General Circulation Flashcards
Geneal Circulation
What conditions (winds, pressure, precipitation, temperature) look like if we average over long periods of time, and over large areas
Typical winds
Easterly in the tropics
Westerly in mid-latitudes
Distribution of precipitation
Persistent rain near the equator and in mid-latitude “storm tracks” and clear skies in the subtropics
The relationships between average wind patterns and pressure patterns and upward and downward air motions
Three-cell model of the ATM
Polar cell (cold, sinking air near the pole spreads equatorward at the surface)
Ferrel cell (rising motion in the mid-latitude “storm tracks”
- Polar jet aloft associated with large horizontal temperature gradient (thermal wind)
Jet streams becomes unstable =>
starts getting wavy
wavy ==> mid-latitude cyclones
Conservation of Angular Momentum:
Unless acted upon by some force, the angular momentum of a parcel of air does not change
Thermal Wind
A horizontal change in temprature causes wind speed to increase with height
Subtropical Jet
Conservation of angular momentum
Problem: jet would be way too fast, and becomes unstable. Waves start to form on the jet
Polar / Mid-latitude Jet:
Strong temperature difference between tropics and high-latitudes => strong jet
Poleward transport of energy
Without this transport of eneergy the poles would be much colder and the tropics much warmer
Poleward energy transport is accomplished by both the atmosphere and the oceans
The region of maximum energy transport liew between latitudes 30 degrees and 60 degrees
Thermohaline Circulation
Water sinks in the North Atlantic and Antarctic, fills the deep ocean around the globe
Returns to surface in Indian, Pacific, and Southern Oceans, and returns to the Atlantic
Thermo:
warm water loses heat as it moves N. in the Atlantic
Haline
Evaporation causes water to become more salty as it moves North
Thermohaline
Water is more dense as it moves toward the North Atlantic
Key Features of the Tropical Pacific Mean State
- Easterly winds
- Thermocline close to surface in East
- Cold(er) water in East - Cold Tongue
- Warm(er) water in West - Warm Pool
- Rainfall in West
Thermocline
Large vertical temperature difference that seperates warm surface water from colder, denser sub-surface water
slopes upward toward the east
Tropical Pacific normal conditions
Easterly trades cause thermocline to deepen in the west, shoal in the east
Why is there a Cold Tongue?
Divergence: causes “upwelling” at the equator
Upwelling brings COLD water to surface in the eastern Pacific
Tropical Pacific normal conditions
Eastelry trades cause thermocline to deepend in the west, shoal in the east
Winds also cause upwelling along the equator, bringing cooler subsurface water to the surface
Cooling from upwelling is most pronounced in the east, where the thermocline is close to the surface
El niño
anomalous warming of the ocean surface in the central and eastern equatorial Pacific
Southern Oscilation
Oscillation in mass (pressure) between the eastern Pacific, and the western Pacific and Indian oceans
El Niño history
Señor Dr. Luiz carranza
sourthern oscilation history
Sir Gilber Walker
Atmospheric component
El Niño / Southern Oscilation
Jacob Bjerknes ENSO: connects el niño with the southern oscilation => it’s a coupled phenomenom
“Proxy Data”
Indirect information that tells us about climatic conditions in the past
Proxy data examples
Ocean Sediments - achieve past climatic info (shells, chemical composition of sediment, thickness of layers)
Ice cores - tell us about climate over last 500 ka
Tree rings (tell us about temperature and precipitation variations)Fossil corals and Speleothems: annual accumulation => temperature, precipitation
Forcing
A process external to Earth’s climate that affects the climate
Volcanoes, orbital changes, changes in the sun’s strength, antropogenic processes
Volcanic activity
aerosols from volcanoes reduce the amount of solar radiation reaching the surface
Obliquity
the amount of “tilt” of Earth’s axis
Eccentricity
How “eliptical” earth’s orbit is
More eliptical => more solar radiation at perihelion
Some dominant forcing mechanisms
Aerosols
Changes in Earth’s orbit
Solar variations
Anthropogenic Greenhouse Gasses
Anthropogenic Forcing
Emissions: rate at which a particular gas is being added to the atmosphere
Concentration: how much of that gas is actually in our atmosphere
Change in Concentration =
Natural Emissions + Anthropogenic Emissions - Natural Sink
Negative forcing
Causes cooling of the planet (aerosols)
Feedback
A process that alters climate changes that are already underway
Positive feedback: amplifies change
Negative feedback:supresses change
Snow and Ice Albedo Feedback
Warmer temperatures => snow melts quicker => more solar radiation absorbed => warmer temperatures
Stefan-Boltzman Feedback
Warmer climate => more emitted radiation => climate doesn’t warm as much
Water Vapor Feedback
Warmer temp and little change in RH => higher mixing ratio => enhanced greenhouse effect => warmer temperature
Global temperature will rise by about
1-5 degrees Celsius (2 degrees Farenheight)
