Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

METEOROLOGY > MOUNTAIN WEATHER > Flashcards

MOUNTAIN WEATHER Flashcards

1
Q

How does atmospheric stability impact airflow over a mountain range?

A

Stable: As much air will try to flow AROUND the barrier as possible, rather than over. Points at either end of the range will experience very strong winds. (terrain channelling)

Unstable: air will tend to rise up and over the barrier, resulting in stronger winds at ridge-top

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is a barrier jet?
When would the West coast of the SI experience this?

A

A strong tube of wind, averaging around 60kts, found 1-2000ft AMSL immediately above the coastline.
Rotation is counter clockwise along direction of travel in SH.

In a strong NW flow.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

How would a NW flow affect the south island?

A
  • Ridge of high pressure on west coast
  • Karamea; low level winds split, Winds that head around farewell spit turn NE then into a strong N. Winds that head south form barrier jet.
  • Jet forces rise of windward side air up over the ranges, rainfall enhanced above coastline
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

In a NW flow, when would the first standing wave generated over the southern alps touch down?

A
  • NW flows develop ahead of sub-polar fronts.
  • As front gets closer, pressure gradient across the SI increases.
  • Touch down usually occurs when pressure difference reaches >8hPa
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

When would a NW flow replace a NE sea breeze on the canterbury plains?

A

Pressure diff between west & east coast will continue to increase, touchdown footprint will grow larger & displace the seabreeze, replacing with a NW.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

How else will wind tend to get up & over the ranges

A

Due to restoring force of stability, wind will tend to funnel through river valleys, passes, saddles & cols. Wind will be very strong in these areas.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

5 factors that affect an airflow across ranges?

A
  1. wind strength
  2. Angle of flow near mountains
  3. Shape of mountain range
  4. stability of the air
  5. vertical profile of wind speed and direction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

5 conditions favourable for well-developed lee waves?

A
  1. Wind flow within 30deg of perpendicular to the ridge line.
  2. At least 20kt wind at ridge top level
  3. Wind speed increasing with height
  4. little variation of wind direction with height
  5. A stable layer in the atmosphere at about ridge top level (provides restoring force for waves)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

How do lee waves form?

A
  • Air displaced upwards on the WW side of the range encounters a stable layer at ridge top level
  • Air is restored & descends on LW side
  • Downstream series of oscillations are formed
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What altitude can a lee wave system extend to?

A
  • up to 80,000ftover southern alps
  • up to 36,000ft over tararua ranges.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What does wavelength depends on for lee waves?

A
  • Vertical speeds can hit up to 1000s of fpm
  • wavelength depends on wind speed & stability of the air.

typically 10-40km

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What defines the amplitude of a lee wave?

A

Determined by the shape of the mountain range

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

If the 5 condxns for lee wave development are met, where will the first wave form?
Increase in wind speed?

A

Immediately over ridge line.

increase beyond 20kt min = increase in wave length & firs wave will move further downstream from ridge line

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

How can multiple ranges affect mountain waves?

A

Can have the effect of cancelling out the wave, or doubling the amplitude and shortening the wave length

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is hydraulic jump?

A

Occurs when extremely strong downslope air meets slower downstream winds

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

How does rotor streaming form?

A

-Strong winds, blowing at right angles to a ridge line (Easterly)
- Marked decrease in wind strength above the ridge line. (Due higher altitude westerlies)
- Lee waves will not form
- Single rotor forms at ridge top level, immediately lee of the range.
- Rotor migrates downstream (nil anchoring wave above)

17
Q

Conditions required for rotor streaming? (2)

A
  • Wind near perpendicular to ridge line
  • Strong winds at ridge top height, decreasing above
18
Q

Features of rotor streaming (2)

A
  • Severe turb in rotor zone on lee side of the ridge (usually about and below ridge top level)
  • Relatively smooth flow above ridge level
19
Q

Where could you expect rotor streaming to occur?

A

Western sides of any of the major NE to SW running ranges in NZ.

20
Q

What is a Fohn wind?

A

A warm, dry and very gusty wind blowing down the lee side of a major mountain range.

21
Q

How does a Fohn wind form?

A
  • Air rises on WW side of range
  • Cloud forms & latent heat is released.
  • Air will cool at SALR
  • If there is rainfall on WW side, water vapour will reduce.
  • Air on LW side will therefore heat up at DALR = warm & dry.
22
Q

What are the five features of a fohn wind?

A
  1. a fohn gap (band of clear skies in lee of ranges, in the descending air of the wave system)
  2. Very high cloud bases on the lee side
  3. turbulent condxns
  4. Lee wave activity
  5. Very warm temps (High DA) in east
23
Q

Weather to expect in fohn wind condxns?

A
  • WW side: very low cloud bases, heavy precip & poor vis. Potntial for embedded TS.
  • Strong winds at ridgetop.
  • Immediately east of ridgeline: rapid clearance of most cloud, often a layer of high cloud (FL150 - FL200)
  • LW side: VFR condxns, but mod-sev turb poss
24
Q

Gen mountain wx: cloud bases

A
  • Lower bases on WW side
  • LW side, high cloud bases. Some lower level cloud may exist in form of rotor clouds (avoid at all costs)
  • Can change rapidly (slight increase in moisture advected into area of rising area can form cloud rapidly)
25
Q

Gen mountain wx: Turb

A

-WW: light to mod turb is common, sev turb only in embedded TS
- LW: sev turb common, esp in rotor zones but common anywhere within the friction layer. Hydraulic jump can also create sev turb.

26
Q

What are the factors affecting the path wind takes wrt mountain ranges? (8)

A
  1. The wind strength
  2. angle of flow near the ranges
  3. Shape of ranges
  4. Stability of the air
  5. vertical profile of wind speed & direction
  6. orientation of valley systems
  7. location of passes & higher peaks
  8. effects of multiple ranges
27
Q

Gen mountain wx: vis

A
  • WW: poor in RA, DZ or SN.
  • LW: very good, but curtains of rain/virga can exist downstream from ranges
28
Q

ROT wrt mountain airfield TAFs (NZQN, etc)

A

If they have three or more QNH forecast lines indicating rapidly falling pressures, wx WILL rapidly deteriorate over the next 5-10hrs

29
Q

4 dangers of flying in Lee wave condxns

A
  1. strong downdrafts
  2. rising ground
  3. low G/S
  4. risk of rotors with sev turb
30
Q
A

METEOROLOGY (26 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions