Abstract
Abstract. This paper presents new atmospheric ozone concentration profiles retrieved from measurements made with two ground-based millimetre-wave radiometers in Kiruna, Sweden. The instruments are the Kiruna Microwave Radiometer (KIMRA) and the Millimeter wave Radiometer 2 (MIRA 2). The ozone concentration profiles are retrieved using an optimal estimation inversion technique, and they cover an altitude range of ∼ 16–54 km, with an altitude resolution of, at best, 8 km. The KIMRA and MIRA 2 measurements are compared to each other, to measurements from balloon-borne ozonesonde measurements at Sodankylä, Finland, and to measurements made by the Microwave Limb Sounder (MLS) aboard the Aura satellite. KIMRA has a correlation of 0.82, but shows a low bias, with respect to the ozonesonde data, and MIRA 2 shows a smaller magnitude low bias and a 0.98 correlation coefficient. Both radiometers are in general agreement with each other and with MLS data, showing high correlation coefficients, but there are differences between measurements that are not explained by random errors. An oscillatory bias with a peak of approximately ±1 ppmv is identified in the KIMRA ozone profiles over an altitude range of ∼ 18–35 km, and is believed to be due to baseline wave features that are present in the spectra. A time series analysis of KIMRA ozone for winters 2008–2013 shows the existence of a local wintertime minimum in the ozone profile above Kiruna. The measurements have been ongoing at Kiruna since 2002 and late 2012 for KIMRA and MIRA 2, respectively.
Highlights
Total column ozone (O3) has decreased by approximately 2.5 % over most of the planet during the 1980s and 1990s due to increased emissions of chlorofluorocarbons (CFCs) (WMO, 2014)
Kiruna Microwave Radiometer (KIMRA) is generally low-biased with respect to Millimeter wave Radiometer 2 (MIRA 2) except for a peak at 30 km and the largest negative value is a peak of −1.1 ppmv at 22.5 km
While there is good correlation, the results suggest that both KIMRA and MIRA 2 measurements of lower stratospheric O3 are likely affected by baseline errors that are not fully characterised by the error estimates here, KIMRA more so than MIRA 2
Summary
Total column ozone (O3) has decreased by approximately 2.5 % over most of the planet during the 1980s and 1990s due to increased emissions of chlorofluorocarbons (CFCs) (WMO, 2014). Thanks to the Montreal Protocol, and the ban on CFC emissions, total ozone columns have remained relatively unchanged since with recent indications of recovery (UNEP, 2015). Models suggest that these concentrations will recover to pre-1980 values by approximately 2060, but the projections are strongly dependant on future emissions of carbon dioxide (CO2), nitrous oxide (N2O), and methane (CH4) (WMO, 2014). Long-term (seasonal, yearly, and decadal) measurements of stratospheric O3 are an essential part of understanding how compositional changes in the atmosphere are linked to the future radiative balance of the planet. Calibrations with respect to ground-based instruments are needed in order to combine data from current and future satellites
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