LOTUS is an international research initiative endorsed by SPARC, IO3C and WMO (GAW) that kicked off at the Quadrennial Ozone Symposium in 2016. LOTUS focuses on revisiting the estimates and understanding of Long-term Ozone Trends and Uncertainties in the Stratosphere, in support of the WMO/UNEP 2018 Ozone Assessment. The LOTUS report was accepted for publication in May 2018, completing the main objective of the first phase of the activity. More detailed information on LOTUS can be found at our main website.
The third LOTUS meeting originally foreseen late May in Helsinki was cancelled due to the outbreak of Covid-19. Instead an online meeting will be organised on Thu 28 May and Fri 29 May 2020 each time at 8-11am MDT = 10am-1pm EDT = 4-7pm CEST = 5-8pm EEST, ....
A link to access the WebEx meeting will be circulated by e-mail on Wednesday.
We gratefully acknowledge the support by
Tentative group picture at our third (online) workshop
In this contribution, we give an overview of the ozonesonde stations that homogenized their ECC time series according to the principles of the O3S-DQA activity. We also present the roadmap to increase the number of homogenized (European) ozonesonde stations, in close collaboration with the station PIs. We will also discuss the different possibilities to make the already homogenized datasets available to the LOTUS community. Finally, we will give a short outlook of further homogenization activities of ozonesonde data: the need of a validation tool, possible additional correction algorithms for the radiosonde pressure sensor bias and background current substraction.
An international effort to improve ozonesonde data quality and to reevaluate historical records has made significant improvements in the accuracy of global network data. However, between 2014 and 2016, ozonesonde total column ozone (TCO; O3) at 14 of 37 regularly reporting stations exhibited a sudden drop-off relative to satellite measurements. The ozonesonde TCO drop is 3-7 % compared to satellite and ground-based TCO, and 5-10 % or more compared to satellite stratospheric O3 profiles, compromising the use of recent data for trends, although they remain reliable for other uses. Hardware changes in the ozonesonde instrument are likely a major factor in the O3 drop-off, but no single property of the ozonesonde explains the findings. The bias remains in recent data. Research to understand the drop-off is in progress; this presentation is intended as a caution to users of the data. Our findings underscore the importance of regular ozonesonde data evaluation.
The recent "drop-off" problem with ozonesondes in the global network has also affected a majority of sites in the Canadian network. Despite considerable effort the issue has not yet been resolved, and the data cannot yet be reliably corrected. However, there is evidence that only some profiles are biased and so it may be possible to filter time series, flagging doubtful data. This problem highlights the need for routine intercomparison of global network observations, in order to assure the quality and consistency of these data.
After the Montreal protocol banned ozone depleting substances, first signs of an ozone recovery in the stratosphere were observed starting in 1997. Recent studies have reported positive trends indicating that ozone is recovering in the upper stratosphere at mid-latitudes. However, stratospheric ozone trends from various ground-based data sets still differ in magnitude.
To partly explain such differences, we investigate how trends are affected by suspicious anomalies in the data. We present trend estimates from ground-based ozone data at mid-latitudes and demonstrate how they can be improved by considering data anomalies in the trend estimation.
Ozone trend profiles are compared for ground-based instruments from the Network for the Detection of Atmospheric Composition Change (NDACC) in Central Europe. Similar analyses are planned for co-located instruments at the supersite in Lauder, New Zealand. The careful analysis of stratospheric ozone time series and their uncertainties is crucial to improve trend estimations of stratospheric ozone profiles.
Within the Network for the Detection of Atmospheric Composition Changes (NDACC), ozone total content and vertical distribution are monitored by various measurement techniques at Observatoire de Haute-Provence (44°N, 6°E) in Southern France. For the vertical distribution, these techniques include two ozone lidars for the measurement of stratospheric and tropospheric ozone vertical profiles, in situ ozone soundings and Dobson Umkehr measurements. For the total content, a Dobson and a SAOZ UV-Visible spectrometers have been implemented in 1983 and 1992 respectively. An intercomparaison campaign involving the NASA reference lidar (McGee et al.) was organized in July 2017 and March 2018 for the comparison of ozone and temperature vertical profile (Wing et al., 2020). Results of the campaign together with long-term comparison of ozone measurements with satellite measurements overpasses will be presented.
