What we have discussed after Midterm 2
• Tropical cyclones
• Airmasses, fronts, and mid-latitude cyclones
• Tropical and extratropical climate
• Weather and climate prediction (Not required)
• Heat island effect (Not required)
• Air pollution (Not required)
• Observed global climate change
• Projection of future climate change
• Feedbacks and abrupt climate change (Not required)
• Mitigation of global climate change

Quantity
Length
Mass
Time
Name meter kilogram second
Temperature Kelvin
Density kilogram
Speed
Force
Pressure
Energy
Power per cubic meter meter per second newton pascal joule watt
Units m kg s
K kg/m 3 m/s m.kg/s 2
N/m 2
N.m
J/s
N
Pa
J
W
Symbol m kg s
K kg/m 3 m/s

nano micro milli centi deci deka hecto kilo mega giga
… yotta
one-billionth one-millionth one-thousandth one-hundredth one-tenth ten one hundred one thousand one million one billion
10 2
10 3
10 6
10 9
10 -9
10 -6
10 -3
10 -2
10 -1
10 1
10 24
0.000000001
0.000001
0.001
0.01
0.1
10
100
1000
1000000
1000000000

•
Tropical cyclone genesis: Western Pacific has the highest averaged number per year. 6 necessary conditions. 4 stages.
•
Tropical cyclone structure: 3 major components, rotation direction of inflow and outflow, location of maximum wind and rainfall, 3 feedbacks
•
Tropical cyclone intensity scale. Category 1: 74mph , category 5:
155mph
•
Hurricane names: alphabetically, 6 lists in rotation
•
Trends and variability in tropical cyclone activity
•
Tropical cyclone destruction: 4 reasons . Which side has the most intense destruction?
•
Tropical cyclone forecast: track and intensity. Currently which skill is better?

Necessary conditions for tropical cyclone formation
1.
SST > 27 o C (Poleward of about 20 o SST too cold for formation. Highest frequency in late summer to early autumn when water is warmest.)
2.
Warm ocean mixed layer is thick enough to supply energy (this is why they weaken quickly upon landfall)
3.
Unstable atmosphere with a moist lower/middle troposphere (central and western ocean basins)
4.
Low vertical windshear (Otherwise upward transfer of latent heat disrupted)
5.
Coriolis force (hurricanes do not form between 5N-5S)
6.
Pre-existing low-level rotating circulations (tropical waves and other disturbances)

Structure of tropical cyclones
• Size and lifetime: about 600km , last up to a week or more
• Make up: many thunderstorms arranged in pinwheel formation
• Three components :
1. Central eye - clear skies, light winds (25 km diameter)
2. Eye wall - maximum rainfall and wind speed .
3. Spiral rainbands
• Cylonic inflow, anticyclonic outflow.

Tropical cyclone Destruction and Fatalities
Destruction caused by:
• Hurricane-scale winds (>74 mph)
• Rainfall (10 in/day)
• Storm surge (winds blowing coast-ward + lower atmosphere pressure)
• Fine-scale Tornadoes
Destruction most intense on right side of cyclone (wind + storm speed)

Airmasses, fronts, and mid-latitude cyclones
1. Definition of airmasses. Bergeron classification of air masses (3 letters).
2. Fronts: 6 types (cold, warm, stationary, occluded, dry line, squall line)
3. Cold front (narrow, fast, heavy precipitation), Warm front
(wide, slow, light precipitation)
4. The developmental stages and vertical structure of middle latitude cyclones (boundary between northern cold air and southern warm air, upper level low to the west of surface low )
5. How upper level longwaves and shortwaves may enhance cyclonic development at the surface (upper level low to the west of surface low)
6. The three regions of cyclogenesis and typical tracks

•
3 letters: e.g. mTk, cPw
•
1st letter for moisture properties: c - continental, m - maritime
•
2nd letter for thermal characteristics: T - tropical, P -polar , A -
Artitic/Antarctic, M - monsoon, E - equatorial, S -superior air (dry air formed by significant downward motion in the atmosphere)
•
3rd letter for stability: k/w - air colder/warmer than ground

•
A weather front is a boundary separating two air masses
•
Types: cold front, warm front, stationary front, occluded front, dry line, squall line
•
Cold front (steep, narrow, fast, heavy precipitation ),
•
Warm front (less steep, wide, slow, light precipitation )

In mid-latitude there is a boundary between northern cold air and southern warm air
In the boundary an initial cyclone can advect warm air northward and cold air southward
If the upper level low is to the west of surface low , the cyclone will amplify and precipitation will form.
Mature stage. Cold air begins to catch up with warm air (occluded).
Cold air cools down the cyclone.
Dissipation.

