Weather & Climate & Associated Hazards Part 2

There are a number of fundamental controls on our climate. These are:

• 1) The Atmospheric Heat Budget
• 2) The Structure of the Atmosphere
• 3) Latitude
• 4) The General Atmospheric Circulation
• 5) Planetary Surface Winds
• 6) Ocean Currents and circulation and Continentality
• 7) Altitude

These 7 controls do not work in insolation; instead they overlap and interact to produce what we call our weather (day to day changes in the atmosphere) and climate (average weather over an area, incl. seasonal patterns and change over years) 

pg 3 for diagram to show natural greenhouse effect

This looks at the distribution of heat energy which the earth receives from the sun. It is the balance between the incoming solar radiation (insolation) and outgoing radiation from theplanet. The budget is best shown in diagrammatic form. (Look at diagram pg 4) 

What % of the insolation (in the form of short wave UV radiation actually reaches the earths surface: 51% 

What happens to rest of incoming solar radiation? : reflected by atmosphere, clouds and earth's surface

The energy which is absorbed warms the earth and the heat is returned to the atmosphere as IR. 70% of this energy is lost to space

If more of this energy is trapped by the atmosphere the earth will warm up and global temps will increase due to EGE (0.8 degree increase) ch4, co2, CFC'S NOx

This looks at the distribution of heat energy which the earth receives from the sun. It is the balance between the incoming solar radiation (insolation) and outgoing radiation from theplanet. The budget is best shown in diagrammatic form. (Look at diagram pg 4) 

What % of the insolation (in the form of short wave UV radiation actually reaches the earths surface: 51% 

What happens to rest of incoming solar radiation? : reflected by atmosphere, clouds and earth's surface

The energy which is absorbed warms the earth and the heat is returned to the atmosphere as IR. 70% of this energy is lost to space

If more of this energy is trapped by the atmosphere the earth will warm up and global temps will increase due to EGE (0.8 degree increase) ch4, co2, CFC'S NOx

In recent years, with the increase of GHG's the atmosphere is able to absorb more IR

The structure of the atmosphere is determined by temperature changes with height. 99% of the atmosphere is nitrogen and oxygen, but there's also water vapour, ozone and carobin dioxide. 

4 layers: troposphere, stratosphere, mesosphere, thermonsphere (diagram pg5)

Troposphere:

• Temp decreases by 6.5 degrees every 1km (ELR - environmental lapse rate). This is because the earths surface is warmed by insolation which heats the air next to it by conduction, convection and radiation
• Pressure falls as gravity decreases
• Wind speed increases with height
• Contains most of atmospheres water vapour, cloud, dust and pollution 

Stratosphere

• steady increase in temp caused by a conc. of ozone. this absorbs uv from sun
• light wind in lower part, but increases with height. pressure continues to fall and air is dry
• acts as a protective layer from meteorites
• stratopause is another isothermal layer where temps do not change with increasing height

Mesosphere

• Temp falls rapidly as no water vapour, cloud, dust or ozone to absorn incoming radiation
• experiences the atmospheres lowest temp (-90degrees) and strongest winds (nearly 3000 km/hr)
• mesopause shows no temp change (like tropopause and stratopause)

Thermosphere

• Temps rise rapidly with height, perhaps to reach 1500 degrees, this is due to an increasing proportion of atomic oxygen in the atmosphere, which like ozone, absorbs incoming UV 

Latitude affects climate in two ways:-    (look at diagram pg 6) latitude ((across))

• 1. The angle of the sun
• 2. The length of daylight. The longer the daylight, the greater the insolation.

In the tropics, the length of daylight is constant at 12 hours. At the poles in their winter, virtually no direct sunlight reaches them so there is almost 24 hours of darkness. This reduces the temperatures significantly. However in summer, they have long days and short nights meaning relatively more direct heating (it is still not warm due to the oblique angle of the sun!).

Further away from the equator there's less insolation

Over land complicated pattern, like in Africa. The lowest levels over equator and highest levels where tropic of capricorn and cancer are. ITCZ has a lot of Cb clouds which block the insolation whereas STA has none.

Low levels of insolation over sea due to the sea refelecting UV - albedo effect.

Steeper change as further away from equator (around mid latitudes). This is due to sun being more oblique so more insolation is lost in space and has longer to travel. Polar regions have no daylight.

So that the equator and tropics do not becoming progressively hotter or the poles progressively colder, a redistribution of heat energy much constantly take place. Hadley Cells which help to recirculate some of the heat energy in the equatorial regions. (diagram pg 8)

Atmospheric pressure is the force per unit are exerted against a surface by the weight of air above the surface. Low pressure areas have less atmospheric mass above their location, whereas high pressure areas have more atmospheric mass above their location.

At sea level, the average atmospheric pressure is 1000mb 

The Tricellular Model

In addition to the Hadley cells, there are two other atmospheric cells - the polar cell and the ferrel cell which operate in similar ways and help to redistribute heat polewards. They form part of the tricellular model. (pg 9 for diagram)

The UK lies roughly between latitude 50deg N and 60deg S. The weather conditions expected in UK: UK is located at the meeting of the polar and ferrel cells. low pressure, southwest (direction of prevailing winds) this brings warm, moist air brought to UK. Air will rise due to low pressure, this produces wet weather, in a temperature climate (i.e not too hot or too cold) and gulf stream SW ocean current keeps UK warm as well as SW winds

The Jet Stream - at boundaries of circulation cells due to temp differences of air (warm and cold) 

(pg 10 for diagram)

There are 4 jet streams circling the globe, 2 each in the northern and southern hemispheres. These are currents of fast flowing air(moving at over 100mph). They flow in the tropopause from west to east. It’s found where temperature contrasts, across short distances, are greatest.It is these stark variations in temperature that provide the energy that drives this narrow stream of powerful winds. The polar jet stream occurs due to temperature difference between the cold polar air and the warm tropical air. The polar jet stream plays a large role in determining the weather of the UK. The “waves” in the Jet stream are known as Rossby waves and these allow depressions to form in the Atlantic which can bring wet weather to the UK. However,the location of the jet stream's path can vary. It is approximately 10km above the ground.

pg 11 for diagram

When the jet stream is strong, it shifts northwards towards polar latitudes, leaving Britain in a region of relatively high pressure from continental Europe. This gives us settled weather with clear skies which cause freezing cold winters but hot summers. But when the jet stream is relatively weak, it meanders widely, rather like a sluggish river, and can shift southwards towards the tropics. This then brings low pressure weather systems (called depressions) directly across the UK to give us very wet conditions. 

The polar jet occurs roughtly the same latitude as the UK because it lies at the boundary of the polar and ferrel cells (their meeting point). UK at boundary of polar and ferrel cells. 

If jet stream shifts northwards: clear skies which cause freezing cold winters but hot summers (HP) in UK weather

If shifts southwards: very wet (LP)

Extreme conditions when the jet stream goes off its path

These are a major player when it comes to transferring energy around the globe. (diagram pg 12) wind goes from HP to LP

Planetary surface winds form when warm air rises (eg forms low pressure at the ITCZ). Cool air sinks (eg forms high pressure over the STA) as they allow the sinking air to replace the rising air. The surface winds are simply equalizing the pressure difference. So the NE and SE trade winds which affect Africa blow from regions of high pressure to regions of low pressure.

