SP17 GEOG. 1900 EXAM 2 REVIEW SHEET
Chapter 3: Energy Balance and Temperature
● Review global maps of temperature distribution. How do those lines vary by season, and across
oceans vs continents?
● What are lines of equal temperature called? → ISOTHERMS
● Where on Earth would you expect to see the largest annual temperature range? And where is the
minimum range? Why?
○ Greatest range: Near Eastern Siberian Sea→ because it is such a large land mass away
○ Minimum range: latitudes near equator
● What are the major controls on global temperature distributions? Be able to list the geographic
factors that control the temperature patterns we see globally.
○ Latitude: tilt of Earth’s axis causes uneven distribution of solar radiation, causes seasons;
temp. Decreases from equator to poles
○ altitude & elevation: temp. Decreases with height in the troposphere because it is heated
from below ○ atmospheric circulation patterns: highests temps on Earth tend to occur in subtropics,
not equatorial regions, because they have less cloud cover and therefore more radiation
reaching surface; have to do with pressure systems
○ Continentality: inland locations favor temperature extremes more than coastal regions
○ ocean current characteristics along coastal regions: the existence of a warm current
offshore can cause a location along the east coast of a continent to have higher
temperatures than would a cold current offshore along a west coast
○ local conditions: slope orientation & steepness, amount & type of vegetation cover,
● What is it called when warmer temperatures are encountered with higher elevation? →
● List 4 reasons why water bodies are more conservative (less contrasts) of temperature than
○ 1. Specific heat of water is 5 times greater than that of land.
○ 2. Radiation received at surface of a water body can penetrate several tens of meters
deep and distribute its energy throughout a very large mass. The insolation absorbed by
land heats only a very thin, opaque surface layer.
○ 3. The warming of a water surface can be reduced considerably because of the vast
supply of water available for evaporation. Because much energy is used in the
evaporative process, less warming occurs.
○ 4. Unlike solid land surfaces, water can be easily mixed both vertically and horizontally,
allowing energy surpluses from 1 area to flow to regions of a lower temperature.
● What influences daily temperature variations at a given location?
○ Solar angle (time of day)
○ Wind speed
○ Surface wetness
○ Cloud cover→ overcast days likely to have lower range of max and min temps
● When would you expect to see maximum and minimum temperatures during the day on a
cloudless day? Why? Explain.
● What is mean temperature? What is the daily temperature range, and how do you compute it?
○ Mean temperature: average of max and min temperatures on given day
○ DTR: Maximum temp - minimum temp
● Describe some instruments used to measure temperature. Why must temperature instruments be
kept in shelters that allow air to flow? ○ Mercury thermometer (less expensive ones use dyed alcohol)
○ Maximum (must use mercury) and minimum thermometers (mercury and/or dyed
○ Bimetallic strip: strip bends an amount based on temp.
○ Resistance thermometers: send an electrical current through a thin filament made of
conductor material exposed to air ; temp. Influences resistance to electric current ; has a
○ Instruments must be kept in shelters to reduce influence of incoming solar radiation on
● What is wind chill? Why do we feel colder when it is windy?
○ If low temps are accompanied by winds, a person’s body loses heat much more rapidly
than it would under calm conditions, due to an increase in sensible heat loss.
○ Wind chill→ what temp actually feels like due to wind conditions
● What is the difference between free and forced convection?
○ forced→ external force causes movement of air
○ free→ air naturally moves because of differences in temp/pressure
Chapter 4: Atmospheric Pressure and Wind
● What is air pressure?
○ Atmospheric pressure→ the weight of the column of air above a given unit area of the
○ Exerted equally in all directions
● How do we measure it? What units do we use? Describe different instruments.
○ SI unit→ pascal (Pa), in US→ millibar (mb) = 100 Pa, in Canada→ kilopascal (kPa) = 1000
Pa= 10 mb
○ Mercury barometer→ avg. height of column at sea level = 76 cm
○ Aneroid barometer→ spring in flexible evacuated chamber
● How does pressure vary in the atmosphere vertically? Draw a profile through the atmosphere.
