A TMS S CI 3600: C LIMATES OF THE W ORLD Anthony R. Lupo.
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Transcript of A TMS S CI 3600: C LIMATES OF THE W ORLD Anthony R. Lupo.
ATMS SCI 3600: CLIMATES OF THE WORLDAnthony R. Lupo
DAY 1
Hydrologic Cycle
Describes the movement of water and processes through the earth-climate system
General outline of atmospheric water cycle
DAY 1
DAY 1
Water evaporates, forms clouds, clouds precipitate over land and water, over land we get runoff back to water sources…and begins all over again.
Can’t ignore transpiration (plants, etc.), hydrological processes underground, etc.
Residence time for water vapor ~ 8 days.
DAY 1
Water Resources
97% in Oceans
Cryosphere is about 1.5% of entire water mass (frozen water)
Fresh Water: 0.09%
DAY 1
In Atmos: 1/1000th of a percent
A lot of importance though
Where do we find this small percentage in the atmosphere?
DAY 1
Water Vapor
Water vapor in the vertical
Since temp decreases with height (lapse rate 6.5 deg C per km, 3.8 F per 1kft)
DAY 1
Therefore water vapor content decreases with height
mixing ratio drops off more dramatically with height than temperature
Above 850 mb, water content drops off rapidly
Most is contained between 1000-850 mb
DAY 1
Water Content (cont)
Where is the water mass on the earth?
See handouts given in class…NCAR Tech Memo- Distribution of Topographical Quantities 1995
Winter cloud cover- in mid-latitudes over the oceans (both northern and southern hemisphere)
India and Sahara less cloudy regions in winter, some subtropical regions as well
DAY 1
Winter cloud cover- in mid-latitudes over the oceans (both northern and southern hemisphere)
India and Sahara less cloudy regions in winter, some subtropical regions as well
DAY 1
Cloudiness (cont.)
In summer, in mid-latitudes over ocean is still cloudy
In summer the cloudiness in N.H. moves slightly northward
DAY 1
July-August low cloudiness, major deserts, Saudi Arabia, Australia, Sahara
Cloud cover over land ~50%
DAY 1 Page 1.40
Relative humidity with height ,averaged in latitudinal bands
Features are fairly similar in both winter and summer
Values greater than 70% represent the boundary layer, which makes sense
In the S.H. boundary layer is fairly moist from equator to pole, N.H dries out around 30 N….trade wind deserts
DAY 1
Function of the land
N.H. 39 % land, and 61 % ocean
S.H. 19% land, and 81 % ocean
Big land ocean dist asymmetry
DAY 1
RH x-y plots
Oceanic areas more humid, land masses are dry, except for the tropical rain forests
Siberia in the summer is relatively humid
SE US with humidity in the summer can be some of the most uncomfortable places in the world
DAY 1
Figure 1.43- PW
Precipitable Water (PW)= The sum of the values of mixing ratio in a column of atmosphere
Lots of PW near the equator where it is warmest
In summer in N.H. high PW values reach the Southern US
DAY 1/2 Figure 1.45
Average precipitation over all longitudes for each latitude belt
High amounts are found in the equatorial regions, where it is warmest (among other processes---ITCZ)
Secondary maximums around 30 N and 30 S…mid-latitude jet streams are found here
X-Y plot is the final diagram…more handouts coming in the near future when we discuss gen circ further
DAY 2
Cloud Formation
3-legged stool example
3 things to get cloud
Moisture Vertical motion (lift) Cloud Condensation Nuclei (CCN)
DAY 2
Natural CCN
Sea Salt, Sand/dirt, Bugs, Pollen, etc.
Anthropogenic CCN
Pollution Sources, etc.
DAY 2
Cloud types
Cloudiness impacts temperature- cloudy nights warmer than clear, for example
High Clouds
Cirrus-type clouds, ice crystals
DAY 2
Middle Clouds
Alto, ice crystals and supercooled droplets
Low Clouds
Main Precip producers…Nimbostratus (uniform sheet) vs. Cumulonimbus (convective heap)
DAY 2
Precip Clouds (cont.)
