Atmosphere revision booklet 2014 cg malia

REVISION ATMOSPHERE

AS GEOGRAPHY 9696 (PAPER 1)

TERMS:

• Condensation• Sublimation• Incoming solar radiation/short wave radiation• Terrestrial/Earth’s radiation• Reflected solar radiation• Latent heat transfer• Sensible heat transfer• Relative Humidity• Temperature inversion

Condensation: Change of water from a vapour to liquid form induced by cooling (e.g. saturated air reaching dew point temperature) Sublimation: the direct change of water vapour to a solid (ice) state. Either by condensation onto a frozen surface or at altitude the production of ice crystals (e.g. cirrus clouds). Incoming solar radiation/short wave solar radiation: radiation derived from the sun that enters the earth’s atmosphere in the form of short wave radiation. Terrestrial (Earth) Radiation/long wave solar radiation: the long wave radiation that is transmitted from the earth’s surface after the heating by solar radiation. Reflected solar radiation is that radiation that is reflected back to space from clouds or from features (e.g. snow) of the earth’s surface (albedo)

One way it is being reflected when entering the atmosphere is reflected by water droplets and ice in clouds or it can be reflected at the earth's surface through the albedo effect, e.g. ice sheets, etc.Latent heat transfer is the heat emitted or absorbed in the change of state. Hence water to vapour etc. Can also be expressed in terms of the transfer of energy from the ground to the atmosphere.Convection: the process whereby (usually) air is heated at the ground surface and then rises because it is warmer and lighter Evaporation is the changing of a liquid (water) to a gas (water vapour) by heating. Conditions include insolation (i.e. heating), proximity of water supply, low humidity of air (vapour pressure), wind speed, ground surface.Water vapour is moisture in the atmosphere as an independent gas (i.e. evaporated water).Relative Humidity: the ratio of the actual amount of water vapour in air to the maximum amount it can hold at that temperature. It is expressed as a percentage.Relative humidity is important because it gives and indication of the humidity of an air mass and its capacity to hold moisture. This it allows some estimate of the chances of precipitation. Sensible Heat Transfer: The transfer of heat by the process of convection (rising hot air) and conduction (the transfer of heat by being in contact with a warm surface).

Temperature inversion

What?An increase rather than a decrease of temperature with height. They can form at the surface (radiative cooling, anticyclonic, frontal, advection cooling) or in the upper atmosphere (stratosphere and thermosphere).When?Radiative cooling, advective and frontal inversion.

Temperature inversion

6 factor day model

Incoming solar radiation:Affected by latitude, season & cloud cover. When sun is high in the sky, more energy received by earth. The less cloud cover & higher the cloud, more radiation received by earth’s surface

Reflected solar radiation:Proportion of energy reflected back to atmosphere-albedo. Light material reflected more dark materials.

Long-wave Radiation:Radiation of energy from The earth (cold body) into atmosphere.(net radiation loss from surface)Outgoing > incoming solar radiation.

Sensible heat transfer-Movements parcels of air into and outForm area being studied. Air is warmed by surface begin to rise (convection)& replaced by cooler air. (convective transfer)

Surface absorption:Energy reaches the earth’s surface potentialTo heat it. Depend nature of surface; If energy concentrated at surfaceSurface warm up but if surface can conduct heat to lower layers, surface remaincool

Latent heat transfer (Evaporation):When liquid water turned into vapour, heat Energy is used up. In contrasts, when water Vapour turns into liquid, heat is released. When water present at surface, energy will beUsed to evaporate it, and less energy availableTo raise local energy levels and temperature.

4 factor night model

Long-wave radiation:During cloudless night, Large energy is loss LWRFrom earth. LittleReturn to atmosphereDue to lack of clouds.Cloudy night, cloudsReturns LWR to surface,Overall loss is reduced.Hot desert, lack cloud coverLoss of energy at nightIs maximised.

Latent heat Transfer (condensation)During night, water vapour close to surface can condense to form water, since air is cooled by cold surface. When water condenses, latent heat is released

Sub-surface supply:Heat transferred to soil & bedrockuring daytime may be released back to surface at night. This off-set night time cooling at the surface.

Sensible heat Transfer:Cool air move into an areaMay reduce temperaturesWhereas warm air maySupply energy & raiseTemperature.

BREEZE

Sea Breeze:It occurs when the land is warmer than the sea. Warm air expands and rises on land creating low pressure area. It is likely to occur during day time. The air parcel, which is now higher up in the atmosphere, travels and cools over sea then creating high pressure area over the sea. The wind blows form the sea (HP) towards the land (LP).

