Review

REVIEW: Understanding Weather and

Climate





Chapter 1 - Chapter 12

What we have learned?

• Chapter 1: Composition and Structure of the Atmosphere

• Chapter 2: Solar Radiation and the Seasons

• Chapter 3: Energy Balance and Temperature

• Chapter 4: Atmospheric moisture

• Chapter 5: Cloud Development and Forms

• Chapter 6: Precipitation Processes

• Chapter 7: Atmospheric Pressure and Wind

• Chapter 8: Air Masses and Fronts

• Chapter 9: Middle Latitude Cyclones

• Chapter 10: Atmospheric Dynamics

• Chapter 11: Atmospheric and Oceanic Circulation

• Chapter 12: ENSO and Present-Day Climate Variability

• Chapter 13: Climate Change and the causes of climate change

Chapter1



Atmospheric Composition and structure





Permanent Gases

Variable

Gases









• Water vapor



•Carbon Dioxide



• Ozone

Temperature

Layers



1) Troposphere



2) Stratosphere



3) Mesosphere



4) Thermosphere

Requirement:

Chapter2: Solar Radiation and the

Seasons

Energy and

Methods of

Energy Transfer

• Conduction

– Molecule to molecule transfer





• Convection

– transferred by vertical movement



• Radiation

– propagated without medium (i.e. vacuum)

– solar radiation provides nearly all energy

Stefan-Boltzmann Law

• the total amount of Energy emitted is f(x) of temperature

• described as:

I = σ T4



where I = intensity (W/m2)

σ = Stefan-Boltzmann constant (5.67x10-8 W/m2/K4)

T = temperature in K



e.g. Earth: avg. temp = 15oC ~290 K

I = (5.67x10-8 W/m2/K4)(290 K)4

= 400 W/m2





Earth = 400 W/m2

Sun = 73,000 W/m2

Wien’s Law

• identifies peak wavelength of emission, based on T



max = 2900 / T



where max = wavelength of max. emission (m)

T = temperature in K



• hotter objects (Sun) have smaller peak wavelengths (max) than

cooler objects (Earth)





Earth’s max = 10 m

Sun’s max = 0.5 m

Orientation

• rotation - spins on its axis

• determines day length

• axis tilted 23.5o (constant)

• pts toward Polaris









REASON FOR

SEASONS







• w/o tilt, no seasonal change  constant Spring/Fall conditions with equal

days/nights everywhere

Four Cardinal

Dates:



Summer Solstice

(June 21st)



Fall Equinox

(Sept 22nd)



Winter Solstice

(Dec 21st)



Spring Equinox

(March 21st)

Requirement:

• Understand the differences and characteristics of the

three energy transfer mechanisms.

• Understand the concept of the two radiation laws

discussed in lecture.

• Know the reasons for seasons. You should

understand:



1 Perihelion & aphelion; 2. June and December solstices;

3 variations in daylength; 4 March and September equinoxes

Chapter3: Energy Balance and

Temperature

What happens to solar radiation as it travels

through the atmosphere?









Atmospheric Influences on Insolation



1. Absorption

2. Reflection and Scattering

3. Transmission

Principal Controls on Temperature



1. Latitude

2. Altitude

3. Atmospheric Circulation

4. Land-Water Contrasts

5. Ocean Currents

6. Local Effects

Requirement:

• What are the atmospheric influences on

radiation? Be able to list and describe

characteristics of these.

• What is albedo? Understand the basics of what

happens to solar and terrestrial radiation as it is

in, the global energy budget.

• What are the influences on temperature?

• Understand the greenhouse effect and know a

few key greenhouse gases.

