Nice UTLS climatologies in tropopause relative coordinates

Abstract

This study presents upper troposphere – lower stratosphere (UTLS) water vapour and ozone climatologies generated from 14 years (June 2004 to May 2018) of measurements made by three Canadian limb-viewing satellite instruments: the Atmospheric Chemistry Experiment – Fourier Transform Spectrometer (ACE-FTS), the Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (MAESTRO), and the Optical Spectrograph and InfraRed Imaging System (OSIRIS; ozone only). This selection of instruments was chosen to explore the capability of these Canadian instruments in representing the UTLS, and to enable analysis of the impact of different measurement sampling patterns. The water vapour and ozone climatologies have been constructed using tropopause-relative potential temperature and equivalent latitude coordinates in an effort to best represent the distribution of these two gases in the UTLS, which is characterized by a high degree of dynamic and geophysical variability. Zonal-mean multiyear-mean climatologies are provided with 5° equivalent latitude and 10K potential temperature spacing, and have been constructed on a monthly, seasonal (3-month), and yearly basis. These climatologies are examined in-depth for two 3-month periods, December–January–February and June–July–August, and are compared to reference climatologies constructed from the Canadian Middle Atmosphere Model 39-year specified dynamics (CMAM39-SD) run, subsampled to the times and locations of the satellite measurements, in order to evaluate the consistency of water vapour and ozone between the datasets. Specifically, this method of using a subsampled model addresses the impact of each instrument’s measuring pattern, and allows for the quantification of the influence of different measurement patterns on multiyear climatologies. In turn, this permits a consistent evaluation of the measurements of these two gas species. For the water vapour climatologies produced, a less than 8 % overall difference was found between the climatologies generated from the two versions of ACE-FTS, while comparisons with the MAESTRO climatologies were found to yield 15–41 % overall differences, depending on the version of ACE-FTS and the season. When considering the ozone climatologies, those constructed from the two ACE-FTS 20 versions agreed to within 2 % overall, and the OSIRIS ozone climatologies agreed with these to within 10 %. The MAESTRO ozone climatologies were found to differ from ACE-FTS and OSIRIS by about 30–35 % for the former, and 25 % for the latter, albeit with regions of better agreement within the UTLS. Overall these findings indicate that this set of Canadian limb sounders provide consistent water vapour and ozone distributions in the UTLS.