the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
17 Feb 2021
17 Feb 2021
Observation and modeling of high-7Be events in Northern Europe associated with the instability of the Arctic polar vortex in early 2003
- 1Department of Physics and Astronomy DIFA, Alma Mater Studiorum University of Bologna, via Irnerio 46, 40126 Bologna (BO), Italy
- 2National Institute of Aerospace, 100 Exploration Way, Hampton, VA 23666, USA
- 3Department of Physics, University of Cordoba, Rabanales Campus, 14071 Cordoba, Spain
- 4Finnish Meteorological Institute, P.O. Box 503, FI-00101, Helsinki, Finland
- 5Faculty of Veterinary Medicine, University of Belgrade, Bulevar oslobođenja 18, 11000 Belgrade, Serbia
- 6Institute of Meteorology, Faculty of Physics, University of Belgrade, Studentski trg 18, 11000 Belgrade, Serbia
- 7Department of Chemistry “G. Ciamician”, Alma Mater Studiorum University of Bologna, via Selmi 2, 40126 Bologna (BO), Italy
- 1Department of Physics and Astronomy DIFA, Alma Mater Studiorum University of Bologna, via Irnerio 46, 40126 Bologna (BO), Italy
- 2National Institute of Aerospace, 100 Exploration Way, Hampton, VA 23666, USA
- 3Department of Physics, University of Cordoba, Rabanales Campus, 14071 Cordoba, Spain
- 4Finnish Meteorological Institute, P.O. Box 503, FI-00101, Helsinki, Finland
- 5Faculty of Veterinary Medicine, University of Belgrade, Bulevar oslobođenja 18, 11000 Belgrade, Serbia
- 6Institute of Meteorology, Faculty of Physics, University of Belgrade, Studentski trg 18, 11000 Belgrade, Serbia
- 7Department of Chemistry “G. Ciamician”, Alma Mater Studiorum University of Bologna, via Selmi 2, 40126 Bologna (BO), Italy
Abstract. Events of very high concentrations of 7Be cosmogenic radionuclide have been recorded in the subpolar regions of Europe during the cold season. With an aim to investigate the mechanisms responsible for those peak 7Be events, and in particular to verify if they are associated with the fast descent of stratospheric air masses occurring during sudden stratospheric warming (SSWs), we analyse 7Be observations at six sampling sites in Scandinavia during January–March 2003 when very high 7Be concentrations were observed and the Arctic vortex was relatively unstable as a consequence of several SSWs. We use the GEOS-Chem chemistry and transport model driven by the MERRA-2 meteorological reanalysis to simulate tropospheric 7Be over Northern Europe. We show that the model reasonably reproduces the temporal evolution of surface 7Be concentrations observed at the six sampling sites. Our analysis of model simulations, surface 7Be observations, as well as atmospheric soundings of ozone and temperature indicates that the 7Be peak observed in late February 2003 (between 20 and 28 February 2003) at the six sampling sites in Scandinavia was associated with downward transport of stratospheric vortex air originated during SSW that occurred a few days before the peak (18–21 February 2003).
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Erika Brattich et al.
Status: final response (author comments only)
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RC1: 'Comment on acp-2020-1121', Anonymous Referee #2, 03 Mar 2021
The manuscript presents the results of an analysis of the atmospheric conditions, in particular, a stratospheric sudden warming (SSW) event in late February 2003, leading to an observed increase of 7Be concentration in the near-ground air. The qualitative analysis is comprehensive, and the association between the SSW event and the observed 7Be increase is convincing and worth publishing. However, the quantitative model contains a serious flaw and needs to be corrected before the manuscript becomes acceptable since the modelled 7Be concentrations cannot be trusted.
