Atmosphere and Severe Weather
What is the main job of the ocean and atmosphere in terms of distributing heat from the equator to the poles?
What IS a greenhouse gas?
What is the most important greenhouse gas (hint: it ain’t CO2!)?
What are patterns of surface winds around planet?
Coriolis effect; in what direction does it deflect the wind and water?
Low and high atnospheric pressure: what does each mean? (=weight of column of atmosphere)
What 's the air circulation attern associated with low pressure? High pressure?
ocean circulation: what are the general directions of air and surface currents at the Equator?
In the North Atlantic Ocean?
In the Pacific?
Recall gyres as a way to keep this straight!
Hadley cells of atmospheric circulation- where does air rise and where does it fall? (recall the 2 high and 2 low pressure regions of the World- know where they occur and what type of climate you expect to find at each- such as rain or deserts)
A common essay question that I've asked in the past: Deserts- why do they occur at 20-30 degrees latitude, which is right next to rain forests, which are at the equator?
What is adiabatic cooling?
What is latent heat (recall that water absorbs and releases heat energy when it changes from on e physical state to another)?
What is a rain shadow? Why do we have one on the east side of the Sierra Nevada Mountains (think about air descending over mountains and the effect this has on the air- molecules brought closed together due to increased pressure, so molecules collide more frequently, and this generates heat!)
Terms: Environmental lapse rate, humidity, saturation.
What affects air’s saturation level- meaning it’s ability to hold water (answer= it’s temperature! saturation point doubles for about eveny 10 degrees C rise in temperature).
What causes cloud formation? A: cool the air to saturation point by having it rise through atmosphere.
What causes air to rise- orographic lifting, Frontal wedging, Convergence
stable versus unstable air: note the difference- unstable air is warmer than surroundings and so it continues to rise.
What are fronts? Warm front- warm air mass pushes into area occupied by cold air; Cold front- cold air mass pushes into area occupied by warm air. Easier to do, as cold air more dense = better pusher. Creates steep front, high rainfall, thunderstorms.
What is a cyclone? (: counterclockwise rotation around a central low pressure center)
What wind patterns do find around high or low pressure centers (recall cyclonic flow versus anticyclonic flow)?
Which has rain associated with it?
What type of pressure center are Thunderstorms Tornadoes and Hurricanes associated with?
Where in the US do thunderstorms or tornadoes most frequently occur? Why? (recall central US has no topographic barrier to separate the Polar High pressure center from the Subtropical Low.
How can thunderstorms have hailstones the size of golf balls (recall updrafts)?
Why does lightning occur?- recall the removal of electrons from upward moving clouds by the cold clouds that they run into.
Tornadoes- form beneath really large cumulonimbus clouds- called supercells.
What is a mesocyclone?- recall it’s a vertical column of rotating air. How does it develop?
Average tornado width = 100-600 meters, Highest wind speeds in nature- approaching 300 mph;
Hurricanes = Tropical cyclones- Fueled by the latent heat of condensation (requires lots of warm (>27C) (>80F) water, so form in the subtropics (5-20 degrees from Equator); how they die? : Cut off source of warm water.
Flooding
What is the current year's El Niño-La Niña weather pattern (i.e. which are we supposed to experience this year?)
Salt: Concerns in agriculture and why the Great Salt Lake is salty (recall how wet western US was at the end of the last Ice Age, and how evaporation has concentrated salt)
Three controls on streamflow: Gradient, channel characteristics, discharge; note that affecting one will cause the others to respond.
What is baselevel? A: The elevation to which streams will erode vertically.
Cut banks and point bars: which direction does the stream migrate?
Younger river versus mature rivers: What does each river valley look like in cross section? (recall that young rivers are cutting to baselevel, and then once they reach it they cut sideways)
Why do streams meander? (recall the changes in discharge and channel characteristics versus stream gradient as a stream matures).
When considering long-term flood hazards for a flood plain, it is important to remember that a stream channel will meander to cover the whole plain at one time or another. Also remember that natural compaction of loose sediment causes floodplains to naturally subside, and the stream will migrate to low areas and dump sediment there. This is what's happened to New Orleans.
