Transcript Midterm 3 Review

Review for Midterm 3
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
Standard units of measurement
SI (System International)
Quantity
Length
Mass
Time
Temperature
Density
Speed
Force
Pressure
Energy
Power
Name
meter
kilogram
second
Kelvin
kilogram
per cubic meter
meter per
second
newton
pascal
joule
watt
Units
m
kg
s
K
kg/m3
Symbol
m
kg
s
K
kg/m3
m/s
m/s
m.kg/s2
N/m2
N.m
J/s
N
Pa
J
W
Scientific Notation
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
10-9
10-6
10-3
10-2
10-1
101
102
103
106
109
1024
0.000000001
0.000001
0.001
0.01
0.1
10
100
1000
1000000
1000000000
Tropical cyclones
• 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 oC (Poleward of about 20o 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
Bergeron classification of air masses
• 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
Fronts
• 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)
How does a mid-latitude cyclone form?
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
Mature stage. Cold air begins to
catch up with warm air (occluded).
If the upper level low is to the west
of surface low, the cyclone will
amplify and precipitation will form.
Cold air cools down the cyclone.
Dissipation.
Regions of cyclogenesis and typical tracks
– 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 and extratropical climate
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
Tropical mean state
• 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
Ocean upwelling
• 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 Niño 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 (CO2, CH4, N2O) since 1750: far exceed
pre-industrial values determined from ice core measurements spanning the
last 650,000 years, which is mainly caused by CO2 fossil fuel use. Lead to
strong radiative heating.
• 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
How do human activities change the
global climate?
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)
Observed change of greenhouse gases
Global atmospheric concentrations of CO2 and CH4 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
Atmosphere
Sea Ice
Coupler
Biogeochemistry
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. CO2, CH4)
• 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
Impacts on ecosystems
4.0
3.0
Mitigation of global climate change
• Rapid increase of greenhouse gases (CO2, CH4, N2O) since 1750
is mainly caused by CO2 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.
International: Kyoto protocol
• 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
About Midterm 3
• There will be <50 multiple-choice
questions