Chapter4: Atmospheric Moisture



Evaporation and Condensation

• evaporation  liberation of water molecules,

requires energy



• Upon saturation, condensation will begin



• saturation: equilibrium between evaporation and

condensation

Methods of Achieving Saturation

(Condensation)





Air may become saturated:

1. through the addition of water vapor to air at a

constant temperature

• e.g.: hot shower

2. by mixing cold air with warm, moist air

• e.g.: Contrails

3. by cooling air to the dew point

• most common way via atmospheric cooling

Indices of Water Vapor Content



• Humidity: amount of water vapor in

air



• Humidity expressed in a number of

ways  Indices:

• Vapor pressure - the amount of pressure exerted on the atmosphere by water vapor



• Saturation vapor pressure (SVP) – maximum vapor pressure

• maximum amt of vapor that can exist at a given temperature



•Absolute Humidity - density of water vapor, expressed in g/m3

mv mv

•Specific Humidity - mass of water vapor, expressed in g/kg q  

m mv  md

•Saturation specific humidity - highest specific humidity for a given

temperature

and pressure

mv

r

•Mixing Ratio- The amount of water vapor relative only to a mass of dry airm d



•Relative Humidity (RH) = (specific humidity) / (saturation specific

humidity)*100%



•Dew-point - Temperature at which saturation occurs. Indicates moisture content.

condensation begins

Diabatic Processes





• involves the addition/removal of heat energy



• energy is transferred from areas of high temperature toward those of

lower temperature



Adiabatic Process



• when temperature changes w/o addition/removal of heat



• Cloud formation: primarily due to temperature changes

with no heat exchange with surrounding environment

Forms of Condensation

• fog

radiation

advection

upslope

• dew

• frozen dew

• frost

• cloud

Requirements:

• Understand the meaning behind the processes

in the water cycle, especially: condensation,

evaporation; what is saturation?

• What are the indices of water vapor content?

know drawback and advantages of each index.

• Distinguish between adiabatic and diabatic

processes

• Know characteristics of the forms of

condensation: dew, frost, frozen dew, fog.

Chapter 5: Development and Forms of clouds

Lifting Mechanisms

(initial uplift push)



1. Orographic Lifting



2. Frontal Lifting



3. Convergence



4. Localized Convection

Three

Examples

of Stability

Cloud types (but not required in the final)

Requirements:

• What are the four mechanisms that lift air?

What happens in each mechanism?

• Understand the differences between

absolutely stable, absolutely unstable, and

conditionally unstable air.

• Know why the saturated adiabatic lapse

rate is less than the dry adiabatic lapse

rate.

• What factors influence the ELR?

Chapter 6: Precipitation Processes:



Why does it rain on us???

Growth of Cloud Droplets





• Gravity and frictional drag  balance to achieve terminal velocity



• terminal velocities for cloud drops, due to their small size, cannot

exceed even weak updrafts



• volume of cloud drop must be 1,000,000 times greater than

average drop to overcome updrafts





1. Growth by Condensation



2. Growth in Warm Clouds -- collision and coalescence



3. Growth in Cool and Cold Clouds --- Bergeron Process

Forms of Precipitation

• Snow results from the Bergeron process, riming, and aggregation



• Rain: always associated with warm clouds and sometimes cool clouds (T > 0C)



• Rain showers – episodic precipitation events associated with convective activity

and cumulus clouds



•Sleet begins as ice crystals which melt into rain through a mid-level inversion

refreeze near surface .



•Freezing Rain forms similarly to sleet, however, the drop does not completely

solidify before striking the surface



•Graupel – ice crystals that undergo extensive riming

Lake effect snows develop on leeside of

water bodies, e.g. Great Lakes



• As cold air from the north or northwest flows over the

lake, heat and water vapor are transferred upward and

make air moist and unstable. As the air passes over the

shore, the wind slow down due to large friction =>

convergence = > air rising => clouds = > heavy snows.



(a) an initial mechanism for uplift

(b) unstable air

(c ) sufficient moisture.

Requirements:

• What is the terminal velocity?

• Distinguish between the collision-coalescence

and Bergeron process. Which occurs in warm

clouds, and cold clouds? Which occurs mostly

in the Tropics?

• Know the types of precipitation and the

processes that form them.

• Know the mechanism of lake effect snows.

Chapter 7 Atmospheric Pressure

and Wind

• Pressure Essentials

• Horizontal Pressure

Gradients

• Cyclones and

Anticyclones

Pressure Gradients

• The pressure gradient force initiates movement of

atmospheric mass, wind, from areas of higher to areas of

lower pressure.