Why the UK has prevailing South Westerly winds: winds blow from HP (30N) to UK (LP at 50-60N)

Wind Strength is shown by the pressure gradient

The winds blow across what is known as the pressure gradient. This gradient is shown on a weather map by the isobars (lines joining points of equal pressure). If they are close together, there is a steeper pressure gradient, pressure changes quickly, so winds are stronger.

Winds influence temperare: If they blow off a cold surface they bring colder temps. vice versa

pg 13 for diagram

Ocean currents are set in motion by prevailing winds blowing over the surface of the ocean. They are also vital in transferring heat from the equator to the poles. 

The 5 main ocean currents follow circular routes (or GYRES). Should be able to identify GIVE distinct "circultions" of water or gyres

Gyres in north travel clockwise and south is anticlockwise (direction of rotation n&s of equator)

warm currents flow along west 

cold currents flow along east

gulf stream is the oceanic transfer of heat that UK benefits from

• In the UK we are well positioned to benefit from the North Atlantic Drift (or Gulf Stream). The relatively warm waters of the North Atlantic Drift are responsible for moderating the climate of western Europe, so that winters are less cold than would otherwise be expected at its latitude.
• Without the warm North Atlantic Drift, the UK and other places in Europe would be as cold as Canada, at the same latitude.
• For example, without this steady stream of warmth the British Isles winters are estimated to be more than 5 °C cooler, bringing the average December temperature in London to about 2°C. 
• The Gulf Stream/ North Atlantic Drift forms part of a thermohaline circulation which is driven by denity differences the warmer, less dense water at the tropics, and the colder, denser, salty water that sinks in the North Atlantic. This deep subsurface water then flows to the Gulf of Mexico until it warms enough to resurface and flow back north as the Gulf Stream. 
• However, global warming could cause this thermohaline circulation to shut down as a result of acrtic warming which would release more freshwater into the North Atlantic so that the water is less saline and so not dense enough to sink. As a resultm the climate of Britain could be considerably cooler.

How the thermohaline circulation in the North Atlantic Ocean works: (diagram pg 14)

The gulf stream / North Atlantic Drift forms part of a thermohaline circulation which is driven by density difference in seawater

1) The warmer, less dense water at the tropics (the gulf stream) flows northwards to greenland

2) Off the coast of greenland the water is now much colder, dense and saltier so sinks

3) There is a deep subsurface flow to the gulf of mexico until it warms enough to resurface and flow back North as the gulf stream. 

Continental areas warm up in summer and cool down quicker in winter than coastal areas because land has a LOW specific heat capacity (heats up and cools down quickly). This creates a more extreme continental climate with a large annual range of temp compared with coastal areas which have a maritime (equable) climate.

The ocean has the opposite influence. Water has a high specific heat capacity so when it heats up it maintains this heat for a long time. In winter it remains relatively warm. In comparison, during summer, the reverse is true and the sea only heats up slowly meaning it is colder than the land. This creates a maritime climate with a smaller temp range.

Sea has high heat capacity -> warmer winters (because sea cools down slowly) and colder summers (sea takes longer to heat up) & lower temp range

Land has low specific heat capacity -> V.cold winters (because loses heat v. quickly)  and hot summers (because land heats up quickly) & higher temp range.

• London, UK (maritime influence): 6deg Jan & 22deg July
• Berlin, Germany (continental influence): 0deg Jan & 19deg July
• Moscow, Russia (continental influence): -6deg Jan & 24deg July

As the UK is surrounded by water its inevitable that our climate will be wet. this is made worse by the fact that the water is warm, the air above is also warmed and warm, moist air rises and adiabatically cools, this then condenses to form clouds which leads to rainfall.

Air which is warm at ground level is UNSTABLE (will want to rise)

If air is cooled at low level it will be STABLE so won't rise and the climate will be dry. So if the ocean current cools the air above it should be dry.

ocean currents

Region affected by cold currents: Humboldt current affects the Western coast of South America g Peru and Chile. Climate: cold currents cool air down. when this blows onshore it lowers the temp, and the air becomes more stable so it remains dry. this has created the coastal desert in a subtropical region - eg the atacama desert, s. america.

Region affected by warm currents: Benguela current affects SW coast of Africa eg Angola and Namibia. Climate: warm currents heat air. When this blows onshore it increases temp and air becomes unstable so is moist. This creates the Namib desert. 

There is one more ocean circulation which plays a major impact on global climate, including having some influence on the UK’s climate.

This is the circulation of water across the Pacific Ocean

To understand what happens we must first understand how sea temperatures vary with depth:

As the earth’s surface is heated from above it is logical that the upper surface of the ocean is warmer than the underlying layers. The change in temperature as you descend is sudden in places and this creates a boundary called the THERMOCLINE.

Thermocline: Boundary in a body of water where the greatest vertical change in temperature occurs. This boundary is usually the transition zone between the layer of warm water near the surface and the cold deep water layer.

However, the simple layering system is altered when deep ocean currents (like the Humboldt current off the coast of Chile/Peru) rise to the surface. This can be seen on the below diagram: (pg 17)

La Nina = normal walker cell circulation.

The ocean on the West side of the Pacific is warmer than that on the East. This means the air above the ocean is heated and so rises, leading to Low pressure. This sets up an atmospheric convection cell across the Pacific, known as the Walker Circulation Cell. It means that it will be WET ON THE WEST side of the Pacific and DRY ON THE EAST.

However, every 2 to 7 years, this circulation is reversed in an event known as ENSO (The El Nino Southern Oscillation) or El Nino for short. (pg 18 for diagram)

This "reversal" of the Walker Cell (El Nino) is obviously going to affect the climatic conditions of the Pacific, BUT, it also impacts on the rest of the world. 

In early 2010, there was an El Nino event which resulted in:

• heavy rain and landslides in Peru
• Fires in Sydney
• A lack fo snow in Vancouver for the winter Olympics (Too warm and wet) 

However, later that same year this was reversed and a La Nina event developed

The effect of altitude on climate is more useful for explaning local variations in climate

• on rainfall (Diagram pg 20)

in the UK, RELIEF (or orographic) rainfall occurs when moist air is forced to rise over mountains. 

• Blackpool receives 950mm rainfall because: prevailing winds blow from SW, these are warm and moist and pick up moisture from the Atlantic Ocean. Blackpool gets a lot of rainfall and wind heading there, the warm moist air is unstable, therefore is rising = rainfall. Blackppol at sea level. 
• At Pennines (eg Oldham) receive 2000mm+ rainfall because: Rainfall higher as warm air is very unstable = lots of rainfall = relief rainfall. 
• On Eastern side, Newcastle is drier (700mm rainfall) because the air descends over Pennines. It adiabatically warms so drier conditions. This always occurs on the Lee side of mountain. Lee side of mountain have rain shadow effect. 

