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Meteorology > Air Masses and Fronts > Flashcards

Air Masses and Fronts Flashcards

1
Q

What is an air mass?

A

A large volume of air that has uniform:

  • Horizontal temperature
  • Relative Humidity
  • Environmental Lapse Rate
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2
Q

What is a front?

A

A narrow boundary of transition between air masses of different temperatures

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3
Q

What are source regions?

A

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.

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4
Q

What classifications of air masses are used in Australia?

A
  • Pm (Polar Maritime)
  • Tc (Tropical Continental)
  • Tm (Tropical Maritime)
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5
Q

What is an airstream?

A

A moving air mass

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6
Q

What occurs if an air mass moves towards the equator?

A

Destabilizes and increases the ELR

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7
Q

What occurs if an air mass moves towards the pole?

A

Stabilizes and decreases the ELR.

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8
Q

What front moves faster, cold or warm?

A

Cold fronts move faster.

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9
Q

Are warms fronts more common in Australia or NZ?

A

NZ

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10
Q

What is the approach of a warm front characterized by?

A
  • 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.
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11
Q

What is the passage of a warm front characterized by?

A
  • Wind backs to west to northwest
  • Rain easing and eventually stopping
  • Cloud clearing to the SE
  • Temperature rising
  • Relative humidity decreasing
  • Barometric pressure steadying
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12
Q

What weather conditions are produced by a cold front?

A
  • Potential thunderstorms and violent winds.

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

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13
Q

What is the approach of a cold front characterized by?

A
  • 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
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14
Q

What is the passage of a cold front characterized by?

A
  • Wind backs to south to southwesterly
  • Temperature falling
  • Humidity rising
  • Pressure starts to rise
  • Possible thunderstorms and squall
  • Low cloud.
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15
Q

What is an occluded front?

A

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

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16
Q

What is quasi-stationary front?

A

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

17
Q

What latitudes cover the tropics?

A

23.5 degrees south and north.

18
Q

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

A
  • In the summer, it migrates towards the pole

- In the winter, it recedes towards the equator

19
Q

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

A
  • In the Southern Hemisphere winter.

- Australia is under the influence of southeast trade winds.

20
Q

What are some hazards to aviation during the dry season?

A
  • Occasional poor visibility due to bushfire smoke
  • Morning inland fog
  • Coastal showers
  • Turbulence associated with trade wind inversion
21
Q

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

A
  • Occurs during the southern hemisphere summer.

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

22
Q

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

A
  • Trade winds
  • An East to Southeasterly wind flow, emanating from the northern side of the subtropical ridge in the southern hemisphere.
23
Q

What are the roaring forties?

A
  • Westerly winds in southern Australia during dry season in northern Australia.
  • Characterized by passage of cold fronts every few days.
24
Q

What is the Intertropical Convergence Zone (ITCZ)?

A
  • 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
25
Q

What is a monsoon?

A
  • 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.
26
Q

What are the typical characteristics of the northern Australian monsson?

A
  • 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.
27
Q

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

A
  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
28
Q

What are the four distinct stages of a tropical cyclone?

A
  1. Formation
  2. Immature
  3. Mature
  4. Decyaing
29
Q

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

A

Below 1000 hPa

30
Q

Where are strongest winds/weather in a tropical cyclone?

A

Let hand front quadrant.

Meteorology (24 decks)

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