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Physical Geography A-level > Weather in cities > Flashcards

Weather in cities Flashcards

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1
Q

Temperature in cities

A
  • buildings retain and release heat more strongly than in rural areas
  • temperatures are higher
  • tarmac surfaces are heated intensely and then strongly heat the air above it
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2
Q

Winds in cities

A
  • winds can be channelled between high-rise buildings increasing velocities
  • buildings also act as windbreaks, reducing velocities
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3
Q

Sunlight in cities

A
  • actual sunlight amounts are lower
  • high-rise buildings block out light
  • high amounts of dust reflect and absorb sunlight
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4
Q

Precipitation in cities

A
  • greater amounts than in other locations

- concentrate surfaces lead to convection currents and cloud formation

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5
Q

Humidity in cities

A

-lower in urban areas as higher temperatures can hold greater amounts of water vapour

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6
Q

Clouds in cities

A

-thicker and more frequent

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7
Q

The percentage of reflected insolation is…

A

1.9 per cent in rural and 0.4 per cent in urban areas(a lot of is absorbed).

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8
Q

Anthropogenic heat is…

A

heat released by human activity(driving, industry). Some cities in colder areas can release more heat from human activity than the area receives from the sun.

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9
Q

The percentage of outgoing infrared is…

A

8.5 per cent in rural and 10.3 per cent in urban areas.

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10
Q

Outgoing infrared is also called…

A

terrestrial radiation.

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11
Q

The percentage of storage heat is…

A

0.3 per cent in rural and 1.3 in urban areas.

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12
Q

Asphalt albedo

A

5-20 per cent

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13
Q

Concentrate albedo

A

10-35 per cent

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14
Q

White paint

A

50-90 per cent

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15
Q

Coloured paint

A

15-35 per cent

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16
Q

Grass albedo

A

25-30 per cent

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17
Q

The percentage heat loss due evaporation is

A

24 per cent in rural and 1 per cent in urban areas(water is stored mainly underground)

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18
Q

The percentage of heat given up by the ground at night is…

A

twice the amount as in the rural areas.

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19
Q

There is temperature…

A

inversion in urban areas at some point. (ground is colder than the air above)

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20
Q

In which ways the urban area modifies the climate?

A
  • wind speeds
  • temperature
  • clouds and precipitation
  • pollution
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21
Q

The greater the urban area…

A

the greater the modification of a climate will be.

22
Q

Winds in urban areas are modified:

A
  • lower speeds
  • greater variability
  • large-scale convection
23
Q

Winds lower speeds

A
  • have lower wind speeds on average per cent less in the city centre
  • due to the roughness of the land surface(different heights of buildings), which increases the surface friction
24
Q

Greater variability of winds in urban areas

A
  • due to layout and height of the buildings
  • urban canyons
  • venturi effect
25
Q

Urban canyons

A

Straight streets lined with tall buildings can produce it. This funnel wind down them producing high velocities thanks to the venturi effect.

26
Q

Venturi effect

A

It is the effect of squeezing the airflow, increased as the buildings tend to get taller towards the city centre.

27
Q

The highest pressure is experienced in…

A

the upper part of the building.

28
Q

Building shape and spacing all affect…

A

the behaviour of the wind.

29
Q

Densely packed buildings allow…

A

air to move over the top, leaving the lower urban canopy layer relatively without turbulence.

30
Q

If no mixing by turbulence occurs…

A

then the pollutants at street level cannot be flushed away, causing smog situations.

31
Q

Large-scale convections

A

The heat island effect also produces large-scale convection and uplift over the whole urban area, leading to lowering the pressure. Air is drawn in from surrounding areas.

32
Q

The urban heat island is on average…

A

1-2 degrees warmer per year than surrounding area.

33
Q

The intensity of the urban heat island is…

A

the maximum difference between the temperature of the rural area and the peak urban temperature. Greater at night.

34
Q

High-pressure systems with clear nights and sunny days tend to…

A

increase the intensity.

35
Q

Heat islands are the result of:

A
  • anthropogenic heat
  • height and the arrangement of buildings
  • the nature of the building materials
  • the presence of water
  • pollutants
36
Q

Height and arrangements of buildings

A
  • tall buildings close together is the most important factor in generating urban heat island
  • more vertical surfaces so radiation tend to be reflected more
  • reduces the sky-view factor
37
Q

The sky-view factor is…

A

the amount of sky we can see without being impeded by a tall building.

38
Q

The sky-view factor tends to…

A

trap radiation, which reduces the chance of it escaping.

39
Q

In cities, there is a good chance of longwave radiation being…

A

intercepted by another surface and absorbed, reducing heat loss. The sky-view factor has a similar effect.

40
Q

Building height and arrangement is the key factor in creating urban heat islands as…

A

it is a way how the inputs and outputs of heat are controlled.

41
Q

Nature of building materials

A
  • the specific heat capacity of materials effects how much heat can be stored
  • e.g. concentrate will warm up more rapidly and store more heat than wet mud
42
Q

Most of the surplus heat in urban areas is lost as…

A

sensible heat, heating up the atmosphere.

43
Q

Vegetation shades…

A

the soil so that stores less heat.

44
Q

The presence of water

A
  • if there is little water at the surface, less surplus heat is lost as latent heat
  • cities have arrangements in the form of drains and sewers to remove surface water
  • twice as much heat is used in evaporation than used in sensible
45
Q

Presence of pollutants

A

-have both cooling and heating effect

46
Q

Sensible heat index gives…

A

the percentage of the total heat energy at the surface to raise the temperature of the air above. 85% in urban and 25% in rural.

47
Q

The presence of dust…

A

aerosols and gases can alter the amount of energy flowing in or out of the city.

48
Q

Smoky, dusty cities can reduce…

A

the amount of sunlight that reaches the city surface.

49
Q

Pollutant dome can absorb…

A

heat and prevent it from escaping. The build-up of ozone, CO2 and particulates help to absorb LW radiation and re-radiate it back.

50
Q

Clouds and precipitation

A
  • urban areas have 5-10% greater cloud cover

- due to a greater concentration of hygroscopic nuclei (100x more than in rural areas)

51
Q

Precipitation is more common in…

A

cities 5-30% more.

52
Q

Fog is less common in…

A

cities due to higher temperatures and a higher concentration of hygroscopic nuclei, forming smaller droplets, which tend to discourage the formation of which fogs.

Physical Geography A-level (33 decks)

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