The Atmosphere, Part 1: The Atmosphere, Part 1: Composition, Structure, & Composition, Structure, &

Heat BudgetHeat Budget

Thomas V. Dagenhart,

M.S.

v 3.8Crepuscular Rays, Manassas, VA;

Dagenhart, 2003

Atmospheric Composition• Reported on a dry basis, water vapor

excluded since it’s so variable.• Only 2 gases comprise 99%• Water vapor normally <1 - 4%

Minor gases exert influence far greater than their abundance would suggest, e.g. greenhouse effect, UV protection, photosynthesis, etc.

Gross & Gross, 1996

Dynamic Equilibrium of Atmospheric Water Vapor

• Atmospheric water vapor varies immensely with place and time.

• For Earth as a whole, evaporation equals precipitation.

• For ocean as a whole, evaporation exceeds precipitation.

• Latent heat of vaporization supplies much of heat to drive convection. Gross &

Gross, 1996

Air parcels change size & temperature as they rise & fall.

• Rising & cooling triggers condensation which forms clouds & rain.

• Latent heat released at condensation further warms air and forces more rising.

Garrison, 2005

Layers of the Atmosphere

• The exosphere tails off into space and meets the solar wind.

• The ionosphere straddles several layers.

• The ionosphere reflects radio waves & hosts the aurora borealis & aurora australis.

Iono

sphe

re

Wikipedia, 2009

Structure & Temperature Profile of Lower Atmosphere• Virtually all weather occurs in troposphere.• Earth’s surface heats troposphere from bottom; favors vertical mixing.• Stratosphere heated most at middle & top because of UV ray absorption by

ozone; limits vertical convective mixing there. • Additional layers found above: mesosphere, thermosphere, exosphere.

strongest heating by UV-absorbing ozone

heating from below

Gross & Gross, 1996

Sun Angle Controls Sunlight Intensity

• At low angles, sunlight spreads over much larger areas & thus heats less effectively.

• At low angles, sunlight reflects from water & ice more efficiently.

Garrison, 2005

Variation of Solar Radiation with Latitude (also with Seasons and with Time of Day)

• 2 cal/cm2/min. at top of atmosphere perpendicular to sun’s rays

• 0.5 cal/cm2/min. on the average at top of atmosphere due to inclination of sun’s rays

• Even less reaches surface on the average

• Intensity = 2 x sine (sun’s <) (cal/cm2/min.)

noon radiation intensity (cal/cm2/min.)

at given latitude on equinox days: @40o = 1.53 @66.5o = 0.80 @89.5o = 0.02

At winter solstice (N.H.) the most

intense radiation is at Tropic of

Capricorn @ noon.

Gross & Gross, 1996

Earth-Sun RelationsTo Polaris (North Star)

Emission Spectrum of Sun & Earth

Wavelength (micrometers)

UVsolar

radiation

near IR solar

radiation

visible solar

radia- tion

• Sun’s “surface” at 6000 oC radiates strongly in UV, visible, & near IR.

• Earth’s surface & atmosphere at 18 oC radiate strongly in far IR.• Consider area under curve when comparing relative intensities of

UV, visible & IR.

Gross &

Gross, 1996

Global Heat Budget• These numbers indicate global averages.• Locally the energy fluxes vary with season, time of day, cloud cover,

snow cover, vegetation patterns, etc.

Garrison, 2005Absorbed Visible Light Converted to

IR, Sensible & Latent Heat

X 16%

X 5% X 39%

Greenhouse Effect

+=

Latitudinal Variations in

Radiation Budget

• Surplus must equal deficits to maintain heat budget.

Garrison, 2005

Excess heat lost near poles must be carried from tropics to poles by ocean currents & winds.

Poleward Heat Transport to Balance Unequal Heating

• Equator would be hotter & poles would be much colder without this transport.

• Transport by winds & ocean currents.

