Abstract
Abstract. The project MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) integrates tropospheric water vapour isotopologue remote sensing and in situ observations. This paper presents a first empirical validation of MUSICA's H2O and δD remote sensing products, generated from ground-based FTIR (Fourier transform infrared), spectrometer and space-based IASI (infrared atmospheric sounding interferometer) observation. The study is made in the area of the Canary Islands in the subtropical northern Atlantic. As reference we use well calibrated in situ measurements made aboard an aircraft (between 200 and 6800 m a.s.l.) by the dedicated ISOWAT instrument and on the island of Tenerife at two different altitudes (at Izaña, 2370 m a.s.l., and at Teide, 3550 m a.s.l.) by two commercial Picarro L2120-i water isotopologue analysers. The comparison to the ISOWAT profile measurements shows that the remote sensors can well capture the variations in the water vapour isotopologues, and the scatter with respect to the in situ references suggests a δD random uncertainty for the FTIR product of much better than 45‰ in the lower troposphere and of about 15‰ for the middle troposphere. For the middle tropospheric IASI δD product the study suggests a respective uncertainty of about 15‰. In both remote sensing data sets we find a positive δD bias of 30–70‰. Complementing H2O observations with δD data allows moisture transport studies that are not possible with H2O observations alone. We are able to qualitatively demonstrate the added value of the MUSICA δD remote sensing data. We document that the δD–H2O curves obtained from the different in situ and remote sensing data sets (ISOWAT, Picarro at Izaña and Teide, FTIR, and IASI) consistently identify two different moisture transport pathways to the subtropical north eastern Atlantic free troposphere.
Highlights
The water cycle is closely linked to the global energy and radiation budgets and has fundamental importance for climate on global as well as regional scales
The study is made for the Izaña observatory and the surroundings of the island of Tenerife, where tropospheric water isotopologues have been measured in coincidence from different platforms and by different techniques: (1) since 1999 by ground-based FTIR remote sensing within NDACC, (2) since 2007 by space-based remote sensing using IASI aboard METOP, (3) since 2012/2013 by commercial Picarro in situ instruments from ground at two different altitudes, and (4) in July 2013 during six aircraft profile measurements using the dedicated ISOWAT in situ instrument
Global remote sensing of tropospheric δD in addition to H2O can open up novel opportunities for tropospheric water cycle research
Summary
The water cycle (continuous evaporation, transport and condensation of water) is closely linked to the global energy and radiation budgets and has fundamental importance for climate on global as well as regional scales. The few existing studies consist of very few indirect comparisons (Worden et al, 2011) or use a δD reference that itself is not comprehensively validated (Schneider and Hase, 2011; Boesch et al, 2013) This situation is rather unsatisfactory: since δD remote sensing measurements are very difficult and the nature of the data is very complex, there is urgent need to support the theoretical quality assessment studies by elaborated empirical validation exercises. The study is made for the Izaña observatory and the surroundings of the island of Tenerife, where tropospheric water isotopologues have been measured in coincidence from different platforms and by different techniques: (1) since 1999 by ground-based FTIR remote sensing within NDACC, (2) since 2007 by space-based remote sensing using IASI aboard METOP, (3) since 2012/2013 by commercial Picarro in situ instruments from ground at two different altitudes, and (4) in July 2013 during six aircraft profile measurements using the dedicated ISOWAT in situ instrument All these data have been generated within the project MUSICA (www.imk-asf.kit.edu/english/musica).
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