WP 4.3: Evaluation of trends from ground-based series
Objectives
Evaluation of long-term trends in stratospheric ozone, NO2, BrO and temperature using the longest available (>10 years) homogenized time series of observations.
Some of the ground-based data series supported within GEOmon extend back more than a
decade. Such series can therefore inform us about the inter-annual changes and the possible
anthropogenic effects on the composition and the physical parameters of the stratosphere. The
difficulty for estimating possible changes due to chlorine loading or greenhouse gas (GHG)
increases (contributing to stratospheric cooling) concerns the separation between natural and
anthropogenic effects. The methodology proposed here is based on multivariate analyses
including stratospheric changes due to external forcings such as solar activity, internal
dynamics, volcanic aerosol loading in the stratosphere and changes associated with chlorine
loading or GHG.
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Trend estimates from ground-based series |
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Assessing ground-based trends against satellite trends |
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Comparison of observed versus model trends |
Trend estimates from ground-based series
Long-term trends in stratospheric O3, NO2, BrO, and temperature of ground-based series delivered in
WP4.1 are retrived. The analyses will be performed using the longest (> 1 decade) homogenized time series of
observations. Multivariate analyses are used to distinguish residual long-term trends from the known variability such as solar changes, volcanoes, the Quasi Biennial Oscillation (QBO) and for ozone Effective Equivalent Stratospheric Chlorine (EESC). The components of the multivariate are defined and
homogenized for each chemical component or observed parameter to allow for robust comparisons among the different data sets. Linear trends are being derived first followed by piecewise trends, as there is a major change as to the direct anthropogenic forcing of the stratosphere through the reduction of chlorine loading. Time periods for piecewise trend estimates need to be adjusted for each parameter.
Assessing ground-based trends against satellite trends
Independent trend estimates and their respective monthly time-series variability
be assessed from ground-based instruments and compared with satellite series. We retrieve ground-based data series with similar
characteristics as the available satellite products (resolution, sampling,…) for similar time
periods. The information from
ground-based is adjusted to satellite measurements using information
provided and tools developed in WP4.2.2 (observation operator). Comparisons of their respective long-term-changes permits conclusions about the
potential drift for satellite instruments or the potential effect of ground-based instrumental
changes. This work allows us to check the compatibility of the observation information derived from ground-based versus satellite instruments for longterm data sets.
Comparison of observed versus model trends
A detailed three-dimensional stratosphere-troposphere chemical transport model is used to produce time series of observed species covering the past observing periods. Using the information on models output (resolution, sampling,…), representative model ground-based data series are produced. Comparisons of their respective long-term changes provide independent trend estimates and their respective monthly time-series variability. This work will be interfaced with WP 5.2.
