Online LOTUS workshop




LOTUS is an international research initiative endorsed by SPARCIO3C 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


    • 16:00 16:10
      Welcome & scope of meeting
    • 16:10 17:35
      Ground-based data records
      • 16:10
        Status of the homogenization activity of the global ozonesonde network 10m

        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.

        Speaker: Dr Roeland Van Malderen (Royal Meteorological Institute of Belgium)
      • 16:20
        A Post-2013 Drop-off in Total Ozone at a Third of Global Ozonesonde Stations: ECC Instrument Artifacts? 10m

        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.

        Speaker: Ryan Stauffer (NASA/GSFC and Univ of Maryland)
      • 16:30
        Canadian ozonesonde network data 10m

        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.

        Speaker: David Tarasick
      • 16:40
        Discussion sonde 15m
      • 16:55
        Ground-based measurements of stratospheric ozone: a „supersite“ trend comparison 5m

        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.

        Speaker: Leonie Bernet (University of Bern)
      • 17:00
        Status and intercomparison of ozone observations at Observatoire de Haute-Provence 5m

        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.,, in review, 2020

        Speaker: Dr Sophie Godin-Beekmann (LATMOS/IPSL, Sorbonne U., U. Paris-Saclay, CNRS, Paris, France)
      • 17:05
        Ozone recovery as detected in NOAA Ground-Based and Satellite Ozone Measurements 5m

        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.

        Speaker: Irina Petropavlovskikh (NOAA/CIRES)
      • 17:10
        Status update harmonisation Swiss O3 MWR time series 5m
        Speaker: Eric Sauvageat
      • 17:15
    • 17:35 19:00
      Satellite data records
      • 17:35
        Update stability OMPS-LP 15m

        Update stability OMPS-LP (tangent height and spectral). Impact on different L2 data records (NASA, USask, UBremen) and merged L3.

        Speakers: Dan Zawada, Natalya Kramarova, Carlo Arosio
      • 17:50
        Discussion OMPS-LP 15m
      • 18:05
        OSIRIS Data Record Update 10m

        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.

        Speaker: Prof. Doug Degenstein (University of Saskatchewan)
      • 18:15
        Recent Advances in the SBUV Merged Ozone Dataset (MOD) for LOTUS Phase 2 Analysis of Stratospheric Ozone Trends and Uncertainties 10m

        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.

        Speaker: Stacey Frith (SSAI/Goddard Space Flight Center)
      • 18:25
        The ISSI Merging Team: towards a Universal Framework for Merging Atmospheric Observations 5m

        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.

        Speaker: William Ball (PMOD/WRC Davos & IAC/ETH Zurich)
      • 18:30
        Discussion 30m
    • 16:00 16:30
      Lat x Lon gridded data records & analyses
      • 16:00
        Overview lat x lon gridded O3 profile data records & analyses 15m

        Overview latxlon gridded O3 profile data records & analyses

        Speaker: Viktoria Sofieva
      • 16:15
        Discussion 15m
    • 18:15 19:00
      Round table discussion & planning
      • 18:15
        Discussion 45m