On the discrepancies in the δD - H2O tape recorder observations by Envisat/MIPAS and SCISAT/ACE-FTS
Abstract
Isotope data can provide complementary information on dehydration processes in the tropical tropopause layer that are critical for the understanding of the stratospheric water vapour budget. The seasonal variation of the isotopic ratio δD-H2O in the tropical lower stratosphere is therefore of major scientific interest. Satellite observations of this variation by Envisat/MIPAS and SCISAT/ACE-FTS, however, exhibit very different results. Steinwagner et al. (2010) observed a clear annual cycle in δD-H2O in the MIPAS data set that could be traced in the stratosphere in a similar way as the known water vapour "tape recorder". An analysis of ACE-FTS data by Randel et al. (2012) shows an annual cycle in δD-H2O in the TTL, but none in the lower stratosphere. They attributed this lack to an influence of the Monsoon circulations, whose δD-H2O transport incoherently enters the upwelling region in the tropical lower stratosphere. Yet, a thorough investigation of the ACE-FTS observations reveals that there appears to be a weak tape recorder signal even in the lower stratosphere. Revisiting the Steinwagner et al. (2010) data reveals an artificial signature that could be misinterpreted as tape recorder, arising from a small mismatch in the vertical resolution of the retrieved HDO and H2O data that are used for the δD-H2O calculation. An empirical method has been employed to correct for this artefact, resulting in much better agreement of the δD-H2O tape recorder signal in the MIPAS and ACE-FTS data set. We discuss what these revised tape recorder results mean for the role of gradual ascent and the evaporation of convectively lofted ice particles for the stratospheric water vapour budget. We also show new MIPAS δD-H2O results in which the mismatch in the retrieved altitude resolutions of HDO and H2O has been removed. References: Steinwagner, J., Fueglistaler, S., Stiller, G. P., von Clarmann, T., Kiefer, M., Borsboom, P., van Delden, A., and Röckmann, T.: "Tropical dehydration processes constrained by the seasonality of stratospheric deuterated water", Nature Geoscience, 3, 262 - 266, doi:10.1038/ngeo822, 2010. Randel, W. J., Moyer, E., Park, M., Jensen, E., Bernath, P., Walker, K., and Boone, C.: "Global variations of HDO and HDO/H2O ratios in the upper troposphere and lower stratosphere derived from ACE-FTS satellite measurements", Journal of Geophysical Research,117, D06303, doi:10.1029/2011JD016632,20.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.A31E0073L
- Keywords:
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- 0341 ATMOSPHERIC COMPOSITION AND STRUCTURE / Middle atmosphere: constituent transport and chemistry