In normal circumstances, temperatures also fall with increasing altitude. As you gain height there is a fall in pressure and this means molecules are further apart. This results in the fall in temperature as there is less kinetic energy between particles. The fall in Temperatures with height in the troposphere is called the environmental lapse rate (ELR) which is roughly 6.5deg per 1000m. Within this overall environment, pockets of warmer air rise and cool as they expand (adiabatic cooling) until they are in equilibrium with the ELR. Alternatively pockets of colder air sink and gain temperature as they are compressed (adiabatic heating ) until they are in equilibrium with the ELR. Rising pockets of air cool at the adiabatic lapse rate. However, the rate at which pockets of air cool depends on whether the air is dry or saturated. If dry air is forced to rise (e.g. over mountains), the consequent expansion in volume causes a temperature fall of approximately 10deg per 1000m. This is called the dry adiabatic lapse rate (DALR). If the pocket of air is saturated and condensation is taking place there is a release of latent heat. This reduces the rate of cooling to 5C per 1000m. This is called the saturated adiabatic lapse rate (SALR). 

The relationship between these Lapse Rates plays a major role in controlling the stability (or instability) of the air and therefore the formation of cloud and precipitation. A parcel of warm air at ground level will rise up in the atmosphere until it becomes the same temperature as the air around it (the air cooling at the ELR). But there are many influences on this, including the point at which condensation takes place (dew point temp)

Dew point: the temp at which air becomes saturated and water vapour condenses

Latent heat: changes state and the stored energy releases heat. (water vapour -> condensation)

UK = 50-60deg North

UK has a COOL TEMPERATE WESTERN MARITIME CLIMATE (CTWM)

• the cool temperate part tells us that its never too hot and never too cold . i.e. we dont suffer from extremes
• the western maritime refers to our position on the western fringe of the eurasian continent and influence by the sea (mariteime) which explains why it's wet.

1) Summer temps

• Summer temp decreases from South to North because insolation of Sun more concentrated over larger area
• Summer temps are lower over mountainous areas and cooling at ELR (6.5deg per km)
• Summer temps are highest in SE
• Urban location - tarmac = darker surface absorbs more UV radiation more ground heating lower albedo 
• Coastal = high specific H.C. = cooler / inland variation (warmer inland) summer temp cools quickly. Low specific H.C. on land

• Winter temp decreases from West -> East
• Winter temps are lowest over mountainous areas and decreases according to ELR
• Urban areas warmer in winter due to tarmac
• S+N difference to effect of latitude
• Winter temp are higher in SW -> due to warm prevailing wind 
• Coastal will be warmer as water returns heat - inland colder

3) Annual rainfall

• Rainfall decreases from W -> E. Relief rain over moutainous areas
• Rainfall is the highest in the NW of Scotland
• Rainfall is highest in moutainous areas
• Urban areas more likely to get convectional rainfall - more ground heating
• Rainfall is lowest in SE
• Most rainfall due to frontal rain - warm and cold are meet. Warm forced to rise = frontal rain

An air mass is defined as a large area of air that has a similar temp and humidity level to the source area it originated from

There are 5 major air masses that affect the British Isles - each air mass will bring with it distinct characteristics and weather conditions and it helps to explain why our weather is so changeable.

Temperate:we don't feel heat of tropics or coldness of poles

Martime: UK feels influence of sea.

• Polar Maritime (PM): Will bring COLD, WET weather. This is because it has originated from a POLAR region. It will also bring wet weather because the 'maritime' indicates that the airstream has had to travel over ocean area to reach Britain and so has picked up lots of moisture in the process.
• Polar Continental (PC): Gives V. COLD temps in London in Winter (below 0). Begins stable, but wamrs slightly crossing the N. Sea to become unstable in lower layers and giving heavy snow in Eastern Britain. (bright and clear on West Coast). Often lasts several days if blocking anticyclone iterrupts prevailing westelies wind chill factor is high. If this air stream occurs in Summer, brings warm conditions and is more stable.
• Arctic or Arctic Maritime (AM): Very cold conditions in Winter; cold in Spring; rare in Summer. Slowly heats up as it crosses the sea, picking up some moisture and becoming unstable in its lower layers. Snow in winter in Scotland; hail in Spring, often in heavy showers. Lasts svereral days. Temps in London may be just above freezing point in Winter and precipitiation is limited winds often strong in North. 

• Tropical continental (TC) Only occurs in Summer when sub tropical high pressures move North. Heatwave conditions. Very stable in lower layers (drought), though upper layers may become unstable with thunderstorms convectional uplifts, gentle winds, dusty haze. North West Sctoland can be cloudy and wet. 
• Tropical Maritime (TM) A common airmass over Britain. Occurs during warm sector of a depression. Very mild and wet in winter, with thick cloud cover. Often stratus cloud giving hill and coastal fog. Poor visibility. No frost. Warm summer, although not hot. Lower air is stable but if fforced to rise over hills, the upper layers can become conditionally unstable to give thundery showers. Winds usually moderate to fresh. 

• Airmass: Polar Maritime 
• Source: Greenland Arctic Sea
• Properties: Wet and cold
• Weather: Cold and showers

• Air mass: Arctic Maritime
• Source: Arctic
• Properties: Wet and cold
• Weather: Snow in Winter

• Air mass: Polar Continental
• Source: Central EU 
• Properties: Cold (winter) Hot (Summer)
• Weather: Snow (Winter) Dry (Summer)

• Air mass: Tropical Continental
• Source: North Africa
• Properties: Hot and dry
• Weather: Hot in Summer

• Air mass: Tropical Maritime
• Source: Atlantic
• Properties: Warm and moist
• Weather: Cloudy rain mild

The air masses will become MORE STABLE or UNSTABLE as they move towards Britain from the source region where they originated. Stability means how likely it is that the air will rise. 

Unstable = air will rise easily as it is warminng

Stable = air unlikely to rise as it is cooling

Lower altitude = warmer

Air masses which will become STABLE as they move towards Britain:

Tropical Maritime and Tropical Continental. Developed where warmer than UK, so to reach UK it cools so becomes more stable. eg TM: Warm air moving Northwards is cooled from below as it travels over cold sea. Air becomes moist and stable = mild conditions, but can be cloudy and drizzly.

Air masses which will become UNSTABLE as they move towards Britain:

Polar Maritime, Arctic Maritime, Polar Continental. Come from colder areas and when come to UK they warm up. Snow showers could occur. Southwards moving air is warmed from below and becomes more unstable. E.g. Polar Maritime, cold as moving Southwards, is heating from below as it travels over warm sea. Air becomes moist and unstable - cool conditions with showers.

Polar Continental (Pc): In winter, this air mass is cold so the airstream warms as it approaches Britian causing it to become more unstable. As a result, it brings very cold weather in winter (-10C), snow in E Scotland and England. In summer, the airmass becomes cooler and more stable as it travels towards Britain. It therefore brings dry conditions in summer (but rarely affects the British Isles in summer)

Polar Maritime (Pm): This airstream starts off cold but warms at its base as it moves towards Britian, picking up moisture from over the sea. This brings unstable, cool and showery conditions. It may result in snow in NW Scotland (common air mass over the UK)

Tropical Continental (Tc): By the time this airstream reaches Britain, it is very stable because the base has cooled. It's unlikely to have cooled to dew point because there is little moisture present. Therefore, it brings hot & dry conditions. It only affects the British Isles in Summer.

