An example of this is in London which has a very dense population in the town centre with lots of pollution and smoke from cars and industries surrounding the town centre. Winds in an urban microclimates are affected by it surroundings.
Urban areas are said to be urban heat islands as under calm conditions, temperatures are highest in the built up city centre and decrease towards the suburbs and countryside.
Humidity is another part of the climate, which is affected by the temperature of the air. This pollution dome allows short-wave insolation to enter, but traps outgoing terrestrial radiation due to its longer wavelength, therefore increasing the amount of heat obtained.
High pressure conditions create calm country breezes which move from colder rural areas to warmer urban area. An urban area is an area with a high density of human created structures in comparison with the areas surrounding it. Climate on a local scale: The reason for this is because convection currents are generated by the higher temperatures of the urban microclimates and so there is a larger number of condensation nuclei which will therefore form more clouds.
Due to these reasons, the mean winter temperatures are on average degrees Celsius higher in urban areas, in comparison to rural areas. This causes there to be more cloud cover over urban areas, and they receive thicker and up to ten per cent more frequent cloud cover than that compared to rural areas.
The spacing of buildings can also affect winds. Further heat is given off by the presence of factories and increased car use within the city, causing pollution which causes smog and a pollution dome to form.
Chicago is nick named the windy city due to its grid system of buildings creating wind tunnels where the wind can pick up speed.
The increase or decrease in amount of cloud cover can directly impact the precipitation levels in urban areas. Closely spaced buildings work together with each other creating more friction drag causing winds to skim over the top and eddy in between them.
In urban areas, the building materials are non-reflective and therefore absorb heat. Whereas, London on the outer suburbs has only 46 hours, and south east England the mean of 7 weather stations has 20 hours.
Climate is the long term behaviour of the atmosphere in a specific area, with characteristics such as temperature, pressure, wind, precipitation, cloud cover and humidity etc.
The general pattern is that winds decrease in urban areas than in suburbs or rural areas. Pollutants in the air in urban environments create more cloud cover and precipitation, giving higher temperatures and reduced sunlight.
These clouds which are formed will cause more heat to be trapped so the temperatures will be raised even more, particularly during the day and at night they prevent solar radiation from entering the city so in extreme winters the urban area may be slightly colder.
Pressure gradients are set up between the windward and leeward side of buildings which causes severe eddying of the winds. The large amount of condensation nuclei in the air is due to the large quantities of gaseous and solid impurities which are emitted into the environment by activities such as the burning fossil fuels by industrial processes and from car exhausts.
For example, Kew in the middle suburbs of London has 79 hours of very dense fog, with visibility being less than 40metres.
The speed of winds is lower in altitudes in built up areas are slower because winds are deflected over high buildings. Strong pressure gradients develop between the windward and leeward side of buildings and can lead to severe eddying winds.Urban areas climate is often significantly different to the surrounding rural areas, this is why urban areas are often described as having their own “micro climate” the differences in urban climates are due to number of different factors.
Describes how variables (temperature, precipitation etc.) differ in urban areas Reasons to explain why this is the case Included case study Explains how it can change for different cities at different times.
To what extent do urban areas create their own climate (40 Marks) An urban area is the region surrounding a city. Jobs are those in a non-agricultural field, making urban areas very developed causing a high density of human structures such as houses, buildings, and transport links.
To what extent do urban areas modify their climate?
Climates can vary a great deal between a large urban area and the surrounding countryside. Urban climates are known to have their own ‘micro climates’ as they are significantly different to the rural areas.
Amelia Scotney ‘To what extent do urban areas modify their climate?’ – 40 marks. Cities create their own microclimates and their sites are almost always warmer, compared to a nearby rural location, than if the city were not there.
Essay from June (AQA) - To what extent to urban areas modify their climate? For each section you will need to: 1. Describe how that variable differs in urban areas.
2. Explain why that is the case and try to include a brief named case study. BBC information about Urban Microclimates. BBC information about urban heat islands.Download