Land Breeze:It occurs when sea is warmer than the land. Warm air expand and rises on sea creating low pressure area. It is likely to occur during night time. The air parcel, which is now higher up in the atmosphere, travels and cools over the land then sinks, creating high pressure over the land. The wind blows from the land towards the sea.

HEAT TRANSFER -HORIZONTAL

Ocean current

Warm currents carry water polewards and raise the air temperature of maritime (sea/marine) environments where they flow. For example Gulf stream is responsible for moving excess heat gained in tropics to the poles. It moves toward the central Atlantic, release heat to the atmosphere and raising temperature of coastal area in coastal region in the North such as Great Britain and bringing cold ocean current such as Labrador back to the equator. Labrador current flowing down from the Arctic makes the winters of New England and Eastern Canada much colder than they otherwise would be.

TRI-CIRCULAR CELLS

Three cells circulation

• This theory of circulation best describes the Earth’s general circulation because it considers effects of coriolis force due to the Earth’s rotation. In this circulation model, the Northern and Southern Hemisphere are each divided into three cells of circulation, each spanning 30 degrees of latitude. The latitudes that mark the boundaries of these cells are the Equator, 30° North and South, and 60° North and South. For our purposes, we consider only the Northern Hemispheric cells shown in figure 2–12:

• Hadley. • Polar. • Ferrel.

Hadley cellGeorge Hadley, an English meteorologist, theorized this first circulation cell in 1735. The Hadley cell is the strongest of the three cells of circulation and is formed as warm air rises above the Equator and starts to flow northward. The northward flow deflects to the right, due to coriolis, becoming an upper-level westerly flow. As this air moves northeastward toward the pole, it cools and a portion of it sinks at about 30°N. This sinking air spreads northward and southward as it nears the surface. The southward moving air again deflects to the right, becoming the northeasterly trade winds.

Because of the circulation in the Hadley cell, two pressure belts are created. The first is a belt of semipermanent high pressure that results from the sinking air at 30°. This belt of high pressure is called the subtropical ridge. The second pressure belt is a trough of low pressure near the Equator. It is called the near equatorial trough.

Polar cell

This is the northernmost cell of circulation and its mean position is between 60°N and the North Pole. At the pole, cold, dense air descends, causing an area of subsidence and high pressure. As the air sinks, it begins spreading southward. Since the coriolis force is strongest at the poles, the southward moving air deflects sharply to the right. This wind regime is called the surface polar easterlies, although the upper winds are still predominantly from the southwest. Near 60ºN, the southeasterly moving air moving along the surface collides with the weak, northwesterly surface flow that resulted from spreading air at 30°N. This colliding air rises, creating a belt of low pressure near 60°N.

Ferrel cellThe mid-latitude circulation cell between the Polar cell and the Hadley cell is called the Ferrel cell. This cell is named after William Ferrel, a Nashville school teacher who first proposed its existence. Oddly enough, Mr. Ferrel published his observations in a medical journal in 1856.

The Ferrel cell circulation is not as easily explained as the Hadley and Polar cells. Unlike the other two cells, where the upper and low-level flows are reversed, a generally westerly flow dominates the Ferrel cell at the surface and aloft. It is believed the cell is a forced phenomena, induced by interaction between the other two cells. The stronger downward vertical motion and surface convergence at 30°N coupled with surface convergence and net upward vertical motion at 60°N induces the circulation of the Ferrel cell. This net circulation pattern is greatly upset by the exchange of polar air moving southward and tropical air moving northward. This best explains why the mid-latitudes experience the widest range of weather types.

WORLD WIND BELT

The unequal heating makes the tropical regions warmer than the polar regions. As a result, there is generally higher pressure at the poles and lower at the equator. Air flows from areas of high to low pressure at the earth’s surface. This horizontal flow of air is called as wind. Wind flows from high to low pressure.

So the atmosphere tries to send the cold air toward the equator at the surface and send warm air northward toward the pole at higher levels.

Unfortunately, the spin of the earth prevents this from being a direct route, and the flow in the atmosphere breaks into three zones between the equator and each pole.

These form the six global wind belts: 3 in the Northern Hemisphere (NH) and 3 in the Southern (SH). They are generally known as:

1) The Tradewinds, which blow from the northeast (NH) and southeast SH), are found in the subtropic regions from about 30 degrees latitude to the equator.

2) The Prevailing Westerlies (SW in NH and NW in SH) which blow in the middle latitudes. (30 to 60) in both Hemispher. Most of North America fits into this belt and that is why our weather usually comes from west.

