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Stability in Meteorology: Lapse Rates, Adiabatic Processes, and Environmental Conditions, Lecture notes of Meteorology

The concept of stability in meteorology, focusing on lapse rates, adiabatic processes, and environmental conditions. It discusses how air parcels expand and contract as they rise or descend, the role of temperature changes, and the importance of adiabatic and diabatic processes. The document also covers the dry and moist adiabatic lapse rates and their significance in determining stability in the atmosphere.

What you will learn

  • What are the dry and moist adiabatic lapse rates?
  • How does the temperature of an air parcel change as it rises?
  • What causes an air parcel to expand as it rises?
  • What is the difference between adiabatic and diabatic processes?
  • How do environmental conditions influence the stability of the atmosphere?

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Chapter 6: StabilityChapter 6: Stability
Concept of Stability
Lapse Rates
Lapse
Rates
Determine Stability and Stability Indices
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Chapter 6: StabilityChapter 6: Stability

  • Concept of Stability• Lapse Rates

Lapse Rates

  • Determine Stability and Stability Indices

Concept of StabilityConcept of Stability

Air Parcel Expands As It Rises…Air Parcel Expands As It Rises…

-^

Air pressure decreases with elevation.

-^

If a helium balloon 1 m inIf a helium balloon 1 m indiameter is released at sealevel, it expands as it floats

d b

f th

upward because of thepressure decrease. Theballoon would be 6.7 m in diameter as a height of 40km.

(from

The Blue Planet

)

What Happens to the Temperature?What Happens to the Temperature?What

Happens to the Temperature?

What Happens to the Temperature?^ •

Air molecules in the parcel (or the balloon) have to use theirAir molecules in the parcel (or the balloon) have to use theirkinetic energy to expand the parcel/balloon.

-^

Therefore the molecules lost energy and slow down their

-^

Therefore, the molecules lost energy and slow down theirmotions Î

The temperature of the air parcel (or balloon) decreases withl

ti^

Th

l^

t^

i^

d t

i^

th

t^

ti l

elevation. The lost energy is used to increase the potentialenergy of air molecular.Si

il^

l^

h^

h^

i^

l d

d^

h^

i l

f

•^

Similarly when the air parcel descends, the potential energy ofair molecular is converted back to kinetic energy. Î

Air temperature rises.

Diabatic ProcessDiabatic Process

•^

Involve the direct addition or removal of heat

•^

Involve

the direct addition or removal of heat

energy.

•^

Example: Air passing over a cool surface loses

•^

Example: Air passing over a cool surface losesenergy through conduction.

Dry Adiabatic Lapse RateDry Adiabatic Lapse Rate

(from

M

eteorology: Understanding the Atmosphere

)

  • Air parcels that do not contain cloud (are not saturated) cool at

p^

(^

the dry adiabatic lapse rate as they rise through the atmosphere.

  • Dry adiabatic lapse rate = 10°C/1km

Dry Adiabatic Lapse RateDry Adiabatic Lapse RateDry

Adiabatic Lapse Rate

Dry Adiabatic Lapse Rate

Moist Adiabatic Lapse RateMoist Adiabatic Lapse Rate

(from

Meteorology: Understanding the Atmosphere

)^

  • Air parcels that get saturated as

they rise will cool at a rate

ll^

h^

h^

d^

di b

i

smaller than the dry adiabaticlapse rate due the heatingproduced by the condensation of water vapor.

  • This moist adiabatic lapse rate

is not a constant but determinedis not a constant but determinedby considering the combinedeffects of expansion coolingand latent heatingand latent heating.

  • In the lower troposphere, the rate is 10°C/km – 4°C/km = 6°C/km.• In the middle troposphere, the rate is 10°C/km – 2°C/km = 8°C/km.

p^

p^

  • Near tropopause, the rate is 10°C/km – 0°C/km = 10°C/km.

Environmental Lapse RateEnvironmental Lapse Rate

pp

•^

The environmental lapse rate is referred to as the

p

rate at which the air temperature surrounding us(or the air parcels) would be changed if we were toclimb upward into the atmosphere.

•^

This rate varies from time to time and from place

•^

This rate varies from time to time and from placeto place.

•^

A rawinsonde’s thermometer measures theenvironmental lapse rate.

Environmental Lapse RateEnvironmental Lapse Rate

-^

The environmental (orambient) lapse rate is

f^

d

h

i^

l

referred to the verticalchange in temperaturethrough still air.through still air.

-^

The environmentallapse rate is not fixedlapse rate is not fixed.It changes from day today and from place to

y

p

place.

environmental lapse rate =0 5

° C/100m

environmental

lapse rate =0.5 C/100m

(from

Understanding Weather & Climate

)

How to Determine StabilityHow to Determine StabilityHow

to Determine Stability

How to Determine Stability

• How do we determine where the

atmosphere is unstable – under which

p

convective clouds and storms may form?

Î

A

C

th

i^

t l l

Î

A

nswer

: Compare the environmental lapse

rate with the dry/moist lapse rate

Static Stability of the AtmosphereStatic Stability of the AtmosphereStatic

Stability of the Atmosphere

Static Stability of the Atmosphere

e = environmental lapse rate

p

d = dry adiabatic lapse rate Γ

m = moist adiabatic lapse rate

  • Absolutely Stable

e <

m

e <

m

  • Absolutely Unstable

Γe >

d

Γe >

d

  • Conditionally Unstable

Γm <

e <

d

(from

Meteorology Today)

Absolutely Unstable AtmosphereAbsolutely Unstable AtmosphereAbsolutely

Unstable Atmosphere

Absolutely Unstable Atmosphere (from

Meteorology Today)

Conditionally Unstable AtmosphereConditionally Unstable Atmosphere

y

p

y

p

(from

Meteorology Today)