Surface
Ch 5
Ch 5Level Low
Vertical Motion and
Stability
Sec A
Sec A
Surface
Level High
Vertical Motion and
Stability
• Vertical Motions: Causes
– Converge/Divergence Caused by Low and High
pressure areas
• Surface Low: updraft; Surface High: Downdraft
• Upper Level Low may create a downdraft at the surface
• Upper Level High may create a updraft
Upper
Level Low
Upper
Level High
1
Ch 5
Ch 5
Vertical Motion
Sec A
2
Vertical Motion
Sec A
• Vertical Motions: Causes
– Fronts:
• Warm fronts are moving over cold air can cause updrafts
• Cold fronts are moving under hot air forcing it up
– Orography (Oro means mountains in Greek)
• Winds go up on the Windward side of Mountains
(Windward: the side the wind blows towards)
• Winds go down on the Leeward side of Mountains
(Leeward: the side the wind blows away from)
3
Vertical Motion
Ch 5
4
Ch 5
Sec A
Sec A
• Vertical Motions: Causes: Fronts:
• Warm fronts are moving over cold air can cause updrafts
• Cold fronts are moving under hot air forcing it up
Vertical Motion
• Vertical Motions: Causes: Orography
– Orography (Oro means mountains in Greek)
• Winds go up on the Windward side of Mountains
(Windward: the side the wind blows towards)
• Winds go down on the Leeward side of Mountains
(Leeward: the side the wind blows away from)
Cold Air
Warmer Air
5
6
1
Ch 4
Ch 5
Vertical Motion
Sec E
Vertical Motion
Sec A
• Vertical Motions: Orography
• Vertical Motions: Causes
– Convection
Leeward
Side of
Mountains
• Bubbles of Hot Air rise
• If they are moist you have convective clouds
Windward
Side
of
Mountains
7
Ch 5
– Mechanical Turbulence:
Drag of the surface on the wind can cause eddies
– Gravity Waves: can be mountain waves which may
propagate several miles beyond the mountains.
Somewhat like ocean waves.
May occur on leeward side of the Galvian Mtns.
8
Or the Sierra Nevada Mtns.
Ch 5
Atmospheric Stability
• Stable
• Unstable
Neutral
Sec B
o
V
Atmospheric Stability
• Boyancy:
– Parcels Less dense than their surroundings will rise
– Parcel More dense than their surroundings will sink
o
V
Sec B
– A parcel of warmer air will rise
– A parcel of colder air will sink
o
9
Ch 5
Sec B
10
Ch 5
Determining Atmospheric Stability
• To Do this we must understand three things:
– 1. Dry Adiabatic Process
– 2. Atmospheric Soundings
– 3. Lapse Rates: LR
• Adiabatic means without loss of heat
– A. Adiabatic Cooling will accompany upward
motion: Movement to an area of less pressure.
– B. Adiabatic Warming will accompany downward
motion: Move to an area of more pressure
11
How is an airliner heated?
Sec B
Determining Atmospheric Stability
• A Dry Adiabatic processes has a temperature
change of approximately 3oC per 1000 feet
• Cooling by expansion
Warming by compression
12
2
Ch 5
Sec B
Ch 5
Determining Atmospheric Stability
• Soundings: Measurement of atmosphere using
satellites, rockets, and aircraft;
but most commonly with balloons
• These balloons are commonly called
radiosondes
(or sometimes rawinsondes)
• Twice a day at 0000 GMT and 1200 GMT
hundreds of these are launched.
• They sample temp., pressure, moisture and
wind at up to 100,000 feet MSL.
13
Ch 5
Sec B
Sec B
Determining Atmospheric Stability
• Soundings most importantly produce a
temperature profile of the atmosphere.
• It is not always like the one you learned in
chapter 2.
• Within the troposphere there may be pauses
called isothermal layers. There may be layers
where it gets warmer in the troposphere.
These are called inversions.
14
Ch 5
Determining Atmospheric Stability
Sec B
Determining Atmospheric Stability
• Lapse Rate is the change in Temperature divided by
the change in Height
• LR = T(bottom) – T(top)
DeltaZ
• Where
– T(bottom) is the temp. at the bottom of a layer
– T(Top) is the temp. at the top of a layer
– DeltaZ is the thickness of a layer.
15
Envisioning DALR
Ch 5
1. Imagine a garbage bag ¼ full of Helium and Sec B
sealed at the bottom.
2. As it rises it will expand and cool at approx.
the DALR rate.
3. If the air outside cools faster than DALR the bag
will rise faster (it will be hotter compared to OA).
4. If there is an isothermal layer the bag may
rise slowly.
5. IF the LR is negative(getting warmer) the bag
may not rise at all.
6. In reality the bag is a parcel of air.
7. What Makes things rise: Pressure Differential
17
What does higher T do to P=NRT/V=DRT;
• DALR is the Dry Adiabatic Lapse Rate
3oC per 1000 feet
• ISALR for the Troposphere is 2oC per 1000 feet
(International Standard Atmosphere)
Envisioning DALR
16
Ch 5
1. Imagine a garbage bag ¼ full of Helium and Sec B
sealed at the bottom.
2. As it rises it will expand and cool at approx.
the DALR rate.
3. If the air outside cools faster than DALR the bag
will rise faster (it will be hotter compared to OA).
4. If there is an isothermal layer the bag may
rise slowly.
5. IF the LR is negative(getting warmer) the bag
may not rise at all.
6. In reality the bag is a parcel of air.
7. What Makes things rise: Pressure Differential
18
What does higher T do to P=NRT/V=DRT;
3
Ch 5
Sec B
Ch 5
Stability Evaluation
Sec B
1.
Stability Evaluation
1. Pick the layer you are interested in from the
sounding temperature graph.
2. Compare the DALR and the LR
3.
IF
Then
LR>DALR
Absolutely Unstable
LR = DALR
Neutral
LR < DALR
Stable
19
Ch 5
Sec B
20
Ch 5
Stability Evaluation
Sec B
1.
1.
LR
ISA
A Capping Inversion
21
Ch 5
Sec B
22
Ch 5
Stability Evaluation
Sec B
Stability’s Impact on Air Movement
1. A Stable airmass has smoother flying air.
2. Stratus clouds mean more stable air than
cumulus clouds.
3. Calm, Cool nights can produce inversions
along with other ways
4. Stability is decreased by heating from below.
23
24
4