McGee, T. J., Whiteman, D. N., Ferrare, R. A., Butler, J. J., and Burris, J. F.: STROZ LITE: stratospheric ozone lidar trailer experiment, Optical Engineering, 30, 31–40, 1991.
Wing, R., et al., Intercomparison and Evaluation of Ground- and Satellite-Based Stratospheric Ozone and Temperature profiles above Observatoire Haute Provence during the Lidar Validation NDACC Experiment (LAVANDE), Atmos. Meas. Tech. Discuss., https://doi.org/10.5194/amt-2020-9, in review, 2020
The study aims to revise historical NOAA Umkehr records with improved stray light corrections. Overpass data are generated for the GB sites using the combination techniques of the NOAA Cohesive (COH) zonal ozone product. The optimized Umkehr and COH station overpass data are compared to evaluate the long-term consistency in these records and improve homogenization techniques. The final goal is to update the stratospheric ozone trend analyses.
Update stability OMPS-LP (tangent height and spectral). Impact on different L2 data records (NASA, USask, UBremen) and merged L3.
This short presentation will give an update related to the continuing OSIRIS data record and how it fits into both the SAGE II/OSIRIS and the SAGE II/OSIRIS/OMPS-LP USask 2D time series. These time series will be evaluated through comparison with an MLS data record that has been converted from pressure and volume mixing ratio to altitude and number density using both ERA Interim and shifted MLS GPH. The evaluation will include an analysis of drifts in the OSIRIS based data records with respect to the MLS based data record.
The motivation for the initial phase of the SPARC Long-term Ozone Trends in the Stratosphere (LOTUS) project was to clarify from a community perspective our best estimate of stratospheric profile ozone trends and related uncertainties based on a variety of satellite and ground-based observations. The satellite-based records were all merged ozone products, many of which in part shared data from common sources. This initial phase culminated in a report published in early 2019, which was included in the 2018 WMO Ozone Assessment. Though an innovative approach was developed to quantify the uncertainty in the trend as estimated from the collection of merged records, the report highlighted the need going forward for a better understanding of the differences between individual satellite records within each merged data product.
The Solar Backscatter Ultraviolet (SBUV) based Merged Ozone Data (MOD) record is one such merged record used in LOTUS. MOD is a 40+ year time series of ozone profile data constructed from a series of eight SBUV instruments and the next generation Ozone Mapping and Profiler Suite (OMPS) Nadir Profiler (NP). Individual instruments are inter-calibrated within the SBUV retrieval algorithm. We have developed a new calibration approach to better understand and characterize the small sources of bias, seasonal variability, and drift that exist between instruments and thereby contribute to the uncertainty of the merged record. We also improved the representativeness of the A Priori in the retrieval algorithm, and now account for diurnal variability between instruments measuring at different times of day. After applying the newly-derived calibrations and several other algorithm improvements, we construct a new version of MOD and reevaluate the long-term ozone trend as well as the uncertainty in the record in accordance with the recommendations for Phase 2 of LOTUS.
There are now more than 40 years of satellite and ground-based ozone observations, a vast amount of data with which to diagnose variability and trends in stratospheric ozone. Despite this, confidence in the status of long-term trends in ozone remains uncertain, with the way that data from disparate sources are merged being a leading reason uncertainties remain high.
We have formed an International Space Science Institute team that aims to build a rigorous state-of-the-art statistical framework to overcome limitations currently associated with merging multiple instrument data sets with different observing characteristics. The aim is to prototype techniques and pave the way to a unified ozone data set, with realistic uncertainties, to make robust conclusions about the state of atmospheric ozone. I will provide a brief outline of the project and an overview of the aims and timeline of the team.
Overview latxlon gridded O3 profile data records & analyses
In this work we provide an update through 2018 of the evolution of changes in the zonal mean vertical distribution of ozone from a number of models participating in the CCMI phase 1 project, using ozone data from the REF-C2 series of simulations. Trends are calculated for the pre- and post-2000 periods, in accordance to the regression analysis and tools presented in the LOTUS SPARC Project and compared to satellite-derived trends for the same period. Results are compared to similar analysis from the fixed-ODS and fixed-GHG simulations pertaining to the same set of CCMI models in order to disentangle and quantify the influences of decreasing ODSs and GHGs on ozone recovery.
