Airborne limb-imaging measurements of temperature, HNO 3 , O 3 , ClONO 2 , H 2 O and CFC-12 during the Arctic winter 2015/16: characterization, in-situ validation and comparison to Aura/MLS

The Gimballed Limb Observer for Radiance Imaging of the Atmosphere (GLORIA) was operated on board the German High Altitude and LOng range (HALO) research aircraft during the PGS (POLSTRACC/GW-LCYCLE/SALSA) aircraft campaigns in the Arctic winter 2015/2016. Research flights were conducted from 17 December 2015 until 18 March 2016 between 80° W–30° E longitude and 25° N–87° N latitude. From the GLORIA infrared limb emission measurements, two dimensional cross sections of temperature, HNO 3 , O 3 , ClONO 2 , H 2 O and CFC-12 are retrieved. During 15 scientific flights of the PGS campaigns the GLORIA instrument measured more than 15 000 atmospheric profiles at high spectral resolution. Dependent on flight altitude and tropospheric cloud cover, the profiles retrieved from the measurements typically range between 5 and 14 km, and vertical resolutions between 400 m and 1000 m are achieved. The estimated total (random and systematic) 1σ errors are in the range of 1 to 2 K for temperature and 10 % to 20 % relative error for the discussed trace gases. Comparisons to in-situ instruments deployed on board HALO have been performed. Over all flights of this campaign the median differences and median absolute deviations between in-situ and GLORIA observations are −0.75 K ± 0.88 K for temperature, −0.03 ppbv ± 0.85 ppbv for HNO 3 , −3.5 ppbv ± 116.8 ppbv for O 3 , −15.4 pptv ± 102.8 pptv for ClONO 2 , −0.13 ppmv ± 0.63 ppmv for H 2 O and −19.8 pptv ± 46.9 pptv for CFC-12. These differences are mainly within the expected performances of the cross-compared instruments. Events with stronger deviations are explained by atmospheric variability and different sampling characteristics of the instruments. Additionally comparisons of GLORIA HNO 3 and O 3 with measurements of the Aura Microwave Limb Sounder (MLS) instrument show highly consistent structures in trace gas distributions and illustrate the potential of the high spectral resolution limb-imaging GLORIA observations for resolving narrow mesoscale structures in the UTLS.