Garrison, 2005

The Greenhouse Effect• Certain atmospheric gases absorb outbound infrared (IR) radiation and then

reradiate it in all directions including downward.• Some of the reradiated IR reaches the ground and lower atmosphere to

make the Earth warmer than it would be without the greenhouse gases.• Much like the glass of a greenhouse allows in light but traps heat.• Without any greenhouse gases, Earth would chill to –18oC.• Water is the main greenouse gas, but it’s self limiting due to precipitation.

Garrison, 2005

CH4

CH4

Greenhouse Effect

• Is it the main cause of global warming?

• Or is the climate cycling due to ice age causes?

Tarbuck & Lutgens, 2005

CO2

CH4

CFC

Greenhouse Gases• Other gases help CO2.• All have significant natural

sources except CFC’s.• Methane = natural gas

from swamps & rice paddies, oil & gas wells, coal mines, land fills, cow & termite flatulence, & decomposition.

• CFC’s being phased out, used in AC and as propellants (hair spray).

• Low altitude ozone partly from man’s pollution.

• N2O from burning, lightning, moist soils.

CH4

CO2

N2O

O3

e.g. CCl2F2

Percentage indicates relative importance, not relative abundance.

Gross & Gross, 1996

Cows

Greenhouse Gas on BBC

Relative Global Temperature Variation 1950-2000• Mean annual temperatures are indicated as a deviation from the 1951-1980 global

mean.• 5oC total temperature rise since last ice age (18,000 years BP) or 0.03 oC per

century, about half of rise is due to increasing solar output.• The 0.5oC rise in the last 25 years looks very significant, = 2oC per century .

Garrison, 2005

0.6

Global Warming

Since 1860

• 1860 begins the period where thermometer readings are available worldwide.

• Annual averages for entire world compared to averages for 1961-1990.

• Larger rise projected during 21st century.

Tarbuck & Lutgens,

2008

CO2 Concentration Vs. Time• Has risen rapidly since industrial revolution due to fossil fuel burning.• Many natural sources: volcanoes, burning, respiration, decomposition.• Rise is less than expected. Key cause of greenhouse effect.

Fossil Fuels = coal, oil, natural gas, peat

Garrison, 2005

Carbon Dioxide vs. Time at Mauna Loa, Hawaii 1958 - 2009

y = 0.0121x2 - 46.733x + 45284

R2 = 0.9898

300

310

320

330

340

350

360

370

380

390

400

1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

Time (years)

CO

2 C

on

cen

trat

ion

(pp

m)

Data from http://noaa.gov.Graph & extrapolation by

Dagenhart, 2009

Carbon Dioxide vs. Time at Mauna Loa, Hawaii: Projection to 2100

y = 0.0121x2 - 46.733x + 45284

R2 = 0.9898

300

350

400

450

500

550

600

650

700

750

800

1950 1960 1970 1980 1990 2000 2010 2020 2030 2040 2050 2060 2070 2080 2090 2100

Time (years)

CO

2 C

on

cen

trat

ion

(pp

m)

Data from http://noaa.gov.Graph & extrapolation by

Dagenhart, 2009

CO2 may be approaching 3X the preindustrial level in 2100.

CO2 Concentrations from 1996 to 2000 at Mauna Loa

355

360

365

370

375

1996 1997 1998 1999 2000

Year

CO

2 C

on

ce

ntr

ati

on

(p

pm

)

• What causes the zig zag detail in the curve?

Graph by Dagenhart from data in EPA, 2002.

Rising Carbon Dioxide (CO2) Levels

• Rapid rise from coal, gas, and oil burning since 1800.

• Causes greenhouse effect, i.e. global warming.

• Missing CO2 puzzle: concentration is lower than predicted by emissions.

• Storage in ocean or plants?

Tarbuck & Lutgens,

2005

Sea Level Change in

Last 20,000 Years

• Water supplied by rapid glacial retreat.

• Little change in last 6,000 years.

