Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 4251-4269, 2016
http://www.atmos-chem-phys.net/16/4251/2016/
doi:10.5194/acp-16-4251-2016
© Author(s) 2016. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
05 Apr 2016
Detecting moisture transport pathways to the subtropical North Atlantic free troposphere using paired H2O-δD in situ measurements
Yenny González1,2,a, Matthias Schneider3, Christoph Dyroff3,b, Sergio Rodríguez2, Emanuel Christner3, Omaira Elena García2, Emilio Cuevas2, Juan Jose Bustos2, Ramon Ramos2, Carmen Guirado-Fuentes2, Sabine Barthlott3, Andreas Wiegele3, and Eliezer Sepúlveda2 1Sieltec Canarias, S. L., Hábitat 2, 38204, San Cristóbal de La Laguna, Santa Cruz de Tenerife, Canary Islands, Spain
2Izaña Atmospheric Research Centre (IARC), Agencia Estatal de Meteorología (AEMET), Santa Cruz de Tenerife, Canary Islands, Spain
3Institute of Meteorology and Climate Research (IMK-ASF), Karlsruhe Institute of Technology (KIT), Karlsruhe, Germany
anow at: Dept. of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139-4307, USA
bnow at: Aerodyne Research Inc., 45 Manning Road, Billerica MA 01821, USA
Abstract. We present two years of in situ measurements of water vapour (H2O) and its isotopologue ratio (δD, the standardized ratio between H216O and HD16O), made at two remote mountain sites on Tenerife in the subtropical North Atlantic. We show that the data – if measured during night-time – are well representative for the lower/middle free troposphere. We use the measured H2O-δD pairs, together with dust measurements and back trajectory modelling for analysing the moisture pathways to this region. We can identify four principally different transport pathways. The air mass transport from high altitudes and high latitudes shows two different scenarios. The first scenario brings dry air masses to the stations, as the result of condensation events occurring at low temperatures. The second scenario brings humid air masses to the stations, due to cross-isentropic mixing with lower-level and more humid air during transport since last condensation (LC). The third pathway is transportation from lower latitudes and lower altitudes, whereby we can identify rain re-evaporation as an occasional source of moisture. The fourth pathway is linked to the African continent, where during summer, dry convection processes over the Sahara very effectively inject humidity from the boundary layer to higher altitudes. This so-called Saharan Air Layer (SAL) is then advected westward over the Atlantic and contributes to moisten the free troposphere. We demonstrate that the different pathways leave distinct fingerprints on the measured H2O-δD pairs.

Citation: González, Y., Schneider, M., Dyroff, C., Rodríguez, S., Christner, E., García, O. E., Cuevas, E., Bustos, J. J., Ramos, R., Guirado-Fuentes, C., Barthlott, S., Wiegele, A., and Sepúlveda, E.: Detecting moisture transport pathways to the subtropical North Atlantic free troposphere using paired H2O-δD in situ measurements, Atmos. Chem. Phys., 16, 4251-4269, doi:10.5194/acp-16-4251-2016, 2016.
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Short summary
Measurements of water vapour isotopologues, dust, and a back trajectory model were used to identify moisture pathways in the subtropical North Atlantic. Dry air masses, from condensation at low temperatures, are transported from high altitudes and latitudes. The humid sources are related to the mixture, with lower and more humid air during transport. Rain re-evaporation was an occasional source of moisture. In summer, an important humidity source is the strong dry convection over the Sahara.
Measurements of water vapour isotopologues, dust, and a back trajectory model were used to...
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