Quiz 5 Flashcards
(40 cards)
General Circulation of the atmosphere
Intertropical convergence zone (ITCZ) Trade winds Subtropical highs Westerlies Polar front (Subpolar lows) Polar easterlies Polar highs
What is the Monsoonal Circulation?
- In summer, air moves upward over the land and downward over the ocean
- Upward movement creates low pressure above land
- Downward movement creates high pressure above ocean
- Precipitation is heaviest in regions with low pressure and upward air motion
What are examples of today’s monsoon areas around the world?
They consist of those in South Asia, Southeast Asia, parts of West Africa which are very weak. The only monsoon systems in the Southern Hemisphere are the Amazon Valley and NE Australia.
Monsoons on pangea ~200 myA
“Supermonsoons” due to strong heating in the summer and strong cooling in winter
Earth’s axis tilt change (obliquity)
- In 41,000-year cycle, larger tilt (closer to 24.5°) produces more insolation at both poles in their respective summers
- ~10,000 years ago earth’s tilt was at its maximum
- Each hemisphere had warmer summers, colder winters
- Today, both hemispheres experience smaller seasonal amplitudes
What is the Precession of the Equinoxes: Insolation Control of Seasonal Variations?
It explains how one full orbit around the Sun is completed in 23,000 years and gives a prediction that in 11,500 years from today June and December solstices will be in exactly opposite positions on the orbit.
What is the evidence of the June 21 solstice position occurring near the aphelion (most distant pass)?
There is reduced radiation during our summer.
11,500 years ago situation was reverse, what happened during that time?
There was increased radiation during the Northern Hemisphere summer (perihelion position); decreased radiation during the Northern Hemisphere winter and greater temperature differences between winter and summer occurred 11.5K years ago.
What is the Orbital Monsoon Theory?
- greater summer radiation intensifies the wet summer monsoon
- decreased winter radiation intensifies the dry winter monsoon
- Monsoonal strength is modified by a 23,000-year precessional cycle
Evidence form the North African Summer Monsoon ~11K years ago, What was the sapropel accumulation in the Mediterranean Sea?
The evidence points deep water is oxygen-rich (sinking of saltier water to the bottom) in which deposits were found on the sea floor dated 10,000-8,000 years old.
What is saporel?
They are organic carbon-rich deposits formed in anoxic conditions.
When are the sapropel layers best developed?
They are best developed near the time of the strongest summer insolation (last time ~11,000 years ago). Earlier sapropel layers occur at regular 23,000-year intervals
What are examples of glaciers?
Continental ice sheets (now only in Greenland and Antarctica), and mountain (alpine) glaciers
How do glaciers form?
They form by compaction of snow; transformation into firn, and finally into glacial ice along with accumulation and ablation.
The fastest moving ice is at the surface why is that?
- It is due to the central portions of large ice sheets which form high central domes
- ice streams down the flanks which forms ice lobes, ice shelves over shallow ocean
- icebergs occasionally break off and float away.
What controls the size of ice sheets?
- Through accumulation in which they initially as snow at mean annual temps below 10°C
- melting begins at mean summer temps above 0°C (= mean annual temps above -10°C).
What is ice mass balance?
It is net balance between accumulation and ablation.
What is the equilibrium line?
The boundary between positive and negative mass balance.
What is The Milankovitch Theory?
- summer insolation controls ice sheet growth
- ice sheet growth in the Northern Hemisphere which occurs during times when summer insolation is reduced
- the amount of summer insolation arriving at the top of atmosphere at 65°N can vary by +/-12% around the long-term mean value
In perfect ice sheet growth conditions, when does Low summer insolation occur?
When:
- the earth’s orbital tilt is small
- the northern summer solstice occurs once the earth is farthest from the sun
- orbit is highly eccentric
What else happens in a low summer insolation?
Decrease in tilt results in diminishing seasonal amplitude such as warmer winters, colder summers. The June 21 solstice position starts to occur near the aphelion (most distant pass) which causes a reduction in radiation during Northern Hemisphere summer and 11,500 years ago (and ~ 11,000 years from now) there will be increased radiation during the Northern Hemisphere summer (perihelion position).
Tops of ice sheets can reach elevations of 2-3 km where temps are cooler
What is the average lapse rate of cooling?
The feedback effect weakens when ice sheets reach high elevations
Annual accumulation rate is ~ 0.3 meters of ice
How long will it take a full-sized glacier to grow up to 3,000 meters thick?
Around 10,000 years
Ice sheets lag behind insolation max & MIN
- Water has a high heat capacity and reacts slowly to changes to heat applied to it
- Similarly, ice sheet rates of growth and ablation react slowly to radiation increase or decrease
- Theoretically, the phase lag between the orbital and ice sheet cycles is ¼ wavelength