Tropical Maritime (Tm): This airstream becomes more stable but cooling is sufficient to cause the moist air to condense at dew point temperature. It brings mild, wet weather in winter and warm damp weather in summer (a common air mass over Britain)

Arctic Maritime (Am): This air mass starts off very cold and warms only slightly as it travels South towards Britian. It also picks up moisture as it travels over the sea. It therefore brings very cold temps in Winter with snow in N. Scotland.

• Arctic air mass: v. cold with snow in winter and early spring; often with very clear skies
• Pm: cold, moist weather; often unstable air associated with heavy showers
• Pc: v. cold temps in winter with snow in eastern england; warm conditions in summer
• Tm: mild air in winter; often moist with stable conditions and low lying cloud, possible advection fog on coasts
• Tc: hot, dry, heatwaves conditions in summer
• Main factor in determining temp of air mass: the region from which it originiates
• What effect does the path taken by the air mass have on its characteristics: Oceanic tracks = gives high levels of moisture, whereas continental tracks = quite dry air masses
• Polar Maritime and Tropical Maritime affect Britain most.

Anticyclone: It is an area of high atmospheric pressure that is usually slow moving or stationary. Anticyclones are generally larger than depressions (up to 3000 km across) and are dominated by subsiding air which produces warming and a decrease in relative humidity. In summer they bring hot, sunny conditions with little cloud or rain although clear skies at night can lead to inversions that produce dew , mist and coastal fogs . In winter these stable conditions favour the development of fog and frost, and pollution may be trapped in the lower layers of the atmosphere by the inversion.

Isobars = join points of equal pressure. Close isobars=strong wind&Steep pressure gradient. Further apart=gentle wind&less steep pressure gradient.

Recap of STA:

• Increase pressure = lower altitude 
• High pressure - air is sinking - air is adiabatically heating because as it sinks the air molecules contract and warming up as a result
• Hot in Summer and not much rain - dry (In Africa) -> clear skies = no condensation because dew point temp not reached(- not cool enough for condensation)
• Winter anticyclone (UK) - winter, clear sunny days temps still quite cold
• Summer anticyclone (UK) - V. warm

• Weather characteristic associated with the anticyclones in the UK & reasons:
• High pressure: Air is sinking
• Clear skies: No clouds as dew point temp not reached. As air descends it adiabatically heats, dew point not reached = no condensation
• Hot in Summer (Over 20deg) (Sun overhead in the Tropic of Cancer, closer to UK): Sun higher angle in the sky, high insolation rays, longer days means long hours of solar radiation by day. High temps. Sun in Tropic of Cancer.
• Cold in Winter (Sun overhead in Tropic of Capricorn-further from UK): Condensation of moisture on and near the ground surface, which produces a mixture of fog, mist and frost. The cold weather due to low insolation and short daylight hours. Oblique Suns rays have to heat up greater area and no cloud = heat escapes. 
• Light winds: Isobars further apart, gentle pressure gradient therefore lighter winds.
• Heatwave in Summer or a big freeze in Winter: Anticyclones move slowly and may remain stationary over an area for several days or weeks. When this happens they are described as blocking anticyclones. Depressions that would normally travel to Britain on Westerly airstreams are deflected away.  
• Radiation fog and advection fog: cont on next card.

Pg 42 for map on weather chart for anticyclone and UK & e15. The wind flows clockwise around the cenre of the HP system (or sinks then moves due to coriolisis effect). As a result, volcanic ash from E15 drifted over UK. The volcanic ash also got carried by jet stream which blew the ash cloud over NW EU. 

FOG

Fog is commonly associated with anticyclones. It occurs due to CONDENSATION AT GROUND LEVEL. There are two main types of fog associated with anticyclonic conditions - RADIATION FOG AND ADVECTION FOG (coastal regions only for advection)

The photograph on the next page was taken in the late afternoon in September 2012. It shows radiation fog over Longendale valley (Holme mast is in the distance). A temperature inversion has occurred. This is where there is colder, damper air is below the warmer, drier air so that temperature actually INCREASES with height rather than the more usual relationship shown by the environmental lapse rate. (where temp decreases with height) (photo on pg 43)

Why does radiation fog form?:

• Fog is a cloud at ground level that restricts visibility to less than 1km. It forms under clear night skies when a moist atmosphere cools through the radiation of heat from the ground surface.
• The cooling extends some distance above the ground surface and is encouraged by light winds that allow slight mixing of the air.
• The air is cooled to its dew point, at which condensation occurs. 
• Common in winter when long hours of darkness allowing maximum cooling.

Why radiation fog occurs in valleys:

In the evening, with clear skies and high humidity, the air on the upper slopes chills more quickly than that in the valley bottom. Cooling on upper slopes increases the density of the air + moves up downslopes. Cold air accumulates in valley bottoms pushing warm air up. Cold air now in valley bottom cools to dew point = dense fog.

Statements of radiation fog:

• Rapid heat loss at night (no cloud cover) 
• The ground surface cools due to radiation loss
• Air cooled by contact with ground
• Condensation occurs at dew point
• Radiational cooling at top of fog layer causes fog to thicken
• Calm conditions result in the radiation fog remaining in low lying areas

Radiation fog is also common in urban areas. This is because the temp inversion traps pollutants and exhaust fumes turning the fog into a smog eg the great london smot 1952 & photochemical smog in LA. -> provide good example of how anticyclonic weather can affect human activity.

When a warm, moist air moves horizontally over a cooler land or sea surface it is cooled from below. If the temp of the air cools below dew point, condensation occurs and advection fog is formed. 

Diagram:

Forms when a mass of warm air moves horizontally across a cooler surface. The air is cooled to its dew point and condensation occurs. This is most common around coastas and over the sea in Summer. Sea dog eg Fret or Harr

In part 1 we came across LP systems associated with the ITCZ and TRS. Depressions are the UKs equivalent to these systems.

A depression is an area of LOW ATMOSPHERIC PRESSURE which rotates in ANTICLOCKWISE DIRECTION.

The formation of a depression (pg 50)

Britain is located between 50-60deg North which positions us at the polar front. This markes the boundary between warm tropical air from the south (part of the ferrel cell) and the cold air polar air from the north (part of the polar cell) of the tricellular model. this means that Britain is located in the low pressure zone.

