A TMS S CI 3600: C LIMATES OF THE W ORLD Anthony R. Lupo.

transcript

ATMS SCI 3600: CLIMATES OF THE WORLDAnthony R. Lupo

Hydrologic Cycle

Describes the movement of water and processes through the earth-climate system

General outline of atmospheric water cycle

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.

Water Resources

97% in Oceans

Cryosphere is about 1.5% of entire water mass (frozen water)

Fresh Water: 0.09%

In Atmos: 1/1000th of a percent

A lot of importance though

Where do we find this small percentage in the atmosphere?

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)

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

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

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

Cloudiness (cont.)

In summer, in mid-latitudes over ocean is still cloudy

In summer the cloudiness in N.H. moves slightly northward

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

Function of the land

N.H. 39 % land, and 61 % ocean

S.H. 19% land, and 81 % ocean

Big land ocean dist asymmetry

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

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

Cloud Formation

3-legged stool example

3 things to get cloud

Moisture Vertical motion (lift) Cloud Condensation Nuclei (CCN)

Natural CCN

Sea Salt, Sand/dirt, Bugs, Pollen, etc.

Anthropogenic CCN

Pollution Sources, etc.

Cloud types

Cloudiness impacts temperature- cloudy nights warmer than clear, for example

High Clouds

Cirrus-type clouds, ice crystals

Middle Clouds

Alto, ice crystals and supercooled droplets

Low Clouds

Main Precip producers…Nimbostratus (uniform sheet) vs. Cumulonimbus (convective heap)

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

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

Different types of drought

Meteorological precipitation versus normal

Agricultural stress on plants

Hydrological level of the rivers and lakes

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

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

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

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

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)

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

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

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)

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

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

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

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

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)

Jupiter Saturn

Venus Pluto

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

Inter-tropical convergence zone

Belt of low pressure Rising motions

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

Subtropical Highs

Located right around 30°N/S

Highs tend to be stronger over the ocean

Associated with anticyclonic and downward motion

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

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

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)

Reflection of the polar front…boundary between low polar temps and moderate continental temps

Jet stream located above the sfc polar front in general

Norwiegen Model

Stage 1 Stage 2

Norwiegen Model

Stage 3 Stage 4

Norwiegen Model

Stage 5 Stage 6

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

Jet and Polar Front are the tracks that storms take

Ridge in Jet Stream…warmer temps

Trough in Jet Stream…more polar air mass

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!

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

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

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

Why do we need heat transport

Fairly straight forward

Incoming radiation at the equator is greater than at the poles

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

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)

Part 2: Momentum Transport

A bit trickier

Don’t look at the relative wind, focus on the absolute

Momentum must be conserved

Earth is rotating as a solid body

Set up: easterlies in the tropics, westerlies in the mid-latitudes

Earth rotates from west to east

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

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

Weaker heat transport, weaker storms, not an increase in storm intensity that some point too

But that is all to be seen

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

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%)

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.

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)

Ferrel Cell, thermally indirect

Polar Cell, thermally direct (lowest)

In between Hadley and Ferrel= Subtropical Jet, Ferrel and Polar= Polar Jet

Walker Circulation

Sir Gilbert Walker, 1920’s Indian Monsoon – Southern oscillation

ENSO roots

Only longitudinal circulation

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

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

Pacific Decadal Oscillation – What is it?

+ (warm) phase (PDO1) -- (cool) phase (PDO2)

Vascillation – and the NAO (Luo et al. 2007)

Why does this occur? What does it mean for our weather?

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)

Climate Diagnostics Bulletin

2005 hurricanes (28) 1933 hurricanes (21)

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.

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.

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.

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.

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)

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.

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.

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.

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.

A TMS S CI 3600: C LIMATES OF THE W ORLD Anthony R. Lupo.

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