Atmospheric Motions & Climate

Climate and Global Change Notes

20-1

Atmospheric Motions & Climate

Vertical Atmospheric Motion

Hydrostatic BalanceNon-hydrostatic Balance

Vertical StabilityDry Adiabatic MotionMoist Adiabatic MotionSkew-T Log-p DiagramStability RulesChanges in Stability

Science Concepts

Newton’s Laws of MotionVertical Forces

Pressure Gradient Force

Gravitational Force

Friction Force

Buoyancy

Latent Heat

The Earth System (Kump, Kastin & Crane)• Chap. 4 (pp. 56-57)


20-2

Atmospheric Motions

What keeps this balloon in the air?

• Scientist Benjamin Franklin witnessed brothers Montgolfiers launch the first manned balloon flight on November 21, 1783 in France, after he had negotiated the end of the Revolutionary War.

• The Montgolfiers believed the balloon’s lift was caused by hot air and smoke, so plied the fire with wet straw and wool.

• Ten days later, Jacques Charles (Charles’ Law fame) flew a silk balloon filled with hydrogen for two hours while traveling 21 miles. Franklin helped finance Charles’ flight.

Franklin Parody -

”If you want to fill your balloons with an element ten times lighter than inflammable air, you can find a great quantity of it, and ready made, in the promises of lovers and of courtiers.”

Walter Isaacson, 2003: Benjamin Franklin - An American Life, Simon and Schuster, NY, pp. 420-422.


20-3

Atmospheric Motions

Vertical Motion

• Vertical Forces and Acceleration

- Gravitational force (GF)

> Generally points toward the center of the Earth

> Depends on the mass of the object or in our case the air parcel

- Pressure gradient force (PGF)

> As before, points toward lower pressure, i.e., upward in the vertical

> Depends on the mass of the displaced fluid, in our case the mass of

the displaced environmental air

- Friction force (FF)

> Not very important because friction depends on the object's speed

and vertical velocities are in general small


20-4

Atmospheric Motions

Vertical Motion (Con’t)

• Hydrostatic Balance

- As a first approximation the PGF is equal to and in the opposite direction

to the GF. Thus these two forces cancel and the net force is zero.

Therefore, the acceleration is zero.

This state is called hydrostatic balance.

• Non-Hydrostatic Balance

- In cases with large imbalances between the PGF and GF, air parcels are

accelerated vertically either up or down.

- This acceleration is referred to as buoyancy or Archimedean

acceleration.

- Warm air accelerating upward and cold air accelerating downward, i.e.,

convection, are examples of non-hydrostatic balance.


20-5

Atmospheric Motions

Surface

PGF

Gravity

Hydrostatic Balance

PGF

Gravity

Non-Hydrostatic Balance

PGF = Gravity PGF Gravity

PGF

Gravity

Zero

Acceleration

Downward

Acceleration

Upward

Acceleration


20-6

Atmospheric Motions

Surface

In a Thunderstorm

Updraft:

PGF >> Gravity

Downdraft:

PGF<< Gravity

PGF

Gravity

PGF

Gravity


20-7

Stability

Vertical Stability

• Consequences of the Gas Law revisited

Boyle’s Law T Changesp Changes

Gas Law Dry Adiabatic

AscentV ConstantT Constant

1000

900

800

700

600

500

400

0

1000

2000

3000

4000

5000

6000

7000

T T TV V V

15°C

15°C

15°C

15°C

-156°C

-99°C

-48°C

15°C

-53.6°C

-24.2°C

-4.6°C

15°C

2.47

1.65

1.28

1.00

1.00

1.00

1.00

1.00

1.91

1.42

1.19

1.00

Altitude (m)

Pressure (mb)


20-8

Stability

Vertical Stability (Con’t)

• Important to determine the occurrence and strength of convection and

afternoon showers.

• Also important to determine the vertical mixing of pollution.