In N.H. nimbostratus dominate in winter, cumulonimbus dominate in warmer seasons
Nimbostratus, are uniform with a large area
of weak forcing, warm frontal (stratiform) precipitation
Cumulonimbus can grow up to 60000+ feet, severe thunderstorms, heavy convective precipitation, high albedo only snow is higher…climate impacts
DAY 2
Drought
Places that are typically moist, but can become dry over a long duration, 2003, 2005-2007 was a recent drought locally
1988 was a widespread drought in the US
Drought “begets” drought – speech to the National Press Club
DAY 2
Different types of drought
Meteorological precipitation versus normal
Agricultural stress on plants
Hydrological level of the rivers and lakes
DAY 2
Drought
Basic drought equation: precipitation minus evaporation
If evaporation exceeds precip for quite a time, the result is a drought
Meteorological drought compares P-E to climatology
DAY 2
Palmer Index
Rates a severity for drought
Long term index (5-6 month composite) …cannot tell you if you have had relief due to a month being rainy
DAY 2
For more information www.drought.noaa.gov/palmer.html
Also see the Drought Mitigation Center…University of Nebraska-Lincoln
www.drought.unl.edu/whatis/indicies.htm
For a summer season forecast see: Global Climate Change Group (MU) http://weather.missouri.edu/gcc
DAY 2
DAY 2
Last Time
Latent heat of fusion: going to solid to liquid or liquid to solid
Snow melting takes energy from atmosphere (cooling), snow on ground takes heat from atmos and surface
Freezing opposite
DAY 2
General Circ and Climate
Two ideas that are closely related
General Circulation: features of the general circulation are statistical entities, long-term statistical analysis of the atmosphere (no specific time scale)
DAY 2
Gen Circ has a specific time and space scale unlike climate which is just a time
Gen Circ- large time and large space (global) scale
DAY 2
Time Scales
For the most part you cannot see general circulation patterns on a weather map
Long-term for gen circ refers to: Monthly Seasonally Annually
These mean features can show through in as little as 15 days
DAY 2
General Circulation Pattern
3 Belts
3 cell model (or 3 belts) of the earth’s atmosphere, Coriolis gives rise to this (earth’s rotation)
See figure (Draw on Board)
DAY 2
Sir George Hadley
If warm air rises and cold air sinks, there has to be this rising air at the equator and sinking at the pole
Had right idea but did not to take in account earth’s rotation
DAY 2
Earned him the naming rights of the tropical cells (Hadley cells on diagram).
Mid-latitude cells are called the Ferrel cell, and we have the nameless Polar Cells
DAY 2
3 Questions to Answer
Q: What gives rise to the Gen. circ?
Q: Why westerlies in midlatitudes, why easterlies in tropics?
Answer: Temp and Momentum Transport
DAY 2
Third Question
Why are these temperature and momentum transports necessary?
Good Exam Question!
We will get at this answer in the next two lectures
Good detailed answer coming up in the future
DAY 2
Other Planets
Can almost see the banded structure on Earth
Not as evident as Jupiter, but banded nonetheless
If we double the rotation of earth, we would have nine bands
Jupiter is about double our rotation…hence has about nine belts (cells)
DAY 2
Jupiter Saturn
DAY 2
Venus Pluto
DAY 3
Features of the Gen Circ
Existing characteristics
Gen Circ Features migrate with the seasons
System sloshes northward during summer
We’ll start at the equator and move to higher
latitudes
DAY 3
ITCZ
Inter-tropical convergence zone
Belt of low pressure Rising motions
DAY 3
DAY 3
Is a place where the horizontal winds are weak (Doldrums)
Rising motions give way to strong convection (thunderstorms)
Can see this in satellite images as bands of convective areas near the equator
DAY 3 ITCZ Starting point for the energy (temp and
momentum) transport toward the North begins
ITCZ will be located as far north as the mid-latitudes in the summer (India and Florida)
Does not progress too far south of the equator due to the large amount of ocean (weak temp gradients)
Meeting ground of the two belts of the trade winds
Height of tropopause (16-17km) greatest here…warmest temps
DAY 3
Subtropical Highs
Located right around 30°N/S
Highs tend to be stronger over the ocean
Associated with anticyclonic and downward motion
DAY 3
DAY 3
Correspond with the majority of the world’s deserts (Great Basin, Sahara, Middle East, Kalahari, Great Sandy Desert)
Circulations give rise to the trade winds (NE wind in N.H., SE wind in S.H.)