• 100 m rise in 11,000 years = 9.1 mm/yr average

• 18.2 m/yr horizontal shoreline shift on VA Coastal Plain

Tarbuck & Lutgens, 2005

Projected Sea Level Rise in This Century • Three different estimates.• Note the accelerating rate of rise!• Worldwide changes are termed eustatic sea

level changes.

Tarbuck & Lutgens, 2005

Causes of Sea Level Sea Level Rise This Century • Note the Antarctic Ice Sheet may actually grow

in spite of global warming & limit sea level rise.

57% of the sea level rise will result from simple expansion of seawater as it warms.

Tarbuck & Lutgens, 2005

Effects of Rising Sea

Level I-95 Coastal Plain

Virginia Beach X

Uplift along an active continental margin may offset sea level rise in CA

Like the East coast in early Tertiary time.

Like the West coast.

Tarbuck & Lutgens,

2005

Coastline Variation Due To Glacially-Induced Sea Level Changes

• Not “Waterworld”

• ~ 100 m drop

• ~ 80 m riseTarbuck & Lutgens, 2005

What does rising sea level mean to islanders?• Land is inundated & barrier reef provides less wave protection.• Great tsunami of December 2004 washed over this island.• Many died.

Island in Maldives Garrison,

2005

Do Jet Contrails, Dust, & Smoke

Increase Reflection of Sunlight and Reduce Global

Warming?• Contrail = condensation

trail • Sublimation trail really?• After 911 terrorist attack

planes were grounded & contrails were absent, a small percentage increase in solar radiation was detected.Satellite Photograph of Contrails & Ship Smoke

Trails over Pacific Ocean; Garrison, 2005

The Ultimate Proof of Global Warming• Let me be brief.

Stratospheric Ozone Layer Depletion• Stratospheric

ozone shields us from UV rays; prevents skin cancer.

• Ozone depletion due to chlorofluo-rocarbons (CFC’s) from man’s pollution.

• Depletion partly due to natural processes?

• Observation only carried out for a limited time.

• Ozone at ground level comes from pollution & irritates lungs.

Ozone “Hole” in Stratosphere Over Antarctica

Garrison, 2005

Variation of CFC-11 Levels from 1977-1996

• A leveling off & slight dip in CFC levels appears to be happening as a result of CFC phase out after 1990 treaty.

Garrison, 2005

Risks from Increased UV Radiation• Higher incidence of skin cancers and mutations.• Loss of phytoplankton & zooplankton from upper 2 m of ocean.• Damage to land plants & reduced crop yields.• Eye cataracts.• Immune system suppression

Malignant Melanoma,Garrison, 2005

• A 1% decrease in ozone is expected to produce a 5-7% increase in skin cancer.

Decreased Phytoplankton

Productivity• As southern

hemisphere summer begins.

• Due to increased influx of UV rays through ozone hole over Antarctica.

• Phytoplankton around Antarctica form the base of a food chain critical to whales and remove much CO2 from atmosphere.

Garrison, 2005

Monthly Variation in Ozone

Concentrations

NASA, 2005

Ozone Video 1978-2001

• Note ozone hole over Antarctica (dark blue).• Note ozone depleted belt near equator (light blue) moves N &

S with seasons.

References

• Environmental Protection Agency (2002) Global Warming Web Site. http://www.epa.gov/globalwarming/publications/impacts/

• Garrison, T. (2005) Oceanography: An Invitation to Marine Science, 5th ed. Brooks/Cole Thomson Learning, Stamford, CT, 522 p.

• Gross, M.G. and E. Gross (1996) Oceanography: A View of the Earth, 7th ed. Prentice Hall, Upper Saddle River, NJ, 472 pp.

• Tarbuck, E.J. and F.K. Lutgens (2005) Earth: An Introduction to Physical Geology, 8th ed. Pearson-Prentice Hall, Upper Saddle River, NJ, 711 p.

Sunrise at OHS, Manassas, VA; Dagenhart, 2003