In this work, we analyse the seasonal dependence of ozone trends in the stratosphere using four long-term merged datasets: SAGE-CCI-OMPS, SAGE-OSIRIS-OMPS, GOZCARDS and SWOOSH, which provide more than 30 years of monthly zonal mean ozone profiles in the stratosphere. We focus here on trends between 2000 and 2018. All datasets show similar results, although some discrepancies are observed. In the upper stratosphere, the trends are positive throughout all seasons and the majority of latitudes. The largest upper stratospheric ozone trends are observed during local winter (up to 6% dec-1) and equinox (up to 3% dec-1) at mid-latitudes. In the equatorial region, we find a very strong seasonal dependence of ozone trends at all altitudes: the trends vary from positive to negative, with the sign of transition depending on altitude and season. The trends are negative in the upper stratospheric winter (-1 to -2% dec-1) and in the lower stratospheric spring (-2 to -4% dec-1), but positive (2-3% dec-1) at 30-35 km in spring, while the opposite pattern is observed in summer. The tropical trends below 25 km are negative and maximize during summer (up to -2 % dec-1) and spring (up to -3% dec-1). In the lower mid-latitude stratosphere, our analysis points to a hemispheric asymmetry hemispheric asymmetry: during local summers and equinoxes, positive trends are observed in the South (+1 to +2% dec-1) while negative trends are observed in the North (-1 to -2% dec-1).
We compare the seasonal dependence of ozone trends with available analyses of the seasonal dependence of stratospheric temperature trends. We find that ozone and temperature trends show positive correlation in the dynamically controlled lower stratosphere, and negative correlation above 30 km, where photochemistry dominates.
Seasonal trend analysis gives information beyond that contained in annual mean trends, which can be helpful in order to better understand the role of dynamical variability in short-term trends and future ozone recovery predictions.
Reliable ozone trends after 2000 are essential to detect early ozone recovery. However, the long-term ground-based and satellite ozone profile trends reported in the literature show a high variability. In order to determine what part of the variability between different datasets comes from measurement timing, Payerne microwave radiometer (MWR) and chemistry-climate model (SOCOL v 3.0) trends were estimated for each hour of the day with a multiple linear regression model. Ozone trend profiles have been quantified as a function of local solar time (LST). In the mid- and upper stratosphere, differences as a function of LST are reported for both the MWR and simulated trends for the 2000-2016 period. However, these differences are not significant at the 95% confidence level. In the lower mesosphere, the 2010-2018 day- and nighttime trends have been considered. Here again, the variation of the trend with LST is not significant at the 95% confidence level. Based on these results we conclude that significant trend differences between instruments cannot to be attributed to a systematic temporal sampling effect.
Multiple linear regression does a surprisingly good job at reproducing the time series of annual mean total ozone since 1968 at Hohenpeissenberg. Hockey-stick and EESC fit give virtually the same long-term trends: significant decline from 1968 to 1997 and consistent increase from 1998 to now. Recently I also tried the Alsing & Ball DLM model - with very similar long-term variation. In my presentation I'll show these results, which are based on annual means. If I get around to it, I'll also show (noisier) results based on monthly means. Ultimately, I want to apply the regression and the DLM to ozone profile time series and have a closer look at trends in the lower stratosphere.
Both stratospheric and tropospheric ozone have changed in concentration over the past few decades and further changes can be expected in the coming decades both as byproducts of human activity and as a result of efforts to limit factors which can affect ozone concentrations. The stratospheric community has been part of an international effort to develop methods of analyzing ozone data for change that have proven useful within and beyond the stratospheric community. The tropospheric ozone community is currently addressing a set of issues which also needs appropriate techniques to look for change including detecting, quantifying and understanding sudden changes, changes in trends, seasonal changes, diurnal changes and changes in extremes. A new international effort is beginning to work on these statistical and analytical challenges. Collaboration between the stratospheric and tropospheric communities is sought to assure the best approaches continue to serve science and society. Input from the LOTUS community is important to assure appropriate application of techniques in both the stratospheric and tropospheric communities. This presentation will include a review of the most common techniques currently in use and a brief summary of planned activities for the tropospheric community.
