Second LOTUS workshop

Europe/Paris
Salle B (WMO, Geneva)

Salle B

WMO, Geneva

Avenue de la Paix 7bis, Geneva, Switzerland
Description

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.

LOTUS will hold its second workshop from Mon 17 Sep (10:30) to Wed 19 Sep (12:30) in Geneva, Switzerland. This invite-only workshop will be informal with selected scheduled oral presentations and with ample time for discussions in large or small groups.

Main objectives

  • Recap of the main results of the first phase of LOTUS and the WMO/UNEP 2018 ozone assessment.
  • News, revisions, and updates of satellite, ground-based and model ozone data records.
  • Reconsideration of the regression model and trend estimates for lower stratospheric ozone (satellite & ground-based measurement).
  • Link between ozone profile trends and total column trends.
  • Discussion of methods to combine trend results.
  • Attribution of profile trends using model data.

We gratefully acknowledge the support by

                          

 

Group picture

 

Participants
  • Alexandra Laeng
  • Carlo Arosio
  • Christos Zerefos
  • Corinne Vigouroux
  • Daan Hubert
  • Daniel Kunkel
  • Doug Degenstein
  • Eliane Maillard Barras
  • Gabriele Stiller
  • Geir Braathen
  • Irina Petropavlovskikh
  • Jean-Christopher Lambert
  • Jeannette Wild
  • John Kapsomenakis
  • Kleareti Tourpali
  • Leonie Bernet
  • Lucien Froidevaux
  • Melanie Coldewey-Egbers
  • Michael Taylor
  • Richard McPeters
  • Robert Damadeo
  • Sophie Godin-Beekmann
  • Stacey Frith
  • Thierry Leblanc
  • Viktoria Sofieva
  • William Ball
  • Wolfgang Steinbrecht
  • Young-Ha Kim
    • Registration Reception and Salle B

      Reception and Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland
    • Status LOTUS and way forward Salle B

      Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland

      Summarize key results & lessons learnt from LOTUS Phase 1. Status of LOTUS Report. List of open issues, roadmap LOTUS Phase 2.

      • 1
        Summary of results, achievements and open issues of LOTUS Phase 1
        Speakers: Daan Hubert (BIRA-IASB), Sophie Godin-Beekmann (CNRS), Dr irina Petropavlovskikh (NOAA/CIRES)
    • 12:30
      Lunch Attic Restaurant

      Attic Restaurant

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland
    • Ozone data records Salle B

      Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland

      Satellite & ground; single-sensor and multi-sensor. Discussion of questionnaire sent out to data providers. What is planned for 2022 assessment? Regularity of updates? Continued comparison of data records. What do LOTUS users need?

