Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 17, 2311-2346, 2017
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
14 Feb 2017
Long-lived contrails and convective cirrus above the tropical tropopause
Ulrich Schumann1, Christoph Kiemle1, Hans Schlager1, Ralf Weigel2, Stephan Borrmann2,3, Francesco D'Amato4, Martina Krämer5, Renaud Matthey6, Alain Protat7, Christiane Voigt1,2, and C. Michael Volk8 1Deutsches Zentrum für Luft- und Raumfahrt, Institut für Physik der Atmosphäre, 82234 Oberpfaffenhofen, Germany
2Johannes-Gutenberg-University, Institute for Atmospheric Physics, Mainz, Germany
3Max-Planck-Institute for Chemistry, Mainz, Germany
4Istituto Nazionale di Ottica, CNR, Florence, Italy
5Forschungszentrum Jülich, Institut für Energie und Klimaforschung (IEK-7), Jülich, Germany
6Université de Neuchâtel, Laboratoire Temps-Fréquence, Neuchâtel, Switzerland
7Australian Bureau of Meteorology, Research and Development Branch, Melbourne, Victoria, Australia
8University of Wuppertal, Department of Physics, Wuppertal, Germany
Abstract. This study has two objectives: (1) it characterizes contrails at very low temperatures and (2) it discusses convective cirrus in which the contrails occurred. (1) Long-lived contrails and cirrus from overshooting convection are investigated above the tropical tropopause at low temperatures down to −88 °C from measurements with the Russian high-altitude research aircraft M-55 Geophysica, as well as related observations during the SCOUT-O3 field experiment near Darwin, Australia, in 2005. A contrail was observed to persist below ice saturation at low temperatures and low turbulence in the stratosphere for nearly 1 h. The contrail occurred downwind of the decaying convective system Hector of 16 November 2005. The upper part of the contrail formed at 19 km altitude 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 in case of a potential future increase of air traffic in the lower stratosphere. (2) Cirrus observed above the strongly convective Hector cloud on 30 November 2005 was previously interpreted as cirrus from overshooting convection. Here we show that parts of the cirrus were caused by contrails or are mixtures of convective and contrail cirrus. The in situ data together with data from an upward-looking lidar on the German research aircraft Falcon, the CPOL radar near Darwin, and NOAA-AVHRR satellites provide a sufficiently complete picture to distinguish between contrail and convective cirrus parts. Plume positions are estimated based on measured or analyzed wind and parameterized wake vortex descent. Most of the non-volatile aerosol measured over Hector is traceable to aircraft emissions. Exhaust emission indices are derived from a self-match experiment of the Geophysica in the polar stratosphere in 2010. 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 radar data show that the ice water content in convective overshoots is far higher than measured along the flight path. These findings add insight into overshooting convection and are of relevance with respect to hydration of the lower stratosphere.

Citation: Schumann, U., Kiemle, C., Schlager, H., Weigel, R., Borrmann, S., D'Amato, F., Krämer, M., Matthey, R., Protat, A., Voigt, C., and Volk, C. M.: Long-lived contrails and convective cirrus above the tropical tropopause, Atmos. Chem. Phys., 17, 2311-2346, doi:10.5194/acp-17-2311-2017, 2017.
Publications Copernicus
Short summary
A long-lived (1 h) contrail and overshooting convection were observed in the tropics, near Darwin, Australia. The data are used to study the contrail life cycle at low temperatures and cirrus from deep overturning convection in the lower tropical stratosphere. Airborne in situ, lidar, profiler, radar, and satellite data, as well as a photo, are used to distinguish contrail cirrus from convective cirrus and to study the origin of the observed ice and aerosol, up to 2.3 km above the tropopause.
A long-lived (1 h) contrail and overshooting convection were observed in the tropics, near...