Geography 370: CLIMATOLOGY

Spring 2009


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Most, if not all, of the following topics and terms will appear on the first midterm, on Monday, March 2 . This two-hour test will consist of ten multiple choice questions, five short answer questions, and one short essay. The material covered includes Chapter 1 through Chapter 4, page 114, in Aguado and Burt. Topics from Wednesday's lecture (Feb 25) will be on the second midterm.

How to study for this test: Go over your notes and compare with readings in the text. Fill in any blanks. Look at all the illustrations, diagrams, and tables in the text. Ask yourself questions about the material, and see if you can answer fully. Try testing yourself with the text CD. Organize a study group with other class members. The test will focus more on material from the lectures and in-class discussions, but will include material from the text on topics that were covered in lecture. It will emphasize both concepts and definitions.

Review Session Sunday, March 1st, STV 3036, 3 p.m.

Topics --

What is Climate?

Normal Weather -- measured in 30-year averages

Climatology as an atmospheric science

Atmosphere -- gaseous layer in constant motion

Solar radiation -- source of all energy, all atmospheric motion

Unequal distribution of heat energy -- causes atmospheric movements, wind

Structure and composition of the atmosphere

History of the atmosphere
First atmosphere -- helium and hydrogen, blown off as earth formed by collisions
Second atmosphere -- volcanic gases, rich in CO2, water vapor, nitrogen, etc. Virtually no free oxygen. Water vapor condensed into clouds, began to rain, filled oceans over billion years
Third atmosphere -- beginnings of life, photosynthesis, put oxygen into atmosphere, took CO2 out of atmosphere. Over time reached present content: 79% nitrogen, 21% oxygen, <1% argon, trace gases. Balance maintained with this composition, more or less, over very long time

Variable and constant gases, aerosols
Characteristics of troposphere, stratosphere, mesosphere, thermosphere
and associated "pauses", e.g. tropopause, stratopause, etc. Know average elevations of pauses.
Vertical variations: temperature, density, chemical composition, motion,
and causes of these variations
Weather -- where does it occur and why there?
Ozonosphere: where is this located, and why?

Energy in the Atmosphere

Nature of Radiation
Energy Transfer Mechanisms (from one body to another) : Conduction, Convection, Radiation
Electromagnetic Spectrum: longwave, shortwave, visible spectrum, infrared, ultraviolet
Rates of molecular motion, electromagnetic spectrum, wavelength
Radiation Laws:
Planck's Law: a body of a specific temperature emits energy at a range of wavelengths characteristic of that temperature (bell shaped curve)
Wein's Law: wavelength of peak emission of a body is inversely proportional to its temperature
Stefan-Boltzmann's Law: Intensity of radiation increases with the fourth powerof its absolute temperature
Inverse Square Law: energy emitted by a body that is intercepted by a second body decreases as the square of the distance from the original body.

Solar mean temperature, ~6000 Kelvin, mean wavelength of emission 0.5 micrometers;
Earth's mean temperature, ~ 288 K, mean wavelength of emission 10 micrometers

Wavelengths, energy amounts, temperature of solar emissions versus earth's energy emissions

What happens to shortwave solar energy (insolation) when it enters the atmosphere?

Reflection, Albedo (no change in wavelength, all SW)
Earth's albedo, albedo of different substances -- clouds, surface characteristics
Scattering (still SW, but in all directions). Why is the sky blue? Why are some sunsets red and orange?
Absorption -- incoming shortwave changed to longwave as it is absorbed
Greenhouse gasses (CO2, H2O, CH4, N2O, CFCs, & O3)
Absorption bands, selective absorption by different gases at different wavelengths, see diagrams in packet

Energy Balance of Earth

Shortwave incoming versus Longwave outgoing, know rough proportions absorbed, reflected, scattered Shortwave insolation -- ultraviolet absorbed by ozone, some near infrared absorbed by greenhouse gases; atmosphere virtually transparent to visible range, 0.4 to 0.7 micrometers
Earth emits Longwave (infrared, heat); radiation from surface heats the atmosphere, absorbed by greenhouse gases at specific wavelengths (see diagrams in packet)
Mean temperature of the Earth's Surface: 15 degress C;
Mean temp without greenhouse effect: -18 degrees C
Recycling of Longwave between the atmosphere and earth's surface
Sensible Heat, conducted and convected from surface