This reviewer was deeply surprised by the rough and inappropriate way the production of 7Be was modelled. The authors state that they used production estimated by Lal & Peters (1967, called LP67 here) for 1958 (was it based in Fig. 20 there?), which is unacceptable for several reasons:
i) the model of LP67 is greatly outdated as based on a very rough and approximate approach (an analytically estimated rate of nuclear “stars” in the atmosphere converted with the mean production yield of 7Be per star). This approach is quite uncertain as compared to modern full Monte-Carlo simulations of the cosmic-ray-induced atmospheric nucleonic cascade. Instead, the most recent and accurate production model by Poluianov et al. (2016, doi: 10.1002/2016JD025034), based on the GEANT-4 Monte-Carlo tool, is highly recommended for use. Comparing to the full Monte-Carlo model, the results by LP67 OVERESTIMATE the 7Be production by 30-50% (cf. Tab.3 of LP67 and Tab.1 of Poluianov et al., 2016).
ii) The level of solar activity and the corresponding modulation of cosmic rays (hence 7Be production) in 1958 was significantly higher than that in 2003, as the authors realize (see line 295). Accordingly, by applying the 1958 production to 2003, the authors UNDERESTIMATE the production.
iii) The authors ignore the change of the geomagnetic field strength, which was reduced by ~4% between 1958 and 2003. In this way, they also slightly UNDERESTIMATED 7Be production.
Altogether, the three errors work in opposite directions making the quantitative result unreliable.
The authors are requested to redo modelling using an appropriate 7Be production model. In case this would require too much work, the authors can make a compromise: the present LP67-based model results can be scaled to the correct global (or polar) production estimated by an appropriate model. However, this would be only an approximate temporal solution. In all further works, the authors are required to use a relevant production model. Before this flaw is corrected, the manuscript cannot be accepted for publication.Other minor comments and suggestions are listed below:
1) The title would sound more correctly if “high-7Be events” was replaced with “high 7Be concentration events”.
2) It would be worth to refer to previous works on full atmospheric dynamical models applied for studies of 7Be transport/deposition: the ECHAM-HAM5 (Heikkilä et al., ACP, 2008, doi: 10.5194/acp-8-2797-2008) and the GISS model (Usoskin et al., JGR, 2009, doi: 10.1029/2008JD011333)
3) Line 32: “stratospheric influence” on what?
4) Line 193: “previously archived restart files” – please specify what it is.
5) Line 218: NMSE does not provide an estimate of whether the difference is statistically significant or not. Z-test is recommended instead, which gives a measure of the statistical significance of the difference.
6) Line 223: the statistical significance of the correlation coefficient should be evaluated. With so short analyzed series, even a high correlation coefficient can be insignificant.
7) Line 273: the correlation of -0.32 for Ivalo implies a failure. This needs an explanation.
8) Line 296: reference to O’Brien (1979) is not appropriate here. A review by Potgieter (Liv. Rev. Sol. Phys., 2013, doi: 10.12942/lrsp-2013-3) is recommended instead.
9) Finland is not a part of Scandinavia. The analyzed region should be called Fennoscandia.
10) The term of the stratospheric fraction of 7Be needs to be strictly defined. Presently, it is presented as the ratio of stratospheric to global concentrations, which is vague. Are these concentrations mean global or polar regions, for what period (tropopause height varies in time). Please provide a formula.
11) Line 413: the model tends to underestimate 7Be concentrations – see the major concern above.
12) Figure 1b: for what periods were the 90% levels defined? The upper dotted line rises many questions: only two points lie above it, how many are overall? Why does the line lie between points? Dotted lines need to be marked as to which station they correspond to. It is recommended that the points are connected, otherwise, it is hardly possible to distinguish data from different sites.
13) Fig.4b looks strange. This reviewer would place a linear fit at a shallower slope. Can the authors specify how the fit was obtained?
14) Fig. 6. The authors are advised to use different colours for the lines. Also, the absence of a peak in Risoe data is worth more discussions. - RC2: 'Comment on acp-2020-1121', Anonymous Referee #3, 19 Mar 2021
Erika Brattich et al.
Data sets
Observation and modeling of high-7Be events in Northern Europe associated with the instability of the Arctic polar vortex in early 2003 Brattich, Erika; Liu, Hongyu; Zhang, Bo; Hernández-Ceballos, Miguel Angel; Paatero, Jussi; Sarvan, Darko; Djurdjevic, Vladimir; Tositti, Laura; Ajtić, Jelena https://doi.org/10.5281/zenodo.4117521
Erika Brattich et al.
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