Ground-based Ku-band microwave observations of ozone in the polar middle atmosphere

<p>Ground-based observations of 11.072 <span class="inline-formula">GHz</span> atmospheric ozone (<span class="inline-formula">O₃</span>) emission have been made using the Ny-Ålesund Ozone in the Mesosphere Instrument (NAOMI) at the UK Arctic Research Station (latitude 78<span class="inline-formula">^∘</span>55<span class="inline-formula">^′</span>0<span class="inline-formula">^′′</span> N, longitude 11<span class="inline-formula">^∘</span>55<span class="inline-formula">^′</span>59<span class="inline-formula">^′′</span> E), Spitsbergen. Seasonally averaged <span class="inline-formula">O₃</span> vertical profiles in the Arctic polar mesosphere–lower thermosphere region for night-time and twilight conditions in the period 15 August 2017 to 15 March 2020 have been retrieved over the altitude range 62–98 <span class="inline-formula">km</span>. NAOMI measurements are compared with corresponding, overlapping observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) satellite instrument. The NAOMI and SABER version 2.0 data are binned according to the SABER instrument 60 <span class="inline-formula">d</span> yaw cycles into nominal 3-month “winter” (15 December–15 March), “autumn” (15 August–15 November), and “summer” (15 April–15 July) periods. The NAOMI observations show the same year-to-year and seasonal variabilities as the SABER 9.6 <span class="inline-formula">µm</span> <span class="inline-formula">O₃</span> data. The winter night-time (solar zenith angle, SZA <span class="inline-formula">≥</span> 110<span class="inline-formula">^∘</span>) and twilight (75<span class="inline-formula">^∘</span> <span class="inline-formula">≤</span> SZA <span class="inline-formula">≤</span> 110<span class="inline-formula">^∘</span>) NAOMI and SABER 9.6 <span class="inline-formula">µm</span> <span class="inline-formula">O₃</span> volume mixing ratio (VMR) profiles agree to within the measurement uncertainties. However, for autumn twilight conditions the SABER 9.6 <span class="inline-formula">µm</span> <span class="inline-formula">O₃</span> secondary maximum VMR values are higher than NAOMI over altitudes 88–97 <span class="inline-formula">km</span> by 47 % and 59 %, respectively in 2017 and 2018. Comparing the two SABER channels which measure <span class="inline-formula">O₃</span> at different wavelengths and use different processing schemes, the 9.6 <span class="inline-formula">µm</span> <span class="inline-formula">O₃</span> autumn twilight VMR data for the three years 2017–2019 are higher than the corresponding 1.27 <span class="inline-formula">µm</span> measurements with the largest difference (58 %) in the 65–95 <span class="inline-formula">km</span> altitude range similar to the NAOMI observation. The SABER 9.6 <span class="inline-formula">µm</span> <span class="inline-formula">O₃</span> summer daytime (SZA <span class="inline-formula">&lt;</span> 75<span class="inline-formula">^∘</span>) mesospheric <span class="inline-formula">O₃</span> VMR is also consistently higher than the 1.27 <span class="inline-formula">µm</span> measurement, confirming previously reported differences between the SABER 9.6 <span class="inline-formula">µm</span> channel and measurements of mesospheric <span class="inline-formula">O₃</span> by other satellite instruments.</p>