ORIGINAL RESEARCH published: 17 June 2021 doi: 10.3389/feart.2021.675084 Representativeness of the Arosa/ Davos Measurements for the Analysis of the Global Total Column Ozone Behavior Eugene Rozanov 1,2,3*, Tatiana Egorova 1,2, Luca Egli 1, Arseniy Karagodin-Doyennel 1,2, Timofei Sukhodolov 1,2,3, Herbert Schill 1, Rene Stübi 4 and Julian Gröbner 1 1Physikalisch-Meteorologisches Observatorium Davos World Radiation Centre, Davos, Switzerland, 2Institute for Atmospheric and Climate Science, Swiss Federal Institute of Technology Zurich, Zurich, Switzerland, 3Faculty of Physics, Saint Petersburg State University, Saint Petersburg, Russia, 4Federal Office of Meteorology and Climatology, MeteoSwiss, Payerne, Switzerland The study investigates the representativeness of the total column ozone (TCO) measurements from the ground-based instruments located at the Arosa/Davos stations in Switzerland to analyze the global ozone layer behavior in the past and future. The statistical analysis of the satellite and model data showed a high correlation of the ground-based TCO data with the near-global and northern hemisphere annual mean Edited by: – Guihua Wang, TCO for the 1980 2018 period. Addition of the Arosa/Davos TCO data as a proxy to the Fudan University, China set of standard explanatory variables for multiple linear regression analysis allows Reviewed by: estimating the TCO behavior from 1926 up to the present day. We demonstrate that Weiwei Fu, the real-time measurements and high homogeneity level of the Arosa/Davos TCO time University of California, Irvine, United States series are also beneficial for quick estimates of the future ozone layer recovery. Jayanarayanan Kuttippurath, Indian Institute of Technology Keywords: Arosa/Davos, total column ozone, trends, representativeness, regression analysis Kharagpur, India *Correspondence: INTRODUCTION Eugene Rozanov [email protected] The local point ground-based measurements of atmospheric quantities are important as a part of global networks (e.g., Fioletov et al., 2008) and can also be used for the validation of satellite data (e.g., Specialty section: This article was submitted to Loew et al., 2017) if they are representative of the time and space over the respective satellite Atmospheric Science, footprint. The representativeness in this sense (Nappo et al., 1982) characterizes how the local a section of the journal measurements reflect the actual conditions in the adjacent location in time and space. This quantity Frontiers in Earth Science can be estimated using different statistical approaches such as the Fourier transform, structure, or Received: 02 March 2021 correlation functions (Nappo et al., 1982). For example, correlation analysis was applied by Schwarz Accepted: 26 May 2021 et al. (2017) to address the representativeness of the local point measurement of the surface solar Published: 17 June 2021 irradiance and their applicability for the satellite measurement validation. For some cases, the local Citation: point measurements provide unique data, which are not supported by a noticeable amount of other Rozanov E, Egorova T, Egli L, observation points. The exploitation of these data for the global analysis requires either pronounced Karagodin-Doyennel A, Sukhodolov T, homogeneity of the measured quantity over different instruments and periods or good Schill H, Stübi R and Gröbner J (2021) representativeness of the measurements for the longer time or larger spatial scales. A classic Representativeness of the Arosa/ example of this problem is the connection of the local climate parameters retrieved from the Davos Measurements for the Analysis of the Global Total Column tree rings with the wider territory. Büntgen et al. (2017) used the correlation analysis and showed that Ozone Behavior. the local tree ring data characterize well the temperature anomalies over most of Western Europe. Front. Earth Sci. 9:675084. Another example is the measurement of the long-lived species concentration from Jungfraujoch (e.g., doi: 10.3389/feart.2021.675084 Rinsland et al., 2012). In this case, the high spatial homogeneity of the long-lived species distributions Frontiers in Earth Science | www.frontiersin.org 1 June 2021 | Volume 9 | Article 675084 Rozanov et al. Representativeness of Arosa/Davos Measurements justifies the application for the analysis of the halogen-containing validation of satellite data and TCO behavior for other ozone-depleting substances’ global trends. The time series of locations and space/timescales, retrieval of the global-scale continuous total column ozone measurements over Arosa ozone behavior in the past (1926–1980), and applicability of (latitude 46.7833°N, longitude 9.6667°E) since 1926 is one of a the Arosa/Davos data for the fast diagnosis of the future