Names: Bermuda and Azores High (Atlantic), SE Pacific High
DAY 3
Mid-latitudes
30°N/S-60°N/S
Battle zone of air masses
Winds are generally westerly aloft and at the surface
Balance between (PGF-Coriolis) We find jet streams in this region
DAY 3
Jet Streams and Polar Front
Were predicted in 1910’s before upper air measurements, all based on math, jet stream was discovered during WWII over the Pacific during bombing runs
Is a gen circ feature (large time and spatial scales)
DAY 3
Reflection of the polar front…boundary between low polar temps and moderate continental temps
Jet stream located above the sfc polar front in general
DAY 3
Norwiegen Model
Stage 1 Stage 2
DAY 3
Norwiegen Model
Stage 3 Stage 4
DAY 3
Norwiegen Model
Stage 5 Stage 6
DAY 3
Jet Stream (cont.)
Jet stream and polar front are not constant…jet stream is strongest off Asia (200 mph in winter)…polar front has large impacts over N. America.
During winter jet is strongest
DAY 3
Jet and Polar Front are the tracks that storms take
Ridge in Jet Stream…warmer temps
Trough in Jet Stream…more polar air mass
DAY 3
Polar Regions
Find two low pressure regions that are located around 60°N
Where cyclones go to die:
Aleutian Low Icelandic Low
“old lows never die…..they just fade away!
DAY 5
Highlights from Last Time
Dry Subtropical Highs
Moist ITCZ, some moisture also associated with the polar front
Jet Stream around 40-50 N, westerly PGF=Co
Jet stream has waves in it
DAY 5 Jet Streams
Waves= has about 3-4 waves
Can see these waves on hemispheric plots
Resemble a clover
Once again land sea differences determine the amplitude and location of the 3-4 wave pattern
Polar front and jet streams are good boundaries of cold arctic air and warm subtropical air
DAY 5
Roaring 40’s
Region in the Southern Hemisphere that experiences high wind and waves and is relatively stormy
The winds and waves are high due to low friction…in S.H. the entire band of latitude from 40-50 S is devoid of land
Made early explorations tough
DAY 5
Revisit the Questions for Gen Circ
Why westerlies in the mid-latitudes and easterlies in the tropics?
What gives rise to the gen circ
Because of heat and momentum transport
Why do we need temperature and momentum transport?
A. On the following slides
DAY 5
Why do we need heat transport
Fairly straight forward
Incoming radiation at the equator is greater than at the poles
DAY 5
Outgoing radiation at the equator is also greater than at the poles but drops off slower than incoming as you move poleward
This results in a net surplus in the tropics and a net deficit at the poles
DAY 5
Why do we need heat transport
2nd Law of Thermo: need equilibrium
Therefore, we must have a net transport of heat poleward
Strength of the heat transport is proportional to the strength of the equator-pole temperature gradient
Therefore, highest in winter (see hmwk. 1)
DAY 5
Part 2: Momentum Transport
A bit trickier
Don’t look at the relative wind, focus on the absolute
Momentum must be conserved
DAY 5
Earth is rotating as a solid body
Set up: easterlies in the tropics, westerlies in the mid-latitudes
Earth rotates from west to east
DAY 5
Part 2: Momentum Transport
Easterly winds are opposite earth’s rotation and extract momentum from the earth…momentum rich (for atmos.)
Westerly winds work with rotation and add momentum to earth’s rotation…momentum poor (for atmos.)
Mid-latitudes are a sink..tropics are a source…must be a net transport poleward
DAY 5
Climate Change and Heat Transport
Global warming is occurring
Affects the poles more than the tropics
Therefore if you heat the poles you decrease the temperature gradient
DAY 5
Weaker heat transport, weaker storms, not an increase in storm intensity that some point too
But that is all to be seen
DAY 5
Climate Change and Momentum Transport
Basically global warming, or any other factor will not act to speed up the earth’s rotation for our purposes
Therefore, the transport of momentum will stay fairly constant
No big impact on climate change, or at least not the focus
DAY 5
3 processes transporting heat, momentum, and moisture
Transport by mean motions (15-20%)
Hadley cell, Ferrel Cell, and Polar Cell
Transport by Standing Eddies (15%)
DAY 5
Aleutian and Icelandic Low, Bermuda High, Monsoon
1 and 2 are Gen Circ Features (stat)
Transient Eddies (65-70%)
Day to day features…fronts, L’s, H’s, hurricanes, etc.