Depressions form due to rising unstable air which creates Low surface pressure. Explain how the following help to trigger unstable conditions:

a) Polar Front Jet Stream (PFJT) kink (rossby wave):

b) contrasting air masses e.g TM and PM

The development of a mature depression 

The warm Tm air forms a bulge into the cold Pm air. As the warm Tm air rises it starts to rotate due to the coriolis force. The whole low pressure system now begins to rotate from the centre in an anticlockwise direction trying to reach the centre where the air is rising. An embryo depression has formed. The depression grows larger and reduces in pressure as it travels across the North Atlantic. Eventually a mature depression forms. By this stage, there are two meeting pints of the air:-

• The warm Tm air is pushing into the Polar Front. This is called the warm front.
• The cold Pm air is pushing into the warm sector. This is called the cold front.

A mature depression: 

3) The numbered lines on the diagram are isobars. These are lines of equal pressure. Where is the lowest pressure and why? : In the centre of the depression, this is where most of the air is rising. 

Why will it be raining at the fronts?

 Warm front:

• Tm air rises over Pm air
• Warm air rises GRADUALLY
• Air expands
• Air cools
• Dew point temp is reached
• Condensation on condensation nuclei 
• Nimbostratus clouds form
• Droplets collide and coalesce (merge) 
• Droplets large enough to overcome weak uplift - LONG SPELL OF DRIZZLE (due to gradual rising) 

Warm, moist air = less dense. Cold, moist air = more dense

• Tm air undercut by Pm air
• The warm air rises STEEPLY
• Air expands
• Air cools
• Dew point temp is reached
• Condensation on condensation nuclei 
• Cumulonimbus clouds form
• Droplets collide and coalesce 
• Droplets large enough to overcome strong uplift = SHORT PERIOD OF HEAVY SHOWERS

A cross section of a mature depression 

Once a depression has matured it has distinctive features such as the fronts and warm sector. These can be illustrated on a cross-section through the system from A to B. The depression and their associated fronts move eastwards or north-eastwards across the North Atlantic bringing unsettled weather

What do you notice about the angle of the warm front compared to the cold front?: Warm front has gentler gradient compared to cold front. (Warm: Tm rises over Pm = gentle) (Cold: Tm undercut by Pm = rapid uplift = steep angle of CF)

What difference has this made in the clouds, why?: At warm front it causes clouds to become gradually lower - start with high cirrus to very low nimbostratus clouds. whereas at cold front, only Cb clouds

The weather changes as a depression and the associated fronts pass over. 

WARM FRONT:

• RAINFALL: Long periods of drizzle - FRONTAL RAIN
• CLOUD TYPE: 1st Cirrus (Ci) & 2nd Nimbostratus (Ns) - lower & more of them. This is the rain bearing cloud. 
• TEMP: Cooler - as in Pm air

WARM SECTOR:

• RAINFALL: Minimal rainfall - Relief rainfall if does rain
• CLOUD TYPE: No cloud
• TEMP: Warm - as Tm air

COLD SECTOR:

• RAINFALL: Short period of heavy rainfall & thunderstorms. (Faster moving when catches up to warm)
• CLOUD TYPE: Cb
• TEMP: Low - as in Pm air 

1) APPROACH OF DEPRESSION

• Pressure: Starts high but falls
• Wind direction: SE
• Wind speed: Starts increasing
• Temperature: Cool
• Cloud cover: Starts to cloud over. Initially, high wispy clouds eg cirrus
• Precipitation: None

2) WARM FRONT

• Pressure: Low
• Wind direction: Veers from SE to SW
• Wind speed: Strong
• Temperature: Sudden rise in temp
• Cloud cover: Low, thick cloud eg Ns
• Precipitation: Long periods of drizzle

3) WARM SECTOR:

• Pressure: Steady
• Wind direction: SW
• Wind speed: Wind speed is decreasing
• Temperature: Warm
• Cloud cover: Less cloud cover (eg St) some sunshine
• Precipitation: Sunshine and showers

4) COLD FRONT

• Pressure: V. Low
• Wind direction: Veers from SW to NW
• Wind speed: V. Strong
• Temperature: Sudden drop in temp
• Cloud cover: Increases - Cb
• Precipitation: Short periods of heavy rain

5) BEYOND THE COLD FRONT

• Pressure: Rises
• Wind direction: NW
• Wind speed: Wind speed is decreasing
• Temperature: Cold
• Cloud cover: Decreasing cloud cover - Some sunshine
• Precipitation: Sunshine and showers

a) What happens to surface pressure at the fronts?: Air is rising therefore low surface pressure. Pm undercutting Tm so rapid gradient/rise so even lower pressure at cold front. 

b) What happens to wind speed at the fronts?: Wind speed increases due to pressure difference. Winds equalize pressure changes.

c) What happens to air temp in the warm sector compared to elsewhere?: The temp is warm as the air is only Tm air.

d) What happens to cloud cover at the fronts?: Warm: High currius clouds initially, these then get lower and become rain bearing nimbostratus (Ns) clouds that are thick and low lying - as grentle gradient rises GRADUALLY. Cold: Increasing Cb clouds because RAPID uplift of air, Pm air undercuts Tm air.

e) Why is the nature and duration of front rain different at the warm front compared to cold front?: Warm front: Long periods of drizzle due to gentle gradient/uplift of air. Cold front: Short periods of heavy rain due to steep/rapid gradient/uplift of air.

f) Why might there still be some rain in warm sector?: Warm air still rising. Relief rainfall can occur.

A depression has a life span of several days on average. As the cold front moves faster than the warm front it eventually catches the warm front to form an occluded front.Warm Tm air in the warm sector is lifted completely off the ground as it is undercut by the Cold Front. 

(diagram pg 57) 

Decay of a depression: The amount of uplift is lower as warm air is already lifted off the ground, therefore condensation is lower, so less cloud cover and precipitation is less

pg 58 - 61 look in s/g

the weather associated with an anticyclone is different from that associated with a depression. How and why is the weather different? ( 8 marks ) 

• A depression is a low pressure system and a anticyclone is a high pressure system. Depression has LP as warm, moist air is rising and cold, moist air undercuts this warm air resulting in a LP system. - These airs do not mix due to density differences.
• A depression is associated with weather which is often cloudy and wet, whereas an anticyclone is associated with clear, sunny conditions. Depression has LP so air is unstable therefore rising and adiabatically cools therefore condensation occurs and results in frontal rain and cloudy. Anticylone has HP so less rising air and less condensation so less rain and no clouds form.
• A depression is associated with strong winds, whereas an anticyclone is associated with light winds. Depression has LP so winds strong to equalize the differences in atmospheric pressure. Anticyclone has HP and less pressure differences so winds are gentler.