○ Pressure always decreases with altitude
○ Decrease NONlinearly because air is compressible→ rate of decrease is larger at lower
altitudes and smaller at higher altitudes
○ Horizontal pressure changes are very minimal
● What is Dalton’s law of partial pressures?
○ Total pressure exerted = sum of partial pressures
● What is the ideal gas law? Write it down and explain the variables.
○ Equation of state:
○ P = ρ * R * T
■ Where P = pressure in pascals
■ Ρ (rho) = density
■ T = temperature
■ R=287 J/kg K (← constant)
● Density is inversely proportional to temperature
● How is pressure related to temperature?
○ Increase in temperature leads to increase in pressure; they are proportional
● Re-write the equation of state to define density. Now, describe how density changes with an air
parcel’s temperature, if pressure is held constant.
○ ρ = P / (R * T )
○ As temperature increases, density decreases→ they are inversely proportional
● What are lines of equal pressure on a weather chart called? → ISOBARS ● What is the pressure gradient? How is this seen on a weather chart?
○ Pressure gradient= rate of change in pressure
○ Spacing of isobars indicates strength of the pressure gradient→ dense clustering of
isobars indicates a steep pressure gradient ( a rapid change in pressure with distance)
● What drives all wind? Explain how.
○ THE PRESSURE GRADIENT→ gives rise to pressure gradient force that sets air in motion
○ If the air over one region exerts a greater pressure than the air over the adjacent region,
the higher-pressure air will spread out toward the zone of lower pressure as wind (always
moves from high to low pressure)
○ Greater the PGF, stronger the wind
● Explain the hydrostatic equilibrium.
○ Vertical pressure gradient force and the force of gravity are normally of nearly equal value
and operate in opposite directions (so the atmosphere doesn’t explode away or get
sucked down to the very surface of the Earth)
● How does the vertical change in pressure differ between columns of warmer and colder air?
○ Cool air has a greater vertical pressure gradient because the warm column of air has the
same mass of air, but expands upwards, thus, to reach the same pressure in each
column, you have to go up higher in the warmer column of air
● Why do we care about the 500 mb heights, and how do we map these?
○ Look similar to isobars but they are telling us lines of equal height and at what height the
pressure is 500 mb, this allows us to determine the pressure gradient force
● Explain how 500 mb heights reflect the relative density of air.
○ The lower the 500 mb height, the denser the air, and vice versa.
● What forces affect the speed and direction of wind?
○ Unequal distribution of air across the globe establishes the horizontal pressure gradient
that initiate movement of air as wind
○ Planetary rotation alters direction of wind (Coriolis Force)
○ Friction slows the speed of the wind
● Describe the Coriolis force and how it changes with respect to latitude, and hemisphere.
○ Apparent deflection of path of objects moving on Earth due to Earth’s rotation; the Earth
is spinning fastest at the equator
○ The intensity of the deflection is proportional to the speed of movement
○ At the equator, the CF = 0, and it increases with higher latitudes
○ In the NH, wind will be deflected to the right
○ In the SH, wind will be deflected to the left
● How does friction impact wind speed and direction?
○ Friction reduces wind speed and the lower wind speeds reduce the Coriolis force and
thereby prevent the the flow from becoming gradient or geostrophic
○ Winds cross the isobars at an angle as they blow from high to low pressure
● Explain geostrophic winds. Where do they occur? How do they differ between hemispheres?
○ If pressure gradient and Coriolis force are equal, then a geostrophic wind occurs.
○ Non-Accelerating flow→ geostrophic flow
■ Flows to right in NH and left in SH
● What is gradient flow?
○ Close to geostrophic.
○ Small accelerations because isobars are not straight
○ Continual mismatch between pressure gradient and Coriolis force ● Under what surface pressure conditions do winds converge and diverge near the surface, and
● What is an anticyclone? Cyclone? Draw the relative motion of winds for each, in both Northern
and Southern Hemispheres.
