Atmosphere and Weather Mark Schemes

Atmosphere & Weather Mark Schemes20148 (a)

(i) Define the terms evaporation and condensation [4](ii) Briefly describe the forms in which moisture is present in the atmosphere [3]

(b) Explain why urban areas have higher temperatures and more rainfall but less mist than surrounding rural areas. [8]

(c) Explain the relationship between the lapse rates that occur with convectional rainfall and with orographic uplift. To what extent do convectional uplift and orographic uplift produce different types of weather? [10]

Atmosphere & Weather Mark Schemes

8 (a) (i) Define the terms atmospheric stability and atmospheric instability. [4]

Stability – where, if a parcel of air is displaced upwards it will return to its original position (because it remains cooler and heavier than the surrounding air). (2)Instability – where, if a parcel of air rises, it will continue to rise as it remains warmer than the surrounding air even though being cooled adiabatically. (2)

(ii) Describe the conditions which may lead to the formation of dew. [3]

Nocturnal (long wave) radiation (on clear nights) leading to cooling of surfaces which cool air in contact with them sufficiently to cause condensation of water vapour droplets on vegetation etc. Three positive points needed.

(b) With the aid of a diagram, explain the generalised pattern of pressure and wind systems in either the northern or southern hemispheres. [8]

Can be achieved totally from a clearly annotated diagram/sketch map showing essentially: equatorial low, polar high and tropical high with the winds deflected appropriately as they move from areas of high to low pressure. Explanation should be in terms of the ITCZ as warmed air at the equator rises, the Hadley and Ferrel cells. Good candidates will show an understanding of the low pressure systems at the polar front.Max. 5 if no diagrams.

(c) Explain how the greenhouse effect occurs in the earth’s atmosphere. How have human activities affected it and with what consequences? [10]

The greenhouse effect is the warming of the earth’s atmosphere with short-wave radiation readily penetrating to the surface, whereas long wave radiation from the earth is impeded by the greenhouse gases in the atmosphere. Thus less heat escapes from the earth’s surface than that arriving. The effect is increased with cloud cover and with particulate matter and certain gases in the atmosphere. Ever since humans started clearing forests and cultivating the land they have affected the composition of the atmosphere and increased the greenhouse effect, but industrialisation since the nineteenth century, pouring CO2 into the atmosphere from burning fossil fuels, will be the main factor, plus emissions from I.C.Es and jet engines. The consequences will have been well rehearsed; global warming, polar and glacial ice melting, rising sea level, increased energy to fuel atmospheric disturbances, changing climatic patterns.

Candidates will probably:Level 3Accurate detail, knowledge and understanding of the science and demonstrated throughout the answer. Well balanced in covering the three demands in the question. Appropriate awareness of the scale of human factors and likely consequences [8–10]

Level 2Covers the essential demands but lacking in some of the accurate detail. Less well balanced on consequences which may be exaggerated or less detailed. [5–7]

Level 1

Atmosphere & Weather Mark SchemesWeak answers lacking accurate understanding of the science behind the topic. Limited coverage of the question with imprecision and generalisations. [0–4]

8 (a) (i) Define the terms environmental lapse rate and adiabatic lapse rate. [4]

Environmental lapse rate is the actual rate at which temperature decreases with altitude at a given place and time.Adiabatic lapse rate is the rate of temperature change with height of a parcel of air.

(ii) Briefly describe the difference between the dry adiabatic lapse rate and the saturated adiabatic lapse rate. [3]

DALR is the change in temperature with height of an unsaturated parcel of air (1c per 100m) whereas the SALR is the change in temperature with height of a saturated parcel of air and is slower (0.4–0.9c per 100m)

(b) Using diagrams, explain how stability and conditional instability occur in the atmosphere. [8]

Diagrams should show the correct positioning of the lapse rates. Explanation should be for conditional instability the forced ascent of air parcels and subsequent cooling to dew point temperatures and the further rise of air at the SALR causing condensation, cloud development and the possibility of precipitation. Stability occurs where a rising parcel of air is always cooler than the surrounding air (DALR and ELR) and hence displacement does not occur.

(c) Explain the more likely climatic and other effects of global warming. [10]

An opportunity for global warming sceptics, but most should explain how global warming is occurring through the enhanced greenhouse effect as a result of human activities. The most likely effects in terms of climate could be many and varied, but the increased warming could lead to a polewards shift of climatic belts with drought and other consequences (fires) extending over wider areas. Another possibility could be an increase in dynamism of climatic systems due to heating hence more extreme events (storms hurricanes etc). Other effects will feature sea level rise and the consequences for areas such as the Maldives, Bangladesh etc. A lot of possibilities so do not expect a global coverage.

