Abstract
Abstract. Time series of stratospheric and lower mesospheric water vapour using 33 data sets from 15 different satellite instruments were compared in the framework of the second SPARC (Stratosphere-troposphere Processes And their Role in Climate) water vapour assessment (WAVAS-II). This comparison aimed to provide a comprehensive overview of the typical uncertainties in the observational database that can be considered in the future in observational and modelling studies, e.g addressing stratospheric water vapour trends. The time series comparisons are presented for the three latitude bands, the Antarctic (80∘–70∘ S), the tropics (15∘ S–15∘ N) and the Northern Hemisphere mid-latitudes (50∘–60∘ N) at four different altitudes (0.1, 3, 10 and 80 hPa) covering the stratosphere and lower mesosphere. The combined temporal coverage of observations from the 15 satellite instruments allowed the consideration of the time period 1986–2014. In addition to the qualitative comparison of the time series, the agreement of the data sets is assessed quantitatively in the form of the spread (i.e. the difference between the maximum and minimum volume mixing ratios among the data sets), the (Pearson) correlation coefficient and the drift (i.e. linear changes of the difference between time series over time). Generally, good agreement between the time series was found in the middle stratosphere while larger differences were found in the lower mesosphere and near the tropopause. Concerning the latitude bands, the largest differences were found in the Antarctic while the best agreement was found for the tropics. From our assessment we find that most data sets can be considered in future observational and modelling studies, e.g. addressing stratospheric and lower mesospheric water vapour variability and trends, if data set specific characteristics (e.g. drift) and restrictions (e.g. temporal and spatial coverage) are taken into account.
Highlights
Water vapour is the most important greenhouse gas and plays a key role in the chemistry and radiative balance of the atmosphere
Time series of stratospheric and lower mesospheric water vapour using 33 data sets from 15 different satellite instruments were compared in the framework of the second SPARC (Stratosphere-troposphere Processes And their Role in Climate) water vapour assessment (WAVAS-II)
Water vapour is an essential component of polar stratospheric clouds (PSCs) which play a key role in Antarctic and Arctic ozone depletion during winter and spring
Summary
Water vapour is the most important greenhouse gas and plays a key role in the chemistry and radiative balance of the atmosphere. Any changes in atmospheric water vapour have important implications for the global climate (Solomon et al, 2010; Riese et al, 2012) and need to be monitored and understood (Müller et al, 2016). Water vapour is an essential component of polar stratospheric clouds (PSCs) which play a key role in Antarctic and Arctic ozone depletion during winter and spring. Water vapour has an important influence on stratospheric chemistry through its ability to form ice particles. Ice particles generally live long enough and grow sufficiently large to fall and remove water vapour permanently from an air mass so that dehydration can generally be defined as an irreversible process. Dehydration in the stratosphere is generally observed over the Antarctic during winter (e.g. Kelly et al, 1989; Vömel et al, 1995; Nedoluha et al, 2000, 2007) and to a lesser extent over the Arctic (e.g. Fahey et al, 1990; Pan et al, 2002; Khaykin et al, 2013; Manney and Lawrence, 2016) as well as at the tropical tropopause (e.g. Jensen et al, 1996; Read et al, 2004; Schiller et al, 2009)
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