To be provided
Since its first application in the 1930s to study vertical ozone distribution, the Umkehr method has provided one of the longest continuous records of stratospheric ozone evolution. These unique datasets are essential for understanding decadal-scale changes while also capturing the state of atmospheric composition prior to the 1987 Montreal Protocol implementation. This presentation discusses an updated evaluation of stratospheric ozone profile trends at key global ground-based stations, including Arosa/Davos, OHP, Boulder, Mauna Loa, and Lauder.
Regular daily observations from space started in 1978 and so far we look at a history of 48 years of ozone observations from space. Satellite measurements have the advantage of global coverage. Ground-based ozone data, in particular Brewer/Dobson spectrophotometer and ozone sondes, are fundamental in validating satellite measurements, but satellite data have also played an important role in improving ozone retrieval from the ground. Both satellite and ground-based observations strongly contributed to ozone science and are complementary in monitoring ozone changes as mandated by the Vienna Convention of 1985.
The lessons from analysing the Arosa/Davos total ozone record will be discussed in terms of what the record has meant for global ozone depletion and the lessons for monitoring. From a personal perspective, the Arosa/Davos total ozone record was central to my PhD work in the 1980s. It gave me my first insights into how the stratosphere worked and subsequent analyses showed what happened as the chlorine maximum passed and as it became more important to separate chemical and dynamical influences.
The processes controlling ozone change a lot from the ground to the stratopause (around 50 km altitude). Dobsons and Brewers provide excellent total column ozone, but we need ozone profiles to see what happens at different altitudes. In Europe we have historic profile records at relatively closeby stations from balloon-sondes, lidars and microwave radiometers. This talk explains measurement principles and shows results.
Total column ozone observations in Switzerland started in 1926, constituting the world´s longest continuous ozone time series. Building on these historical measurements, we present the homogenized total column ozone time series covering the period from 1990 to 2024, based on six collocated instruments: three Brewer and three automated Dobson spectroradiometers. This unified total column ozone record, with well-characterized uncertainty, forms the foundation for our trend analysis and recovery signal detection.
Over the 100 years of continuous total ozone measurements, the Umkehr profile timeseries began in Switzerland in 1956. Since 2000, six collocated Brewer and Dobson spectrophotometers have been providing continuous ozone profiles over Arosa/Davos. These profiles were merged with other European ground-based data records using the Bayesian Integrated and Consolidated (BASIC) methodology. We will discuss how this approach significantly reduces the uncertainty of the resulting partial columns composite timeseries and its subsequent trend estimates.
The recovery of the ozone layer is expected to continue over the coming decades, but the timing of ozone return varies between models and remains uncertain. This presentation will describe how multi-model ensembles are used to project future changes in total column ozone and estimate ozone return dates. It will also show how satellite observations can be used to evaluate model performance and constrain future projections, reducing uncertainty in estimates of ozone recovery. The results demonstrate how observations and models can be combined to improve confidence in projections of future ozone change.