Candidates will probably:

Level 3Good explanation of global warming and its human component. Well selected examples of climatic and other effects with some attempt at justification. [8–10]

Level 2Brief explanation and a tendency to launch into effects often somewhat sensationalised. Little attempt at justification. [5–7]

Level 1Only stray effects with little/no attempt at explanation or justification. [0–4]


8 (a) (i) Define the terms fog and dew. [4]

Fog is water droplets caused by condensation in the surface part of the atmosphere with a visibility of less than 1km.Dew is moisture deposited as water droplets on the surface of vegetation or other surface objects due to condensation from radiation cooling.

(ii) Briefly describe one set of conditions under which fog may be formed. [3]

Fog occurs where cooling of air takes place at the surface and water condenses around hygroscopic nuclei. Either advection cooling or radiation cooling is acceptable.

(b) Using diagrams explain the differences between the local energy budget (the heating and cooling of the atmosphere), during daytime and night time. [8]

Diagrams should show the day ‘model’ of incoming short wave radiation with scattering and reflection heating the earth’s surface and the atmosphere warmed n by terrestrial long wave radiation % not required but can be credited. The night time model has no incoming radiation, earth cooling and cooling of the atmosphere through terrestrial radiation. Well annotated diagrams would be sufficient for all marks.

(c) Explain the extent to which the climate in rural areas differs from that of nearby urban areas. [10]

A reversal of the more usual way of asking the question, which many will find taxing and probably ignore. Rural areas will be cooler at night due to the lack of thermal capacity of vegetation of bricks and mortar and anthropogenic derived heat. Similarly the relative lack of hygroscopic nuclei and convection may lead to less rainfall but more frosts, dew etc. RH may be higher due to greater evapotranspiration which could lead to fogs but with less pollution smogs will be uncommon. Winds will not be restricted by buildings but will not have funnel effects. Very good answers may provide some quantitative data.


Level 3Informed attempts to answer question by dealing with rural and then urban contrasts. [8–10]

Level 2The more usual urban climate approach with understanding of the driving mechanism of heat islands. [5–7]

Level 1Little understanding other than hotter/ colder, wetter/ drier approach. [0–4]


8 (a) (i) Define the terms solar radiation and earth (terrestrial) radiation. [4]

Solar radiation is incoming short wave radiation from the sun.Terrestrial radiation is outgoing long wave radiation from the earth’s surface which has been heated by solar radiation.

(ii) How does radiation cooling occur at the earth’s surface? [3]

Radiation cooling at the earth’s surface occurs due to the loss of long wave radiant heat during the night. The surface loses heat faster than the air in contact with it thus cooling the lower layers of the atmosphere.

(b) Using a diagram or diagrams, explain why the earth’s surface receives less solar radiation in polar areas than in equatorial areas. [8]

Simple diagram or diagrams showing the greater amount of atmosphere that solar radiation has to pass through at the polar latitudes. Seasonal tilt also means that polar areas receive little or no solar radiation during winters. Distance from the sun is not acceptable as an explanation. The overhead sun is thus concentrated on equatorial areas reducing scattering and other losses. Some may well introduce albedo etc from snow and ice surfaces.

(c) Explain how human activities have contributed to global warming. [10]

Human activities have largely been responsible for the increase in greenhouse gases which have enhanced the greenhouse effect. This should be explained and the sources of increased carbon dioxide and methane explained in terms of increased use of fossil fuels, increased agricultural activity (pastoral and rice growing), as well as the destruction of carbon sinks (e.g. tropical rainforest). Emphasis should be on the greenhouse effect rather than the nature of the human activities.


L3 Good understanding of the greenhouse effect and its effect on global warming. Human activities directly linked to this. [8–10]

L2 Some grasp of greenhouse gases and their contribution to global warming, but more emphasis on the human activities (e.g. car ownership, power supplies destruction of TRF). [5–7]

L1 Doomsday account of the effects of global warming with little exploration of the causes or nature of the greenhouse effect. [0–4]


8 (a) (i) Define the terms short wave radiation and long wave radiation. [4]

Short wave radiation is incoming solar radiation.Long wave radiation is outgoing terrestrial radiation whereby the earth’s surface has been heated by solar radiation.