ozone couple of unique data sets (Brönnimann et al., 2003) covering the layer recovery. early 20th century when anthropogenic hODS (halogen- containing ozone-depleting species) emissions were absent and the possible ozone and climate change can be caused by solar DATA DESCRIPTION activity and anthropogenic emissions of greenhouse gases and tropospheric ozone precursors (Egorova et al., 2018). The Arosa/Davos Total Column Ozone Time knowledge of the past ozone trends is useful for understanding Series the background state of the ozone layer during the periods not The longest continuous total column ozone time series worldwide disturbed by anthropogenic hODS. The modeling of climate started in 1926 at the Lichtklimatisches Observatorium Arosa, change during this period is difficult because the connection Switzerland. Since 2010, simultaneous measurements at Arosa between the solar spot number and solar irradiance has not been and in the nearby valley of Davos have been ongoing, to support robustly established yet. Our model experiments (Egorova et al., the transfer of the instrumentation to the Physikalisch- 2018) suggested that solar irradiance forcing should be much Meteorologisches Observatorium Davos and World Radiation higher during the early 20th century (and on centennial Center (PMOD/WRC) at Davos (Stübi et al., 2017; Stübi et al., timescales in principle) than commonly accepted to 2020). Figure 1 illustrates the TCO evolution during the successfully simulate the observed climate warming. This measurement period as well as the exploited set of the hypothesis can be supported or denied by the comparison of instruments. the simulated and observed total ozone over Arosa reflecting solar Due to a timespan of over 90 years, the Arosa/Davos time UV changes during the considered period (Egorova et al., 2020). series is a unique data set of worldwide importance to the climate Therefore, it will be interesting to compare the simulated and community and specifically, to the international ozone observed historical total ozone trends to investigate whether the community. Stratospheric ozone depletion over midlatitudes Arosa time series are representative of the regional and global was first observed using the total column ozone time series scales. over Arosa due to its long measurement period extending Even more interesting and important problem is the expected back to pre-ozone depletion conditions, its high intrinsic ozone recovery in the future related to the limitation of hODS homogeneity, and quality (Staehelin, 1998a; Staehelin, 1998b; emissions introduced by the Montreal Protocol and its Staehelin et al., 2018). As discussed by Staehelin et al. (2018) and Amendments (MPA). The current and projected states of the Gröbner et al. (2021), the Arosa/Davos total ozone time series ozone recovery have been recently discussed by Solomon et al. requires continuous efforts to homogenize the measurements (2016), Kuttippurath and Nair (2017), Pazmiño et al. (2018), across different instruments and periods to produce the required Kuttippurath et al. (2018), and Dhomse et al. (2018). Although level of uncertainty to be used for the assessment of ozone the recovery is already foreseen in the upcoming decades, a changes and observe the eventual recovery of the ozone layer. continuous evaluation of the current and future TCO and other species behavior remains very important to discover Ozone Multi-Sensor Reanalysis potential problems or apply additional measures to meet the The applicability of the Arosa/Davos TCO for the validation of declared aims of the MPA limitations. satellite sensors is evaluated using ozone multi-sensor reanalysis Usually, the analysis of the ozone recovery state is slow due to version 2 (hereafter MSR2, van der A, et al., 2015) product the necessity to carefully evaluate and homogenize different available for download from http://www.temis.nl/protocols/ sources of data (e.g., Ball et al., 2018; SPARC/IO3C/GAW O3global.html. The MSR2 data set contains long-term et al., 2019), while the continuous point measurements can be (1970–2019) total column ozone records constructed using the a good tracker of the current situation. However, further analysis chemistry-transport model and assimilation of all available is necessary to establish how the local point measurements (like satellite and ground-based observations with Brewer and the Arosa/Davos TCO time series) can be applied for a fast Dobson instruments. The result is represented as 6-hourly diagnosis of the ozone recovery progress on a global scale. This global ozone columns with 0.5 × 0.5 degrees horizontal investigation will be based on the reanalysis of the already resolution and forecast error fields and can be applied for case available model results