Of all the activities conducted by weather reconnaissance crews over the years, the most controversial involved attempts at weather modification

Regional Variations in U.S. Diurnal Temperature Range for the 11 14 September 2001 Aircraft Groundings: Evidence of Jet Contrail Influence on Climate.

The grounding of all commercial aircraft within U.S. airspace for the 3-day period following the 11 September 2001 terrorist attacks provides a unique opportunity to study the potential role of jet aircraft contrails in climate. Contrails are most similar to natural cirrus clouds due to their high altitude and strong ability to efficiently reduce outgoing infrared radiation. However, they typically have a higher albedo than cirrus; thus, they are better at reducing the surface receipt of incoming solar radiation. These contrail characteristics potentially suppress the diurnal temperature range (DTR) when contrail coverage is both widespread and relatively long lasting over a specific region. During the 11 14 September 2001 grounding period natural clouds and contrails were noticeably absent on high-resolution satellite imagery across the regions that typically receive abundant contrail coverage. A previous analysis of temperature data for the grounding period reported an anomalous increase in the U.S.-averaged, 3-day DTR value. Here, the spatial variation of the DTR anomalies as well as the separate contributions from the maximum and minimum temperature departures are analyzed. These analyses are undertaken to better evaluate the role of jet contrail absence and synoptic weather patterns during the grounding period on the DTR anomalies.[...]

[*adsabs.harvard.edu]

September's Science: Shutdown of airlines aided contrail studies

Immediately after four hijacked airliners slammed into New York's World Trade Center, the Pentagon, and a field in southwestern Pennsylvania, the Federal Aviation Administration shut down all U.S. commercial air traffic for 3 days. The unprecedented grounding of airliners enabled airports to step up security measures. At the same time, scientists stepped up to a unique opportunity to study the influence of high-flying aircraft on Earth's climate. [...]

Travis and his colleagues looked at the average diurnal temperature range (DTR)—the difference between the day's high and low temperatures—reported at more than 4,000 weather stations across the continental United States. During the 3-day hiatus of air traffic last September, the average DTR was a little over 1°C wider than normal, even though the average DTRs computed for the 3-day periods immediately before and after that period were below normal.

Furthermore, says Travis, the Pacific Northwest, the Midwest, and the Northeast—areas of the country typically blanketed with aircraft contrails in mid-September—showed the largest changes in diurnal temperature range, mostly from increased daytime high temperatures. This bolsters the argument that contrails can significantly affect climate, Travis contends. He and his colleagues will report their findings next week in Portland, Ore., at a conference of the American Meteorological Society

[*sciencenews]

Pdf - Pagina 16, in fondo

[*aero-net-org]