Adiabatic Diagrams

• Use to determine atmospheric stability

• Plot of temperature versus pressure

- Several types- Skew-T Log-p diagrams

• Compare measured lapse rate with dry or moist adiabatic parcel lapse rates

- Adiabatic - No energy (heat) added or subtracted


20-9

Simple Skew-T Log-p Diagram

Stability

30

20

10

0-10-20-30-40-50-60400

500

600

700

800850

10001050

Pressure

(mb)

Temperature (°C)


20-10

Stability

Skew-T Log-p Diagram with Dry Adiabats

30

20

10

0 -10 -20 -30 -40 -50 -60

340 310 300 290 280

400

500

600

700

800850

1000 1050

330 320 270

260

250

Pressure

(mb)

Temperature (°C)


20-11

Stability

Stable Atmosphere

Parcel beginning at 1050 mb is lifted to 600 mb dry adiabatically. Note theparcel is colder than its environment, thus it is

accelerated back toward its original position. This atmosphere is considered to

be stable.

400

500

600

700

800850

10001050

Dry AdiabatObserved orMeasured Lapse Rate

Tp=Te

Tp<Te

Pressure

(mb)

Temperature (°C)


20-12

Stability

Unstable Atmosphere

Parcel beginning at1050 mb is lifted to 600 mbdry adiabatically. Note the parcel is warmer than itsenvironment, thus it isaccelerated away from itsoriginal position. This

atmosphere is considered tobe unstable.

400

500

600

700

800850

10001050

Dry Adiabat

Observed orMeasured Lapse Rate

Continues to accelerate upward until

Tp=Te

Tp>Te

Pressure

(mb)

Temperature (°C)


20-13

Stability

Unstable Atmosphere

Observed orMeasuredLapse Rate

400

500

600

700

800850

10001050

Dry Adiabat

Pressure

(mb)

Temperature (°C)

Stable

Unstable


20-14

Stability

Stability Rules

• When a parcel is displaced (moved) from its original position to a new position,

> If the net force accelerates the parcel back toward its original position

then the atmosphere is considered “stable” (Tp<Te)

> If the net force accelerates the parcel away from its original position then

the atmosphere is considered “unstable” (Tp>Te)

> If the net force is zero then the atmosphere is considered “neutral”

(Tp=Te)


20-15

Vertical Stability

• Consequences of the Gas Law revisited again

Stability

Boyle’s Law T Changesp Changes

Gas LawDry Adiabatic

AscentV ConstantT Constant

1000

900

800

700

600

500

400

0

1000

2000

3000

4000

5000

6000

7000

T T TV V V

15°C

15°C

15°C

15°C

-156°C

-99°C

-48°C

15°C

-53.6°C

-24.2°C

-4.6°C

15°C

2.47

1.65

1.28

1.00

1.00

1.00

1.00

1.00

1.91

1.42

1.19

1.00

Moist AdiabaticAscent

T V(Ms)

15°C

1.52

1.23

1.00(10.70)

-7.8°C

4.4°C

-30.2°C

Gas Law

Altitude (m)

Pressure (mb)

(0.76)2.14

(6.64)

(3.42)


20-16

Stability

Skew-T Log-p Diagram with Moist Adiabats

32 28 16 12

30

20

10

0 -10 -20 -30 -40 -50 -60

310 300 290 280

400

500

600

700

800850

1000 1050

330 320 270

260

250

8 20 24 340

Pressure

(mb)

Temperature (°C)


20-17

Stability

Stable Moist Atmosphere

400

500

600

700

800850

10001050

Observed orMeasured

Lapse Rate

Moist Adiabat A saturated parcel beginning at1050 mb is lifted to 600 mb moist adiabatically. Note the

parcel is colder than itsenvironment, thus it is

accelerated back toward itsoriginal position. This

atmosphere is considered to be stable.