– Gulf of Mexico , east coast
– Alberta Clipper from eastern side of Canadian Rockies
– Colorado Low from eastern slope of American Rockies
• Lee-side lows, lee cyclogenesis

Tropical climate:
•
Mean state: The two basic regions of SST? Which region has stronger rainfall? What is the Walker circulation?
•
Mean state: Two types of ocean upwelling, ocean-atmosphere feedback
•
El Nino and La Nina: Which region has warm SST anomaly during El
Nino ? 4-year period .
•
Land-sea contrasts: seasonal monsoon
Extratropical climate:
•
Mean state: westerly winds, polar vortex
•
What is the primary way El Nino affect extratropics? ( Pacific/North
American Oscillation )
•
The oscillations associated with strengthening/weakening of polar vortex : Arctic Oscillation , Antarctic Oscillation

• Determined by east-west sea surface temperature contrast :
Indo-Pacific warm pool, eastern Pacific cold tongue
• Walker circulation, which interacts with underlying ocean and causes equatorial upwelling and coastal upwelling
2 basic regions
Indo-Pacific warm pool
Eastern Pacific cold tongue

• is an oceanographic phenomenon that involves wind-driven motion of dense, cooler, and usually nutrient-rich water towards the ocean surface, replacing the warmer, usually nutrient-depleted surface water.
• Equatorial upwelling: Due to Coriolis effect
• Coastal upwelling: Due to Coriolis effect

El Nino/Southern Oscillation (ENSO):
The 4-year oscillation
• El Nino: Very warm sea surface temperature over central and eastern tropical Pacific , which occurs every 3-7 years. The Walker Circulation becomes disrupted during El Ni ño events, which weakens upwelling in eastern Pacific.
• La Nina: the opposite condition to El Nino
• Southern Oscillation: The atmospheric oscillation associated with the El Nino-La
Nina cycle.
• The whole phenomena is now called El
Nino /Southern Oscillation (ENSO)

Land-Sea Contrast: Seasonal “ Monsoon ”
• A seasonal reversal of wind due to seasonal thermal differences between landmasses and large water bodies ( landsea contrast )
• Orographic lifting often enhances precipitation totals

Observed global climate change
•
3 ways human activities affect the climate.
•
Rapid increase of greenhouse gases (CO
2
, CH
4
, N
2
O) since 1750: far exceed pre-industrial values determined from ice core measurements spanning the last 650,000 years, which is mainly caused by CO
2 strong radiative heating.
fossil fuel use . Lead to
•
The developed countries and developing countries contribute almost equally to the emissions of GHGs .
•
Observed change of mean: air temperature, ocean temperature, melting of arctic sea ice, Greenland ice sheet, snow and glaciers, rising of sea level.
•
Observed change of extreme events: extreme precipitation events, heat waves, strongest hurricanes

Human beings are changing the global climate system in three different ways:
• Release or cleanse greenhouse gases
• Release or cleanse pollutants (aerosols)
• Change land cover (deforestation and urbanization)

Global atmospheric concentrations of CO
2 and CH
4 have increased markedly as a result of human activities since 1750 and now far exceed pre-industrial values determined from ice core measurements spanning the last 650,000 years!

Global map of temperature change:
Largest warming in Arctic (“Arctic amplification”)
Larger warming over land than ocean

Retreat of Mountain Glaciers: a major contributor to sea level rise
Glacier retreat is a world-wide phenomena.
Will affect water supply for millions :
• Kenya/Tanzania
• Northern India
• Andes Mountains
IPCC (2001)

Projection of future global climate change
•
Global climate models: Earth system models (5 components)
•
Global climate models can reproduce the observed warming in the 20th century. The warming is largely caused by human activities .
•
Projected change: mean temperature ( largest warming over
Arctic, larger over land ), mean precipitation, sea level, extreme temperature, extreme precipitation, fresh water, ecosystems
•
Future climate scenarios show that reducing greenhouse gas emissions can substantially mitigate warming in the latter half of this century.

Framework of Earth System Model
Biogeochemistry Atmosphere
Coupler
Sea Ice Ocean
Land
• Include 5 components: atmosphere, ocean, land, sea ice, biogeochemistry
• Based on the conservation laws of mass, energy, momentum, water vapor and other chemical species (e.g. CO
2
, CH
4
)
• Based on future assumptions of external forcing (GHG concentrations, solar variability, pollution, land use changes)

Can the GCMs Reproduce the 20th Century
Temperature Trend?
The GCMs can reproduce the 20th century temperature trend
The warming is caused by anthropogenic forcings!

Projected Change in Global Mean Temperature

Global map of projected change
Temperature: Largest warming over Arctic, larger over land
Precipitation: Increase in tropics/poles, decrease in midlatitudes

4.0
3.0
Impacts on ecosystems

•
Rapid increase of greenhouse gases (CO
2
, CH
4
, N
2
O) since 1750 is mainly caused by CO
2 fossil fuel use .
•
The developed countries and developing countries contribute almost equally to the emissions of GHGs .
•
Mitigation: International (Kyoto Protocol)
•
Green economy ( Renewable energy, Sustainable transportation,
Green buildings, Energy-efficient industry and carbon capture,
Land management, afforestation, waste management )
•
We can make a difference by reducing waste of energy, food and other materials, and by purchasing environment-friendly products.

Greenhouse gas emissions per capita
The developed countries and developing countries contribute almost equally to the emissions of GHGs.

• Negotiated in 1997. Commits parties to internationally binding emission reduction targets.
• “Common but differentiated responsibilities”
– Specific reduction targets for developed countries
– Measures to slow the growth of emissions in developing countries
• Non-parties:
– Canada
– USA
– Andorra
– South Sudan
– Palestine
– Vatican City

GHG Emissions by Sector

Green economy

• There will be <50 multiple-choice questions