unstable atmosphere: - air forced upwards will continue to...

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


Sinking Air Warms

Temperature



expands and cools


Sinking Air Warms

Temperature



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


A.  Surface heating leading to Convection

B.  Topography (Mountains) = Orographic Uplift




C.  Ascent due to Convergence




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

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"

unstable atmosphere: - air forced upwards will continue to...

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