      • 3
        First results from the 2017/2018 LidAr VAlidation NDacc Experiment at Observatoire Haute Provence
        In July 2017 and March 2018, the mobile NDACC reference lidar from NASA GSFC took part in an intercomparison campaign for stratospheric ozone and temperature profiles at the Observatoire Haute Provence in Southern France. Here we report on the initial comparison of 1.) ozone profiles from the NASA lidar, the stratospheric ozone lidar at Haute Provence, ECC sondes, the tropospheric ozone lidar and ozone profiles from the MLS and SABER satellite instruments 2.) temperature profiles from the NASA lidar, the stratospheric ozone lidar at Haute Provence, the stratospheric/mesospheric temperature lidar at Haute Provence, ECC sondes, Nimes Radiosondes and NCEP operational analyses, and temperature profiles from the MLS and SABER satellite instruments. In most cases, profiles from all sources agree within their respective uncertainties.
        Speaker: Wolfgang Steinbrecht (Deutscher Wetterdienst)
      • 5
        Merging of ozone profiles from SCIAMACHY, OMPS and SAGE II observations to study stratospheric ozone changes
        A continuous monitoring of the stratospheric ozone layer over a global scale is done by means of several techniques. Observations in limb geometry from satellite platforms provide ozone profiles with a good vertical resolution, spatial and temporal coverage. SCIAMACHY and OMPS-LP are two satellite instruments able to collect shortwave scattered radiance in limb geometry. Ozone profile data sets from SCIAMACHY (2002-2012) and OMPS-LP (2012-2018) were created at the University of Bremen using the same radiative transfer model, spectroscopic databases and a similar retrieval algorithm. The aim of this study is the merging of these data sets, to obtain a consistent time series of ozone global distributions. Since the two missions overlap only for 3 months, a transfer function is needed to overcome issues related to the sensors calibration. To this aim, we chose measurements performed by the MLS instrument as a reference. Monthly latitude- and longitude-resolved time series of ozone profiles were calculated for the two instruments, exploiting the high spatial resolution of the data sets. Their merging has been then performed minimizing the differences between OMPS-LP and SCIAMACHY ozone number density profiles with respect to MLS values, for each latitude, longitude and altitude independently. The seasonal cycle was not subtracted, because it was found to be consistent enough among the three instruments. Short-term changes in ozone profiles were calculated over 2003-2018 using a multilinear regression (MLR) analysis, including fit proxies as QBO, ENSO and a solar forcing. Positive trends were detected between 35 and 45 km at mid-latitudes, with an increasing ozone concentration up to 2-3% per decade. Negative changes were found in the lower tropical stratosphere but, above 20 km, statistically non-significant. A comparison with short-term trends calculated over the SCIAMACHY time period has been done: while a general agreement is found, some discrepancies are seen in the tropical mid-stratosphere. A merging with SAGE II ozone profiles was also performed: zonal monthly anomalies from the 3 instruments are merged to study ozone trends over the last 35 years. Applying the same MLR analysis, consistent results with previous studies were found: negative trends before 1997 up to -6% per decade at mid-latitudes around 40 km and the expected recovery after the ozone turn-around point at the end of ‘90, related also to the implementation of the Montreal protocol and its amendments.
        Speaker: Mr Carlo Arosio (Institute of Environmental Physics, University of Bremen)
      • 6
        Metrological requirements for quality assurance of ozone datasets at the climate data store
        With the rationalisation of climate data sets brokered from data providers through portals like the C3S Climate Data Store (CDS) and NASA GES-DISC, a key element of quality assurance is the provision of traceable uncertainty information. In important climate data records like total column ozone and ozone vertical profile data sets, ideally one would like uncertainties to be traceable back to a community defined reference and derive traceable uncertainties from the lowest level of data (e.g. raw detector counts) through to the final retrieval which may be gridded at different spatial and time scales. Given that not all products have uncertainties developed to this level, information is still needed in terms of data quality and to help assess this in a structured way, the C3S Evaluation and Quality Control of Observations (EQCO) Project has developed a framework to collect and rank available quality information and to perform an independent validation. In the case of total ozone, and also in most other essential climate variables considered in EQCO, a common gap is the lack of quantitative uncertainties propagated from Level-0 data. The Horizon 2020 project FIDUCEO has developed a measurement equation approach to recalibrate in-flight satellite remote sensing data and to demonstrate how to propagate uncertainties at the radiance level through optimal estimation algorithms to retrieved products at Level-2+ including sea surface temperature and aerosol optical depth. We present an example of the FIDUCEO method and how it can be applied to ozone and explain how harmonisation rather than homogenisation of sensor series data is required to ensure the fidelity and stability of climate data records.
        Speaker: Dr Michael Taylor (University of Reading)
      • 7
        Constructing a unified ozone composite: needs and outcomes
        A lot of effort has been put into acquiring, post-processing, and constructing composite timeseries of ozone observations. It is well documented that much of the uncertainty in long term ozone trends stems from the methodologies applied. Further, often composites lack comparable uncertainties and typically are not independent of each other. These issues lead to difficulties in gaining an accurate estimate of the long-term ozone layer changes, with representative uncertainties; this is the primary problem that LOTUS aims to tackle. Here, we lay out a new methodology for merging all observations in a robust and principled framework. The approach has the potential to estimate realistic uncertainties, and breach barriers that restrict or impair merging data with different spatial- and temporal-sampling, vertical resolution, and drifts. We aim this talk as an open discussion to: (i) understand current caveats and limitations of our approach; (ii) integrate essential community knowledge; and (iii) discuss data availability to achieve such a unified product. There are multiple benefits of this approach, although the most relevant to LOTUS should be enhanced trust in trend estimates.
        Speaker: Dr William Ball (PMOD/WRC Davos & IAC/ETH Zurich)
    • 15:30
      Coffee, tea & posters Corridor, Salle B

      Corridor, Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland
    • Ozone data records Salle B

      Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland

      Satellite & ground; single-sensor and multi-sensor. Discussion of questionnaire sent out to data providers. What is planned for 2022 assessment? Regularity of updates? Continued comparison of data records. What do LOTUS users need?

      • 8
        Review and discussion of planned developments and data provision schedule
        Speaker: Daan Hubert (BIRA-IASB)
    • Regression of ozone time series Salle B

      Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland

      Do we need different proxies for GND/MOD/SAT? Analyse seasonal trends? Weighted regression? DLM vs MLR? Complete sensitivity studies?

