Atmospheric water is an enormously crucial trace gas. It is responsible for ~70 % of the natural greenhouse effect (Schmidt et al., JGR, 2010) and carries huge amounts of latent heat. The isotopic composition of water vapor is an elegant tracer for a better understanding and quantification of the extremely complex and variable hydrological cycle in Earth’s atmosphere (evaporation, cloud condensation, rainout, re-evaporation, snow), which in turn is a prerequisite to improve climate modeling and predictions. Within the last years progress was made in measuring HDO and H216O concentrations by infrared remote sensing instruments, which provide the opportunity to gather long-term (ground-based in the framework of NDACC) and area-wide (satellite based sensor IASI) observations.
MUSICA (MUlti-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) aims to generate a tropospheric dataset of HDO/H216O based on remote sensing measurements from satellite/ground and to validate the remote sensing measurements by in situ-components.
Ground-based in-situ measurements
A commercial Picarro Analyzer (L2120-i) is operated at Karlsruhe in Southwestern Germany, next to a ground based FTIR. This analyzer is continuously measuring the isotopologues H216O, HDO and H218O of atmospheric water vapor since January 2012. The record of H216O, HDO and H218O shows clear seasonal, synoptic and diurnal characteristics and reveals the main driving processes affecting the isotopic composition of water vapor in the Middle European BL.
Changes in continental plant transpiration and evaporation throughout the year lead to a slow seasonal HDO/H216O-variation, that cannot be explained by pure Rayleigh condensation.
Cold-front passages from NW lead to a fast and pronounced depletion of the HDO/H216O-ratio within minutes and show the effect of rain-evaporation.
Superimposed to these variations are local diurnal processes like dewfall, which cause a diurnal pattern captured by the deuterium excess.
Air-borne in-situ measurements
For validation of vertical HDO/H216O-profiles an aircraft campaign will be conducted in 2013 at Tenerife (Canary Islands). During this campaign the ISOWAT-Instrument will be installed on a CASA C212 aircraft and measures vertical profiles of HDO and H216O above a ground based FTIR located at the Izaña Observatory.
Based on 5-day-back trajectories a new isotope model is used, to characterize source regions of sampled air masses and the strength of sources and processes affecting the isotopic composition of atmospheric water (Fig.1).
Fig. 1: Measured and modeled dD at Karlsruhe (2012-2013).