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UHI At Heathrow Airport

October 10, 2015

By Paul Homewood 


Wansteadmeteo highlighted some odd differences between minimum temperatures at Heathrow and Northolt yesterday:


Paul: Further to your reservations on the temperature at Heathrow did you know that last night (early hours of the 9th) the minimum was 6.7C, while down the road at Northolt the minimum fell to 4.6C.
I recorded a minimum of 3C in my garden in Wanstead with a grass minimum of -2C! St James’s Park, 8.6 miles to my south-west, only fell to 7C.
It emphasises just how variable the climate of the capital is.

Heathrow and Northolt are only about seven miles apart, and in pretty similar surroundings. Northolt is about 14m higher, but other than that there is no geographical reason why temperatures should be different at all.

As we know, Heathrow is an extremely busy international airport, and the temperature sensor is only about a hundred yards from the main runway.

Northolt is also an airport, but an RAF one, which presumably is much less used.




According to the Ogimet website, which maintains a database of weather information from around the world, both Heathrow and Northolt experienced the same foggy conditions overnight, which seems to rule out cloud cover as the difference.

Ogimet, as well as confirming wansteadmeteo’s figures also give the last 30 days data.







From this, we can plot the daily differences in minimum temperature.




As we can see, minimum temperatures have been consistently much higher at Heathrow, averaging 1.01C.

This is a difference we do not see with maximum temperatures. Although Heathrow temperatures are slightly higher, it is only by 0.2C





This is just about as strong as you can get evidence that temperatures at Heathrow are heavily biased by the airport activities there.

As the comment points out, temperatures in London also seem to be biased to a similar extent by UHI.


Given the preponderance of airport and urban sites in GHCN, it once again raises the question of how much of the increases in temperature in the last century have been due to UHI.

  1. Joe Public permalink
    October 10, 2015 6:47 pm

    I’m unsure whether this immediately affects local early-morning temperatures, but here are no scheduled flights between 11pm and 4:30am.

    If the before-11pm flights do affect local temperatures, remember that the MetOffice claims that ” turbulence generated by passing aircraft would help mix the air close to the ground and so, is more likely to lower the air temperature rather than raise it.” (Their 15th July reply timed at 12:01 to Paul)

    • Kelvin Vaughan permalink
      October 11, 2015 6:13 pm

      I would think hot aircraft engines parked in the vicinity would radiate heat for a long time.

  2. Stephen permalink
    October 11, 2015 8:51 am

    Does anyone know how the global-mean temperature trend breaks down into daily T_max and T_min trends? Or any national/continental-scale breakdown rather than global mean?

  3. Stephen permalink
    October 11, 2015 9:22 am

    I found the following quote in Box 2.1 in following link:
    “Since the 1950s both daily maximum and minimum temperatures are available over more than 50% of the global land area. These data indicate that on average the mean minimum temperature has increased at nearly twice the rate of the maximum temperature, reducing the daily temperature range by about 0.4°C over these areas. ”
    They go on to assume that this is due to precip and cloud cover, no need to test further!

  4. NeilC permalink
    October 11, 2015 10:12 am

    I think a reason temperatures are different between the two places (Heathrow and Northolt) is the thermal qualities of concrete/tarmac and grass.

    Northholt has, apart from runways, stands and peritracks, a lot of grass, whereas Heathrow has very little grass and therefore retains heat more readily.

  5. Hivemind permalink
    October 11, 2015 10:34 am

    Canberra is build over three valleys (Belconnen, Civic and Woden). Each of the valleys receives different daily temperatures and also rainfall. So it isn’t surprising that a place as large as London has patterns within it’s weather.

    • A C Osborn permalink
      October 11, 2015 11:39 am

      Except London is pretty FLAT, apart from the Thames running through it there are very few physical changes to the terrain.

  6. Peter Duffy permalink
    October 11, 2015 10:42 am

    Northolt is in the SunTel today because it’s “unsafe”. The Queen’s Flight is based there, quite a lot of movements as it’s used by Ministers and senior officers. However, it’s main use is by private jets, and there’s a lot of activity. No idea if that influences the point you make about LHR being v busy, but Northolt’s not just silent grazing.

  7. A C Osborn permalink
    October 11, 2015 11:43 am

    Paul, how do they calculate the “Average” temp, it is obviously not (Max+Min)/2.
    It is also not Min + (Max-Min)/2.
    So do they have many values per day and average those?

    • October 11, 2015 12:15 pm

      It looks like it must be hourly then, but I can’t say for certain.

    • NeilC permalink
      October 11, 2015 1:08 pm

      Observations are taken 1/2 hourly at most lareger civil airports and 1 hourly at military bases and private airports.

      Max+Min/2 is very misleading as there can be, depending on airmass and timing big differences. For example, you can have 20 hourly readings in a warm setcor airmass and then a cold front goes through, and the temperature drops for the last 4 hours. The average would be quite a bit higher than max+min/2.

      The way I work out daily averges is 24 (hourly readings) Max + 24 (hourly readings) Min/2 which I think is the way the MO do it, but I may be wrong.

      • A C Osborn permalink
        October 11, 2015 1:22 pm

        I agree with you about Max + Min, but that is how it has been done for Global Temps for decades, although they use anomalies,TOBS, Pairing, Homogenising, Gridding and Krigging to confuse things.

  8. Dave Ward permalink
    October 12, 2015 8:57 pm

    Northolt may have “quite a lot of movements” but they will be of much smaller aircraft than typically use Heathrow. It only has a single runway 07/25 of 1,687m, compared to 09L/27R (3,902m) & 09R/27L (3,660m) at Heathrow, and this limits its availability to bizjets and smaller airliners such as the BAe 146 of the Queens flight. So the amount of heat generated will be a small fraction of that produced “down the road”. Having a single runway also precludes simultaneous landings and take-offs, as is normal at Heathrow.

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