Lec 5 - Radiation, Monsoons, Ice sheets

Question 1

Why are there regional differences in insolation?

Answer 1

atmospheric differences (clouds)

Question 2

What is albedo?

Answer 2

percentage of energy reflected by an object

Question 3

What is the average albedo of the Earth?

Answer 3

0.13

• lower than the albedo of most surface types since most of Earth surface = covered in oceans

Question 4

What are atmospheric windows?

Answer 4

• regions of the EM spectrum that can pass through our atmosphere
• optical and infrared especially have influence on energy flows/Earth energy balance

Question 5

What are some sources of longwave radiation?

Answer 5

Everything! Earth, sun, etc
- longwave radiation is constantly transferred between the earth and atmosphere

Question 6

What role do clouds play in the global energy balance?

Answer 6

• shortwave radiation: clouds scatter and reflect 50W/m^2 more!
• long wave radiation: clouds prevent 30 W/m^2 from leaving!
• on average, clouds cool the planet

Question 7

Why does pressure decrease with altitude?

Answer 7

1. gravity
2. air is compressible

Question 8

What happens in a low-pressure system?

Answer 8

• suck air in
• moist, rising air
• create winds, bring undesirable weather

Question 9

What happens in a high-pressure system?

Answer 9

• push air away
• dry sinking air
• associated with clear blue skies

Question 10

What is the main climate factor that controls monsoons?

Answer 10

• Insolation, which affects land faster than water
• forced by precession cycle, as evidenced by diatom records

Question 11

What happens during the Summer portion of the monsoon cycle?

Answer 11

• land warms rapidly, while ocean stays relatively cool
• upward movement of air over land causes air to rise, ocean air to be sucked in (low-pressure system)
• (continental regions with the same insolation are too far from the ocean to get this effect)

Question 12

What happens during the winter portion of the monsoon cycle?

Answer 12

• solar radiation = weaker, the land cools down faster than the ocean
• air over land sinks, pushing air out over the sea (high pressure system)

Question 13

Why do monsoons occur mainly in Africa and Asia?

Answer 13

in Northern hemisphere - large landmasses, high elevation

(monsoons = weaker in Southern hemisphere where landmasses are smaller, topography is lower)

Question 14

What would Pangaea’s monsoons have looked like?

Answer 14

Stronger than our current monsoon cycles (due to higher insolation and larger landmasses 200mya)

Question 15

What is the recent history of ice sheets on Earth?

Answer 15

• ice sheets first appeared within last 3Myr
• ice sheets last covered Europe and NA 20kya
• ice sheets disappeared by 6kya

Question 15

When do ice sheets form?

Answer 15

when the rate of snow/ice accumulation equals or exceed the rate of ice loss (ablation)

Question 16

What conditions allow ice sheets to accumulate?

Answer 16

• when mean annual surface temp is below -20C
• accumulation will still be below 0.5m/yr

Question 17

What conditions allow ice sheet ablation?

Answer 17

• can begin at -10C mean surface temp
• ablation can happen at several m per yr

Question 18

What is stable equilibrium of ice sheets?

Answer 18

• if net accumulation is in balance with ablation

Question 19

What is the Melankovich Theory?

Answer 19

• ice growth happens when summer insolation is reduced
• low insolation happens when the axial tilt is small, and during aphelion

Question 20

What is the temporal relationship between ice sheets and summer insolation?

Answer 20

ice sheets lag behind summer insolationi and temperature changes by about 6000 years (compared to orbital precession archives)

Question 21

What positive feedback loop exists between ice sheets and bedrock?

Answer 21

• bedrock depression and rebound lags behind changes in ice mass
• ice sheet grows = bedrock sinking is delayed = ice is at higher elevation (colder) = more positive ice mass balance since the top of the sheet is above the equilibrium line = more ice
• same is true in reverse, since ice sheet rebound is delayed for thousands of years
• as ice sheet melts, the bedrock doesn’t rebound, leaving ice below the equilibrium point = ice melts faster

Question 22

What method is used to investigate historical changes in ice sheets?

Answer 22

• d18O (temperature proxy)
• confirmed to be effective through coral reefs (tell us about sea level)
• indicates ice sheets have fluctuated at same scales as orbital cycles

Question 23

What doesn’t the Milankovich Theory explain about ice sheets?

Answer 23

does not explain why there was a shift in dominant cycles
- from 41ky cycle to 100ky cycle