Elements of the Sun; Solar Radiation

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Chapter 1 Introduction to the Climate System

• This chapter discusses
• Earths atmosphere
• Oceans
• Cryosphere (sea ice/glacial ice)
• Land and biosphere

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The Effects of the Atmosphere

• Blocks ultraviolet radiation

• Meteors burn

• Sound waves can travel
• Birds and airplanes can fly
• Diffuses heat
• Scatters sunlight (blue skies and sunsets)

• Hydrologic cycle
• Weather and climate

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The Atmosphere

• A thin envelope around the planet
• 90 of its mass (5.1 x 1018 kg) is within 16 km
  (10 mi) of the
• surface (about 0.0025 times the radius of the
  Earth)
• Atmospheric motions can therefore be considered
  to occur
• at the Earths surface

• The basic chemical composition of dry air is
  very uniform across the
• globe and up to about 100 km

• The greatest and most important variations in
  its composition involve
• water in its various phases
• Water vapor
• Clouds of liquid water
• Clouds of ice crystals
• Rain, snow and hail

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Composition of the Atmosphere
Dry Air
Solid particles (dust, sea salt, pollution) also
exist
Water vapor is constantly being added and
subtracted from the atmosphere, and varies from
near 0 (deserts) to 3-4 (warm, tropical oceans
and jungles)
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Greenhouse Gases

• Nitrogen, Oxygen and Argon (99.9 volume mixing
• ratio) have only limited interaction with
  incoming
• solar radiation, and they do not interact with
  the
• infrared radiation emitted by the Earth
• A number of trace gases (carbon dioxide,
  methane,
• nitrous oxide, and ozone) do absorb and emit
• infrared radiation (as does water vapor)
• Water vapor, carbon dioxide and ozone also
  absorb
• solar shortwave radiation
• Because they emit infrared radiation up- and
• downward, these greenhouse gases increase the
• energy received at the Earths surface, thus
  raising
• the temperature

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Changing Atmospheric Composition Indicators of
the Human Influence
Global, well-mixed greenhouse gas
(GHG) concentrations
CO2

• 31 increase since 1750 Highest levels
• since at least 420,000 years ago
• Rate of increase unprecedented over
• at least the last 20,000 years

1000 1200 1400 1600 1800
2000 Year
1000 1200 1400 1600 1800
2000 Year
CH4

• Increased 150 since 1750 to its highest
• levels in at least 420,000 years
• Has both natural (e.g., wetland) and
• human-influenced sources (e.g., landfills,
• agriculture, natural gas activities)
• Accounts for 20 of total GHG forcing

N2O

• Increased 16 since 1750 to its highest
• levels in at least 1,000 years
• Has both natural (e.g., soils and oceans)
• and anthropogenic sources
• Accounts for 6 of total GHG forcing
• Halocarbons (e.g., CFCs) account for 14

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Changing Atmospheric Composition Indicators of
the Human Influence
Global, well-mixed greenhouse gas
(GHG) concentrations
CO2

• 31 increase since 1750 Highest levels
• since at least 420,000 years ago
• Rate of increase unprecedented over
• at least the last 20,000 years

CH4

• Increased 150 since 1750 to its highest
• levels in at least 420,000 years

1000 1200 1400 1600 1800
2000 Year
1000 1200 1400 1600 1800
2000 Year
N2O

• Increased 16 since 1750 to its highest
• levels in at least 1,000 years
• Has both natural (e.g., soils and oceans)
• and anthropogenic sources
• Accounts for 6 of total GHG forcing
• Halocarbons (e.g., CFCs) account for 14

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Changing Atmospheric Composition Indicators of
the Human Influence
Global, well-mixed greenhouse gas
(GHG) concentrations
CO2

• 31 increase since 1750 Highest levels
• since at least 420,000 years ago
• Rate of increase unprecedented over
• at least the last 20,000 years

CH4

• Increased 150 since 1750 to its highest
• levels in at least 420,000 years

N2O

• Increased 16 since 1750 to its highest
• levels in at least 1,000 years

1000 1200 1400 1600 1800
2000 Year
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Atmospheric CO2 Since 1750
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Composition of the Present Atmosphere
Venus Earth Mars Surface Pressure 100,000
mb 1,000 mb 6 mb CO2 gt98 0.03
96 N2 1 78 2.5 Ar 1 1 1.5 O2 0.0
21 2.5 H2O 0.0 0.1 00.1
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The Vertical Structure of Earths Atmosphere
Four layers
Troposphere
(overturning)
From surface to 8-18 km
Stratosphere
(stratified)
From troposphere top to 50 km
Absorption of solar radiation by O3
Mesosphere
Extremely thin air very low temperature
Thermosphere
Extremely thin air very high temperature
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Vertical Structure of the Atmosphere
4 distinct layers determined by the change
of temperature with height
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• Extends to 10 km in the extratropics, 16 km in
  the tropics
• Contains gt80 of the atmospheric mass, and 50
  is
• contained in the lowest 5 km (3.5 miles)
• It is defined as a layer of temperature decrease
• The total temperature change with altitude is
  about 72C
• (130F), or 6.5C per km (lapse rate)
• It is the region where most weather occurs, and
  it is kept
• well stirred by rising and descending air
  currents
• Near 11 km resides the jet stream
• The transition region of no temperature change
  is the
• tropopause it marks the beginning of the
  next layer