Earth-Sun Geometry

Earth's orbital variations that cause long term climate cycles, glaciations versus interglacials during Pleistocene:
Tilt of earth's axis, 21.5 to 24.5 degrees over 41,000 year cycle
Wobble of earth's axis (like a spinning top), ~21,000 year cycle, changes time of year of perihelion and aphelion
Obliquity of earth's orbit around the sun, ~100,000 year cycle
Cause of Seasons, day length variations
Tilt, 23.5 degrees to the perpendicular to the ecliptic
Slightly elliptical orbit, perihelion (when earth closest to sun) Jan. 3, aphelion, July 4
Variations in temperature distribution
Day Length, seasonality, varies with latitude
High latitudes: more extreme seasonal variations
Low latitudes: little variation in day length, little seasonal temperature variations
Intensity of radiation -- controlled by Angle of Incidence
Seasonal Lag in maximum and minimum temperatures -- January and July
Diurnal Lag in maximum and minimum temperatures -- late afternoon and just before dawn

Other factors that influence temperature

Evaporation, Cloudiness, Land-Water differences (Continentality), Ocean Currents, Thermal conductivity, Aspect, Topography, Elevation, Vegetation and other surface covers, Windiness

Storage of Latent Heat -- cools air or surfaces when evaporation occurs

Specific Heat -- water versus other substances, moderates temperatures
The amount of energy required to raise 1 gm of a substance, such as pure water, 1 degree Celsius, at 1 atmosphere (sea level air pressure)

Thermal conductivity of different materials, earth vs. water, air

Energy surplus (tropics), deficit (poles) balanced at ~38 degrees N & S Latitude

Modes of energy transport from low to high latitudes -- latent heat carried in atmospheric water vapor, sensible heat in ocean currents, sensible heat carried in atmosphere

Greenhouse Effect

Electromagnetic spectrum, absorption bands
Greenhouse gases -- carbon dioxide (CO2), water vapor (H2O), methane (CH4), CFCs, nitrous oxide (N2O) , tropospheric ozone (O3)

Positive and negative feedbacks, Postive and Negative Forcing
Other things that affect energy balance: increased cloudiness & aerosols (reflect more insolation, negative forcing), ocean circulation, deforestation (changes in surface albedo, CO2 released into atmosphere, positive forcing)

Latent Heat
Phase changes -- Solid (ice), liquid, gas (vapor); melting, evaporation, sublimation; freezing, condensation, deposition
Energy storage and release, Latent Heat -- During which processes is latent heat stored, and about how much; during which processes is latent heat released, and about how much?
How much heat used to evaporate 1 gm of water; how much to melt 1 gm of ice? How much heat to cause sublimation of ice to vapor?
Implications regarding heat released when vapor condenses, deposits?
Phase changes of water -- what happens to latent heat when water condenses, freezes?

Forces in atmospheric motion -- what makes the wind blow?

Role of Air Pressure, Temperature

Isobaric surfaces, e.g. 500, 300 mb surfaces

Ridges and troughs -- along Polar Front

How is air pressure measured? How does it vary with altitude?

Driving forces for winds -- Gravity, Air Pressure Gradient force

Hydrostatic equilibrium
Isobars as indicators of pressure gradient

Resisting forces for winds --

Coriolis effect, factors influencing strength, spatial variations, where?
Friction, where, how?

Centripetal force -- role in gradient wind, reinforces rotation -- in your text, Supergeostrophic flow

Geostrophic winds and Gradient winds -- why do they flow parallel to isobars?

Look at maps, p. 114, variations with different mb surfaces -- 850 mb, 500 mb, 300 mb
How do highs and lows vary with altitude above the land surface?
Low and High pressure cells at surface; Ridges and Troughs aloft and slightly to the west of surface cells

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