1 - global controls on climate

Question 1

define the weather and climate

Answer 1

WEATHER - state of the atmosphere at a given time/place

CLIMATE - average weather conditions of a place over a period of 30 years or more

Question 2

what is the atmosphere comprised of

Answer 2

The atmosphere is the mixture of gases, with some liquids and solids, held close to the earth by gravity.

It is comprised of the following gases:
- Nitrogen
- Oxygen
- Argon
- Carbon Dioxide
- Water Vapour

Question 3

what is humidity and relative humidity

Answer 3

Humidity: a measure of the amount of water in the air (g/m3).

Relative humidity: the amount of water as a percentage of the maximum that a body of air of a certain temperature could hold.

Question 4

where is most water vapour found

Answer 4

Most water vapour is held in the lowest 15km – it can vary spatially and over time, causing fluctuations in pressure, temperature and humidity.

Question 5

what are the four layers in the atmosphere

Answer 5

1. TROPOSPHERE - temperatures generally decrease with height. top of this layer marked by a boundary called tropopause where temps remain constant (height of 8km at poles and 17km in tropics)
2. STRATOSPHERE - 50km above surface, temps increase with height and ozone absorbs and filters out UV radiation. upper limit of stratosphere marked by stratopause. lacks dust and water vapour, thin
3. MESOSPHERE - temps decrease with altitude to the mesopause
4. THERMOSPHERE - virtual vacuum, rise in absorbed energy due to energised short wave radiation. temps rise again at constant rate up to as much as 1500 degrees

Question 6

what is long wave re-radiation

Answer 6

short wave energy is converted to long wave energy which can be absorbed by the atmosphere, some is re-radiated back. water vapour acts as an insulator

Question 7

what are latent heat transfers

Answer 7

energy is used to convert water into water vapour (evaporation) the heat is retained as latent heat

when vapour turns back into water the heat is released

Question 8

what is compression heating

Answer 8

when air contracts its temperature increases

Question 9

what is conduction and convection

Answer 9

CONDUCTION - heat passes from ground to air because it is cooler, air is a poor conductor

CONVECTION - heated air expands, lower density leads to air rising

Question 10

how does energy come into the atmosphere

Answer 10

• Majority of incoming energy into the atmosphere is from insolation (incoming short wave radiation from the sun).
• Some further energy derives from the Earth, i.e., volcanic sources and energy released from large urban areas.

Question 11

what are the determinants of how much energy the atmosphere receives

Answer 11

• The solar constant – varies slightly and affects longer-term climate rather than short term weather.
• Distance from the sun - due to variations in Earth’s eccentricity orbit – can cause variations of up to 6% in the insolation.
• Angle of the sun in the sky – the equator receives more energy as solar radiation strikes the Earth head-on, whereas at higher latitudes (60-65’) it approaches at an oblique angle, giving twice the area to heat up and more atmosphere to pass through.
• Length of day and night – the tilt of the Earth on its axis (23.5’) means that regions near the poles (>66.5’ N and S) receive little insolation during the certain times of year. This varies with the position of the sun over head, influencing length of day and night.
• Cloud cover – cloud can absorb and reflect insolation

Question 12

what is the tri-cellular model (long explanation)

Answer 12

1. sun always high = ground heating rapid causes low pressure area in equatorial latitudes called intertropical convergence zone (ITCZ)
2. hot air at equator rises in convection currents forming low pressure area. rising air cools to dew point, height increases = condensation and heavy rainfall
3. high altitudes = air moves polewards. air circulates as upper westerly winds due to Coriolis effect, net effect is movement of air towards poles
4. 30’N and 30’S - colder air at high latitudes sink to earth’s surface at which high pressure created with stable conditions = subtropic anticyclones
5. air reaches ground and some returns to equatorial areas as pressure gradient = consistent trade wind. winds subject to Coriolis effect blowing from NE direction in N. hemisphere and SE direction in S. hemisphere
6. two trade winds converge at ITCZ completing Hadley cell
7. Ferrel cell occurs between 30’ to 60’ and some air from sinking limb of Hadley cell pulled towards poles forming warm SW winds in N. hemisphere and NW in S. hemisphere
8. these winds pick up moisture over oceans, meeting cold drifting towards lower latitudes at the poles at 60’N and 60’S
9. warmer air from tropics rise over colder denser polar air causing area of low pressure and unstable conditions. resultant weather is mid-latitude depressions experienced by cool temperate western maritime (CTWM) eg W Europe
10. forms rising limb of Ferrel cell, some air returns to tropics as Ferrel cell and some flows northwards as part of Polar Cell
11. at surface of poles, cool descending air = high pressure, winds blow across pressure gradient towards mid-latitude low pressure belt at 60’N and 60’S
12. explains and describes tri-cellular model of atmospheric circulation and addresses imbalance in heat budget

Question 13

factors influencing heat budget

Answer 13

• urbanisation
• ocean currents
• seasons
• distance from ocean
• albedo
• prevailing wind
• cloud cover
• altitude
• aspect
• latitude

Question 14

how are urbanisation and ocean currents factors influencing heat budget

Answer 14

URBANISATION = alter albedo, energy released from urban environments through people, transport, power stations and residential environments = ‘ heat islands’ creation

OCEAN CURRENTS = warm currents carry heat polewards to balance heat budget. can cause temperature anomalies at locations at same latitudes eg Gulf Stream

Question 15

how are seasons and distance from ocean factors influencing heat budget

Answer 15

SEASONS = insolation (UV radiation) only received during daylight hours and reaches its peak at noon. at equator there is no variation but in polar regions no insolation is received during winter but can receive up to 24h during part of summer as Earth tilts on its axis

