unstable atmosphere: - air forced upwards will continue to...
TRANSCRIPT
Unstable Atmosphere:
- Air forced upwards will continue to rise
- As air rises, Temperature decreases and RH increases
if RH=100% => condensation and cloud formation => latent heat released => possibility of storm formation
Clicker Question
Which type of clouds are more likely to form in unstable conditions? (A) stratus clouds (layered) (B) cumulus clouds (vertically developed) (C) fog (cloud in contact with surface)
Set Frequency to "BB"
1. WHAT CAUSES ATMOSPHERE TO BECOME MORE/LESS UNSTABLE? 2. WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?
1. WHAT CAUSES ATMOSPHERE TO BECOME MORE/LESS UNSTABLE? ONE WAY IS THROUGH MIXING => Rising Air Cools
Sinking Air Warms
Temperature
Height initial profile of environment air
compresses and warms
expands and cools
Height
Temperature
ΓDRY (10°C/km) Stable
ΓM (6°C/km)
Unstable
Conditionally Unstable
1. WHAT CAUSES ATMOSPHERE TO BECOME MORE/LESS UNSTABLE? ONE WAY IS THROUGH MIXING => Rising Air Cools
Sinking Air Warms
Temperature
Height initial profile of environment air
compresses and warms
expands and cools
1. WHAT CAUSES ATMOSPHERE TO BECOME MORE/LESS UNSTABLE? ONE WAY IS THROUGH MIXING => Rising Air Cools
Sinking Air Warms
Temperature
Height initial profile of environment air
compresses and warms
expands and cools
final profile of environment air
Another way the atmosphere can become more unstable: The large-scale lifting an entire layer of air - here a large-scale layer of air is much larger than a parcel
- layer may be 100's of kilometers across
- the lifting of a layer typically happens with a low pressure system (more later in course)
1000 m
Temperature
Height
- Original layer (in blue) is very stable
1000 m
1500 m dry adiabatic lapse rate (10C/km)
Temperature
Height
- Original layer (in blue) is very stable - As layer rises, it expands - As air rises => cools at dry adiabatic lapse rate (10°C/km) (assume no condensation) - Top of layer rises 500 meters more than bottom of layer
=> Top of layer cools more than bottom of layer - Result => environment lapse rate within layer more likely unstable This occurs when low pressure over area. Opposite happens with high pressure system.
Low Pressure => Rising Air => Increasing INSTABILITY High Pressure => Sinking Air => Increasing STABILITY
1000 m
1500 m
dry adiabatic lapse rate (10C/km)
Temperature
Height
- Bottom of layer moist (RH=100%), top of layer dry (RH<<100%) - Bottom of layer cools at moist adiabatic lapse rate (6°C/km) - Top of layer cools at dry adiabatic lapse rate (10°C/km)
=> Now even more unstable than before!! CONVECTIVE INSTABILITY
moist adiabatic lapse rate (6C/km) RH=100%
RH << 100%
SPECIAL CASE: CONVECTIVE INSTABILITY
2. WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?
2. WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?
A. Surface heating leading to Convection
2. WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?
A. Surface heating leading to Convection
B. Topography (Mountains) = Orographic Uplift
2. WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?
A. Surface heating leading to Convection
B. Topography (Mountains) = Orographic Uplift
C. Ascent due to Convergence
2. WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?
A. Surface heating leading to Convection
B. Topography (Mountains) = Orographic Uplift
C. Ascent due to Convergence
D. Uplift along Weather Fronts
2. WHAT CAUSES AN AIR PARCEL TO INITIALLY RISE?
A. Surface heating leading to Convection
B. Topography (Mountains) = Orographic Uplift
C. Ascent due to Convergence
D. Uplift along Weather Fronts
Wind
Windward Side Leeward Side
Clicker Question
Mountain
Which side of the mountain would generally receive more precipitation? (A) Windward
(B) Leeward
(C) Both sides would receive equal amounts
Set Frequency to "AB"
Prevailing Wind
Prevailing Wind
Collision - Coalescence Process (Warm process)
Clicker Question
In general, which cloud would you expect to produce larger rain drops through the collision-coalescence process? (A) cumulus cloud (B) stratus cloud (C) cirrus cloud
Set Frequency to "AB"