○ Anticyclone→ enclosed areas of high pressure marked by roughly circular isobars or
height contours; wind rotates clockwise around ACs in NH because of Coriolis force
○ cyclones→ closed low-pressure systems; air at surface spirals counterclockwise into
cyclones in NH ■
● How do anemometers and aerovanes measure wind?
○ anemometers→ have rotating cups mounted on a moving shaft, wind blowing generates
electrical current (speed)
○ aerovanes→ when wind changes direction, it pushes against the tail and points the
aerovane towards the wind (speed and direction)
Chapter 5: Atmospheric Moisture
● Explain the hydrologic cycle, and draw the various flows and reservoirs.
○ The continuous transfer of water among terrestrial, oceanic, and atmospheric reservoirs.
○ Residence time for water molecule in atmosphere is on average 10 days
○ Precipitation, Evaporation, Condensation (cloud formation)
● What are two processes by which water vapor enters the atmosphere? How does water then
return to the ocean via the land?
○ Water vapor enters atmosphere through evaporation and transpiration
○ Water returns to land/ocean via precipitation and goes from land to water via runoff
● Explain the concept of saturation in terms of condensation and evaporation.
○ When the rates of condensation and evaporation are equal, saturation occurs ○ Water will evaporate into the atmosphere as water vapor until the air becomes saturated,
meaning it is holding the maximum amount of water vapor that it can, at which point the
water vapor will condense into clouds.
○ At higher temperatures, more moisture is required for saturation.
● How does water change phase? What is each change called, and how much energy is required?
○ Water changes phases based on temperature and pressure
○ Evaporation: liquid water→ water vapor; process by which molecules break free of liquid
○ Condensation: water vapor→ liquid water
○ Sublimation: ice→ water vapor (without passing through liquid phase)
○ Deposition: water vapor→ ice (without passing through liquid phase)
● What is that energy called, and how does it influence temperature?
○ Latent heat?
○ Kinetic energy?
● What is humidity? Describe different ways to measure it.
○ Humidity refers to the amount of water vapor in the air
● Define vapor pressure→ the part of the total atmospheric pressure due to water vapor
○ Millibars, pascals, kilopascals
● How does saturation vapor pressure vary with temperature?
○ Higher temperatures→ higher saturation vapor pressures
○ Nonlinear relationship
○ SVP increases more rapidly with higher temperatures
● What is absolute humidity? Specific humidity? What units do we use for each?
○ Absolute humidity→ the density of water vapor, expressed as number of grams of water
vapor contained in a cubic meter of air; value changes when air expands or contracts
even though moisture content doesn’t change→ not widely used for this reason
○ Specific Humidity→ expresses the mass of water vapor existing in a given mass of air;
proportion of atmospheric mass accounted for by water vapor; number of grams of water
vapor per kilogram of air; affected a small amount by atmospheric pressure; doesn’t
change as air expands or contracts; not temperature dependent.
● What is the mixing ratio? Saturation mixing ratio?
○ Mixing ratio: measure of the mass of water vapor relative to the mass of all of the other
gases of the atmosphere; mass of water vapor/ mass of dry air; mixing ratio and specific
humidity will always have nearly equal values
○ Saturation mixing ratio: maximum possible mixing ratio.
● Explain relative humidity, and define different ways we can calculate it.
○ Relative humidity: relates amount of water vapor in the air to the maximum possible at
the current temperature
○ RH = (mixing ratio/ saturation mixing ratio) x 100% (could also probably use specific
humidity and saturation specific humidity)
● What is the dew point? What happens when air temperature equals the dew point?