DISTANCE FROM OCEAN = land/sea differ in ability to absorb/retain heat. sea - greater heat capacity than land. water - requires 5x as much energy as sand to raise its temp, but retains heat longer. summer = land increases in temp rapidly, but very cold during winter, ocean moderate temps

Question 16

how are albedo and prevailing wind factors influencing heat budget

Answer 16

ALBEDO = snow/ice reflect over 90% of sun’s energy helps to reduce temps at low latitudes

PREVAILING WINDS = temp of wind determined by area of origin and characteristics of surface it blows over. wind over is sea warmer in winter and cooler in summer than wind from land

Question 17

how are cloud cover and altitude factors influencing heat budget

Answer 17

CLOUD COVER = clouds reduce incoming UV radiation and outgoing infrared radiation. thicker the cloud = greater absorption/reflection. clouds can reduce daytime temperatures but also insulate to retain heat at night

ALTITUDE = troposphere atmosphere warmed by heat radiated by land and distributed by convection/conduction. height of mountain increases amount of land surface from which to heat surrounding air decreases. as air pressure decreases ability to retain heat decreases. because the molecules retaining/absorbing heat grow further from each other

Question 18

how are aspect and latitude factors influencing heat budget

Answer 18

ASPECT = hillsides alter angle of the sun’s energy. in N. hemisphere north facing slopes are cooler as they are in shadow for most of year/day the higher the sun in sky more energy north facing slop receives

LATITUDE = as latitude increases angle of sun decreases, area heated by sun’s energy increase. insolation passes through more atmosphere increasing absorption or reflection

Question 19

what is atmospheric motion controlled by

Answer 19

a combination of following forces:
- Coriolis force
- pressure-gradient force
- geostrophic wind
- gradient wind
- friction

Question 20

what is the pressure gradient force

Answer 20

pressure gradient wind is movement of air occurring along pressure gradients from high to low pressures

Question 21

what is the Coriolis force

Answer 21

is the deflection of winds due to the earth’s rotation

deflection is to the right in the N. hemisphere and to the left of a path in the S. hemisphere

Question 22

what is the gradient wind

Answer 22

where isobars are curved, centrifugal and centripetal forces act upon the wind to maintain a flow parallel to the isobars.

curved path called a gradient wind

Question 23

what is the effect of friction

Answer 23

• frictional drag from earth’s surface modifies balance between horizontal gradient force and Coriolis force
• friction decreases wind speed but also changes wind direction
• friction causes wind to cross isobars at an angle
• with increasing height effect of friction is reduced meaning wind changes direction with height
• change in pattern known as Ekman spirals

Question 24

what is the geostrophic wind

Answer 24

in mid-latitudes, pressure-gradient force and Coriolis force directly balanced

leads to air moving not from high to low pressure but between the two, parallel to the isobars. this is called geostrophic wind

Question 25

what are new circulation models and what do they do

Answer 25

new models change relative importance of three convection cells in each hemisphere. changes influenced by:
JET STREAMS - strong/regular winds blowing in upper atmosphere 10km above surface, blowing between poles and tropics
ROSSBY WAVES - ‘meandering rivers of air’ formed by westerly winds, 3 to 6 waves in each hemisphere

Question 26

what is the atmospheric heat budget

Answer 26

The global heat budget describes the balance between incoming solar (short-wave) radiation and outgoing terrestrial (long-wave) radiation

Estimates of the total heat flow from Earth’s interior to surface span a range of 43 to 49 terawatts (TW)

Question 27

what is insolation

Answer 27

Input is received in the form of short-wave solar energy. This is called insolation.

Insolation is solar radiation received in the Earth’s atmosphere or at its surface.

Only approximately 52% of this insolation reaches the earth’s surface. The rest is absorbed by water vapour, dust and clouds, or is reflected by the Earth’s surface and scattered by particles in the air.

Question 28

where is there surplus and deficit of solar energy

Answer 28

there is a surplus of energy between 35˚ North and 35˚ South. In this region, incoming insolation exceeds outgoing radiation

There’s an energy deficit between 35˚ North and the North Pole, and between 35˚ South and the South Pole. Here the outgoing radiation exceeds incoming insolation.

Question 29

what is thermohaline circulation

Answer 29

also called Global Ocean Conveyor or Great Ocean Conveyor Belt, the component of general oceanic circulation controlled by horizontal differences in temperature and salinity.

It continually replaces seawater at depth with water from the surface and slowly replaces surface water elsewhere with water rising from deeper depths.

Question 30

what does thermohaline circulation drive/carry

Answer 30

this process is relatively slow, tremendous volumes of water are moved, which transport heat, nutrients, solids, and other materials vast distances.

Thermohaline circulation also drives warmer surface waters poleward from the subtropics, which moderates the climate of Iceland and other coastal areas of Europe

Question 31

where can thermohaline circulation occur

Answer 31

The basic thermohaline circulation is one of sinking of cold water in the polar regions, chiefly in the northern North Atlantic and near Antarctica.

These dense water masses spread into the full extent of the ocean and gradually upwell to feed a slow return flow to the sinking regions.

The theory for the thermohaline circulation pattern was first proposed by Henry Stommel and Arnold Arons in 1960.

Question 32

how might thermohaline circulation change in the future

Answer 32

• believed that global warming could shut down this ocean current system by creating an influx of freshwater from melting ice sheets and glaciers into the subpolar North Atlantic Ocean.
• freshwater is less dense than saline water, intrusion of freshwater would lower the density of the surface waters so inhibit the sinking motion that drives large-scale thermohaline circulation.
• as a consequence of large-scale surface warming, such changes could even trigger colder conditions in regions surrounding the North Atlantic.