Atmosphere Revision, As geo 9696, paper 1

1. REVISION ATMOSPHERE
AS GEOGRAPHY 9696 (PAPER 1)

2. 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

3. 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)

4. 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).

5. 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.

6. Temperature inversion

7. 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.
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 be
Used to evaporate it, and
less energy available
To raise local energy
levels and temperature.
Sensible heat transfer-
Movements parcels of air into and out
Form 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 potential
To heat it. Depend nature of surface; If energy concentrated at surface
Surface warm up but if surface can conduct heat to lower layers, surface remain
cool

8. 4 factor night model
Long-wave radiation:
During cloudless night,
Large energy is loss LWR
From earth. Little
Return to atmosphere
Due to lack of clouds.
Cloudy night, clouds
Returns LWR to surface,
Overall loss is reduced.
Hot desert, lack cloud cover
Loss of energy at night
Is 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 area
May reduce temperatures
Whereas warm air may
Supply energy & raise
Temperature.

9. 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.

10. HEAT TRANSFER -HORIZONTAL

11. 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.

12. TRI-CIRCULAR CELLS

14. 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.

15. Hadley cell
George 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.

16. 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.

17. Ferrel cell
The 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.

18. WORLD WIND BELT

19. 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.

20. 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.

21. World map showing distribu on
temperature and pressure
JULY –SUMMER (NH)
WINTER (SH)
summer
ITCZ
ITCZ move
North in July
winter

22. 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.

23. 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.

24. FACTORS INFLUENCING TOTAL
VARIATION WITHIN GLOBAL PATTERNS
• LATITUDE
• LAND AND SEA DISTRIBUTION
• INFLUENCE OF OCEAN CURRENTS

25. 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.

26. 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.

27. Ocean currents
Water 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.

28. TERMS
• ALR
• DALR
• SALR
• ELR

29. TERMS
ALR-Adiabatic lapse rate
The 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 Rate
The rate at which unsaturated air cools as it rises or warms as it descends.
SALR-Saturated Adiabatic Lapse Rate
The 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)

30. Stability

31. 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.

32. Instability/unstable air

33. 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

34. Conditionally instability air

35. 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.

36. 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.

37. WEATHER PHENOMENA:
Snow Frost Dew Fog
Precipitation in the
form of snowflakes of
complex hexagonal ice
crystals.It is formed in
cold clouds through the
process of deposition,
where vapour forms
straight away into ice
crystals (solid). The
largest falls of snow
occur when air
temperatures are just
below freezing point.
The deposit of fine ice
crystals onto a surface
of grass, plant leaves
and walls.
It forms under clear,
calm, anticyclonic
conditions in winter
when there has been a
rapid loss at night with
temperatures below
freezing point. Water
vapour condenses
directly to ice crystals
by deposition onto
these surfaces.
* Glazed frost (next
slide)
Deposition of water
droplets on the surface
of grass & the leaves of
plants. As with frost,
dew also forms under
clear, calm, anticyclonic
conditions (clear nights
with no cloud cover)
when there is a rapid
heat loss at night. As
nearby air cooled to
dew point, the moisture
in the air condenses and
deposited as tiny
droplets onto these cold
surfaces.
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
reduces visibility to less
than one kilometer.
(cooling result 3 types
of fog; Radiation, frontal
and advection.

38. 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.

39. TYPES
a) 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

40. UPLIFT OF AIR

41. 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.

43. FORMATION OF RAINFALL
Collision-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.

45. 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.

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

47. 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.

48. 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.

49. Climatic differences in urban areas
1. 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. Humidity
lack 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

50. 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.

51. 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.

52. 4. Pollution
Large 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.

53. 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.

54. 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.

55. GREEN HOUSE EFFECT & GLOBAL
WARMING

56. 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)

57. 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.

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

59. Predicted possible effects
1. 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 precipitation
With 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.

60. 4. Rise in sea level
As 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 currents
These 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.