How Certain are We of the Uncertainties in Recent Ozone Profile Trend Assessments of Merged Limbo Ccultation Records? Challenges and Possible Ways Forward

Most recent assessments of long-term changes in the vertical distribution of ozone (by e.g. WMO and SI2N) rely on data sets that integrate observations by multiple instruments. Several merged satellite ozone profile records have been developed over the past few years; each considers a particular set of instruments and adopts a particular merging strategy. Their intercomparison by Tummon et al. revealed that the current merging schemes are not sufficiently refined to correct for all major differences between the limb/occultation records. This shortcoming introduces uncertainties that need to be known to obtain a sound interpretation of the different satellite-based trend studies. In practice however, producing realistic uncertainty estimates is an intricate task which depends on a sufficiently detailed understanding of the characteristics of each contributing data record and on the subsequent interplay and propagation of these through the merging scheme. Our presentation discusses these challenges in the context of limb/occultation ozone profile records, but they are equally relevant for other instruments and atmospheric measurements. We start by showing how the NDACC and GAW-affiliated ground-based networks of ozonesonde and lidar instruments allowed us to characterize fourteen limb/occultation ozone profile records, together providing a global view over the last three decades. Our prime focus will be on techniques to estimate long-term drift since our results suggest this is the main driver of the major trend differences between the merged data sets. The single-instrument drift estimates are then used for a tentative estimate of the systematic uncertainty in the profile trends from merged data records. We conclude by reflecting on possible further steps needed to improve the merging algorithms and to obtain a better characterization of the uncertainties involved

Validation strategy for satellite observations of tropospheric reactive gases

Over the last twodecades, satellite observations of tropospheric composition have becomepossible using nadir viewing spectrometers operating in the UV, visible, nearinfrared, and thermal infrared spectral range. [...

Ozone recovery and stratospheric cooling - What can we see from a few long-term stations?

Thanks to the Montreal Protocol, the decline of stratospheric ozone has been stopped. Ozone has now started to recover. The Kyoto Protocol, however, has been less successful. CO2 levels keep increasing, the stratosphere keeps cooling. Among other things, this cooling does affect ozone recovery. What can data from just a few NDACC stations tell us about these long-term changes? In our presentation we will look at long-term variations of stratospheric ozone and temperature since the 1960s. We will show results from NDACC stations and from Europe, and will put those into the context of global observations. At Hohenpeissenberg (47.8°N, 11.0°E), ozone in the upper stratosphere (40km / 2hPa) has been increasing since about 2000, by almost 10%. Levels are already comparable to what was measured in the late 1980s. At the same time, temperature has been declining substantially since about 2000, by more than 3 K. Total ozone, where variations are coming mostly from the lower stratosphere, has been increasing since the mid 1990s at Hohenpeissenberg. This increase, and the previous decline, largely track the evolution of Equivalent Effective Stratospheric Chlorine (EESC). Superimposed are natural variations, which were particularily large in 2010 and 2011. 2010 had very large ozone columns, comparable to the early 1980s. 2011, on the other hand, was a year with very low ozone columns, and with unprecedented large ozone losses in Arctic spring. At Hohenpeissenberg, the total ozone annual mean of 2011 was the 3rd lowest on record since 1968. Only 1992 and 1993, after the Pinatubo eruption, had lower ozone columns. Multiple linear regression analysis indicates that this large swing from 2010 to 2011 is connected to meteorological changes, i.e. the change of the Arctic Oscillation from pronounced negative phase in 2010, to pronounced positive phase in 2011

A different way to look at the intercomparison of datasets - illustrated with SCIAMACHY v5.02 versus lidar ozone profiles

International audienceIn traditional validations of atmospheric profiles, the intercomparison of two datasets is usually carried out in predefined groups of observational characteristic like longitude, stellar magnitude or solar zenith angle. Here we present an alternative method in which we trained a self organizing map (SOM) with a full time series of relative difference profiles of SCIAMACHY limb v5.02 and ozone profiles from seven NDACC lidar. For each individual observation, a set of observations characteristics from the SCIAMACHY and lidar data was mapped to the trained SOM. These maps were studied to see if the variation for a given characteristic corresponds to the variation seen in the SOM map. For the studied datasets, altitude-dependent relations for the global dataset were found between the difference profiles and studied variables. From the lowest altitude studied (18 km) ascending, the most influencing factors were found to be longitude, followed by solar zenith angle and latitude, sensor age and again solar zenith angle together with the day of the year at the highest altitudes studied here (up to 45 km). Clustering into three classes showed that there are also some local dependencies, with for instance one cluster having a much stronger correlation with the sensor age (days since launch) between 36 and 42 km. The validation approach based on using SOM proved to be a powerful tool for the exploration of differences between datasets without being limited to a-priori defined data subsets

Uncertainties in recent satellite ozone profile trend assessments (SI2N, WMO 2014) : A network-based assessment of fourteen contributing limb and occultation data records

International audienceNumerous vertical ozone profile data records collected over the past decades from space-based platforms have the potential to allow the ozone and climate communities to tackle a variety of research questions. A prime topic is the study and documentation of long-term changes in the vertical distribution of atmospheric ozone, as targeted by the recent SPARC/IO3C/IGACO-O3/NDACC Initiative (SI2N) and WMO’s ozone assessment. Such studies typically require data records with documented mutual consistency in terms of bias and long-term stability. Ground-based networks play a pivotal role in evaluating which satellite records comply with end-user requirements and are fit for their purpose. They provide high-quality, independent measurements on a pseudo- global scale from the ground up to the stratosphere.Here, we present an assessment of the long-term stability and mutual consistency of fourteen limb/occultation ozone profile data records, using NDACC/GAW/SHADOZ ozonesonde and NDACC lidar network data as reference standards. We show how a harmonized analysis framework and robust statistical methods allow us to derive reliable estimates of the drift, bias, and short-term variability of each satellite data record. We examine the dependence of these parameters on altitude and, whenever feasible, on latitude and season. The analysis is furthermore performed in four different ozone profile representations, as it turns out that auxiliary data used for unit and representation conversions can impact data quality. We discuss the mutual consistency and compliance of satellite data sets with respect to specific user requirements from GCOS and from climate research groups. We conclude by reflecting on the implication of our results for trend assessments on recently merged ozone profile records (Ozone_CCI, GOZCARDS, SWOOSH, ...