NASA Studying Linear Contrails
BYLINE: Edward H. Phillips
SECTION: AIR TRANSPORT; Vol. 152, No. 3; Pg. 428
LENGTH: 484 words
DATELINE: Hampton, Va.
NASA/Langley Research Center is studying the formation of contrail-induced cirrus clouds stemming from increased air traffic and their future effect on the Earth's climate.
''One of the biggest uncertainties in global climate change is the effect of clouds,'' which are important because they modulate the flow of solar energy into and out of the Earth's ecosystem and affect Earth's daily radiation budget, said Patrick Minnis. He is a research scientist at Langley's Atmospheric Sciences Div. Although contrails reflect solar radiation and absorb and emit thermal infrared radiation, whether the radiative effect is detrimental to climate depends chiefly on cloud longevity and coverage, he said.
Contrails form in the exhaust stream of a jet engine operating high in the troposphere, particularly during the winter months, but fewer appear during the warm season. Minnis said the presence of contrails can trigger cirrus cloud formations that not only become persistent, but also can cover a wide area. Their long-term effect on the Earth's radiation budget, however, remains unclear.
According to NASA, current estimates are that contrails cover only 0.1% of the Earth's surface, but over parts of Europe and the U.S. coverage can be as high as 0.4%. As air traffic continues to increase, the growth of persistent contrails is predicted to be 2.5% per year up to the year 2050, when predictive models indicate that as much as 0.5% of the Earth's surface could be covered. That gradual increase over time translates to about a 0.1-deg. Celsius rise in surface temperature globally, but much higher increases in surface temperature can occur where contrails are concentrated, Minnis said. Data for a recent study of the U.S. was derived from NOAA-11 and -12 satellites equipped with Advanced Very High Resolution Radiometers to detect contrails over time based on their linear shape and temperature differences. Surface observations also were employed to help validate satellite information. The information is being used to estimate the ''potential longwave radiative impact on the U.S. based on a radiative transfer model,'' Minnis said.
Preliminary results indicate that contrail-induced cloud coverage over the U.S. is ''much greater than estimated from models,'' but more research and funding is needed to complete an estimation of the annual cycle of linear contrails, he said. The heaviest concentration was observed in the Northeast area, Montana, and the Northwest region of the nation. Minimum coverage occurred over the Southwestern area, but was heaviest along routes from New York via Chicago to San Francisco.
In addition, Minnis is studying the spreading of linear contrails across the U.S. using data from the Goes-8 geostationary satellite. He said studies indicate coverage of persistent contrails worldwide is higher than what has been observed by satellites.