• Hydrostatic Equilibrium









• State equation of ideal gas

• High pressure areas (anticyclones)  clockwise airflow in

the Northern Hemisphere (opposite flow direction in S.

Hemisphere)

– Characterized by descending air which warms creating

clear skies



• Low pressure areas (cyclones)  counterclockwise airflow

in N. Hemisphere (opposite flow in S. Hemisphere)

– Air converges toward low pressure centers, cyclones are

characterized by ascending air which cools to form

clouds and possibly precipitation



• In the upper atmosphere, ridges correspond to surface

anticyclones while troughs correspond to surface cyclones

Requirements:

• What does the equation of state relate?

• What is the pressure gradient? How does

density affect this?

** remember! The pressure gradient force is

the sole generator of the winds. The Coriolis

force changes wind direction; friction changes

wind speed.

• What are cyclones, anticyclones, trough, and

ridges?

Chapter 8: Air Masses and Fronts

Formation of Air Masses



(1) air gains temperature and humidity characteristics of the

surface.



(2) Topographically uniform areas.



(3) It requires days for temp/moisture

imprinting to form air masses.



(4) air masses classified by temp/moisture

characteristics of source region



– moisture: continental (dry) v. maritime (marine) – c or m

– temp: tropical (warm), polar (cold), arctic (very cold) – T, P or A









•

Fronts

• separate air masses  leads to changes in temperature and humidity

as one air mass is replaced by another



• changes in temp  lead to uplift and ppt



• four types of fronts:

cold  cold advancing on warm

warm  warm advancing on cold

stationary  air masses not advancing



occluded  does not separate tropical

from polar/arctic, boundary btw two

polar air masses

Types of fronts

Identification of fronts



1. Sharp temperature changes

2. Change in the air’s moisture

3. Shifts in wind direction

4. Pressure and pressure change

5. Clouds and precipitation

patterns









Course: Introduction to Atmospheric sciences(ATOC210) by GyuWon LEE

Requirements:

• Know the types of fronts, and the

characteristics of each

• Know the type of air masses, and the

characteristics of each (which are moist, warm,

etc).

• How to identify fronts in weather maps?

Chapter 9: Mid-Latitude

Cyclones

The Life Cycle of a Mid-Latitude Cyclone

• cyclogenesis – formation of mid-latitude cyclones along the polar front

•

• boundary separating polar easterlies from westerlies

•

• low pressure area forms  counterclockwise flow (N.H.)

•

• cold air migrates equatorward

•

• Warmer air moves poleward

Mature Cyclones

• Well-developed fronts circulating about a deep low pressure center

characterize a mature mid-latitude cyclone.

• Deep low pressure center;

• Chance of precipitation increases toward the storm center

– cold front: heavy ppt. (cumulus clouds)

– warm front: lighter ppt. (stratus clouds)

– warm sector: unstable conditions

Occlusion

• when the cold front joins the warm front, closing off the warm sector,

surface temperature differences are minimized

• effectively the warm air is cut-off from the surface

• The system is in occlusion, the end of the system’s life cycle

• evolution  eastward migration

Rossby Waves and Vorticity

• vorticity  rotation of a fluid (air)



• Absolute vorticity:

- relative vorticity  motion of air relative to Earth’s surface

- Earth vorticity  rotation of Earth around axis



• Air rotating in same direction as Earth rotation  counterclockwise  +ive vorticity

• Air rotating in opposite direction as Earth rotation  clockwise  -ive vorticity

• maximum and minimum vorticity associated with troughs and ridges, respectively

WHAT’S THE POINT OF VORTICITY????

• changes in vorticity in upper troposphere leads to surface pressure changes

• Increase in absolute vorticity  convergence

• decrease in absolute vorticity  divergence



• decrease vorticity  divergence  draws air upward from surface  surface LP

• referred to as dynamic lows (v. thermal lows)

• dynamic lows (surface) exist downwind of trough axis



• increase vorticity  convergence  air piles up, sinks downward  surface High

Necessary ingredients for a developing wave cyclone

1. Upper-air support









- A shortwave moves through this region, disturbing the flow.