3) The Polar Easterlies which blow from the east in the polar regions. (From poles i.e. 90 to 60 latitudes in both hemisphere)

* Northern Hemisphere deflected to right and southern hemisphere it is deflected to the left.

July (NH)

In July, the Northern Hemisphere is experiencing its summer season because the North Pole is now tilted towards the Sun(ITCZ is shifting to the Northern Hemisphere). Some conspicuous hot-spots include the south-central United States, Arizona and northwest Mexico, northern Africa, the Middle East, India, Pakistan, and Afghanistan. Temperatures over oceans tend to be relatively cooler because of the land's ability to heat quickly. Two terrestrial areas of cooler temperatures include Greenland and the Plateau of Tibet. In these regions, most of the incoming solar radiation is sent back to space because of the presence of reflective ice and snow.

In July (S.H)

In the Southern Hemisphere, temperatures over the major landmasses are generally cooler than ocean surfaces at the same latitude. Antarctica is bitterly cold because it is experiencing total darkness. Note that Antarctica is much colder than the Arctic was during its winter season. The Arctic consists mainly of ocean.

FACTORS INFLUENCING TOTAL VARIATION WITHIN GLOBAL PATTERNS

• LATITUDE• LAND AND SEA DISTRIBUTION• INFLUENCE OF OCEAN CURRENTS

Latitudes

Latitude-areas close to equator receive more heat than areas that are close to the poles, because:Incoming solar radiation (insolation) is concentrated near the equator, but dispersed near the poles.Insolation near the poles has to pass through a greater amount of atmosphere and there is more chance of it being reflected back out to space.At the equator insolation is concentrated, but near the poles it is dispersed over a wider area.

Land and sea distribution

As the surface of the earth is not uniform, this influences its response to solar radiation. Land masses absorb short-wave energy and radiate long-wave energy more rapidly than water (e.g. river, lakes, oceans) causing more extreme temperatures than are found at the same latitude over the oceans.

Ocean currentsWater form an effective mechanism for the transfer of energy across latitudes. Major, long term flows of water which can extend over thousands of kms are termed ocean currents, generated by prevailing winds that blows across the surface. The effects of ocean currents on temperatures depend upon whether the current is cold or warm. Warm currents from the equatorial regions raise the temperatures of polar areas (with the aid of prevailing westerly winds) noticeable only in winter. By contrast, other areas are cooled by ocean currents such as the Labrador current off the north east coast of North America which reduce summer temperatures.

TERMS

• ALR• DALR• SALR• ELR

TERMSALR-Adiabatic lapse rateThe changes in temperature of a parcel of air as it expanded (cooled) or compressed (heated). Often expressed as rising or falling.

For a parcel of air, the decrease in temperature with increasing in height are expressed as:

DALR- Dry Adiabatic Lapse RateThe rate at which unsaturated air cools as it rises or warms as it descends. SALR-Saturated Adiabatic Lapse RateThe rate at which saturated air cools.

ELR-the decrease in temperature expected with an increase in height of surrounding air. (o.5C per 100 m ascent)

Stability

STABILITY AIR

The state of stability is when a rising parcel of unsaturated air (DALR) cool more rapidly than the surrounding air (ELR). If there is nothing to force the parcel of air to rise it will sink back to its starting point. Hence the air is described as stable because the dew point may not have been reached and the only clouds which might have developed would be shallow, flat-topped cumulus which do not produce precipitation. Stability give rise to dry, sunny conditions where any convection currents are suppressed/block by sinking air. DALR cooler (denser) than ELR –sink-stable.

Instability/unstable air

INSTABLE AIR

Localised heating of the ground warms nearby air by conduction, creating higher lapse rate.The resultant parcel of rising unsaturated air (DALR) cools less rapidly than the surround air. The rising air remains warmer and lighter than the surrounding air. Should it be sufficiently moist and if dew point is reached then the upward movement of air may be accelerated to produce towering cumulus or cumulonimbus cloud. Thunderstorm are likely to develop and the saturated air, following the release of latent heat, will cool at the SALR. DALR is warmer and lighter than ELR-continued to rise-Instable air

Conditionally instability air

Conditionally instability:

At lower layers the rising air is stable and being cooler than the surround air would normally sink back again. However if the mechanism which initially triggered the uplift remains the air will be cooled to its dew point. Beyond this point, cooling takes place at the slower SALR and the parcel may become warmer than the surrounding air. It will now continue to rise freely even if the uplifting mechanism is removed, as it is now in an unstable state.