(ii) Briefly explain what is meant by a temperature inversion. [3]

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). Explanation of all causes not required; just some exemplars.

(b) Explain how the global distribution of temperatures is influenced by areas of land and sea. [8]

Land and sea areas affect temperatures through their different thermal capacities, i.e. land heats up faster and cools faster than the seas. This leads to a greater migration and concentration of isotherms over land masses rather than oceans. The annual range of temperatures is greater in continental than in coastal locations. The oceans absorb and store vast amounts of heat, making them warmer in winter producing a poleward shift of isotherms over oceans. The role of ocean currents (e.g. N.Atlantic Drift pushing isotherms poleward in N hemisphere winter and cold Peruvian current displacing isotherms towards the equator).

(c) What are greenhouse gases? Explain how build-ups of greenhouse gases are caused and the effects they may have upon global warming. [10]

The main greenhouse gases are water vapour, carbon dioxide, methane, nitrous oxide and in the stratosphere, ozone. They are particularly effective in absorbing out going (terrestrial) LWR. Whilst most occur naturally, there have been significant increases in the past century or so in gases such as CO2 and N2O due to industrialization. Intensive farming has also led to a great increase in methane. This has had the effect of increasing the greenhouse effect, whereby SWR relatively easily passes through the atmosphere whilst outgoing LWR is effectively trapped within the atmosphere leading to global warming.


L3 Have a good grasp of greenhouse gases (even if not complete) and will be able to explain the greenhouse effect and hence impact upon global warming. [8–10]

L2 A more limited appreciation of gases mainly CO2 and methane. Some idea of heat being trapped within the atmosphere but less certain about the processes. [5–7]

L1 Gases limited to CO2 and confused with pollutants in general. Very limited grasp of greenhouse effect and its link to global warming. [0–4]


8 (a) (i) Define the terms water vapour and sublimation. [4]

Water vapour is moisture in the atmosphere as an independent gas (i.e. evaporated water).Sublimation is the change of state from a solid directly to a gas e.g. ice crystals to water vapour.

(ii) Briefly explain what is meant by relative humidity. [3]

RH is 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.

(b) With the help of diagrams, explain how land and sea breezes can affect the weather experienced in coastal areas. [8]

Many will approach this on a local scale with diagrams of land and sea breezes. They should explain the different specific heat capacities of land and sea and the development of small scale pressure cells inducing on shore and off shore winds. This ameliorates temperatures but can also produce coastal fog in circumstance of a colder landmass or advection fog out to sea.

(c) Explain how atmospheric stability, instability and conditional instability can produce different weather conditions. [10]

Stability, instability and conditional instability should be explained in terms of lapse rates, etc.This can be most easily achieved through diagrams with an explanation of the nature of adiabatic cooling. The weather associated with stability can be described in terms of clear skies etc – the usual anti-cyclonic type of conditions. In the case of instability and conditional instability weather is dependent upon the possibilities of air continuing to rise after condensation has been reached. In cases where it doesn’t, then stratiform clouds might result in little rainfall. Where uplift continues at the SALR then large vertical extent of cloud may form with resultant thunderstorms and intense rainfall, hail, etc.

Level 3Good understanding of lapse rates and their effects upon condensation and cloud formation.Some variability in weather conditions i.e. not just clear or rain. [8–10]

Level 2General grasp of the three conditions although precise nature of lapse rates might be less developed. Simple contrast in weather. Clear skies or condensation, cloud and rain. [5–7]

Level 1Little comprehension of the nature or results of adiabatic cooling and lapse rates if mentioned at all will be very confused. Sunshine and rain the only weather features. [0–4]


8 (a) (i) Define the terms sensible heat transfer and latent heat transfer. [4]

Sensible heat transfer is heat energy that is transferred by convection or by direct conduction.Latent heat transfer is that heat which is transferred during a change in state e.g. water to water vapour by evaporation or water vapour to water by condensation.

(ii) Briefly explain the formation of fog. [3]

Fog is formed due to cooling of air and subsequent condensation around hygroscopic nuclei close to the earth’s surface. Can be radiation or advection cooling.

(b) With the help of a diagram, describe what happens when solar radiation enters the earth’s atmosphere. [8]

Solar radiation enters the earth’s atmosphere as short wave radiation. Of this about 27% is absorbed or reflected by clouds, 24 % absorbed by the atmosphere (scattering) and 4% reflected by the earth’s surface leaving c 45 % absorbed by the earth’s surface where it is converted to long wave radiation and released by conduction and convection to heat the atmosphere. Simple annotated diagram could account for most marks.

