Houghton Ch 5 (Modelling the climate) Flashcards Preview

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Flashcards in Houghton Ch 5 (Modelling the climate) Deck (12):

What does setting up a model of the atmosphere for a weather forecast require at its most basic level?

A mathematical description of the way in which energy from the Sun enters the atmosphere from above, some being reflected by the surface or by clouds and some being absorbed at the surface or n the atmosphere.


Why is water vapour in modelling climate?

Because of its associated latent heat (gives out heat when it condenses) and also because the condensation of water vapour results in cloud formation.
Variations in these inputs modify atmospheric temperature structure.


Why is to forecast the weather for several days ahead a model covering the whole globe is required.

The southern hemisphere circulation today will affect northern hemisphere weather within a few days and vice versa.


In a global forecasting model what are the parameters (i.e pressure, temperature, humidity, wind velocity and so on) that are needed to describe the dynamics specified as?

A grid of points.


What is a chaotic system?

One whose behaviour is so highly sensitive to the initial conditions from which it started that precise future prediction is not possible.


Why is it that in the tropics the atmosphere is particularly sensitive to sea surface temperature?

Because the largest contribution to the heat input to the atmosphere is due to evaporation of water vapour from the ocean surface and its subsequent condensation in the atmosphere, releasing its latent heat.


Whats a good example of the strong coupling which occurs between circulations of ocean and atmosphere?

El Nino events- the main driver of ocean circulation is stress exerted by atmospheric circulation (wind) and heat input from atmosphere into ocean.


What is a sequence of an El Nino event that shows the effect of different kinds of wave motions that can propagate within the oceans triggering a cold event?

A Rossby wave, propagates west from a warm anomaly in ocean surface temp near equator.
At western boundary it is reflected as a Kelvin wave, which travels east.
This cancels and reverses the sign of the original warm anomaly = cold event.


Feed backs in the climate system

Water vapour feedback

Warmer atmosphere = more evaporation from the ocean and wet land surfaces.
On average, therefore a warmer atmosphere will be a wetter one = more water vapour = powerful greenhouse gas = even warmer


Feed backs in the climate system

Cloud radiation feedback

Reflect a certain proportion of solar radiation back to space so reduce total energy available to system.
Act as a blanket to thermal radiation from the Earth's surface in a similar way to greenhouse gases.
By absorbing thermal radiation emitted by earth surface and by themselves emitted thermal radiation, they reduce heat lost to space.


What important ways do oceans act on the climate?

Evaporation from the oceans provides the main source of atmospheric water vapour.
They posses a large heat capacity compared with the rest of the atmosphere (a large quantity of head is needed to raise the temperature of the oceans only slightly) (oceans warm much more slowly than the atmosphere.
Through internal circulation, oceans recirculate heat throughout the climate system.


Ice albedo feedback

Ice or snow surface is a powerful reflector or solar radiation.
As some ice melts, therefore, at the warmer surface, solar radiation which had previously been reflected back to space by the ice or snow is absorbed.