Instability is conditional upon the air being force to rise in the first place and later becoming saturated so that condensation occurs. The associated weather is usually fine in areas of altitudes below condensation level but cloudy and showery in those areas at altitude above condensation level as towering cumulus clouds tend to develop.

WEATHER PHENOMENA:

FOG

• Fog is a mass tiny water droplets suspended in the air (of lower atmosphere). The ideal conditions for fog, are calm air, clear skies and long nights, when prolonged cooling will lead to condensation of moisture in the air at ground level. When condensation occurs at ground level, water droplets limit visibility. Formation of fog reduced visibility to less than one kilometer.

• Fog is formed by the cooling of air at ground level by cooling from below (either radiation, frontal or advection). Condensation then takes place at ground level.

TYPESa) Radiative cooling –surface inversion, this is cause by radiational cooling of lower air when terrestrial radiation occur, land surface radiates more heat than the air, thus ground is cooled more rapidly than the air. (snow-covered surface, long clear winter night, clear skies without clouds) b) Advective cooling-a thick layer of warm air over a cold surface produces an inversion of temperature in the lower layers of the atmosphere - the warm air is cooled by conduction.-warm air passes over a cold water surface.-also occur over cold land surface or snow-covered ground -same way, during summer the oceans are cooler than the adjacent land masses. c) Frontal inversion- when differing air masses are brought together by converging movements; the warmer air being relatively higher tends to overlie the colder and denser air in a horizontal layer.-a mass of cold air moves into a region that was previously occupied by a warm air mass. The cold air, being more dense slides in underneath the warmer air lifting the warm air up. This results in the warm air mass overlaying the cold air

UPLIFT OF AIR

FORMATION OF CLOUD

• Clouds are visible masses of water droplets and/or ice crystals in the atmosphere. It consists of water droplets that are sufficiently small (below 0.04 mm) to remain suspended in the air through external friction.

• • Clouds are formed when air cools to dew point and vapour

condenses into water droplets, a process known as condensation.

• • It is formed due to the uplift if air through convectional

heating, orographic or frontal uplift causing air to cool adiabatically.

FORMATION OF RAINFALLCollision-Coalescence Process• Temperatures in the cloud are above freezing• Cloud droplets exist in a variety of sizes (however, all are too small to fall as rain)• Heavier droplets begin to fall and collide with other droplets on their way down• After collision, the droplets merge or coalesce to form larger drops that continue the process until

large enough to fall as rain

Bergeron Ice Crystal Process• Both ice crystals and liquid water droplets must co-exist in clouds at temperatures below freezing• Water droplets existing as a liquid at temperatures below freezing are called supercooled water

droplets• There are more water vapor molecules surrounding the water droplets than around the ice crystals -

this is a difference in vapor pressure. Remember, there will be a flow from where there is too much of something to where there isn't enough.

• There is a net flow of water vapor molecules from the supercooled water droplets to the ice crystals, causing the ice crystals to grow (see diagram below).

• Therefore, the ice crystals grow by "using up" the water droplets.• Process is called accretion or riming.

Urban Heat island

• Large cities and conurbations experiences climatic conditions that differ from the surrounding countryside i.e. urban area is warmer than surrounding area/countryside during daytime temperature is 0.6C and night time 3C to 4C warmer than surrounding or countryside.

Why occur?

• Dust and cloud acts as a blanket reducing radiation and buildings giving out heat like storage radiators.

Urban environment (causes)1. Lower wind speeds if compare to rural areas allow warmth to accumulate. Wind velocities is reduced by buildings which create friction and act as windbreaks.

2.Dark-coloured roofs, concrete or brick walls and tarmac roads have high thermal capacity which means that they are capable of storing heat during the day and releasing it slowly during the night.

Compared to soil and vegetation, buildings have a higher capacity to retain and conduct heat: windows let is sunlight that is absorbed by dry surfaces.

3. The burning of fossil fuels in homes, offices, factories, power stations, central heating and transportation are some of major sources of heat.

4. Smog and pollution traps outgoing radiant energy and this can help maintain higher urban temperatures. 5. A kilometer of an urban area generally contain greater surface area than a kilometer of countryside. Thus large amount of surfaces in urban areas allows a greater area to be heated, contributing to higher urban temperatures. 6. Fewer bodies of open water (less evaporation) and fewer plants (less transpiration) found in urban areas. As little energy is used for evapotranspiration thus more is available to heat the atmosphere contributing to high urban temperatures.

