CUE - Urban Climates

Question 1

Urban climate

Answer 1

A set of climatic conditions that prevail in a large metropolitan area which differ from the climate of the rural surroundings

Question 2

Albedo

Answer 2

The reflectivity of a surface- the amount of incoming insolation that is absorbed and reflected back

Darker surfaces have a lower albedo

Question 3

Insolation

Answer 3

Solar radiation

Question 4

Anticyclonic

Answer 4

High atmospheric pressure - dry, calm conditions

Summer - heatwave
Winter - cold and clear

Question 5

Condensation nuclei

Answer 5

Water-attracting particles e.g dust in the atmosphere around which raindrops can form condensation nuclei

Question 6

Micoclimate

Answer 6

Small-scale variations in temperature, precipitation, humity, wind speed and evapouration that occur in a particular environment

Question 7

Urban dome

Answer 7

The urban microclimate within which the weather is different fom the surrounding rural area

Two levels to the dome, the Urban Canopy and the Urban Boundary

Question 8

Particulates

Answer 8

Microscopic matter in the air e.g PM10 - exhaust fumes, ash, cement dust

Question 9

Photochemical pollution

Answer 9

A form of air pollution that occurs mainly in cities - can be dangerous to health

Exhaust fues become trapped by temperature inversions and react with sunlight to form low-level ozone

Question 10

Temperature inversions

Answer 10

An atmospheric condition where a layer of warm air lays on top of colder air underneath

This does not allow convection so pollution becomes trapped in the lower layer of the atmosphere around the city

Question 11

The urban heat island effect

Answer 11

The zone around and above cities that has higher temperatures than the surrounding rural areas

Question 12

Isotherm

Answer 12

A line joining places wth equal temperatures

Question 13

Chanelling

Answer 13

Wind redirected down long, straight canyon-like streets where there is less friction

Sometimes referred to as urban canyons

Question 14

What causes the urban heat island effect?

Answer 14

Urban surfaces have a lower albedo so absorb more insolation which is released slowly when the air cools at night

Effective urban drainage removes surface water quickly so less evapouration takes place (has a cooling effect)

There is less vegetation for evapotranspiration (has a cooling effect)

Anthropogenic heat sources e.g heating systems, machines, cars and industrial processes

Question 15

Why are precipitation and storms more frequent and intense in urban areas?

Answer 15

Urban areas have up to 10% more rainfall than surrounding areas

The urban heat island effect causes low atmospheric pressure and convectional uplift -> convectional rainfall

Particulate pollution means more condensation nuclei present in the urban air

Question 16

Why is humidity less frequent in urban areas?

Answer 16

More rapid runoff of water
Less evapotranspiration
Less bodies of water

Question 17

Why is fog more frequent in urban areas?

Answer 17

Greater concentration of airborn particulates that act as condensation nuclei

Question 18

Why are thunderstorms more frequent and intense in urban areas?

Answer 18

In urban areas the liklihood of thunderstorms is 25%

Low pressure caused by convectional uplift form tall cumulonimbus clouds

Rising heat, water vapour and particulates creates intense rainfall and thunderstorms

During condensation, latent heat is released that fuels convectional uplift. Raindrops are split in the uplift creating a positive electrical charge which forms lightning

Question 19

What are the wind speeds like in urban areas?

Answer 19

Average wind speeds are lower in cities than surrounding areas as the buildings exert a powerful frictional drag on the moving air creating turbulence (rapid changes in wind speed and direction)

Average wind speeds can also be high as high rise buildings can channel air into the ‘canyons’ between them to create the Venturi effect so gusts of wind are stronger

Question 20

How can a single building modify the flow of air passing over it?

Answer 20

Air is displaced upwards and around the sides of the building

the descending flow causes a vortex when it reaches the ground

Question 21

How can a group of buildings modify an airflow passing over them?

Answer 21

If the buildings are widely spaced the airflow ill be similar to that of a single building

If the buildings are close together the airflow is interrupted by the next strcuture so produces an unpredictable pattern of airflow

Question 22

What is air quality like in urban areas?

Answer 22

Key atmospheric pollutants are ozone, nitrogen dioxide, sulphur dioxide and particulate matter

Photochemical smog can be very harmful to people’s health e.g headaches, eye irritation and chest pain

Question 23

Give an atmospheric measure in urban areas

Answer 23

UK Clean Air Acts of 1956 and 1968 reduced domestic pollution by introducing smoke control areas and reduced industrial pollution with taller chimneys to disperse pollutants higher in the atmosphere

Question 24

Give a policy for vehicle control

Answer 24

Congestion charges in central London - people are charged if they use their vehicle in certain areas at certain times

Reduced traffic and emissions in the congestion zone by 15% in the first year

Question 25

Give a policy for public transport systems

Answer 25

Encouraging people to use public transport services instead of their cars to reduce pollution e.g improved bus services and park and ride schemes

e.g the Metrolink in Manchester which took over 2.5 millon cars off of the road

Question 26

How is photochemical smog formed?

Answer 26

Pollutants e.g nitrous oxides and hydrocarbons trapped in the lower atmosphere by temperature inversions comes into contact with sunlight and the UV rays break them down into ozone which can produce harmful photochemical smog