The composition of the upper troposphere / lower tratosphere (UTLS) is affected by the Brewer Dobson Circulation (BDC) as well transport across the tropopause and the jets. Since these dynamical processes involve the coupling of transport and mixing processes on very different temporal and spatial scales, long-term changes or even mean distributions from observational data sets on the distribution of tracers in the UTLS are therefore difficult to detect. Complications arise particularly from the short term variability of the tropopause and jet locations, which introduce variability in tracer distributions, especially for those with strong gradients at the tropopause. Therefore it is essential to account for the dynamically induced variability by, e.g., the tropopause location when looking at trends in dynamical processes such as stratosphere-to-troposphere exchange (STE) or the BDC and assessing their effects on trace gas distributions and long-term changes. The relationship of tracer distributions to the tropopause and jet locations as given in reanalysis data thus plays a key role in accounting for the variability and in the interpretation of tracer distributions.
OCTAV-UTLS (Observed Composition Trends And Variability in the UTLS) will use different observational data sets from soundings, lidar, aircraft and satellite to investigate the effect of dynamical variability on the ozone distributions. This is done by remapping of observations in different jet or tropopause based coordinates with the JETPAC-tool (Jet and Tropopause Products for Analysis and Characterization) using MERRA-2 reanalysis data. Some examples of the method are shown demonstrating the effect on the distribution and a reduction of variability.
Tropospheric ozone is a greenhouse gas and pollutant detrimental to human health and crop and ecosystem productivity. However, it is difficult to observe and quantify on the global scale, due to its acute spatial variability, resulting from its variable lifetime and its range of sources (injection from the stratosphere, or photochemical production from natural and anthropogenic precursor gases) and sinks (surface deposition and chemical destruction). To improve our understanding of ozone, the International Global Atmospheric Chemistry Project (IGAC) initiated the Tropospheric Ozone Assessment Report (TOAR) in 2014. With over 220 member scientists and air quality specialists from 36 nations, TOAR’s mission is to provide the research community with an up-to-date scientific assessment of tropospheric ozone’s global distribution and trends from the surface to the tropopause. TOAR built the world’s largest database of surface ozone observations and generated ozone exposure metrics at thousands of measurement sites around the world. The open-access database is facilitating new research on the global-scale impact of ozone on climate, human health and crop/ecosystem productivity. This presentation will provide an overview of global-scale tropospheric ozone trends, facilitated by the TOAR database and new research findings from the TOAR initiative. Trends are based on observations from remote surface sites, IAGOS commercial aircraft profiles, ozonesonde profiles and satellite retrievals. I will also provide an assessment of long-term surface ozone trends based on historical data from the early and mid-20th Century. The historical data have large uncertainties, however they indicate that surface ozone increased by 30-70% in the Northern Hemisphere from the mid-20th Century to the present. Modern observational techniques are more accurate and they indicate a general increase of free tropospheric ozone from the late 20th Century to the present, while trends at the surface are highly variable.
We analyse stratospheric ozone changes due to greenhouse gases and their impact on DNA active UV-B irradiance at ground level. The analysis is an extension of the recent study by Eleftheratos et al. (2020) who showed that solar ultraviolet-B irradiance that produces DNA damage would increase after the year 2050 in mid latitudes by +1.3% per decade. Results were based on chemistry climate model simulations with the EMAC model at 5 lidar stations, namely Hohenpeissenberg, Haute Provence, Table Mountain, Mauna Loa and Lauder. Such change in the model was found to be driven by a significant decrease in cloud cover due to the evolution of greenhouse gases in the future and an insignificant trend in total ozone.
Here, we increase the number of stations and analyze ozone and ultraviolet-B radiation measurements at 18 ground-based stations from the northern to the southern high latitudes contributing data to NDACC. The ground-based data are used to evaluate the EMAC CCM calculations of UV-B irradiance. Then the model is used to study the long-term variability of stratospheric ozone and UV-B irradiance due to the evolution of greenhouse gases in the future. We present regional, latitudinal and global changes in DNA active UV-B irradiance until the end of the 21th century with respect to changes in total ozone and cloud cover.