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Vertical Structure of the Atmosphere
4 distinct layers determined by the change
of temperature with height
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• Extends to about 50 km
• It is defined as a layer of temperature increase
  and
• is stable with very little vertical air
  motion a good place to fly!
• Why does temperature increase? In part because
  of ozone, formed
• as intense ultraviolet solar radiation breaks
  apart oxygen molecules
• Near the ozone maximum (about 25 km), there are
  still only
• 12 ozone molecules for every million air
  molecules
• Yet, the absorption of ultraviolet radiation by
  ozone shields the
• surface and warms the stratosphere
• The transition region to the next layer is the
  stratopause

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Vertical Structure of the Atmosphere
4 distinct layers determined by the change
of temperature with height
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• Extends to about 85 km
• Few ozone molecules, and the extremely thin air
  loses more energy
• than it gains, so the temperature decreases
  with height
• With so few molecules to scatter light, the sky
  is dark
• The air pressure is 1000 times lower than at the
  surface
• (99.9 of the atmospheres mass is below the
  mesosphere)
• Exposure to solar radiation would severely burn
  our bodies!
• The transition region to the next layer is the
  mesopause

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Vertical Structure of the Atmosphere
4 distinct layers determined by the change
of temperature with height
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• Contains 0.01 of the atmospheric mass
• An air molecule can travel 1 km before colliding
  with another!
• If we measure temperature with a thermometer,
  the reading
• is near absolute zero (0 K, or -460F), not
  1500F. Why?
• The temperature of a gas is related to the
  average speed at
• which molecules are moving
• Even though air molecules in this region are
  zipping around at very
• high speeds, there are too few to bounce off a
  thermometer bulb
• to transfer energy to record a reading
• This explains why astronauts on space walks can
  survive such high
• temperatures the traditional meaning of hot
  and cold is no
• longer applicable

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Vertical Structure of Earths Atmosphere
1. Four layers defined by
temperature
Troposphere
T decreases with altitude
T increases with altitude
Stratosphere
Mesosphere
T decreases with altitude
Thermosphere
T increases with altitude
2. Importance to climate and climate change
Troposphere
Contains 80 of Earths gases
Most of Earths weather occurs
Most of the measurements is available
Stratosphere
Contains 19.9 of Earths gases
Ozone layer
Blocking Suns ultraviolet radiation
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Atmospheric Temperature
1. Most widely recognized climatic variable
(Global warming)
Tc TK T0
Tc temperature in degrees Celsius (C) 5(TF
32)/9
TK thermodynamic temperature in kelvins (K)
T0 273.15 K the freezing point
Global mean surface temperature 288 K, 15C,
59F
2. The lapse rate
G ?T/?z, G gt 0 in the troposphere
Varies with altitude, season and latitude
Global mean 6.5 K km-1
Determined by a balance between radiative
cooling and convection of heat
Glt 0, temperature inversion
At high latitudes in winter and spring
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Atmospheric Temperature (continued)
3. Pole-to-pole distribution of zonal-mean
temperature
Greatest near the equator, gt 26C lowest at
the poles
Stronger seasonal cycle in the Northern
Hemisphere than in the south
Amplitude of the seasonal cycle decreases from
the poles to the equator
4. Geographic distributions
Land heats up and cools down much more quickly
than oceans, hence larger seasonal variations.
Large seasonal variations in North America and
Asia
Smaller seasonal variations in the Southern
Hemisphere.
See IRI Data Library
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Annual Climate in Seattle
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Atmospheric Pressure
PressureForce/Area Pressure decreases with
altitude. Gravity pulls gases toward earth's
surface, and the whole column of gases weighs
14.7 psi at sea level, a pressure of 1013.25 mb
or 29.92 in.Hg. Standard sea level pressure
101325 Pa 101.325 kPa 1013.25 mb
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Vertical Pressure Profile
Pressure decreases at a curved rate proportional
to altitude squared, but near the surface a
linear estimate of 10 mb per 100 meters works
well.
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Hydrostatic Balance
Force Mass Acceleration Given a unit area
with thickness dz, volume dz, mass ?dz
Gravity force g ?dz Pressure force dp
Without atmospheric motions, dp g? dz dp/dz
?g p(z) ?z8 ?g dz m(z)p(z)/g m(0)p(0)/gp
s/g 1.03104 kg m2
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Hydrostatic Balance (continued)
dp/dz ?g For an ideal gas, p?RT where the
gas constant R 287 J K-1 kg-1 dp/dzpg/(RT) dp
/p dz/H d lnp dz/H where HRT/gscale
height If the atmosphere is isothermal, ?psp d
lnp ?0z dz/H ppsexp(z/H) H 7.6 km for the
mean T
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Water Vapor
1. Highly variable spatially

