Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 12273-12286, 2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
29 Sep 2016
Evidence of horizontal and vertical transport of water in the Southern Hemisphere tropical tropopause layer (TTL) from high-resolution balloon observations
Sergey M. Khaykin1, Jean-Pierre Pommereau1, Emmanuel D. Riviere2, Gerhard Held3,*, Felix Ploeger4, Melanie Ghysels2,a, Nadir Amarouche5, Jean-Paul Vernier6,7, Frank G. Wienhold8, and Dmitry Ionov9 1LATMOS, CNRS, Université de Versailles St Quentin, Guyancourt, France
2GSMA, Université de Reims Champagne Ardenne and CNRS, Reims, France
3Instituto de Pesquisas Meteorológicas (IPMet), UNESP, Bauru, S.P., Brazil
4Forschungszentrum Jülich, IEK-7, Jülich, Germany
5Division Technique de l'INSU, CNRS, Meudon, France
6Science Systems and Applications, Inc, Hampton, Virginia, USA
7NASA Langley Research Center, Hampton, Virginia, USA
8ETH Zurich, Institute for Atmospheric and Climate Science, Zurich, Switzerland
9St. Petersburg State University, St. Petersburg, Russian Federation
anow at: National Institute of Standards and Technology, Gaithersburg, MD, USA
Abstract. High-resolution in situ balloon measurements of water vapour, aerosol, methane and temperature in the upper tropical tropopause layer (TTL) and lower stratosphere are used to evaluate the processes affecting the stratospheric water budget: horizontal transport (in-mixing) and hydration by cross-tropopause overshooting updrafts. The obtained in situ evidence of these phenomena are analysed using satellite observations by Aura MLS (Microwave Limb Sounder) and CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observation) together with trajectory and transport modelling performed using CLaMS (Chemical Lagrangian Model of the Stratosphere) and HYSPLIT (Hybrid Single-Particle Lagrangian Integrated Trajectory) model.

Balloon soundings were conducted during March 2012 in Bauru, Brazil (22.3° S) in the frame of the TRO-Pico campaign for studying the impact of convective overshooting on the stratospheric water budget. The balloon payloads included two stratospheric hygrometers: FLASH-B (Fluorescence Lyman-Alpha Stratospheric Hygrometer for Balloon) and Pico-SDLA instrument as well as COBALD (Compact Optical Backscatter Aerosol Detector) sondes, complemented by Vaisala RS92 radiosondes. Water vapour vertical profiles obtained independently by the two stratospheric hygrometers are in excellent agreement, ensuring credibility of the vertical structures observed.

A signature of in-mixing is inferred from a series of vertical profiles, showing coincident enhancements in water vapour (of up to 0.5 ppmv) and aerosol at the 425 K (18.5 km) level. Trajectory analysis unambiguously links these features to intrusions from the Southern Hemisphere extratropical stratosphere, containing more water and aerosol, as demonstrated by MLS and CALIPSO global observations. The in-mixing is successfully reproduced by CLaMS simulations, showing a relatively moist filament extending to 20° S. A signature of local cross-tropopause transport of water is observed in a particular sounding, performed on a convective day and revealing water vapour enhancements of up to 0.6 ppmv as high as the 404 K (17.8 km) level. These are shown to originate from convective overshoots upwind detected by an S-band weather radar operating locally in Bauru.

The accurate in situ observations uncover two independent moisture pathways into the tropical lower stratosphere, which are hardly detectable by space-borne sounders. We argue that the moistening by horizontal transport is limited by the weak meridional gradients of water, whereas the fast convective cross-tropopause transport, largely missed by global models, can have a substantial effect, at least at a regional scale.

Citation: Khaykin, S. M., Pommereau, J.-P., Riviere, E. D., Held, G., Ploeger, F., Ghysels, M., Amarouche, N., Vernier, J.-P., Wienhold, F. G., and Ionov, D.: Evidence of horizontal and vertical transport of water in the Southern Hemisphere tropical tropopause layer (TTL) from high-resolution balloon observations, Atmos. Chem. Phys., 16, 12273-12286, doi:10.5194/acp-16-12273-2016, 2016.
Publications Copernicus
Short summary
The study makes use of a series of field experiments conducted in Brazil and aimed at studying the processes controlling the composition of the tropical lower stratosphere. High-resolution balloon-borne measurements together with global-coverage satellite observations and weather radar acquisitions are analysed using trajectory and transport modelling in order to evaluate the contribution of different transport pathways to the stratospheric water budget.
The study makes use of a series of field experiments conducted in Brazil and aimed at studying...