The record highest ever recorded July temperature by the Met Office at Heathrow Airport was given huge media coverage. The record was broken during one single heat spike that lasted just over 20 minutes between 14:06 and 14:30. What caused that heat spike? Mark McCarthy argues it was due to a break in clouds, and refutes Paul Homewood’s proposal that a change in wind direction sucked in hot Jet exhausts . However Mark doesn’t explain why a similar sun burst just 30 minutes later produced no temperature response whatsoever. He instead writes : “In this instance there is no compelling evidence to suggest the measurement is incorrect”. I disagree. There is compelling evidence that such a sharp temperature peak lasting just 20 minutes was actually caused by 3 long haul flights landing in quick succession, then exacerbated by the SE wind direction and late runway exits.
The weather station is located on the northern border of Heathrow just beyond the North Runway. On July 1st the North runway was being used for landing aircraft arriving from the west because there was an increasing 4 m/s SE wind. This wind was also blowing directly up a major exit runway lane directly pointing towards the Met station.
A BA 747-400 originating from San Francisco, a BA 777 from Tokyo and an Etihan A380
superjumbo all landed within minutes of each other between ~ 14:00 and ~14:30 on July 1. Smaller aircraft normally exit well before they reach that exit, but large heavy aircraft need far more runway to stop. They must exit directly alongside the Met station, and as they turn SE towards the terminals their Jet engines accelerate thereby pumping hot exhausts directly towards the Stephensen screen. The wind directon on July 1 ensured that those hot gases reached the station. This, in my opinion, is a far more likely explanation for the sudden spike in temperature rather than any short sunny spell. Timings on plots shown below confirming this are approximate C/O Plane Finder on July 1.
is neither a registered WMO station nor is it is not one of the ~7300 stations included in CRUTEM4, NCDC GHCN V3 analysis. I am pretty well convinced that the Met Office made a mistake on this one. Did their zeal to find a record July temperature anywhere cloud their judgement? Heathrow was bound to be contentious because it is one of the world’s busiest and most compact airports. The ‘heat wave’ only lasted one single day so who really cares anyway? On balance I think Paul Homeward was more likely than not correct in his original analysis.
Correction: Heathrow is a WMO registered site and in CRUTEM4 !