Chapter 5: Climate Change and Atmospheric Circulation

Question 1

The general circulation of the atmosphere describes the

Answer 1

global three-dimensional structure of atmospheric winds

Question 2

basic drivers behind the atmospheric circulation

Answer 2

The sphericity of the Earth, and the resulting spatially nonuniform distribution of solar heating,

1. tropics absorb twice the solar energy than higher latitude
2. Meridional gradient in temperature and potential energy
3. PE converted to KE
4. manifested as wind
5. deflected by rotating eart
6. create complicated flow patterns of the general circulation

Question 3

Atmospheric flow leads to

Answer 3

systematic transports and conversions of energy within the Earth climate system

reducing the contrast between geographical regions

• because the energy transports are directed against spacial gradients
• decreasing the temperature contrast between low and high latitude
  
  • wind from warm air in tropics to extratopics
  • cold air in the opposite direction

Question 4

the general circulation redistribute

Answer 4

• redistribute water (precipitation)
• Moderating influence: reduce the extremes in weather elements

Question 5

atmospheric winds help

Answer 5

• drive the ocean and redistribute heat from low to high latitudes
• nutrients from the ocean interior to the surface
• carbon from the atmosphere to the ocean

Question 6

forms of energy:

Answer 6

• sensible heat
• latent heat
• PE
• KE

Question 7

the extratropics, large-scale motions

Answer 7

• goverened by quasi-geostrophic theory
• near perfect balance between the PGF and corriolis force
• extratropical circulation is dominated by cyclones.
  
  • called:
    
    • storms
    • eddies
    • simply waves
  • cyclones r product of baroclinic stability
    
    • develops strongly during winter due to
      
      • the intense pole to equator temperature gradient during that season
  • preferred locations for the development of such systems: the storm track over the western parts of the pacific and atlantic oceans

Question 8

tropics motion

Answer 8

• distinct from the extratopics
• coriolis is week
• important effects:
  
  • friction
  • diabatic heating
  • latent heating
• ****The Hadley cell ****

Question 9

the hadley cell

Answer 9

• the most prominent tropical circulation feature
• extends through the entire depth of the troposphere from the equator to the subtropics (30o latitude) over both hemispheres
• develops in response to intense solar heating in the Inter Tropical Convergence Zone (ITCZ) near the equator.

Question 10

how does the hadley cell form?

Answer 10

• moist tropical air warms,
• becomes buoyant,
• rises toward the upper troposphere.
• The rising air cools adiabatically,
• leading to condensation, release of latent heat, and production of clouds and intense precipitation.
• In the upper troposphere,
• the air then diverges toward the poles and
• descends in the subtropics.
• The air is now dry and warm since it lost its moisture but retained much of the latent heat gained while rising.
• the climate under the descending branch of the HC is characterized by dry conditions and relatively high pressure.
• • The HC is closed by the trade winds at the surface, which take up moisture from the oceans before they converge into the ITCZ.

Question 11

how is HC related to extratropical circulation

Answer 11

The meridional overturning associated with the HC

Question 12

the subtropical jet

Answer 12

the poleward moving air in the upper branch of the HC tends to conserve angular momentum, spinning up a region of high zonal winds over the subsiding branch of the HC

Question 13

eddy stresses

Answer 13

or divergences and convergences of eddy momentum

The jet, however, is not entirely angular momentum conserving, mainly because of the stirring action of the midlatitudes storms. The stirring creates net fluxes of zonal momentum out of the jet and into the midlatitudes

Question 14

The jet, however, is not entirely angular momentum conserving, mainly because of the stirring action of the midlatitudes storms. The stirring creates net fluxes of zonal momentum out of the jet and into the midlatitudes, which are so-called eddy stresses or divergences and convergences of eddy momentum.

 The consequence of these fluxes is

Answer 14

a slowing of the subtropical jet and

the creation of another jet poleward of the subtropical jet.

• This second zone of high wind speeds is the eddy-driven or polar-front jet.
• This jet is often merged with the subtropical jet, giving the appearance of only one tropospheric jet centred at ~30􀯢 latitude.