DAY 5
3-cell diagram
Good website http://www.ux1.eiu.edu/~cfjps/1400/
circulation.html
Hadley Cell, higher vertical extent … thermally direct (warm rising, cold sinking)
DAY 5
Ferrel Cell, thermally indirect
Polar Cell, thermally direct (lowest)
In between Hadley and Ferrel= Subtropical Jet, Ferrel and Polar= Polar Jet
DAY 5
Walker Circulation
Sir Gilbert Walker, 1920’s Indian Monsoon – Southern oscillation
ENSO roots
Only longitudinal circulation
DAY 5
In general, western Pacific has higher SST’s, lower pressure and eastern Pacific is opposite
Stormy over the western Pacific basin (suck zone, net divergence aloft)
Every so often this pressure pattern reverses (El Nino), storms and SST’s slide eastward
DAY 5
El Nino and it’s Impacts
History of El Nino – known for a long time.
Life cycle (draw on board – ocean – atms interaction) and recurrence time – 2 – 7 years
Good papers on the El nino (Kelsey et al. I, II links on the http://weather.missouri.edu/gcc
El Nino impacts on North America, Missouri
DAY 6
DAY 6
DAY 6
DAY 6
DAY 6
Pacific Decadal Oscillation – What is it?
+ (warm) phase (PDO1) -- (cool) phase (PDO2)
DAY 6
Vascillation – and the NAO (Luo et al. 2007)
Why does this occur? What does it mean for our weather?
DAY 7
Quasi – Biennial Oscillation:
As name suggests, happens every 24 – 28 months and is confined to the tropics (20 N – 20 S).
Associated with hurricane activity – more when easterly, less when westerly – so hurricane season of 2005, had easterly QBO and La Nina, both favorable to hurricane activity (Lupo et al. 2008)
DAY 7
Climate Diagnostics Bulletin
DAY 7
2005 hurricanes (28) 1933 hurricanes (21)
DAY 7
Madden – Julian Oscillation / Madden and Julian (1972)
A tropical oscillation in cloudiness and precipitation that occurs every 30 – 60 days. Also goes by the name intraseasonal oscillation.
Influences tropical storm activity (e.g. Dec tropical storms of 2003), and can influence summer precipitation in mid-west.
DAY 7
Types of Ocean Currents
2 Types of Ocean Currents
1. Surface Currents--Surface Circulation
These waters make up about 10% of all the water in the ocean.
These waters are the upper 400 meters of the ocean.
DAY 7
Types of Ocean Currents
2. Deep Water Currents--Thermohaline Circulation
These waters make up the other 90% of the ocean
These waters move around the ocean basins by density driven forces and gravity.
DAY 7
The density difference is a function of different temperatures and salinity
These deep waters sink into the deep ocean basins at high latitudes where the temperatures are cold enough to cause the density to increase.
DAY 7
Influencing Forces
1. Primary Forces--start the water moving
The primary forces are: 1. Solar Heating 2. Winds 3. Gravity 4. Coriolis (frame of reference)
DAY 7
Winds and Surface Flow
Winds blowing on the surface of the ocean push the water. Friction is the coupling between the wind and the water's surface. Westerlies and Trades most influential.
DAY 7
Winds and Surface Flow
A wind blowing for 10 hours across the ocean will cause the surface waters to flow at about 2% of the wind speed.
Water will pile up in the direction the wind is blowing.
Gravity will tend to pull the water down the "hill" or pile of water against the pressure gradient.
DAY 7
Coriolis and Surface Flow
But the Coriolis Force intervenes and cause the water to move to the right (in the northern hemisphere) around the mound of water.
DAY 7
Gyres
These large “mounds” of water and the flow around them are called Gyres. The produce large circular currents in all the ocean basins.
Northern Hemisphere Gyre flows clockwise southern Hemisphere flows counterclockwise.