Ground-based remote sensing of tropospheric water vapour isotopologues within the project MUSICA

Abstract

Abstract. Within the project MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water), long-term tropospheric water vapour isotopologue data records are provided for ten globally distributed ground-based mid-infrared remote sensing stations of the NDACC (Network for the Detection of Atmospheric Composition Change). We present a new method allowing for an extensive and straightforward characterisation of the complex nature of such isotopologue remote sensing datasets. We demonstrate that the MUSICA humidity profiles are representative for most of the troposphere with a vertical resolution ranging from about 2 km (in the lower troposphere) to 8 km (in the upper troposphere) and with an estimated precision of better than 10 %. We find that the sensitivity with respect to the isotopologue composition is limited to the lower and middle troposphere, whereby we estimate a precision of about 30 ‰ for the ratio between the two isotopologues HD 16 O and H 16 2 O. The measurement noise, the applied atmospheric temperature profiles, the uncertainty in the spectral baseline, and the cross-dependence on humidity are the leading error sources. We introduce an a posteriori correction method of the cross-dependence on humidity, and we recommend applying it to isotopologue ratio remote sensing datasets in general. In addition, we present mid-infrared CO 2 retrievals and use them for demonstrating the MUSICA network-wide data consistency.In order to indicate the potential of long-term isotopologue remote sensing data if provided with a well-documented quality, we present a climatology and compare it to simulations of an isotope incorporated AGCM (Atmospheric General Circulation Model). We identify differences in the multiyear mean and seasonal cycles that significantly exceed the estimated errors, thereby indicating deficits in the modeled atmospheric water cycle.

Airborne in situ vertical profiling of HDO / H<sub>2</sub><sup>16</sup>O in the subtropical troposphere during the MUSICA remote sensing validation campaign

“…Quality assessment of remotely sensed δD has been performed theoretically (Worden et al, 2006;Schneider et al, 2006;Schneider and Hase, 2011;Lacour et al, 2012;Schneider et al, 2012;Boesch et al, 2013). So far empirical validation studies of tropospheric δD remote sensing products have been made with very few indirect references or have used a δD reference that itself was not comprehensively validated (Schneider and Hase, 2011;Boesch et al, 2013).…”

“…Tropospheric profile measurements have already been reported from ground and space by means of Fourier Transform Infrared (FTIR) spectroscopy or other techniques (Kuang et al, 2003;Zakharov et al, 2004;Worden et al, 2006;Frankenberg et al, 2009; Published by Copernicus Publications on behalf of the European Geosciences Union. Risi et al, 2010;Randel et al, 2012;Risi et al, 2012;Schneider et al, 2012). Since changes of δD are usually small, uncertainties in its determination (accuracy) may lead to misinterpretation of the physical processes involved in the H 2 O transport.…”

The MUSICA MetOp/IASI H<sub>2</sub>O and δD products: characterisation and long-term comparison to NDACC/FTIR data

“…Schneider et al (2012) present an extensive theoretical characterisation of the MUSICA ground-based FTIR remote-sensing data set.…”

“…In Sect. 3 we use the formalism as presented for the NDACC/FTIR data set by Schneider et al (2012) for characterising MUSICA's MetOp/IASI products. Then, the IASI and the FTIR products are compared in Sect.…”

“…2 of Schneider et al, 2012) as well as four spectral auxiliary microwindows containing CO 2 lines (in order to optimally estimate the temperature from the measured spectra; Schneider and Hase, 2008). We use HITRAN 2008 (High-Resolution Transmission Molecular Absorption Database) spectroscopic parameters (Rothman et al, 2009(Rothman et al, , with 2009, while for the water vapour isotopologues we use parameters that have been adjusted for the speeddependent Voigt line shape (Schneider et al, 2011b O, O 3 , N 2 O, CH 4 , HCl, and C 2 H 6 .…”