2.2 The global energy budget Flashcards
What is the global energy budget?
The atmosphere is an open energy system receiving energy from both Sun and Earth
What are the variations in the receipt of solar radiation and why?
- Due to the tilt of the Earth and its orbiting around the Sun, with latitude, there is a positive budget in the tropics and negative at the poles
- It is also due to the tilt of the Earth that the Southern hemisphere in January is summer, July winter and vice versa.
Define thermal equator
An imaginary line round the earth running through the point on each meridian with the highest average temperature
What is the annual temperature pattern (thermal equator)?
- In January, the thermal equator is further South
- In July, the thermal equator is closer to the actual equator
- In general, there’s a decline in temperatures northwards from the Tropic of Capricorn
How is balance achieved between the negative energy budget (at the poles) and positive energy budget (at the tropics)?
By the horizontal transfer of energy from the equator to both poles by winds and ocean current to compensate for differences in global insolation. Warm air rises at the equator, spreads northwards and southwards and then sinks
What does the surface pressure belt consist of?
- Equatorial low pressure trough
- Sub-tropical high pressure belt
- Sub-Antarctic and sub-Polar areas
- Polar highs
Why does the equatorial low pressure trough have low pressure?
This is an area of low pressure because it is an area of high temperature and humidity due to the sun heating it directly. In the northern hemisphere in July, the belt is north of the equator whereas in the southern hemisphere during January
Define Intertropical Convergence Zone (ITCZ)
- The area encircling the earth near the equator where the northeast and southeast trade winds come together.
- The convergence of warm, moist air over the equator transports large volumes of air aloft, to the top of the troposphere. This air is confined vertically by the base of the stratosphere and thus spreads out north and south toward the poles
Define doldrum
Refers to the part of Atlantic ocean/Pacific affected by ITCZ
How does pressure vary at the sub-tropical high pressure belts (30 degrees N and S)?
- In SH continuous about 30 degrees latitude
- In NH discontinuous because of the land
- Over oceans, high pressure occurs as discrete cells, the Azores and Pacific Highs
- Over continental areas, southwest USA, southern Asia and Sahara, major fluctuations: high pressure in winter and low in summer due to overheating
How does pressure vary at the sub-Arctic or sub-Polar areas (temperate latitudes)?
- In the northern hemisphere, there are strong winter low pressure zones over Icelandic and oceanic areas but over Canada and Siberia, there is high pressure due to the coldness of the land.
- In summer, high pressure is reduced, especially over continental areas
- In SH, it does not vary as much because here is more ocean in the Southern Hemisphere- and oceans do not vary in pressure or temperature as much as land does
What’s the pressure at the poles?
- Polar highs
- Pressure is high relatively throughout the year, especially over Antarctica due to the coldness over the landmass
How does the wind move?
From high pressure to low pressure and also due to the Coriolis effect, tends to follow more east-west trends rather than north-south trends.
Define Trade Winds
- In the NH, air blows from the northeast to the southwest
- In the SH, blow from the southeast toward the northwest
- These are Trade Winds
Define monsoon
Reversing wind systems/direction
How is monsoon induced?
- Induced by Asia which causes wind to blow outwards from high pressure in winter but pulls the southern trades into low pressure in summer => influenced by the reversal of land and sea temperatures between Asia and Pacific during winter and summer
- In winter, surface in Asia can be as low as -20 degrees and surrounding oceans have temp of 20 degrees
- During summer, land heats up more quickly => 40 degrees while summer 27 degrees
Define Upper Westerlies
Prevailing winds at the upper latitudes (between 30 and 60) that travels from west to east
Define Easterlies
Winds that travel from east to west
How is land-sea breeze induced?
- Blowing from the cooler sea (high pressure) in summer to warmer land (low pressure)
- In winter, air flows out of the cold land mass (high pressure) to warm water (low pressure)
What are the 3 cells the tri-cellular model consist of?
- Polar
- Ferrell
- Hadley
What happens in the Hadley cell?
- At the equator the sun shines directly and warms the surface => warm air rises => low pressure
- In the subtropics (20-30 N and S) air sinks because it’s colder and denser, it then returns to the tropics to replace rising air. Cycle repeats.
What happens in the Polar cell?
Warm air rises at lower latitudes and moves pole wards. Air reaches the polar areas cooled considerably and descend as cold dry high pressure area
What happens in the Ferrell cell?
- Warm air is transferred to high latitudes and shifts cold air back to the subtropics where it is warmed
- It exists due to the other 2 cells and it mirrors the other cell movements
What is the Coriolis effect?
The deflection of moving objects caused by easterly (West to East) rotation of the Earth