Question 15

jets in the southern hemisphere

Answer 15

Only over the southern hemisphere (SH) and during winter are the two jet systems fairly well separated

Question 16

The Walker zonal circulation

Answer 16

is another important tropical circulation system, representing east-west oriented overturning of air across the equatorial Pacific

• It is driven by
  
  • low pressure and convection in the west and high pressure and subsidence in the east.
• The pressure differences across the Pacific are due to
  
  • warm sea surface temperatures (SSTs) over the west and rather cool SSTs over the east.
• Variations in these SSTs and the Walker circulation are closely related to the El Nino Southern Oscillation (ENSO) phenomenon, a naturally occurring instability of the coupled atmosphere-ocean system that has worldwide climate impacts.

Question 17

How does climate change impact the atmospheric circulation?

Answer 17

• modify regional temperature and humidity structures.
• The winds respond to the resulting gradients and
  
  • change the intensity and
  • structure of the circulation

Question 18

Alterations of the radiative balance of the Earth due to climate change modify

Answer 18

• regional temperature and
• humidity structures

The winds respond to the resulting gradients and change the intensity and structure of the circulation.

Question 19

The changes in circulation that are already taking place due to climate change are:

Answer 19

• The poleward expansion (widening) of the tropical circulation
• The decreasing intensity of the tropical circulation
• Change in extratropical circulation

Question 20

The poleward expansion (widening) of the tropical circulation

Answer 20

• 1o latitude widening per decade over the recent decades.
• the widening trend is strongest during summer of the respective hemisphere
  
  • more pronounced over SHS than over NHS.

Question 21

The decreasing intensity of the tropical circulation

Answer 21

• weakening of the zonally asymmetric Walker circulation
  
  • largely due to anthropogenic forcing

Question 22

Change in extratropical circulation

Answer 22

• poleward shift of the zone of high westerly winds in the midlatitudes.
  
  • caused by increases in greenhouse gases and stratospheric ozone depletion.

Question 23

The changes in circulation that are already taking place due to climate change summery

Answer 23

• key-elements of the atmospheric circulation have been moving poleward during the last few decades.
  
  • human activity in association with
    
    • greenhouse gas increases and
    • stratospheric ozone depletion is the most likely cause for the trends.
• it cannot be ruled out that natural climate variability also plays an important role.

Question 24

Atmospheric circulation change may also alter

Answer 24

• ocean currents.
  
  • Because oceans are important regulators of climate, this may further modify the original effect of change.
• Because of the important role of the atmospheric general circulation for climate, any change in its structure is of concern.
• It may lead to profound changes in other parts of the global climate system with potentially important implications for natural ecosystems and human societies.

Question 25

Extreme Weather Events

Answer 25

“An extreme weather event is an event that is rare at a particular place and time of year.”

• values in temperature plot will fall within bell curve with many values near average and fewer occurences far away from the average
• extreme temperatures are in the tails

extreme climate events such as drought and heavy precipitation occur of the tails of the distribution (same as temperature)

Question 26

Changes in Extreme Events Due to Climate Change

Answer 26

• As the global climate continues to adjust to increasing GHG concentrations
  
  • aspects of extremes have the potential to change
    
    • change in frequency and
    • intensity
    • temporal considerations:
      
      • time of occurance
      • duration
• average and tail of distributions are expected to wam
  
  • number of average days may be small
  • the percentage change in the number of very warm days can be large

Question 27

Possible Changes in Extreme Weather Events

Changes can arise from any of three different factor

Answer 27

• If a climate mean (e.g. temperature) shifts upwards, then
  
  • high temperatures are recorded more often but
  • low temperatures are experienced less often.
• In a second type of variation, there is increased climate variability,
  
  • leading to more climate extremes, both high and low.
• A third type of variation could arise from a change in the shape of the probability of a given climate measurement.

Question 28

Possible Changes in Extreme Weather Events

for precipitation

Answer 28

model and observational evidence points to increases in the no. of heavy rain events and decreases in the no. of light precipitation events.

Question 29

As the human and natural systems have adapted to their historical range of extreme events, changes in extreme events will have impacts on

Answer 29

socioeconomic and natural systems

Question 30

extreme events are often studied as a

Answer 30

• statistical problem, with the emphasis on their
  
  • frequency of occurrence as
  • a function of magnitude,
• but are also investigated in terms of their
  
  • underlying mechanisms and
  • dynamics.