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| Home > Publications database > Long-lived contrails and convective cirrus above the tropical tropopause |
| Journal Article | FZJ-2016-07571 |
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2016
EGU
Katlenburg-Lindau
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Please use a persistent id in citations: http://hdl.handle.net/2128/13629 doi:10.5194/acp-2016-940
Abstract: Contrails of the Russian high-flying research aircraft M-55 "Geophysica" are investigated in measurements above the tropical tropopause during the SCOUT-O3 field-experiment near Darwin, Australia, in 2005. The aircraft reached 19 km altitude, far above the tropopause with −87 °C temperature at 17 km. In-situ, lidar, and microwave-temperature profiler measurements on board the Geophysica are used. An upward-looking lidar on the German research aircraft "Falcon", the CPOL radar near Darwin, and NOAA-AVHRR satellites provide complementary data. Exhaust emission indices are derived from a self-match experiment of the Geophysica in the polar stratosphere in 2010. Plume positions are estimated based on measured or analyzed wind and parameterized wake vortex descent. One contrail is detectable in a photo, and characterized in-situ during contrail formation downwind of the overshooting convective system "Hector" of 16 November 2005. The upper part of the contrail formed in the tropical lower stratosphere at ~ 60 % relative humidity over ice at −82 °C. The ~ 1-h lifetime is explained by engine water emissions, slightly enhanced humidity from Hector, low temperature, low turbulence, and possibly nitric-acid hydrate formation. The long persistence suggests large contrail coverage from future high-flying aircraft. Further Geophysica contrail parts are found in the measurements inside the strongly convective Hector clouds on 30 November 2005. Most of the non-volatile aerosol measured over Hector is traceable to aircraft emissions. Cirrus clouds observed by lidar above the anvil occur in coincidence with computed contrail positions. The upper part of the stratospheric anvil can be explained as contrail cirrus in this case. The radar indicates that the cirrus was measured in-situ mostly besides and above overshooting convection, and the maximum ice water content in the overshoots is far higher than measured along the flight path. The evidence suggests that parts of the ice clouds measured are contrails or mixtures of convective and contrail cirrus. The number of ice particles in the contrails is less than 1 % of the number of non-volatile aerosol particles, possibly because of sublimation losses and undetected very small ice particles. The findings are of relevance with respect to hydration of the lower stratosphere, overshooting convection, and future increases of air traffic in the lower stratosphere.
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