Speaker
Description
Uncertainties in observations often considerably limit our ability to assess long-term changes in the vertical distribution of water vapour. ESA's Climate Change Initiative (CCI) was set up to address the difficulties in harmonizing and merging climate data records (CDRs) of key climate variables and to provide climate modellers and researchers with high-quality, stable, long-term time series from current and past European (and third-party) satellite missions. As part of the CCI Water Vapour project, two vertically resolved water vapour data records have been developed (https://climate.esa.int/en/projects/water-vapour/data). The first product, CCI WV-strato, provides monthly zonal mean data in the stratosphere and lower mesosphere, combining observations from limb emission, scattering and occultation sensors. The second product, CCI WV-UTLS, is a three-dimensional monthly mean data record covering troposphere and UTLS, merging limb and nadir measurements.
In this contribution, we focus on the recently released CCI WV-strato (v3.3) and assess its potential for climate applications through a comparison to other recent CDRs, such as NOAA’s SWOOSH v2.7b and NASA’s GOZCARDS v1.10. We summarize the differences in input data, merging approach and general characteristics of these data records. All time series were analysed using regression techniques to infer multi-annual mean, seasonal cycle, quasi-biennial oscillation and long-term trends of water vapour across the stratosphere. For CCI WV-strato, the trend estimates are somewhat sensitive to the choice of quality flag applied for data screening. We present the coherence of the spatial structure of the parameters estimated from all three CDRs. We find that the magnitude and the spatial structure of the temporal (quasi)cycles are very similar. Residual long-term water vapour changes are modelled as a piecewise continuous linear function with two change points, in January 1998 and January 2004. The sign of the trend in the three periods generally agrees well between CDRs. However, trend values for the 1998-2003 and 2004-2019 periods differ significantly between CDRs in certain regions of the stratosphere. We relate these differences to, for example, differences in contributing sensors and data versions. In conclusion, ESA's vertical-resolution CCI data sets on water vapour provide valuable new independent sources of information for long-term global studies and climate applications.