Tp<Te

accelerates

downward

Tp=Te

Pressure

(mb)

Temperature (°C)


20-18

Stability

Unstable Moist Atmosphere

400

500

600

700

800850

10001050

Observed orMeasured

Lapse Rate

Moist Adiabat A saturated parcel beginning at1050 mb is lifted to 600 mb

moist adiabatically. Note the parcel is warmer than its environment, thus it is accelerated away from itsoriginal position. This

atmosphere is considered to be unstable.

Tp>Te

Continues to

accelerate upward until

Tp=Te

Pressure

(mb)

Temperature (°C)


20-19

Stability

Unstable Moist Atmosphere

400

500

600

700

800850

10001050

Observed orMeasuredLapse Rate

Pressure

(mb)

Temperature (°C)

Stable

Unstable

Moist Adiabat


20-20

Stability

Combined Stability Regions

400

500

600

700

800850

10001050

Moist AdiabatThree

Observed orMeasured

Lapse Rates

Pressure

(mb)

Temperature (°C)

AbsoluteStablility

Dry Adiabat

AbsoluteInstablility

ConditionalStability


20-21

Skew-T Log-p Chart

QuickTime™ and aTIFF (Uncompressed) decompressorare needed to see this picture.

Pressure

(mb)

Temperature (°C)


20-22

Stability

Conditional Stability

• Note: In this region the stability criterion depends on if the parcel is saturated or

not

- If the parcel is saturated, then the atmosphere is considered to be

“Unstable” and if the parcel is unsaturated, then the atmosphere is

considered to be “Stable”

Causes of Changes in Stability

• Destabilizes

- Solar heating- Cold air advection over a warm surface

• Stabilizes

- Radiational cooling- Warm air advection over a cold surface

“As it usually does on the Colorado Plateau, night defeated the storm. It drifted northeastward, robbed of the solar power that fed it, and exhausted its energy in the thin, cold air over the Utah canyons and mountains of northern New Mexico.”

Tony Hillerman, 1986: Skinwalkers, p. 261.


20-23

Stability Effects on Convective Clouds

• 21 November 2005 “cloud streets” over Hudson Bay

• Cloud streets are parallel lines of cumulus clouds that align with the wind

• Result of thermals, or rising columns of warmed air formed when the surface is a little warmer than the air above

• Here a cold northwest wind (red arrow)is blowing off the ice covered land over the still warmer water of Hudson Bay

• This destabilizes the air and creating convective clouds through lifting the air to its saturation level

• These clouds are then carried by the steady wind forming lines of clouds

aligned along the direction of the wind

Stability

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17108

WindDirection


20-24

Stability


• Surface solar heating destabilizes the air sometimes allowing afternoon convective clouds and showers to form

• 7 September 1999Radar Reflectivity

QuickTime™ and aVideo decompressor



20-25

Stability


• Lightningintensity

• Diurnaldistribution

• Beginning at midnight local time

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20-26

Stability


• Lightning intensity

• Diurnal distribution

• Clock - 1200 &2400 up

QuickTime™ and aTIFF (LZW) decompressor




Minimum~7:00 am

Maximum~5:00 pm


20-27

Stability



• Blue = lessGreen = more



Global Lightning vs Time

Latitudinal LightningDistribution vs Time

White Line = Annual Mean Latitudinal LightningDistribution

Longitudinal White Line = Annual Mean Latitudinal Lightning Distribution Lightning Distribution

Month/Year


20-28

Stability


• LightningIntensity

• June 1995-May 1999distribution

QuickTime™ and aAnimation decompressor



20-29

Stability


• Lightningintensity

• Annualdistribution(Jan-Dec) QuickTime™ and a

Animation decompressorare needed to see this picture.


20-30

Stability



• Note difference between February and August






20-31

Stability Effects of Air Pollution

• Fanning

• Fumigation

• Looping

• Coning

• Lofting

• Trapping

Stability

Atmospheric Motions & Climate

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