• Stability of air: unstable
• Air pressure: LP
• Air masses: contrasting air masses (Pm and Tm)
• Rotation of air: anticlockwise
• Lifespan: several days
• Speed of movement: rapid
• Precipitation: frontal rain. warm front = long period of drizzle. cold front = short period of heavy showers
• Temperature: variable - warmest in warm sector
• Wind speed: varies - strongest at cold front 
• Cloud cover: warm = cirrus and nimbostratus. cold = cumulonimbus

• Stability of air: stable
• Air pressure: HP
• Air masses: dominated by 1 air mass
• Rotation of air: clockwise
• Lifespan: few days - few weeks
• Speed of movement: slow
• Precipitation: dry, don't get a lot of rain but get radiation & advection fog. In Summer, water droplets on grass = dew. In Winter, water condenses on ground = frost
• Temperature: hot in summer. cold in winter
• Wind speed: lower, light, calm
• Cloud cover: low cloud cover

Impact of weather systems on UK, Generally

Positive impact of DEPRESSIONS:

• temps generally milder than winter anticyclone
• lots of crops due to lots of rain
• lots of rain = regulat and relaible water supply
• farmlands good for cattle and livestock
• wind can be used for renewable energy 
• wind came from west and are warm so temps not that cold

Problems associated with DEPRESSIONS:

• lots of rain and flooding
• high amounts of wind
• could lead to death - severe storms
• strong winds can come at any time
• powercut, fallen trees
• storms damage property. flod cause damage to land, sporting events etc (eg wimbeldon)

positive of summer anticyclones:

• hot daytime and warm night
• generally clear skies
• ice cream sales increase
• less rain, boost of tourism
• more people can enjoy holidays

problems associated with summer anticyclones:

• some early morning mist
• thunderstorms may form
• drought - affects farmers
• public drinking water shortages. low winter rainfall so water in reservoir decreases so water conservation methods have to be taken (eg hose pipe bans, showers not baths)
• heat stroke, sun burn etc
• transport disrupted

Positive impacts of winter anticyclones:

• Clear skies
• Snow days
• Pests get killed
• Frost helps rhubarb grow

Problems associated with winter anticyclones:

• Smog (The Great London Smog, 1952)
• Icy conditions - dangerous for people and travel
• Pipes can break/burst
• Potholes develo
• Hard to plough frozen ground
• Possible blizzards
• Heavy snow - Big Freeze (2009/2010)
• Disrupted transport
• Sporting abandoned

Storms are a common feature of the UK's climate largely due to its position as a Cool Temperate Western Maritime Climate (CTWM). This means the air is unstable and moist:

• Cold Polar Air meets warm Tropical Air creating the polar front and thus depressions
• Rapid movement across the Atlantic driven by the Polar Jet stream
• Maritime air so high moisture levels creating high rainfall 
• Autumn storms due to warmth of ocean from summer heating, resulting in unstable rising air
• Steep pressure gradient creating very strong winds

Some of the UK's storms are remnants of Tropical Storms which started life in the Caribbean/Gulf of Mexico. However, they have lost most of their energy as they have travelled across the cooler Atlantic Ocean 

There is some evidence to show that Atlantic storms are becoming more common and increasing in intensity; possibly linked to global warming and the increased heating of the ocean. However, this is still debated and more evidence is needed.

A recent study (April 2009) by Paul Della-Marta of Meteo-Swiss, Zurich provides some evidence for an increase in frequency of North Atlantic storms by 2100. The storms which hit the UK do result in some damage. Power lines are brought down and transport networks can be disrupted. In 2006, Nicholas Stern’s report on the impacts of Global Warming on the UK suggested that extreme storms and other weather events could result in a fall of 1% in the UK’s GDP.

The worst UK storm in nearly 300 years hit the southern part of England in October 1987. The storm began on the 15th October as an embryo depression in the Bay of Biscay marking a front between very warm Tm air and very cold Pm air. On the evening of the 15th October, the low pressure centred over the Bay of Biscay had begun to unexpectedly deepen. The  deepening of the depression was thought to be due to an exceptionally strong jet stream (linked to Hurricane Floyd on the East coast of North America) and aided by unstable air over the extremely warm waters of the Bay of Biscay.

960mn pressure by midnight & dropped by 20mb - steep pressure gradient leads to strong winds 

however, storm veered NE at midnight on 15th Ot. people couldn't be warned

S. West of France LP weather system 

Pg 71 for map and annotations

• 15 million trees are thought to have been blown down or severly damaged (97% trees lost in woodland)
• Broadleaf trees were particularly badly hit, with the equivalement of 2 yrs of UK production destroyed
• In the SE millions were terrified by the high wind speeds and the extent of the structural damage
• Non-native trees were hard hit and important scientific speciments were lost incl. several at Kew and Ventnor
• Orchards in Kent and Essex were devastated, incl. some with rare traditional English species
• Tree damage was frequently caused by snapping in coniferous species but many broadleaf trees were uprooted (the fate of six of the seven oak trees at Sevenoaks). The frequency of uprooting was caused by the heavy rainfall during the weeks before the storm which had saturated the ground giving support roots less grip and greater lubrication.

• Broadleef trees were badly hit, with 2 years of UK production destroyed
• Power cables and pylons damaged by the wind and by falling trees which cut electricity to widespread areas. The Underground was brought to a halt. 
• For 2 days the employed population struggled to get to work; many factories and offices were forced to close temporarily.
• Roads and rail services throughout the South, South East and East Anglia were paralysed by fallen trees
• Shipping in the Channel came to a standstill and the port of Dover closed for the 1st time in the 20th centure. cross channel services were suspended. 
• The 'forced' release of large volumes of timber onto the market stimulated carpentry and reduced the price of temperature hardwoods.

• 18 people were killed as a DIRECT result of storm. peak wind velocities were in the early hours of the morning
• houses and cars were damaged throughout the South and South East. £1.4 billion insurance costs
• Schools were closed, with 30 damaged by falling trees
• The London Fire Brigade dealth with 6000 calls in 24 hours

• Time of storm - everyone asleep at midnight bu this decreased death toll as people in houses safe
• Very LP - intensified winds - over 80mph-110mph winds 
• Direction - where it travelled to wasn't predictable before it hit
• Heavy storm surges in Devon and Cornwall meaning sea water flooded peoples homes
• High precipitation (40mm) means floods were caused
• Unexpected deepening of depression at Bay of Biscay. 970mb to 950mb
• Strong Jet Stream and also very warm waters off the Bay of Biscay
• High antecedent precipitation so trees easily taken out of the ground
• Flash flood - 18 people died and majority linked to dying due to flash flooding
• Storm moved quickly over S. England so potentially less damage caused by strong winds.

• MET office gave warning but technique was slow. Storm was unexpcted to public. However, didn't have super computers etc. so they couldn't predict properly
• High population density - hit London and so damage was higher to infrastructure, buildings etc. 
• Stronger buildings - MEDC so buildings didn't fully collpase
• Immediate response to storm - it was rapid. Fallen over trees chopped down, tried clear up debris, army on call 
• Public advised on 16th Oct to stay indoors and at home - helped limit further issues
• 1 in 300 yr event. So we aren't used to this - which is why MET office wasn't prepared. but now developed further, eg have supercomputers

The Met Office

During the evening of 15 October, radio and TV forecasts warned the public in the South and South east of England of bad weather but indicated heavy rain would be the main problem.

There was no mention of hurricane force winds. However, at 1.35am on 16th October, an emergency weather warning was issued to the Ministry of Defence. It warned that the anticipated consequences of the storm were such that civil authorities might need to call on assistance from the military. 

An internal inquiry into the event was held. The outcome involved broadening its observations of weather data into areas further south of the UK in the future.

