How Climate Works Flashcards
How does pressure work?
Pressure decreases vertically because, as we move upward through the atmosphere, the weight of overlying air diminishes. It varies laterally because of differences in the intensity of solar heating of the atmosphere.
How does solar radiation affect air pressure?
Where solar radiation is intense the air warms up, expands and its density declines; air pressure falls. Where cooling occurs, the air contracts, its density increases and air pressure becomes greater.
How air reacts at the surface and at higher altitudes
At the surface the air will move from cold to warm zones; at higher altitudes the flow will move from warm to cold.
What is the coriolis force?
Earth is gradually turning, and so, relative to the ground surface, the parcel of air will appear to follow a curved track towards the right in the northern hemisphere and to the left in the southern hemisphere. This is called the Coriolis force.
What is the pressure gradient? and its effects?
The basic force causing atmospheric motion is the pressure gradient; the gradient arises from the unequal heating of the atmosphere by solar radiation. At the equator solar radiation is converted into heat. The air expands and rises and flows out towards the poles. Cool, dense air from the poles returns to replace it.
Circulation at the tropics
The circulation within the tropics consists of two cells. Air blows in towards the low-pressure belt of the equator across the subtropical seas. As it does so evaporation of water from the ocean utilizes vast quantities of energy so that the sensible heat transfer to the atmosphere is often small. The trade winds approaching the equator rise as they meet the equatorial trough, creating cloudy zone.
As the air rises and cools, the water vapour condenses and releases latent heat. The equatorial air then diverges and flows polewards, so the potential energy is exported to higher latitudes. The cycle is completed as radiational cooling causes subsidence of the air.
The trade wind belt:
Around the equator, in the low pressure equatorial trough, occurs a zone of convergence where easterly trade winds meet the south-easerly trade winds. Either side of the equatorial trough these winds dominate, giving the trade-wind belt
Westerlies and easterlies
Polewards, of the tropics, in the temperature latitudes, we find a zone of prevailing westerlies, while around the belt occurs a belt of easterlies.
ITCZ
The Intertropical Convergence Zone is a shallow trough of low pressure generally situated near the equator. Over the oceans it is fairly static, because seasonal temperature changes are small. In the Pacific its average position varies by no more than 5 degrees of latitude within the course of a single year.
During summer in continental areas the trough sweeps polewards, reaching 30 degrees of even 40 degrees over eastern China.
Westerly winds
Behind the trough the winds are predominantly westerly and are the main rain-bearing winds to most of those areas. Where they reach into higher latitudes they are called monsoons and show an almost complete reversal of direction from summer to sinter.
Winds in the upper atmosphere
Winds in the upper atmosphere can be affected by forces operating in a different direction from those at the surface and may appear to be part of a different system of circulation. With increasing height, winds tends to follow a gradually more zonal (east-west) direction and they become stronger.
Rossby waves
In the circumpolar areas, for example, there occur wave-like patterns of flow called Rossby waves that play a vital role in the energy exchange between the temperate and polar areas. In order to see these waves it is necessary to plot the height at which a particular pressure surface is reached. This is because the geostrophic winds blow parallel to the isobars, at a speed inversely proportional to the distance between the isobars and, similarly, the winds blow parallel to the contours of the pressure surface.
Jet Streams are:
A jet is basically a very narrow current of air travelling at great speed.
Jets are formed in regions of rapid temperature gradient. Typically, the westerly jets are connected with the zone of maximum slope or fragmentation of the tropopause, which coincides with the maximum poleward temperature gradient.
They can lead to intense accelerations of air in their vicinity. When air is forced to change its raete of flow, tropospheric vertical motion may be started In turn this may influence events at lower levels