○ Dew point= the temperature at which saturation occurs
○ Dependent entirely on amount of water vapor present
○ Air is saturated/RH=100% when the air temperature equals the dew point
○ Dew point can never exceed temperature of air
○ High dew point → higher vapor content
○ Low dew point → lower vapor content
● Explain how dew point temperature is a good way to estimate overnight minimum temperature. ○ If no major wind shifts or other weather changes are anticipated, the minimum temp will
often approximate the dew point. If the air temp drops to the dew point and there is little
to no wind, a radiation fog has a good chance of forming. The fog would then inhibit
further cooling → overnight low = dew point temp
● What is fog? Explain different types, and how/where they occur?
○ Fog is essentially a cloud whose base is at or near ground level
○ Precipitation fog: results from evaporation of falling raindrops
○ Steam fog: occur when cold, dry air mixes with warm, moist air above a water surface
○ Fogs resulting from cooling the air to the dew point:
■ Radiation (ground) fog: develop when nighttime loss of longwave radiation
causes cooling to the dew point
● Most likely to form on cloudless night with light wind
● Most begin to dissipate within a few hours of sunrise; cloud droplets
radiate away as air temp rises (“burned off” not lifted)
● Forme dby diabatic cooling; associated with cold air
■ Advection fog: form when relatively warm, moist air moves horizontally over a
cooler surface; as air passes over cooler surface, it transfers heat downward,
causes it to cool diabatically
● Ex: Bay Area
● Can also form over ocean when warm and cold currents are in proximity
to each other
● Associated with greater winds than radiation fogs
■ Upslope fog: formed by adiabatic cooling; when air flows along a gently sloping
surface, it expands and cools as it moves upward
● Where is most fog found in the US? Why are dew point temperatures lower in January than July?
○ Lower Jan. temps preclude existence of high water vapor contents
● What processes can lead to saturation? Explain.
○ Adding water vapor to air: ex: steam in bathroom when taking hot shower
○ Mixing cold air with warm, moist air: causes contrails to form behind planes flying at high
○ Lowering air temp to dew point: most common process for cloud formation
● What factors affect condensation?
○ Temperature, moisture vapor content
○ Considerable curvature of water droplets increases amount of moisture needed for them
to be maintained relative to larger masses of water with flat surfaces
○ The curvature effect is largely offset by the fact that droplets do not occur as pure water
but instead exist as solutions
● Explain the curvature effect, and how does it impact the amount of water required for saturation?
○ Larger spheres have smaller curvature effect than smaller ones (ex: Earth compares to
○ A highly curved droplet of pure water at any given temp has a higher saturation vapor
○ Highly curved droplets of water require relative humidities in excess of 100% to keep
them from evaporating away
○ Supersaturated: air with RH exceeding 100%; can exist because because the highly
curved nature of suspended water droplets would cause them to rapidly evaporate in an
atmosphere at 100% RH with respect to flat water surfaces
● What are condensation nuclei and ice nuclei? Which is more abundant?
○ Condensation nuclei: small particles typically 0.2 µm, or 1/100th the size of a cloud
droplet on which water vapour condenses. Water requires a non-gaseous surface to
make the transition from a vapour to a liquid (condensation)
○ The atmosphere contains more condensation nuclei than ice-forming nuclei
○ Most condensation/deposition of water vapor occurs on particles, or nuclei, which make
the droplets/ice crystals more stable
○ Ice-forming nuclei activity is temperature dependent; formation of ice crystals at temps
near ) degrees C requires ice nuclei
■ Ice-nuclei are rare in the atmosphere
● What is supercooled water? → water having a temp below the melting point of ice but still
existing in a liquid state ● Explain how a wet bulb thermometers work. What is a psychrometer? Hair hydrometer? Describe
how they work, and what they measure.
○ Sling psychrometer: consists of a pair of thermometers, one wet-bulb and dry-bulb one→
difference between temps on 2 thermometers depends on moisture content of air
■ Evaporation results in loss latent heat and cools the wet-bulb
■ Evaporation, and hence cooling, is proportional to air moisture
■ If the air is saturated (100% RH) then both thermometers read the same temp.
■ The greater the difference between the thermometer readings, the lower the RH
○ Hair hydrometer: hair expands and contracts in response to relative humidity; easy way to