SE
• Temperature rising
• Relative humidity decreasing
• Barometric pressure steadying

Question 12

What weather conditions are produced by a cold front?

Answer 12

• Potential thunderstorms and violent winds.

- Icing could be a problem, especially in winter and visibility may be reduced due to precipitation.

Question 13

What is the approach of a cold front characterized by?

Answer 13

• The formation of cirrus cloud, forming to the SW
• General speed of advance of 15 - 50 kts
• Wind from the NW, backing and strengthening
• Temperature increasing
• Barometric pressure failing
• Cumulus and possible cumulonimbus with increasing rain

Question 14

What is the passage of a cold front characterized by?

Answer 14

• Wind backs to south to southwesterly
• Temperature falling
• Humidity rising
• Pressure starts to rise
• Possible thunderstorms and squall
• Low cloud.

Question 15

What is an occluded front?

Answer 15

When two fronts collide with one another, and cloud is forced up at the boundary between then.

Question 16

What is quasi-stationary front?

Answer 16

A front along which one air mass is not replacing another air mass.

Question 17

What latitudes cover the tropics?

Answer 17

23.5 degrees south and north.

Question 18

Where does the Hadley cell migrate to in the summer and winter?

Answer 18

• In the summer, it migrates towards the pole

- In the winter, it recedes towards the equator

Question 19

When does the dry season occur? What is Australia under the influence of?

Answer 19

• In the Southern Hemisphere winter.

- Australia is under the influence of southeast trade winds.

Question 20

What are some hazards to aviation during the dry season?

Answer 20

• Occasional poor visibility due to bushfire smoke
• Morning inland fog
• Coastal showers
• Turbulence associated with trade wind inversion

Question 21

When does the wet season occur? What is Australia under the influence of?

Answer 21

• Occurs during the southern hemisphere summer.

- Intertropical continental zone moves over north Australia bringing thunderstorm weather.

Question 22

What are the prevailing winds during the dry season and which direction do they flow in?

Answer 22

• Trade winds
• An East to Southeasterly wind flow, emanating from the northern side of the subtropical ridge in the southern hemisphere.

Question 23

What are the roaring forties?

Answer 23

• Westerly winds in southern Australia during dry season in northern Australia.
• Characterized by passage of cold fronts every few days.

Question 24

What is the Intertropical Convergence Zone (ITCZ)?

Answer 24

• The point where the trade winds from both hemispheres converge in the NH during the NH monsoon and SH during the SH wet season.
• Bad weather can occur

Question 25

What is a monsoon?

Answer 25

• A seasonal wind that blows from an ocean towards a large landmass, under the influence of a thermal depression, and accompanied by changes in precipitation.

Question 26

What are the typical characteristics of the northern Australian monsson?

Answer 26

• Wind speed generally moderate to fresh northwesterly.
  Stronger at lower latitudes
• Occurs during wet season
• Great depth of moisture
• Thunderstorms and showers
• Goes through series of active and non-active cycles over a varying timescale.

Question 27

What are the 7 conditions required for the formation of tropical cyclones?

Answer 27

1. Sea surface temperature of at least 26 C to a depth of 60m - latent heat energy source
2. Instability over a large area
3. Available moisture
4. South or north of 5 deg from the equator to allow Coriolis force to be sufficient to provide cyclonicity.
5. Pre-existing disturbance with convergence and existing cyclonic vorticity
6. Light upper level winds to allow extensive vertical development of the system.
7. TUTT - forms along the tropical upper tropospheric trough

Question 28

What are the four distinct stages of a tropical cyclone?

Answer 28

1. Formation
2. Immature
3. Mature
4. Decyaing

Question 29

What is typical pressure of middle of tropical cyclone during height of tropical cyclone?

Answer 29

Below 1000 hPa

Question 30

Where are strongest winds/weather in a tropical cyclone?

Answer 30

Let hand front quadrant.