Chapter 5: Climate Change and Atmospheric Circulation Flashcards
The general circulation of the atmosphere describes the
global three-dimensional structure of atmospheric winds
basic drivers behind the atmospheric circulation
The sphericity of the Earth, and the resulting spatially nonuniform distribution of solar heating,
- tropics absorb twice the solar energy than higher latitude
- Meridional gradient in temperature and potential energy
- PE converted to KE
- manifested as wind
- deflected by rotating eart
- create complicated flow patterns of the general circulation
Atmospheric flow leads to
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
the general circulation redistribute
- redistribute water (precipitation)
- Moderating influence: reduce the extremes in weather elements
atmospheric winds help
- 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
forms of energy:
- sensible heat
- latent heat
- PE
- KE
the extratropics, large-scale motions
- 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
- develops strongly during winter due to
- preferred locations for the development of such systems: the storm track over the western parts of the pacific and atlantic oceans
- called:
tropics motion
- distinct from the extratopics
- coriolis is week
- important effects:
- friction
- diabatic heating
- latent heating
- ****The Hadley cell ****
the hadley cell
- 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.
how does the hadley cell form?
- 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.
how is HC related to extratropical circulation
The meridional overturning associated with the HC
the subtropical jet
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
eddy stresses
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
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
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.
jets in the southern hemisphere
Only over the southern hemisphere (SH) and during winter are the two jet systems fairly well separated