The comprehensive multi-annual MUSICA IASI dataset of daily global free tropospheric {H2O, δD}-D}- pairs

Concomitant observations of water vapour content and isotopologues allow fundamental insights into the transport and phase transitions of water in the atmosphere and are therefore a key to a better understanding of the atmospheric part of the water cycle. Here we present the new MUSICA (Multi-platform remote Sensing of Isotopologues for investigating the Cycle of Atmospheric water) product providing atmospheric {H2O, δD}-pairD}-pairs from the space-borne nadir thermal infrared sensor IASI onboard the Metop satellites, with a main focus on the free troposphere. 

 

The MUSICA IASI retrieval processor, as presented in Schneider et al. (2016), has been continually developed and evaluated using independent measurements over the past 10 years. Recently, the retrieval processor has been combined with an improved processing chain aiming at a time efficient retrieval of H 2O, water vapour isotopologues ({H2O, δD}-pairD}-pairs), CH4, N2O and HNO3. Based on the orbit structure of the Metop satellites, there are about 650,000 measurements per day for cloud free conditions and with a horizontal nadir pixel size of 12 km diameter, covering the atmosphere daily on a global scale for morning and evening overpasses (at about 9:30 and 21:30 local time, respectively). 

 

Best sensitivities for {H2O, δD}-pairD}-pairs are achieved for an altitude of about 4.2 km, for which approx. 70% of all retrievals pass the defined set of quality filters. Estimated uncertainties are about 2 - 10% for H 2O and 5 - 30‰ for δD}-pairD. Additionally, for approx. 30% of all retrievals there is vertical profile information in the {H 2O, δD}-pairD}-pair product, i.e. the atmospheric conditions at about 2.9 km can be independently estimated from the conditions at 5.6 km. 

 

The current MUSICA IASI dataset comprises the continuous five year period from 2014 to 2019 with a twice daily almost global coverage. In total these are more than 1000 million individual cloud free {H2O, δD}-pairD}-pair observations. The data are currently used in several international research projects that combine observations and state-of-the-art model simulations (ICON-ART-Iso, COSMOiso, IsoGSM) with the objective to link {H2O, δD}-pairD}-pair distributions with microphysical processes and atmospheric water transport on different scales. For such combinations of the highly variable observed and modeled water isotopologue fields the use of a retrieval simulator is highly recommendable. 

 

The whole observational dataset is made freely available to the scientific community. Here we will describe the data structure, data characteristics, inform about data access and discuss the usage of the MUSICA IASI retrieval simulator for model studies.