By increasing the quality and quantity of observations from ships, aircraft, buoys and satellites they would be able to improve their ability to predict storm tracks more accurately

The emergency services

Fire services, police etc were informed by the Met Office to prepare for a severe weather event. However, they were “overwhelmed” by the scale of the devastation.

Fallen trees closed roads and meant that they initially struggled to reach those injured or trapped. Many staff could not make it to work. 

In the clear up process, Thames Water had its staff working around the clock with overtime opportunities.

The risk of flooding was high due to the trees blocking the rivers, especially at bridges and culverts. Staff were given extra training in tree surgery and given a free rein to “go and clear the rivers”.

Recent research shows that the rush to “clear up” was overzealous, and not enough consideration was given to the “habitat potential” of the areas

the goverment

Task Force Trees (TFT) set and given a £6million for new tree “amenity planting” (it was wound up in 1994). Local Authorities were also given money to create new departments to look after trees. As a result there are now 7500 active Tree Wardens working for local Authorities across the UK

individuals

Many people went to bed the night before the storm not realising that there would be hurricane force winds hitting the south and south east of England the next morning.

During the clear up process, anyone with a chainsaw could now make money and the clear-up spawned a number of new “tree surgery” companies, some still going today (e.g. Angry Beaver Tree Surgery” in Surrey) 

Large urban areas can play an important role in modifying the climate, creating their own "microclimates"

Urban areas compared to rural 

• Sunshine duration: 5-15% less
• Annual mean temp: 0.5 to 1.0deg higher
• Temp on sunny days: 2-6deg more
• Occurrence frosts: 2-3weeks fewer
• Total precipitation: 5-10% more
• Number of rain days: 10% more
• Number of days with snow: 14% fewer
• Cloud cover: 5-10% more

THE URBAN HEAT ISLAND EFFECT

Urban areas tend to be warmer than the surrounding rural areas and the degree to which this is trie is proportional to the size and density of the urban area. In large cities such as London, LA, NYC, the impact can be as great as an 11deg increase in max temp.

• Heat comes from industries, buildings and vehicles, which all burn fuel. Air conditioning units release hot air into the atmosphere. Even people generate heat and cities contain large populations in a small space.
• More cloud because more condensation nuclei due to sutt particles etc.
• Air pollution from industries and vehiles increases cloud cover and creates a pollution dome which allows in short wave radiation as well as reflecting it back to the surface
• Building materials such as concrete, brick and tarmac (lower albedo) act like bare rock surface, absoring large quantities of heat during the day. This heat is stored and released during the night. Some urban surface, especially buildings with big windows have high reflective capacity and multi stori buildings concentrate the heating effect in the surrounding streets by reflecting energy downwards.
• Water falling on surface is disposed of quickly as possible (evapotranspiration involves absorbing latent heat due to drains. less evapotranspiration = less heat removed from atmosphere so increased temp. Changes heat budge and moisture - less evapotranspiration = more energy available to heat atmosphere.

Change over time (temporal)

What are the diurnal (day to night) changes in temp: Daytime temp on average 0.6deg higher and night time temps may be 3-4deg higher as dust and cloud act like a blanketto reduce radiation and buildings give out heat like storage radiators - buildings have high thermal capacity.

What are the seasonal variations in temp: Mean winter temp is 1-2deg higher (rural areas are even colder when snow covered as higher albedo=cooler surface). The mean summer temp may be 5deg higher due to stronger insolation. The mean annual temp is higher between 0.6deg in Chicago and 1.3deg in London compared with that of the surrounding area.

Change over space (areal or spatial changes):

What effect do park areas have: Cooler temp, no buildings so no electricity, have higher albedo (more UV reflectected - grass is lighter than tarmac). More evapotranspiration - latent heat is absorbed (removing heat energy from atmosphere) = lower temp. Exposed and windier = lower temp.

Wind lowers temps slightly. Wind velocity is usually lower in urban areas (so warmer)

Rate of change of temp across London from the map (pg 80):

Steep temp (lines closer together) = rapid changes in temp over short distance eg urban,park,rivers

Temp plateau = gradual change in temp over long distance - gentle temp gradient eg acros suburban areas, across CBD.

Abrupt change in temp further out from CBS = less built up and more open = heat escapes

Majority of urban area has steep temp gradient = less buildings etc, more open space

CBD highest temp - more buildings absorb heat due to dark surface, traffic people etc = lower albedo

As with temp, precipitation levels tend to be higher in urban areas than surrounding.

As air rises, it expands and cools, condensation takes place. This condensation occurs on particles of dust, salt or pollutants (eg carbon diesel engines) and this creates clouds and ultimately precipitation.

• Dark surface = more ground heating = more air rises = more rai. It is warmer due o urban heat island affect - war air which is unstable
• Get convectional rainfall  - due to ground heating (heavy bursts of rain sometimes thunder)
• Polluted air - industrial emissions results in moist air - so contains water vapour. Results in lots of condensation nuclei (eg dust, sutt particles) so encourages condensation
• Tall/large buildings - air converges so air forced up. Encourages uplift of air. 

• Convectional rainfall is more frequent in urban areas (stronger uplift of air)
• There may be a higher incidence of thunder and lightning in urban areas (linked to convectional rainfall)
• Lightning is a violent electric spark between the clouds and the ground. violent air currents blow droplets of water and ice crystals up and down inside towering cb clouds. static electricity is created in the clouds as these water droplets/ice crystals crash into one another. Thunder is the noise heard as a result of the violent expansion of the air around lightning.
• Hail is formed when ice crystals repeatedly melt and refreeze by being blown up and down in cb clouds.
• the higher urban temps may turn the snow of rural areas into sleep. urban areas also have days with snow lying on the ground.
• london (also la,mexico city, athens etc) suffer from a higher incidience of fog because they are located within a basin, surrounded by higher land, especially under anticyclonic conditions. 

Summary of how radiation fog forms in anticylonic conditions (pg 83)

1) Fog develops overnight due to IR heat loss under clear skies - becomes v.cold

2) Air cools more quickly on upper slopes, becomes dense and moves downslope into the basin (where london is)

3) Forces warm air upwards creating a temp inversion 

4) The cold mosit air in the basin now condenses at dew point temp to form radiation fog.

Closely related to fog, smog (smoke and fog) has been synonymous with major cities since the industrial revolution

Smogs were common in many British cities in the late 19th and early 20th centuries, when deomestic fires, industrial furnaces and steam trains were all emitting smoke and other hygroscopic pollutants by burning fossil fuels. the smogs were worse during winter months and when temperature inversions built up under high pressure, causing the pollutants to become trapped in the lower atmosphere and for water vapour to condense around these particles.

In London, the issue came to a head in 1952..

CASE STUDY: THE GREAT LONDON SMOG, DECEMBER 1952

• Cause: Anticyclone conditions resulted in radiation fog forming. Cold conditions at ground level, so water kept condensing and fog got thicker and thicker.
• Effect: The air was dark, tinged with yellow and smelt like rotten eggs (due to sulphur dioxide); smog caused breathing problems and choking; the anticyclonic conditions trapped the polluted air over london (as air was sinking) and no wind; lasted 5 days (5th-9th dec);12,000 died due to respiratory diseases like bronchitis, 4000 deaths, in 1962, 750 londonders died from another smog event
• Response: govt. introduced the clean air act in 1956 which phased out the use of coal in homes. also chimney height increased - so above temp inversion. 

