Essay on Lecture 7

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Lecture 7: The Atmosphere and the Oceans
PHS 109
Week of 10/7/14

Announcements
• HW 2 due Thurs, 10/9
• Quiz 2 next Thurs, 10/16
– Will cover chapters 4-6
– Similar format to last time
– Review guide to be posted by Thurs
– Review/trivia next Tues

Salinity can also be measured by satellites!
• NASA Aquarius (launched in 2011)

https://www.youtube.c om/watch? v=5xQP_B18vMw

How does solar (shortwave) radiation hit the surface of the Earth?
• The amount of it is “constant” everywhere, but the amount per unit area depends on location and season! The Earth’s heat budget
• Solar radiation in=energy out (emission, reflection, etc.) • Out of 100% incoming radiation at the top of the atmosphere – ~50% absorbed by Earth’s surface – ~30% reflected out to space – ~20% absorbed by clouds and atmospheric gases

Figure 6.2

The Earth’s heat budget
• Whatever energy is absorbed must be emitted, or re-radiated, from a body or surface (infrared or longwave radiation)
• Surface, clouds, gases emit IR radiation • Note also outgoing heat fluxes exist – Latent heat flux occurs due to evaporation and condensation of water – Sensible heat flux due to heated rising air

The heat budget is balanced globally, but not at every latitude!
• The Poles have an energy deficit (In < Out)
• The Equator has an energy surplus (In>Out)
• The middle latitudes have energy balance (In=Out)
• How is balance maintained such that the Equator doesn’t get hotter and hotter, and the
Poles get colder and colder?

The atmosphere
• A thin envelope of gases above our surface

Atmospheric composition

Atmospheric structure

Thermosphere=temperature increases with height because level most influenced by incoming solar radiation Mesosphere=temperature decreases with height

Stratosphere=temperature increases with height due to ozone as main constituent (ultraviolet absorption)
Troposphere=where our weather happens, level closest to Earth’s surface, ~10km , temperature decreases with height

Density is also related to air temperature and water vapor in the air
• Which is denser, cold or warm air? Why?
• Which is denser, dry or moist air? Why?

Density is also related to air temperature and water vapor in the air
• Which is denser, cold or warm air? Why?
– Cold air moves slower, takes up a smaller volume

• Which is denser, dry or moist air? Why?
– Dry air weighs more than moist air since lighter water vapor is replacing heavier nitrogen and oxygen molecules

Carbon dioxide: a trace gas, but…
• Very important atmospheric constituent because it is major gas (along with methane, ozone and water vapor) involved in the greenhouse effect
• This effect makes Earth’s average temperature sufficient for life…if it didn’t exist, neither would we!

Average Earth Temperature = 0°F

Average Earth Temperature = 59°F

Fig 2.13 from Ahrens, 2009

Anthropogenic CO2 concentrations
• Since the Industrial
Revolution (1700s), atmospheric CO2 concentrations have risen steadily to the present day
(reached 400 ppm in 2013 for the first time)
• This has enhanced the greenhouse effect and contributed to global warming along with natural causes

Atmospheric pressure
• Force with which a column of overlying air presses on an area of Earth’s surface
• Air that is less dense exerts a lower surface pressure; air that is more dense exerts a higher surface pressure • Questions
– Does cold or warm air exert lower surface pressure?
Why?
– Does moist or dry air exert lower surface pressure? Why?

Atmospheric pressure
• Force with which a column of overlying air presses on an area of Earth’s surface
• Air that is less dense exerts a lower surface pressure; air that is more dense exerts a higher surface pressure • Questions
– Does cold or warm air exert lower surface pressure?
Why?
– Does moist or dry air exert lower surface pressure? Why?

Pressure and density
• Both decrease exponentially with height in the atmosphere! Fig. 1-21 from Lutgens

How does a sea breeze form?
• Differential…