      • 9
        Preliminary analyses of seasonal dependence of ozone trends in the stratosphere
        Preliminary analyses of seasonal dependence of ozone trends in the stratosphere using the long-term merged datasets will be shown. The first results show that the ozone trends in the tropics depend significantly on season.
        Speaker: Dr Viktoria Sofieva (Finnish Meteorological Institute)
      • 10
        Optimisation of piecewise linear trend fitting of porous ozone time series with LOESS sum of sines and Monte-Carlo SSA
        We present a 5-step method to estimate piecewise linear trends in SBUV MOD v6 monthly zonal mean (MZM) profile ozone timeseries containing gaps (e.g. associated with volcanic perturbations). The method is non-parametric and does not use proxies. In Step 1, an optimised local regression (LOESS) to the porous data is obtained using bootstrap in a way that guarantees trend stationarity via the KPSS hypothesis test. In Step 2, the discrete Fourier transform is computed for the longest gap-free segment of the LOESS-centered data to identify the highest relative variance frequencies in the data. In Step 3, these Fourier peaks are used together with the LOESS trend to construct a sum of sines fit to the full timeseries and interpolate any missing data. In Step 4, Monte-Carlo Singular Spectrum Analysis (MC-SSA) is applied to the reconstructed timeseries to calculate a (5%, 95%) confidence interval around the median long-term nonlinear trend obtained from a bootstrap sample of 2000 runs. In Step 5, a turnaround point is set at January 1997 and used to regress a 2-segment PWLT fit pre- and post-1997 to the MC-SSA trend using least squares optimisation. We present data-driven profile ozone trend estimates (% / decade) from 25.45 hPa to the top of atmosphere in the equatorial bands (20oS-20oN and 50oS-50oN) and in mid-latitude bands (50oS-35oS and 35oN-50oN) for comparison with proxy-driven approaches. The maximum negative trend detected is -7.41 % / decade (pre-1997) in the Northern mid-latitude band in the 2.55 - 1.61 hPa pressure layer which switches to a positive trend of 1.74 % / decade post-1997. In addition to providing predicted values for missing months in the dataset, Fourier peak frequencies extracted can also be used to test for the presence of known cyclical proxies. Some results from wavelet analysis are presented to illustrate.
        Speaker: Dr Michael Taylor (University of Reading)
      • 11
        Upgrading dynamical linear modelling (DLM): fast, public code release and its capabilities
        DLM has been postulated to be an improvement on standard multiple linear regression (MLR) approaches to timeseries analysis, but it is relatively new and seldom implemented. Among other things, it has three significant advantages over MLR: (i) for trend estimation, no a priori assumption is made about the linear nature of trends, nor when the recovery inflection date in ozone timeseries, typically fixed between 1998 and 2000, should occur; (ii) the shape and magnitude of seasonal cycle is allowed to slowly vary over time, something that is difficult to account for in standard preparation procedures for MLR analysis, but may nevertheless lead to bias in trend estimates; and (iii) uncertainties are treated in a rigorous manner, uncertainties on proxies can easily be included, and there is no requirement for orthogonality of proxies. Here, we present a new DLM algorithm that is faster than previous versions, and is able to run on a laptop. The code is in python format and will be provided with a clear jupyter notebook tutorial to allow anyone to start implementing DLM on timeseries. We will give an online, working example of this code, show the diagnostic tools that will be available within the python package, and demonstrate visually the benefits of DLM.
        Speaker: Dr William Ball (PMOD/WRC Davos & IAC/ETH Zurich)
    • 10:30
      Coffee, tea & posters Corridor, Salle B

      Corridor, Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland
    • Regression of ozone time series Salle B

      Salle B

      WMO, Geneva

      Do we need different proxies for GND/MOD/SAT? Analyse seasonal trends? Weighted regression? DLM vs MLR? Complete sensitivity studies?

      • 12
        Regression of ground-based data
        Speaker: Dr irina Petropavlovskikh (NOAA/CIRES)
    • Lower Stratospheric ozone Salle B

      Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland

      What analyses are planned in coming years? Coordination of efforts? Are data & tools available & sufficient? Link between total column trends and stratospheric ozone trends.

      • 13
        Status of SHADOZ ozonesonde homogenization
        Speaker: Dr Anne Thompson
    • WMO award ceremony Salle B

      Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland
    • 12:30
      Lunch Attic Restaurant

      Attic Restaurant

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland
    • Lower Stratospheric ozone: + link with analyses of total column data Salle B

      Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland

      What analyses are planned in coming years? Coordination of efforts? Are data & tools available & sufficient? Link between total column trends and stratospheric ozone trends.

    • 15:30
      Coffee, tea & posters Corridor, Salle B

      Corridor, Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland
    • Trend attribution Salle B

      Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland

      What are plans of CCMI? Intercomparison between model and observed data.

      • 17
        Evolution of pre- and post 2000 changes and trends in the vertical distribution of ozone from CCMI models
        Changes and trends in the vertical distribution of ozone in the recent past
        Speaker: Dr Kleareti Tourpali (Lab of Atmospheric Physics, Aristotle University of Thessaloniki, Greece)
    • 19:30
      Dinner La Véranda, Rue des Alpes 20

      La Véranda, Rue des Alpes 20

    • Trend combination Salle B

      Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland

      Review & discuss methods, challenges & possible solutions.

      • 18
        Summary of phase 1 work
        Review of what has been done during Phase 1. Listing of challenges and open issues.
        Speaker: Dr Viktoria Sofieva (Finnish Meteorological Institute)
    • 10:30
      Coffee, tea & posters Corridor, Salle B

      Corridor, Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland
    • Trend combination & close out Salle B

      Salle B

      WMO, Geneva

      Avenue de la Paix 7bis, Geneva, Switzerland