Seasonal Warming trends

Winter months in the Northern Hemisphere are responsible for most of the observed land warming in CRUTEM4.  The summer months (June, July, August, September) essentially show no warming at all from 1850 to 1990. Overall,  NH winters have warmed about twice as much as  NH summers.

Winter is the average anomaly for Nov,Dec,Jan,Feb. Summer for June,July,August,September

Winter(blue) is the average anomaly for Nov,Dec,Jan,Feb. Summer(red) for June,July,August,September

The same exercise for the southern hemisphere shows very little difference where of course the seasonal months  are inverted. So why is the NH different and why?

SH-compare-summer-winter

Summer(blue)  is (Nov,Dec,Jan,Feb) whereas Winter(red) is (June,July,August,September)

The SH is dominated by oceans and the coverage before 1900 was very poor.  The SH is also sparsely populated having less human impact on the environment than the NH. Clearly the NH effect is real and shows that the seasonal variation in temperature between summer and winter has reduced for some reason since the 19th century. This reduction is mostly due to an increase in minimum winter temperatures rather than maximum summer temperatures.

This story  is reminiscient of  the observed reduction in the Diurnal Temperature Range (DTR).  Several papers have shown  that most ‘global warming’ has occured through an increase in minimum night-time temperatures rather than any increase in maximum daytime temperatures. Could there be an anthropogenic cause for both effects?

Perhaps an increase in winter clouds reduces  winter heat loss, thereby reducing extreme cold temperatures. Could perhaps  coal burning for indudstry and domestic heating prior to 1960 be partly responsible?

Is the slow increase in solar activity over the 20th century to blame? An increase in solar activity leads to a higher flux of UV producing more stratospheric ozone. This warms the stratosphere transfering heat to the dark polar  winter as the lapse rate collapses. Could a new Maunder like solar minima bring back freezing winters to the NH?

Any other ideas?

Posted in AGW, Climate Change, Physics, UK Met Office | Tagged | 9 Comments

Did an arriving ‘Dreamliner’ cause July’s record temperature at Heathrow ?

I have looked in detail at aircraft landing data for the North Runway on July 1st to try to answer the following question. Was the heat pulse that produced the record breaking July temperature at Heathrow due to an aircraft, or was it due to a break in the clouds? The balance of evidence is that it was likely caused by the hot exhausts from an arriving China Southern B787 Dreamliner taxiing past the Met station on its way to terminal 4, then exacerbated by a 10 knot SE wind.

CZ303 landing from the West to the North Runway was the only arrival to terminal 4 during this period.

CZ303 landing from the West to the North Runway was the only arrival to terminal 4 during this period. (click to expand)

Shown below is the landing data (thanks to Dave Ward). All times are now in GMT in agreement with the Met data. The flight data in the previous post was wrong – it was in CET!

Flight no. Plane Terminal Time
CX257 B777 3 1404
PK785 B777 3 1406
BA038 B747 5 1408
CZ303 B788 4 1409
TK1985 A330 3 1411
BA272 B777 5 1413
BA274 B747 5 1415
BA775 A320 5 1416
BA905 A319 5 1418

The graph below shows the landing data on the North Runway compared to the recorded temperatures. Smaller jets exit early to reach terminals 1,2,3,5. Larger jets travel further down the runway but still exit lower down in order to also reach terminals 1,2,3 & 5. Only CZ303 will have exited late to reach terminal 4. The 787 also has two of the world’s most powerful Jet engines.

Comparison of Hetahrow temperaure measurements with arriving aircraft graded by size. 747=5 units, 787=4 , 777=3, A320=1. CZ303 = 7

Comparison of Hetahrow temperaure measurements (red) with arriving aircraft graded by size. 747=5 units, 787=4 , 777=3, A320=1. CZ303 = 7. The Kew station data is shown in blue for comparison.

The alternative explanation for the heat pulse is that it was due to a break in clouds increasing solar radiation. This is shown below.

Compare Heathrow, Kew temperatures to solar radiation measurements.

Compare Heathrow, Kew temperatures to solar radiation measurements. Red is Heathrow and Blue is Kew. The relevant solar radiation data is shown by the red/blue histograms

There was indeed an increase in solar radiation at Heathrow coincident with the temperature peak, but if this was the cause then why did a similar increase 30 minutes later produced no response at all. The Kew station shows a much  slower response to changing solar radiation. Stephensen screens are also supposed to shield thermometers from the sun and allow air mixing. Therefore the solar radiation explanation is in my opinion inconsistent.

I think it is more likely that CZ303 was the real cause.

Posted in Institiutions, Meteorology, Science, UK Met Office | Tagged | 9 Comments

That Heathrow temperature record ?

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 record was broken during a heat spike that occured between 14:06 and 14:30

The record was broken during a heat spike that occured between 14:06 and 14:30

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.

Location of the Met Office weather station at Heathrow is shown by the orange icon. The blue arrow shows the wind direction from the SE.

Location of the Met Office weather station at Heathrow is shown by the orange icon. The blue arrow shows the wind direction from the SE.

 

A BA 747-400 originating from San Francisco, a BA 777 from Tokyo and an Etihan A380

Heathrow wind speed July 1st

Heathrow wind speed July 1st

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.

BA 747-400 lands from San Francisco

BA 747-400 lands from San Francisco

Etihad A380 lands on North Runway

Etihad A380 lands on North Runway

Heathrow 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 !

Posted in Meteorology, UK Met Office | Tagged | 43 Comments