Groundwater: Porosity, permeability and subsidence due to groundwater removal; remember that subsidence is irreversible, and so loss of porosity (=groundwater storage potential) is irreversible!
Sustainability of western US water usage: recall subsidence of San Joaquin Valley from 1925-1975. Note that this subsidence makes heavily used (and populated) areas most prone to flooding.
Consequence of urbanization on runoff: how does a hydrograph change as a consequence of urbanization?
Floods: The Great Missoula Flood and development of the Channeled scablands of Eastern Washington
Loess: What is it and what did the Dust Bowl of the 1930s have to do with it?
1993 Mississippi River Flood at St. Louis: What caused this upstream flood?
What are the weather events that can cause excessive rainfall in the United States (recall El Niño and Middle Latitude Cyclones).
What effect will global warming have on the California snowpack, which makes up 30% of our water supply?
What effects do dams have on delivery of sediment to downstream areas, and ultimately the coastline?
Waves- crest, trough, wavelength, wave height
oscillatory motion of water waves (waves transfer energy, not water, across the ocean)
Energy of water waves = wind (at the surface of the water column)
At what depth does a wave “feel bottom”?
How does the shape of the coastline affect the refraction (focusing and divergence) of wave energy (i.e. headlands vs. bays)?
Longshore Transport (= beach drift)- what are the physical factors that cause sand to migrate down current? (A: waves and gravity)
Rip currents- how do they form and how do you get out of one most safely?
Coastal landforms: Depositional (due to beach drift): spits, baymouth bars, barrier islands
Coastline protection- groins, jetties, sea walls, breakwaters, beach nourishment. What are the advantages and disadvantages of each?
West Coast and East Coast problems with coastline protection: west = sediment starvation and coastal erosion (caused by dams). East = migration of barrier islands.
Tsunamis: Watch video: Tsunami: The wave that shook the World (DVD in Library: #1269)
What were the warning signs of an impending tsunami?
Might we expect tsunami events along the California Coast?
How does the shape of the coastline affect tsunami wave energy?
Is there just one tsunami wave?
What causes tsunamis?
Climate and Climate Change
Recognition that climate changes naturally at all time scales
There is no “magic” baseline against which you can compare changes (e.g. arbitrarily choosing 1950’s weather may not be a reasonable comparison).
Clear evidence of global warming during the 20th century by 1 degree F (=0.6 degree C).
Evidence seen at places where frozen versus liquid water would occur (permafrost in Alaska, retreating mountain glaciers). All scientists agree with that.
Effect for California projected to change amount of rain slightly, but the big concern is raising the snowline in the Sierra (and consequently the loss of temporary water storage)
New Orleans - flooding not because of global warming, but rather because of subsidence of the sediment.
Human induced global warming projections are uncertain, but tend to all show a temperature increase over the next century of perhaps 1-6 C. Not all scientists are convinced yet, because most studies do not prove correlations of cause and effect at:
95% confidence supposed to be the scientific standard of proof, but many climate projections do not state model uncertainties, or they find that uncertainties do not reach the scientific standard of proof.
Carbon dioxide has ranged from 180 ppm to 280 ppm from glacial to interglacial periods, respectively, but presently is at 370 ppm. This added ~ 90 ppm is due to fossil fuel burning.
carbon dioxide is an important greenhouse gas, but is second in importance to water vapor (and changes in water vapor have not been documented for very long, leading to uncertainty in correlating global warming solely to carbon dioxide emissions).
Carbon dioxide alone SHOULD have caused global warming of at least twice the amount that has been measured, and so it is possible that other human and natural effects are countering this warming (for instance, sulfur dioxide – a byproduct of fossil fuel burning, causes cooling by reflecting light back into space).
If we use clean fossil fuels (those without sulfur dioxide) we could cause an increase in global warming because sulfur dioxide has a 1-2 year residence time in the atmosphere, whereas carbon dioxide has a 100 year+ residence time…sometimes it doesn’t pay to be clean!