Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
doi:10.5194/acp-2017-152
© Author(s) 2017. This work is distributed
under the Creative Commons Attribution 3.0 License.
Research article
21 Mar 2017
Review status
This discussion paper is under review for the journal Atmospheric Chemistry and Physics (ACP).
Importance of the Saharan Heat Low on the control of the North Atlantic free tropospheric humidity deduced from IASI δD observations
Jean-Lionel Lacour1,4, Cyrille Flamant1, Camille Risi2, Cathy Clerbaux1,3, and Pierre-François Coheur3 1UPMC Univ. Paris 06; Université Versailles St-Quentin, LATMOS-IPSL, Paris, France
2UPMC Univ. Paris 06; UMR8539, CNRS/INSU, LMD-IPSL, Paris, France
3Spectroscopie de l’Atmosphère, Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles (ULB), Brussel, Belgium
4Institute of Earth Sciences, University of Iceland, Reykjavik, Iceland
Abstract. The isotopic composition of water vapour in the North Atlantic free troposphere is investigated with IASI measurements of the D/H ratio (δD) above the ocean. We show that in the vicinity of West Africa, the seasonality of δD is particularly strong (160 ‰), which is related with the installation of the Saharan Heat Low (SHL) during summertime. The SHL indeed largely influences the dynamic in that region by producing deep turbulent mixing layers, yielding a specific water vapor isotopic footprint. The influence of the SHL on the isotopic budget is analysed at various time and space scales and is shown to be large, highlighting the importance of the SHL dynamics on the moistening and the HDO-enrichment of the free troposphere over the North Atlantic. We also report important inter-annual variations of δD above Izana (Canary Islands) that we interpret, using backward trajectory analyses, in terms of the ratio of air-masses coming from the North Atlantic and air-masses coming from the African continent. Finally, we present spatial distributions of δD and humidity above the North Atlantic and we show that the different sources and dehydration pathways controlling the humidity can be disentangled thanks to the added value of δD observations.

Citation: Lacour, J.-L., Flamant, C., Risi, C., Clerbaux, C., and Coheur, P.-F.: Importance of the Saharan Heat Low on the control of the North Atlantic free tropospheric humidity deduced from IASI δD observations, Atmos. Chem. Phys. Discuss., doi:10.5194/acp-2017-152, in review, 2017.
Jean-Lionel Lacour et al.
Jean-Lionel Lacour et al.
Jean-Lionel Lacour et al.

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Short summary
We present temporal and spatial δD distributions derived from IASI obtained above the North Atlantic in the vicinity of West Africa. We show that the seasonality of δD in the North Atlantic is closely associated with the installation of the Saharan Heat Low (SHL). We provide an interpretation of the temporal and spatial variations of δD and show that the interactions between the large scale subsidence, the ITCZ and the SHL can be disentangled thanks to the added information contained in δD.
We present temporal and spatial δD distributions derived from IASI obtained above the North...
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