(c) Describe the global pattern of atmospheric pressure. Explain how this pattern is produced and why it varies seasonally. [10]

The global distribution of pressure exists in broad belts. Lower pressure at the equator is followed by sub tropical highs low pressures in mid latitudes and polar highs. This is disturbed by the seasonal movement of the thermal equator and the seasonal effects over continental areas and oceans. Thus continental interiors have high pressure during the N hemisphere winter and low pressure during the summers. Some may describe it in terms of junctions between the cells on the tricellular model, which is acceptable. Rising air produces lower pressure due to surface heating, whilst radiation cooling will produce sinking air and high pressure (e.g. over oceans and polar areas).

Level 3Good description of the distribution of pressure belts and the reasons for high and low pressures and seasonal effects due to the input of solar radiation. [8–10]

Level 2A general grasp of the distribution of pressure and some idea of its causes due to heating.Only a vague appreciation of seasonal change. [5–7]

Level 1Little beyond a vague appreciation of high and low pressure with poor description of distribution and little attempt at explanation. [0–4]


7 (a) (i) Define the terms sensible heat transfer and latent heat transfer. [4]

Sensible heat transfer is heat that can be transferred within the atmosphere by either convection or conduction.Latent heat transfer occurs when there is a change of state i.e. in condensation or evaporation.

(ii) Explain one way in which solar radiation is reflected. [3]

Solar radiation 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.

(b) With the help of a diagram, describe the global distribution of pressure belts and explain why this varies seasonally. [8]

Only broad semi-permanent pressure belts need to be identified in diagram or description.That is the equatorial low pressure belt (equatorial trough), sub-tropical highs, mid latitude troughs and polar highs. These might be seen in the context of the tri-cellular model, which is acceptable. The pressure belts migrate polewards, seasonally due to the passage of the overhead sun. This is complicated, particularly in the northern hemisphere, by the larger continental areas. As only 8 marks are available do not expect great detail on the land/sea or hemispheric differences.

(c) Explain how stability and instability within the atmosphere produce different weather conditions. [10]

Stability is when the air remains cooler than surrounding air (DALR to left of ELR in diagrams) thus no uplift and cooling. This gives rise to clear (anticyclonic) conditions with no ppt and less cloud cover, etc. Cool nights can lead to frost, dew, etc. Instability is when air remains warmer than surrounding air meaning that air rises and cools adiabatically until dewpoint is reaches and condensation takes place. Further rise at the SALR leads to cloud development and to rainfall. Diagrams could be used effectively.

Candidates will probably:L3 show a good understanding of lapse rates and explanation of the resultant weather phenomena. [8–10]

L2 show an understanding of uplift as against stable air, although lapse rates may not be fully grasped. Distinction between rainy and clear weather. [5–7]

L1 have a vague appreciation that there are weather differences but little clear indication as to why. [0–4]


7 (a) (i) Define the terms condensation and water vapour. [4]

Condensation is the conversion from gaseous state to that of a liquid i.e. water vapour to moisture, usually through the assistance of hygroscopic nuclei and cooling.

Water vapour is the gaseous state of moisture in the atmosphere that has been evaporated from the earth’s surface

(ii) Briefly explain the conditions necessary for the formation of snow. [3]

Snow is solid precipitation produced when conditions are below freezing. In clouds this can be the result of sublimation or vertical updrafts carrying rain drops to high and cold altitudes. To fall to earth temperatures at the ground level must be below freezing.

(b) Using diagrams, explain how convectional uplift and orographic uplift of air occur. Outline the effects of such uplift on weather. [8]

Convectional uplift is produced through the surface heating (conduction) of a parcel of air which will rise at the DALR. It will rise as long as it remains warmer than the ELR. Adiabatic cooling can lead to condensation and the development of clouds. Whether these develop ppt will depend upon the ELR and SALR. It is possible that only fair-weather Cumulus will be produced. Orographic uplift is the forced ascent of air over hills and mountains. Initially the parcel of air is cooler than its surrounding air, but the forced ascent can reduce the temperature to the point of condensation, particularly in moisture laden maritime air. The result is clouds and precipitation on the windward side of the mountains.

(c) To what extent does an urban area experience a climate different from that of a surrounding rural area? [10]

An opportunity to compare the urban heat island and its effects with that of the rural areas.There should be some comparative element i.e. how much warmer, wetter, cloudier urban areas are. Good answers may be able to address features such as relative humidity in urban and rural areas. Most will however, deal with the differences in thermal capacity and heat retention of urban areas, their increased levels of pollutants and propensity for higher rainfall and cloudier days. Mists and fogs are likely to be more common in rural areas as are frosts.


