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Weather Eye: cooling contrails

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11 May, The Times

On the morning of May 11, 1944, a bombing raid of 900 American aircraft took off from airfields across southeast England. Their mission was to bomb railway marshalling yards in France, ready for the D-Day invasion the following month, to prevent the Germans sending reinforcements to Normandy.

That morning 70 years ago was warm sunny, with hardly a cloud in the sky. But as the aircraft circled to assemble into their formations, they formed stunning contrails in the sky from their hot engine exhausts — something the pilots feared because it made their aircraft far easier to track and shoot down.

Recently, a study of the weather records at the time of that bomber raid has given a unique insight into how contrails could impact our climate. The research was prompted by a BBC radio programme about US airmen in the UK during the Second World War, including a witness who recalled seeing the sky “covered in white contrails” when bombing raids were forming over eastern England. “This led us to wonder if the contrail cover imposed by bombers had generated a detectable meteorological signal,” said Roger Timmis at the Environment Agency.

The team of researchers combed through historical records from the Meteorological Office and the military — detailed weather observations were made during the war because conditions were crucial to the success of bombing missions. The scientists compared the temperatures immediately beneath the contrails to those just a few miles away under clear skies. This comparison gave a good idea of how the weather on the ground was affected by contrails. The study, published in International Journal of Climatology, revealed that the mass of contrails significantly cooled the relative morning temperature by 0.8C (1.4F) under the flight paths of the aircraft.

Contrails are created as the hot engine fumes from aircraft mix with cold air at high altitudes and turn moisture into white ribbons of cloud. Although some contrails vanish quickly, others persist so long they turn into cirrus clouds and block out sunshine, cooling the ground below. On the other hand, contrails at night act as a blanket and trap heat on the ground.

Period10/05/2014

11 May, The Times

On the morning of May 11, 1944, a bombing raid of 900 American aircraft took off from airfields across southeast England. Their mission was to bomb railway marshalling yards in France, ready for the D-Day invasion the following month, to prevent the Germans sending reinforcements to Normandy.

That morning 70 years ago was warm sunny, with hardly a cloud in the sky. But as the aircraft circled to assemble into their formations, they formed stunning contrails in the sky from their hot engine exhausts — something the pilots feared because it made their aircraft far easier to track and shoot down.

Recently, a study of the weather records at the time of that bomber raid has given a unique insight into how contrails could impact our climate. The research was prompted by a BBC radio programme about US airmen in the UK during the Second World War, including a witness who recalled seeing the sky “covered in white contrails” when bombing raids were forming over eastern England. “This led us to wonder if the contrail cover imposed by bombers had generated a detectable meteorological signal,” said Roger Timmis at the Environment Agency.

The team of researchers combed through historical records from the Meteorological Office and the military — detailed weather observations were made during the war because conditions were crucial to the success of bombing missions. The scientists compared the temperatures immediately beneath the contrails to those just a few miles away under clear skies. This comparison gave a good idea of how the weather on the ground was affected by contrails. The study, published in International Journal of Climatology, revealed that the mass of contrails significantly cooled the relative morning temperature by 0.8C (1.4F) under the flight paths of the aircraft.

Contrails are created as the hot engine fumes from aircraft mix with cold air at high altitudes and turn moisture into white ribbons of cloud. Although some contrails vanish quickly, others persist so long they turn into cirrus clouds and block out sunshine, cooling the ground below. On the other hand, contrails at night act as a blanket and trap heat on the ground.

References

TitleWeather Eye: cooling contrails
Media name/outletNewspaper
Media typePrint
Duration/Length/SizeThe Times
Date10/05/14
Producer/AuthorPaul Simons
PersonsRob MacKenzie, Annette Ryan, Roger Timmis, Sarah Watkins