Atmospheric Science 60

Atmospheric Science 60 Name ___________________

Mid-term exam, November 3, 2000

Time allowed: 50 minutes

Part I

1. (5 pts) (a) Using the axes below (l El versus l , where El is monochromatic irradiance--the energy per unit wavelength per unit square meter, as used in the Planck's equation-- and l is wavelength in microns plotted on a logarithmic scale), plot spectral curves for solar and for terrestrial radiation. Assume they are smooth blackbody curves (following Planck's equation), and that solar radiation is reduced to the mean orbital distance of the earth. Be sure to indicate which curve is which and to locate the spectral peaks with reasonable accuracy.

(b) Give a general statement concerning differences between how the atmosphere interacts with solar and with terrestrial radiation streams.

2. (4 pts) (a) The hydrostatic equation expresses the rate of change with height of a meteorological variable. What is this variable? The equation represents a balance of two forces. What are these forces, and in what direction does each of them act?

(b) What is an adiabatic process? Give an example of a meteorological process that is approximately adiabatic, and one that is diabatic (not adiabatic).

(c) Define potential temperature either in words or with an equation (defining all terms). How does the potential temperature change, if at all, along a dry adiabat? Explain your answer.

3. (3 pts) Outline a procedure by which you could estimate the radiative temperature of a planet in a solar system different from our own. What information would you need to perform a calculation of such temperature? What assumptions would you need to make?

4. (3 pts) (a) Considering the effect on the vertical displacement of a parcel of air, what are meant by stable and unstable atmospheres? How would you determine whether a layer of atmosphere is stable or unstable using a skew-T diagram? What is meant by conditional stability?

(b) What is the basis for the Lifted Index (LI), and what use can be made of it?

Part II (circle the best answer, one point per question)

1. Because of the earth’s rotation, the equator is moving

A. towards the east at about 1000 mph

B. towards the west at about 800 mph

C. towards the east at about 500 mph

D. towards the west at about 300 mph

2. Approximately what portion of the mass of the atmosphere lies within the troposphere?

A. 50%

B. 25%

C. 75%

D. 95%

3. Sunsets are red because of

A. Rayleigh scattering by air pollutants

B. Rayleigh scattering by air molecules

C. Mie scattering by air molecules

D. selective absorption by air pollutants

4. A planet in our solar system with half the orbital distance of earth would have a solar constant

A. half the size

B. one fourth the size

C. twice as large

D. four times as large

5. Temperature generally decreases with height through the following layers

A. troposphere, thermosphere

B. mesosphere, troposphere

C. stratosphere, mesosphere

D. thermosphere, stratosphere

6. Which of the following globally and annually averaged irradiances is largest?

A. terrestrial radiation emitted by the earth's surface

B. solar radiation reaching the surface

C. terrestrial radiation emitted to space

D. terrestrial radiation emitted by the atmosphere reaching the surface

7. Which is the correct form of the equation of state?

A. pa =RT

B. p=a RT

C. p=r R/T

D. p=a /RT

8. The term pda is the expression for an increment of

A. the internal energy of a gas

B. work done by the gas during expansion

C. the heat input to a thermodynamic system

D. adiabatic compression

9. Which of the following are important greenhouse gases?

A. nitrogen, carbon dioxide, oxygen

B. argon, water vapor, methane

C. carbon dioxide, oxygen, helium

D. water vapor, carbon dioxide, methane

10. A layer of atmosphere is unstable if a parcel of air, when displaced vertically downwards,

A. becomes warmer than its surroundings

B. becomes more dense than its surroundings

C. becomes warmer than it was originally

D. increases in pressure

11. What is the magnitude of the adiabatic lapse rate?

A. 287 °C/km

B. 8.31 °C/km

C. 9.8 °C/km

D. 6.5 °C/km

12. Geostationary satellites

A. do not orbit the earth but stay in one fixed location

B. are sun-synchronous

C. orbit the earth at a height of about six earth radii

D. can be placed over any desired latitude

13. The negative feedback aspect of possible increased cloudiness during global warming is a consequence of the following:

A. increased planetary albedo

B. the fact that clouds are strong absorbers of solar radiation

C. the fact that clouds are strong absorbers of terrestrial radiation

D. Rayleigh scattering of solar radiation

14. CO₂ concentrations exhibit an annual cycle as well as a long-term trend. The annual cycle is such that

A. northern and southern hemisphere cycles are in phase

B. CO₂ concentrations are minimum in the summer months

C. the cycle has greater amplitude in the southern hemisphere

D. CO₂ concentrations might double by the middle of the 21^st century

15. Seasonal changes in weather are caused by

A. rotation of the earth about its axis

B. rotation of the earth around the sun

C. changes in the distance between the earth and the sun

D. the inclination of the earth's axis and rotation about the sun

16. Objects at 200 Kelvin emit thermal radiation with a spectral peak at about 15 m m. Objects with temperatures of 1000 K would emit most strongly at about

A. 1.5 m m

B. 0.6 m m

C. 3 m m

D. 75 m m

17. The lifting condensation level (LCL) is determined on a skew-T diagram by lifting a parcel such that

A. parcel temperature follows a dry adiabat, dew point is constant

B. parcel temperature follows a moist adiabat, dew point is constant

C. parcel temperature follows a dry adiabat, dew point follows a moist adiabat

D. parcel temperature follows a dry adiabat, dew point follows a constant mixing ratio

18. A superadiabatic lapse rate means

A. temperature decreases more rapidly with height than the adiabatic rate

B. the atmosphere is very stable

C. the atmosphere is unstable if dry, stable if saturated

D. thunderstorms are likely

19. The convective condensation level (CCL) is the level at which condensation occurs when

A. air is lifted dry adiabatically from the surface

B. surface heating creates an adiabatic layer which is saturated at the top

C. surface air is lifted moist adiabatically until condensation occurs

D. condensation inside a convective cloud causes precipitation

20. When calculating the temperature of a parcel of air that has undergone adiabatic lifting in the atmosphere to a new pressure level, from some known pressure and temperature, one would use the following:

A. Poisson’s equation

B. an expression for the adiabatic lapse rate

C. the hydrostatic equation

D. the first law of thermodynamics