The ozone profile records of a large number of limb and occultation satellite instruments are widely used to address several key questions in ozone research. Further progress in some domains depends on a more detailed understanding of these data sets, especially of their long-term stability and their mutual consistency. To this end, we made a systematic assessment of 14 limb and occultation sounders that, together, provide more than three decades of global ozone profile measurements. In particular, we considered the latest operational Level-2 records by SAGE II, SAGE III, HALOE, UARS MLS, Aura MLS, POAM II, POAM III, OSIRIS, SMR, GOMOS, MIPAS, SCIAMACHY, ACE-FTS and MAESTRO. Central to our work is a consistent and robust analysis of the comparisons against the ground-based ozonesonde and stratospheric ozone lidar networks. It allowed us to investigate, from the troposphere up to the stratopause, the following main aspects of satellite data quality: long-term stability, overall bias and short-term variability , together with their dependence on geophysical parameters and profile representation. In addition, it permitted us to quantify the overall consistency between the ozone profilers. Generally, we found that between 20 and 40 km the satellite ozone measurement biases are smaller than ±5 %, the short-term variabilities are less than 5-12 % and the drifts are at most ±5 % decade −1 (or even ±3 % decade −1 for a few records). The agreement with ground-based data degrades somewhat towards the stratopause and especially towards the tropopause where natural variability and low ozone abundances impede a more precise analysis. In part of the stratosphere a few records deviate from the preceding general conclusions ; we identified biases of 10 % and more (POAM II and SCIAMACHY), markedly higher single-profile variability (SMR and SCIAMACHY) and significant long-term drifts (SCIAMACHY, OSIRIS, HALOE and possibly GO-MOS and SMR as well). Furthermore, we reflected on the repercussions of our findings for the construction, analysis and interpretation of merged data records. Most notably, the discrepancies between several recent ozone profile trend assessments can be mostly explained by instrumental drift. This clearly demonstrates the need for systematic comprehensive multi-instrument comparison analyses.

Correlated magnetic noise from Schumann resonances threatens to contaminate the observation of a stochastic gravitational-wave background in interferometric detectors. In previous work, we reported on the first effort to eliminate global correlated noise from the Schumann resonances using Wiener filtering, demonstrating as much as a factor of two reduction in the coherence between magnetometers on different continents. In this work, we present results from dedicated magnetometer measurements at the Virgo and KAGRA sites, which are the first results for subtraction using data from gravitational-wave detector sites. We compare these measurements to a growing network of permanent magnetometer stations, including at the LIGO sites. We show the effect of mutual magnetometer attraction, arguing that magnetometers should be placed at least one meter from one another. In addition, for the first time, we show how dedicated measurements by magnetometers near to the interferometers can reduce coherence to a level consistent with uncorrelated noise, making a potential detection of a stochastic gravitational-wave background possible.

Abstract. The long-term evolution of total ozone column inside the Antarctic polar vortex is investigated over the 1980–2017 period. Trend analyses are performed using a multilinear regression (MLR) model based on various proxies for the evaluation of ozone interannual variability (heat flux, quasi-biennial oscillation, solar flux, Antarctic oscillation and aerosols). Annual total ozone column measurements corresponding to the mean monthly values inside the vortex in September and during the period of maximum ozone depletion from 15 September to 15 October are used. Total ozone columns from the Multi-Sensor Reanalysis version 2 (MSR-2) dataset and from a combined record based on TOMS and OMI satellite datasets with gaps filled by MSR-2 (1993–1995) are considered in the study. Ozone trends are computed by a piece-wise trend (PWT) proxy that includes two linear functions before and after the turnaround year in 2001 and a parabolic function to account for the saturation of the polar ozone destruction. In order to evaluate average total ozone within the vortex, two classification methods are used, based on the potential vorticity gradient as a function of equivalent latitude. The first standard one considers this gradient at a single isentropic level (475 or 550 K), while the second one uses a range of isentropic levels between 400 and 600 K. The regression model includes a new proxy (GRAD) linked to the gradient of potential vorticity as a function of equivalent latitude and representing the stability of the vortex during the studied month. The determination coefficient (R2) between observations and modelled values increases by ∼ 0.05 when this proxy is included in the MLR model. Highest R2 (0.92–0.95) and minimum residuals are obtained for the second classification method for both datasets and months. Trends in September over the 2001–2017 period are statistically significant at 2σ level with values ranging between 1.84 ± 1.03 and 2.83 ± 1.48 DU yr−1 depending on the methods and considered proxies. This result confirms the recent studies of Antarctic ozone healing during that month. Trends from 2001 are 2 to 3 times smaller than before the turnaround year, as expected from the response to the slowly ozone-depleting substances decrease in polar regions. For the first time, significant trends are found for the period of maximum ozone depletion. Estimated trends from 2001 for the 15 September–15 October period over 2001–2017 vary from 1.21 ± 0.83 to 1.96 DU ± 0.99 yr−1 and are significant at 2σ level. MLR analysis is also applied to the ozone mass deficit (OMD) metric for both periods, considering a threshold at 220 DU and total ozone columns south of 60∘ S. Significant trend values are observed for all cases and periods. A decrease of OMD of 0.86 ± 0.36 and 0.65 ± 0.33 Mt yr−1 since 2001 is observed in September and 15 September–15 October, respectively. Ozone recovery is also confirmed by a steady decrease of the relative area of total ozone values lower than 175 DU within the vortex in the 15 September–15 October period since 2010 and a delay in the occurrence of ozone levels below 125 DU since 2005.