Climatic differences in urban areas1. Localised differences in temperatures within the urban environment:-in forest shades, temperatures are lower during the day but at night leaves trap radiant heat, keeping temperature higher-other places might receive extra light reflected from glass buildings-concentration of tall buildings may block out sunlight. 2. Humiditylack of moisture due to:-warmer air can hold more moisture-lack of vegetation-water surface limits evapotranspiration-high drainage density (sewers and drains) which remove water

3. Precipitation-Higher temperature encourage lower pressure over cities which draws air from the surroundings are. This then leads to upward air movement and cooling of rising air leading to condensation. Cumulus clouds builds up rapidly which in turn encourage convectional rainfall, further enhanced by orographic rainfall due to relief of tall buildings.In cities huge quantities of dust and particles (3-7 greater over cities than surrounding rural areas) which once in the atmosphere form a dome over urban area.

Hydroscopic nuclei encourage condensation to take place. Studies conducted in St Louis in the late 1970s showed that there was a higher incidence of cumulus cloud development over the city, particularly late in the day, and summer rainfall totals were 20% higher than surrounding area. This was because of a high concentration of condensation nuclei and instability associated with higher urban temperature.

4. PollutionLarge quantities of gaseous and solid impurities are emitted into urban skies by the burning of fossil fuels, by industrial processes and from car exhausts.(urban areas may have 200X more sulphur dioxide & 10X more nitrogen oxide than rurals, as well as 10X more hydrocarbons and 2x carbon dioxide). These pollutants tend to increase cloud cover (thicker and up to 10% more frequent cloud cover than rural areas) and precipitation, giver higher temperatures and reduce sunlight.

5. Winds:Urban heat island effect seem capable of producing its own winds. Higher temperature in urban area lead to lower pressure over cities, drawing air in from surroundings. This winds can also be responsible for preventing a heat island effect in smaller towns only when wind speeds are greater than 20km/hr. The position of buildings, streets or path layouts can influence wind speeds to some extent. Clustered buildings has the effect of concentrating winds between buildings.

High rise buildings such as sky-scrappers of New York and Hongkong form canyons through which wind may be channelled. These wind may be strong enough to cause tall buildings to sway and pedestrians to be blown over and troubled by swirling litter and rubbish. Streets built parallel to wind direction lead to powerful gusts , streets built at right angles to the wind direction are sheltered by buildings and generated very little wind.

GREEN HOUSE EFFECT & GLOBAL WARMING

GREENHOUSE EFECT

Warming of the atmosphere caused by entrapment of Long Wave Radiation.

What is greenhouse gases?Green house gases:Greenhouse gases i.e. Carbon Dioxide and other gases such as methane, nitrous oxide and ozone are able to trap heat (LWR) from escaping into space. These gases also absorb and emit energy back toward the earth’s surface and energy is stored long enough before it can increase the temperature of the atmosphere. (Like a greenhouse where it let sun through but allowing radiant energy from objects inside to escape)

The increase in greenhouse gases concentration are due to population increase and human activities; agriculture and industries. With the increase in amount of Green house gases concentrations more heat will be trapped thus leading to global warming.

Global warming

Rise in the earth’s average temperature, possibly due to increased emissions of greenhouse gases.

Predicted possible effects1. Increase in world temperature, in the future there will be a further increase of temperature by 1.5 C to 4.5C by the year 2100. 2. Frequent storms:increase heat in the atmosphere will also increase wind velocity hence increasing the frequency of major storm events. If the Mediterranean heats to over 26C, hurricanes could develop and devaste the coastal areas. 3. Change in global precipitationWith increase in temperature there is an increase in evaporation over the oceans leading to greater global precipitation. The distribution of precipitation across the world is likely to change where some parts of the world will become wetter (agriculture more productive), esp those around 40N, will become drier with less reliable rainfall. As these latitudes contain many cereal growing regions, there could be additional consequence of food shortage. Whereas in Greenland and Antarctica will get thicker as these areas experience increased snowfall.

4. Rise in sea levelAs the atmosphere gets warmer so too will water in the oceans. As seawater warm, it will expand, causing eustatic rise in its level by predicted 0.25 to 1.0 m by the year 2100. The predicted rise in sea level could partly submerged low-lying coral islands such as Maldives, and increases the flood risk in countries with river deltas such as Egypt and Bangladesh. 5. Changes in ocean currentsThese is evidence that the North Atlantic Drift will be weakened. If this occurred, one result of global warming for the UK would be colder and more severe winters.