• Less than 1 in a dry atmosphere

• More than 3 in the moist tropics

• Decreases rapidly with altitude most is within
  a few km of the surface

• Decreases rapidly with latitude at the equator
  is 10 times that at the poles

2. Importance to climate and climate change
Important part of the water cycle
ocean-to-land atmospheric vapor transport
balances land-to-ocean runoff.
The most important greenhouse gas water
vapor-temperature feedback.
Water vapor condenses to form clouds, thus
cloudsradiation feedback. Clouds release
rainfall, reflect solar radiation, and reduce the
infrared radiation emitted by Earth.
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Oceans
Area covers 70 of Earths surface
Volume 97 of all the water on Earth
Depth 3.5 kilometers
Albedo 5-10, lowest on Earths surface
Heat capacity high thermal inertia high
Temperature less variable than in the atmosphere
Freezing point 1.9C, not 0C
Salinity water and dissolved salts most common
salt table salt (NaCl).
Density 1034-1035 kg/m3 (greater than pure water
1000kg/m3)
Average salinity 35 parts per thousand (ppt) or
3.5 by weight
Density depends on temperature and salinity
Cold water ? high density
Formation of sea ice ? high density
Evaporation ? high salinity ? high density
Precipitation and river discharge ? low salinity
? low density
Two main forms of circulation
Surface currents wind-driven, horizontal,
surface waters, fast
Deep-ocean circulation thermohaline, vertical,
deep waters, slow
Surface is not level due to currents, waves,
atmosphere pressure, and variation in gravity.
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Sea Ice
Locations in the Arctic Ocean surrounded by
landmass
in the Southern Ocean, surrounding Antarctica.
Depth 14 m in the Arctic 1 m in the Southern
Ocean.
Longevity in the Arctic, 45 yrs in the
Southern Ocean, forms and melts yearly.
Albedo 60-90, highest on Earths surface
Density less than seawater, hence floats on top.
The role in the climate system
Albedo-temperature feedback
Prevents the underlying (warm) ocean from
interaction with the atmosphere, thus cools the
air.
Melting of sea ice extracts heat from the
atmosphere Formation of sea ice releases heat to
the atmosphere.
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Glacial Ice
Two forms
Mountain (alpine) glaciers
Continental ice sheets.
Locations
Near sea-level at hi. lat. gt 5 km near equator
Antarctica and Greenland (polar ice caps)
Sizes
A few km in length, tens to hundreds of m in
width and thickness.
Hundred to thousands of km in length, 14 km in
thickness.
Area of the two current ice sheets
11 of land surface 70 m sea level rise when
all melted.
Movement
Flows downhill by gravity along mountain valleys
Flows to the lower margins.
The weight depresses bedrock.
Albedo
60-90, highest on Earths surface
The role in the climate system
Stores 70 of worlds fresh water
Changes salinity, circulation and sea level when
melt
Albedo-temperature feedback
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Example of a positive feedback
More energy retained in system
Albedo decreases Less solar energy reflected
Warm temperatures
Ice and snow melt
If this were the only mechanism acting, wed get
a runaway temperature increase
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The law of the minimum the factor that is least
available has the greatest effect on plants. The
law of the maximum too much of a certain factor
also limits a plants existence.
Global Climate Pattern and Vegetation
Af tropical wet (rainforest) Aw tropical wet
and dry (savanna) Am tropical monsoon Bs dry
semiarid (steppe) Bw dry arid (desert) Cs
mediterranean Cfa humid subtropical Cfb
marine Dw dry winters Ds dry summers Df wet
all seasons ET polar tundra EF polar ice caps
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Satellite-Derived Plant Geography
Satellite remote sensing provides global,
systematic, continuous measurements. Monitor
land use and land cover changes. Quantitative.
Must be validated by comparing with ground-based
data.
Early maps are constructed based on atlas,
surface surveys. Emphasize climate factors
(Precip, Temp). Neglect human factors.