New paper published in Atmospheric Measurement Techniques Discussion entitled “Validation of SCIAMACHY HDO/H2O measurements using the TCCON and NDACC-MUSICA networks” by Scheepmaker et al.
Measurements of the atmospheric HDO/H2O ratio help us to better understand thehydrological cycle and improve models to correctly simulate tropospheric humidity andtherefore climate change. The space-based measurements play here a key role and the documentation of their quality is a needed step to use these observations with high confidence.In this context, this paper presents an updated version of the column-averaged HDO/H2O ratio dataset from the remote sensor SCanning Imaging Absorption spectroMeter for AtmosphericCHartographY (SCIAMACHY). The dataset is extended with two additionalyears, now covering 2003–2007, and is validated against co-located ground-based totalcolumn δD measurements from Fourier-Transform Spectrometers (FTS) of the TotalCarbon Column Observing Network (TCCON) and the Network for the Detection ofAtmospheric Composition Change (NDACC, produced within the framework of the MUSICAproject). In particular, this study uses six stations of the TCCON network and six stations of the NDACC-MUSICA network, among them, the Izaña Atmospheric Observatory(see Figure 1).
As a result of FTS-SCIAMACHY comparison, it has been determined a mean negative bias in SCIAMACHY δDof -35±30‰ compared toTCCON and -69±15‰ compared to MUSICA (the uncertainty indicating the station-to-station standard deviation). The bias shows a latitudinal dependency, being largest(δ -60 to -80‰) at the highest latitudes and smallest (δ -20 to -30‰) at the lowestlatitudes. Also, above the high-altitudestations of Izaña and Jungfraujoch we find considerable positive biases, which are expectedfrom the depletion of HDO with altitude and the fact that SCIAMACHY is biasedtowards the lower-altitude areas surrounding mountains due to its spatial footprint of 120kmx30 km.Certain ground stations show a clearasymmetry in δD during the transition from the dry to the wet season and back, which is also detected by SCIAMACHY. This asymmetry points to a transition in the source regiontemperature or location of the water vapor, and shows the added information thatHDO/H2O measurements provide, if used in combination with variations in humidity.
Figure 1. Time series of δD from six MUSICA-NDACC stations (dark grey dots and magenta curve) compared to δD from SCIAMACHY within a 500 km radius (light grey dots and blue curve). The curves are 60-day running averages.
For further details, please refer to:Scheepmaker, R. A., Frankenberg, C., Deutscher, N. M., Schneider, M., Barthlott, S., Blumenstock, T., Garcia, O. E., Hase, F., Jones, N., Mahieu, E., Notholt, J., Velazco, V., Landgraf, J., and Aben, I.: Validation of SCIAMACHY HDO/H2O measurements using the TCCON and NDACC-MUSICA networks, Atmos. Meas. Tech. Discuss., 7, 11799-11851, doi:10.5194/amtd-7-11799-2014, 2014. http://www.atmos-meas-tech-discuss.net/7/11799/2014/amtd-7-11799-2014.html.