L3 Give an indication of the difference between urban and rural, even if only in terms of percentages of temperature or rainfall. Good understanding of the urban heat island and its impact on a range of climatic phenomena. [8–10]

L2 More of a straightforward account of urban climates with little or no reference to rural areas. [5–7]

L1 Some urban climatic features, such as pollution, winds and a very limited understanding of heat islands. [0–4]


(a) (i) Define the terms solar radiation and terrestrial (earth) radiation. [4]

Solar radiation is short wave radiation that enters the earth’s atmosphere. Earth or terrestrial radiation is long wave radiation formed by the re-radiation at longer wave length of solar radiation that penetrates to the earth’s surface.

(ii) Briefly explain why the lower part of the earth’s atmosphere cools at night. [3]

The lower part of the atmosphere is cooled by terrestrial radiation. The earth cools faster than the atmosphere and hence at night cools the layer immediately above it.

(b) With the help of diagrams, show how lapse rates influence the formation of clouds and rainfall. [8]

Lapse rates are the change of temperature with height. Diagrams showing DALR, SALR and ELR should demonstrate stability and instability and the cooling induced on rising air. On reaching dew point temperature, condensation will occur producing cloud and possibly rainfall. Conditional instability is perfectly acceptable, but not necessary for full marks.

(c) Explain how buildings, tarmac and concrete can affect the climate in urban areas. [10]

An opportunity to tackle urban climates but focused upon the impact of surfaces that absorb heat and only slowly re-radiates it. This allows urban areas to retain heat, particularly in the evenings and at night, raising urban temperatures. This in turn will allow greater convection giving rise to slight increases in rainfall. The relatively rapid dispersal of rainwater and the lack of vegetation tends to lower humidity. Buildings also provide increased friction, lowering overall wind speeds, although, skyscrapers and roads may channel winds.


L3 8–10 concentrate on how buildings and tarmac bring about heat island effects. This in turn will be employed to demonstrate factors of humidity, convection, and wind.

L2 5–7 demonstrate some appreciation of the urban heat island but with less explanation of the role of tarmac, buildings etc. More of a general account of urban climates.

L1 0–4 give an all purpose account of random elements of urban climates (including smogs etc), with little reference to either heat islands or of the effects of buildings and roads.


7 (a) (i) What is meant by the term urban heat island? [4]

The area (island) of relatively higher temperatures that are found in urban areas as compared with surrounding rural areas. Produced mainly by the capacity for buildings to retain heat and re-radiate it at night.

(ii) Briefly describe one effect that atmospheric pollution may have upon urban climates. [3]

Increases in smogs and photo-chemical smogs and fogs through particulate matter acting as hygroscopic nuclei and car exhausts in the atmosphere close to the surface. Reduction in solar radiation due to particulate matter over urban areas at higher altitudes. Increase in cloudiness and hence rainfall due to increase in hygroscopic nuclei.Any one of these.

(b) With the use of diagrams, explain how the earth’s atmosphere is heated by solar radiation. [8]

Essentially a diagram showing the six factor ‘day model’. Incoming solar radiation, reflected SR, energy absorbed by the surface, sensible heat transfer, long wave terrestrial radiation, latent heat transfer and absorption of heat through greenhouse effect etc.

(c) Explain how winds can influence the distribution of global temperatures. [10]

The earth receives more solar radiation in equatorial and tropical areas than at the poles, requiring the heat to be transferred latitudinally around the globe. Winds and ocean current are the means of achieving this. Where solar radiation is at its highest surface warming induces uplift and the air is moved in cell like movements in the atmosphere. The Hadley cell can be briefly explained. Much can be achieved with simple diagrams.


L3 show an awareness of how the tri-cellular model is driven by solar radiation and how it transfers heat excess to areas of deficit. Some awareness of how winds occur, but a concentration on global temperature distribution. [8–10]

L2 use the Hadley cell to illustrate the impact of wind on temperature redistribution. Some confusion between local and global, so may introduce land –sea breezes etc. [5–7]

L1 show a vague notion of the distribution of winds (e.g. Trades, westerlies etc.) but little appreciation of either their generation or role in influencing temperature. Confusion of local and global. [0–4]

Atmosphere and Weather Mark Schemes

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