Photochemical smog is now occurring in some urban areas. people are experiencing breathing problems and asthma attacks. this smog needs a lot of sunshine.

In LA air pollution is very high, caused by:-

• relief of LA basin. there is often a temp inversion which traps the pollution
• there is a high number of vehicles with exhaust gases being pumped out
• the bright sun reacts with the trapped pollutants (nox and hydrocarbons in vehile exhaust gases to form ozone). this turns fog into a photochemical SMOG. It happens most afternoons in Summer and results in a brown haze hanging over the LA basin so that it is impossible to see across the city.
• Impact: local residents in LA suffer the same amount of lung damage as someone who smokes 10 cigs per day. 

pg 86 for diagram

Solutions to particulate pollution and photochemical smog in urban areas

Despite the continued growth of most cities, the smog problems in many MEDCs has relented over the last 30yrs, for example, by reducing car emissions.

Attempted solutions to the smog problem in L.A. (up to 1999).

• pollution controls in cars - began in 1965 and since made tighter (eg caalytic converters)
• federal clean air act 1970 - industries must control pollution output
• some attempt to limit the number of cars on the road on high smog alert days - given by local radios. companies can be fined if their car parks are full on those days. car pooling encouraged instead.
• local residents are encouraged to stay indoors on high smog alert days.

Synoptic link (from energy AS)

BIOFUELS IN BRAZIL

• cars use ethanol - fermentation of sugar cane
• use flex cars
• reduced car emissions in sao paulo by 25%

MEXICO CITY

• no driving today scheme - certain number plates can't drive on certain days. however some had 2 cars and got around it.

Clean Air Act, UK - 1956

The Great London Smog led o the clean air act and drive for smokeless coal. a later clean air act introduced the use of taller chimneys (higher than temp inversion) which allowed the pollution from coal combustion to be released higher into the atmosphere (but this then led to acid deposition issues for scandinavia)

• Congestion charges - London congestion charge was introduced in 2003 and has charged drivers £8 a day to drive in the Central London Congestion Zone. the scheme was introduced because London had the UK's worst traffic congestion. In theory the congestion charge should encourage people to make more use of public transport, which is cheaper and more fuel efficient. the income from the congestion charge has been used to replace or upgrade every vehicle in the fleet of London buses. the positive effects: reduced traffic by 15%, bus passanger numbers have increased and cyclists . cut congestion by 30%. reduced NOx and CO2 emissions by 12%
• Park and ride schemes - car sharing schemes. car parks on public transport routes to make it easier to use public transport (eg York)
• Lane restrictions  - bus only lanes into city centres, make it faster for buses so more people take bus to avoid traffic jams
• Public transport improvements - Trying to persuage people use public transport instead of cats. eg manchesters development of a tram system (metrolink) - taken 3million cars off the road
• Planning for industry - industry has been located downwind of cities if at all possible and planning legalisaion has forced companies to build higher factory chimneys to emit pollutants above the inversion layer.
• boris' bicycles in London - borris johnson has launched a city wide cycle hire scheme. designed for short journeys and first 30 mins are free. Barclay Bank has provided £25mill of sponsorship and the scheme is set to expand to 20,000 bikes.

This is another climatic change caused by urban areas. When an uniterrupted wind reaches an urban area and strikes the buildings, it will inevitably be deflected over and around the obstacle.

1. The main effect in urban areas is a reduction in mean wind speed

The surface area of cities is very uneven due to the varying height of the buildings. Buildings create frictional frag so average wind speeds are lower in cities than the surrounding areas. wind speeds are also lower in city centres than in suburbs. buildings will also slow don wind speed creating shelter on the leeward (falling) side of buildings.

2. Winds are affected by the shape and size of buildings (pg 89 for diagram and pg 90)

Movement of air over and around a building:

Building is in the way so creates eddies (swirling around) and vortacies. this creates a steeper pressure gradient so has local gusts of winds.

on the windward side (rising side), HP results in strong uplift of air so that air flow is increased over the top of the building but also displaced around the sides of buildings in the form of strong vortacies and eddies which swirl up litter and make walking along the pavements difficult

Why do industrial chimneys (stacks) need to be substantially taller than the surrounding buildings: pollutants could get trapped in air flow and descend down to street level of leeward side of building. Bad for residents health. E.G. in Glossop - Aluminium caused Alzheimers so built chimney higher

CASE STUDY OF BUILDING DESIGN - Leeds' Bridgewater Place gets new high wind road band.

Gusts of wind around the Bridgewater Place building in Leeds were blamed by a coroner for blowing over a lorry that crushed Dr.Edward Slaney in 2011. The inquest into his death heard the area around the tower had become known for strong winds since it was completed in 2007. Proposals would see large screens and baffle boards to deflect the wind - up to 50ft (17m) high and 66ft (20m) long -built near the building and above the road. Wind acceleration around the sides of buildings.

• Bridgewater Place owner CPPI wants to put up screens and boards to deflect the wind
• Initial proposals to protect the public from dangerous winds around the building were unveiled before Leeds City Council's Plans Panel
• Future plants to prevent: plans for 3 vertical screens and glass canopy on building also revealedpedestrians and traffic will be barred from a road junction near yorkshires tallest building when wind speeds reach 45mph, a council has said.

3. Airflow affected by spacing of building

when high rise buildings are close together, they can channel air into the canyons between them creating areas of higher pressure. winds in such places can be so powerful that they make buildings sway and knock pedestrians off their feet. This is called the "Venturi effect" (air flow concentrated between 2 buildings)

(pg 92 for sketch map)

2 buildings located close together can cause chanelling of the airflow between the buildings resulting in high wind speeds. the chanelling of the wind is called venturi effect. 

Urban climates and global warming

During summer months in an urban area, the increased use of air conditioning and refrigeration needed to cool indoor spaces causes a positive feedback into global warming. :

Urban heat island effect = increased use of air con and fridges in summer = increase in electricity consumption = burning more fossil fiels in power stations = increase in co2, nox and ch4 = more IR trapped = EGHE (0.85 increase since 1880's)

Rapid industrialisation : 10% increase in GDP p.a. since 1990s

Rapid urbanisation : x3 increase in no. of millionaire cities since 1990s

Global effect : Burning of fossil fuels = increased GGE (co2,ch4,nox,cfcs)

Pop increase : Pop increase by 0.9% p.a. worlds largest pop at 1.3 billion

Local effect: UHI effect more pronounced, increase in rainfall, more photochemical smog, decreased wind speed (bigger urban area, he bigger the differeence between urban and rural)

National effect: increased levels of energy consumptions + increased pollutants and increased traffic (burn high levels of high sulphur coal in china) = levels of nox and so2 = acid deposition (wet/dry deposition)