The SPARC water vapour assessment II: comparison of stratospheric and lower mesospheric water vapour time series observed from satellites
2018
Time series of
stratosphericand lower
mesosphericwater
vapourusing 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
vapourassessment (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 addressing e.g
stratosphericwater
vapourtrends. 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° N–60° N) at four different altitudes (0.1, 3, 10 and 80 hPa) covering the
stratosphereand lower
mesosphere. The combined temporal coverage of observations from the 15 satellite instruments allowed considering 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 ratio 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
stratospherewhile larger differences were found in the lower
mesosphereand 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 all data sets can be considered in the future in observational and modelling studies addressing e.g.
stratosphericand lower
mesosphericwater
vapourvariability and trends when data set specific characteristics (e.g. a drift) and restrictions (e.g. temporal and spatial coverage) are taken into account.
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