- Diverging air aloft causes the sfc pressure to decreases beneath

position 2  rising air motion.

- Cold air sinks and warm air rises: potential energy is transformed into

kinetic energy

- Cut-off low

Necessary ingredients for a developing wave cyclone

2. Role of the jet stream: upper-level divergence above the surface low

Requirements:

Chapter 10: Atmospheric

Dynamics

Forces We Will Consider

• Gravity

• Pressure Gradient Force

• Coriolis Force

• Centrifugal Force / Centripetal

Acceleration

• Friction

Coriolis force (CF)

- The Coriolis force causes the wind to deflect to the right of its

intended path in the Northern Hemisphere and to the left of its

intended path in the Southern Hemisphere. It acts at a right angle

to the wind.

- The Coriolis force is largest at the pole and zero at the equator

- The stronger the wind speed, the greater the deflection

- The Coriolis force changes only wind direction, not wind speed.

- We measure motion on the rotating Earth. Thus, we need to be

concerned with the Coriolis force

Atmospheric Force Balances

• First, MUST have a pressure gradient force

(PGF) for the wind to blow.



• Otherwise, all other forces are irrelevant.



• Already discussed hydrostatic balance, a

balance between the vertical PGF and gravity.

There are many others that describe

atmospheric flow…

Geostrophic Balance

• Balance between PGF and Coriolis force









Fig. 6-15, p. 172

• Therefore, wind blows parallel to isobars, which is useful

to consider when looking at weather map.

• Buy-Ballot’s “law”: If you stand with your back to the wind

in the N.H, low pressure will be on your left and high

pressure on your right.

Gradient Wind Balance

• Balance between PGF, Coriolis force, and

centrifugal force

Supergeostrophic flow

(CF > PGF )



PGF + Ce = CF



Subgeostrophic flow



(CF < PGF)



PGF = CF + Ce

Comparison

Requirements:



Pressure gradient force Geostrophic winds:

straight-line flow aloft

Surface winds Coriolis force

Centripetal force

Frictional force Hydrostatic balance (equilibrium)



Gravitational force

Gradient winds:

Curved winds

around lows and

highs aloft

Chapter 11: Atmospheric/Oceanic

Circulation

polar Cell

Farrell

Cell

The pattern of surface wind with the rotation of Earth

• Sea breeze and land breeze

• Valley breeze and mountain breeze

• Chinook wind

• Monsoons

Oceanic Circulation





• Surface current: Ekman current

Coriolis Force = Wind stress. The surface current is 45°

to the right of the wind in the northern hemisphere.

• subsurface current: geostrophic current

Coriolis Force = Pressure gradient force

• Deep circulation: thermohaline circulation

• Ekman mass transport. The

transport is perpendicular to the

wind stress, and to the right of the

wind in the northern hemisphere.

Requirements:

• What are the three cell models? What are

the characteristics of each cell?

• What are the ITCZ, and what are the

pressure and wind distributions

corresponding with the three cells?

• Know local circulations including monsoon,

land and see breeze etc.,

• What are the oceanic circulation? What

are the mechanisms responsible for

different oceanic currents?

Chapter 12: Present-Day Climate

Variability

ENSO MODE

PNA: 4 centers:

Hawaii(20N,160W);

North Pacific Ocean

(45N 165W);

Alberta (55N

115W); and the Gulf

Coast region of

USA (30N 80W)

AO

AO is the dominant mode

of mean-monthly sea level

pressure variability

over the Northern

Hemisphere with

an out-of-phase relation

between the sea level

pressure over the Arctic

basin and that at the mid-

latitudes (Thompson and

Wallace 1998).

Requirements:

• What are ENSO, AO, NAO and PNA?

• How do these climate variability modes

impact the climate over the northern

America?

• Know the simple hypothesis of EL Nino

mechanism.

Final Exam.

• Part A: Answer all 60 multiple-choice questions.

This part is 60%.



• Part B: Answer questions. This part is worth 40%.



• Electronic calculators are not allowed.



• Final Exam. covers chapter 1 to 12 of lecture notes.