
Urban heat island - onetimemanytime
https://en.wikipedia.org/wiki/Urban_heat_island
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gavia1
London is regularly 3-4° warmer than the towns and village that border the M25
ring road. You can genuinely feel the difference when you take a train into
the city and vice versa.

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quickthrower2
Is that allowing for the time difference between when you get on and get off
the train affecting the temperature?

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gavia1
Absolutely. If you so wish you can take the train at noon and get off at 12:30
where any temperature difference due to the sun should be minimal.

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majewsky
Not terribly relevant to your point, but: Noon is actually a time in the day
where it is still getting warmer. Temperature usually peaks around 16:00 or
17:00 in the summer.

Example:
[http://wetterstationen.meteomedia.de/?station=104870&wahl=vo...](http://wetterstationen.meteomedia.de/?station=104870&wahl=vorhersage)
(the forecast diagram for my local weather station)

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onetimemanytime
any idea why? The ground starts releasing accumulated energy or what?

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gavia1
It probably reaches saturation at that time of day where it can no longer
absorb anymore heat.

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Uhhrrr
From the article: 'If the urban heat island theory is correct then instruments
should have recorded a bigger temperature rise for calm nights than for windy
ones, because wind blows excess heat away from cities and away from the
measuring instruments. There was no difference between the calm and windy
nights, and one study said that "we show that, globally, temperatures over
land have risen as much on windy nights as on calm nights, indicating that the
observed overall warming is not a consequence of urban development."'

This is really surprising to me. Not least because, on a sunny day, SF can go
from pleasant to brutal as soon as a breeze kicks up.

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Albertchrist
Not only in US. This is applicable to all the major cities in the world.

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ccheath
isn't this also (at least partly) why cities are less likely to be affected by
tornadoes?

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eesmith
Quoting the link:

> Research has been done in a few areas suggesting that metropolitan areas are
> less susceptible to weak tornadoes due to the turbulent mixing caused by the
> warmth of the urban heat island.

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haunter
So every big city pretty much

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quickthrower2
Sydney is one of those.

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H8crilA
Aren't all cities one of those? Bigger=bigger impact.

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quickthrower2
I think it has quite an effect in the summer because the city is cooled by
being near the ocean but the western suburbs get super hot, so a 10 degree
difference might not be unusual at times, for two places about 30km away.

