Assessing stratospheric transport in the CMAM30 simulations using ACE-FTS measurements

Abstract

Abstract.Stratospheric transport in global circulation models and chemistry-climate models is an important component in simulating the recovery of the ozone layer as well as changes in the climate system. The Brewer-Dobson circulation is not well constrained by observations and further investigation is required to resolve uncertainties related to the mechanisms driving the circulation. This study has assessed the specified dynamics mode of the Canadian Middle Atmosphere Model (CMAM30) by compar-5 ing to the Atmospheric Chemistry Experiment Fourier Transform Spectrometer (ACE-FTS) profile measurements of CFC-11 (CCl 3 F), CFC-12 (CCl 2 F 2 ), and N 2 O. In the CMAM30 specified dynamics simulation, the meteorological fields are nudged using the ERA-Interim Reanalysis and a specified tracer was used for each species, with hemispherically-defined surface measurements used as the boundary condition. A comprehensive sampling technique along the line-of-sight of the ACE-FTS measurements has been employed to allow for direct comparisons between the simulated and measured tracer concentrations. 10The model consistently overpredicts tracer concentrations in the lower stratosphere, particularly in the Northern Hemisphere winter and spring seasons. The three mixing barriers investigated, including the polar vortex, the extratropical tropopause, and the tropical pipe, show that there are significant inconsistencies between the measurements and the simulations. In particular, the CMAM30 simulation exhibits too little isentropic mixing in the June-July-August season.

Model evaluation of short-lived climate forcers for the Arctic Monitoring and Assessment Programme: a multi-species, multi-model study

“…Evaluating models with ACE-FTS measurements also provides insight into models' transport and upper-tropospheric chemistry. As was shown in Kolonjari et al (2018), 3-hourly model output (rather than monthly mean output) is required for accurate comparisons to ACE-FTS data; thus, only models that provided output at this time frequency were compared to ACE-FTS measurements. The model output was sampled to match the times and locations of ACE-FTS measurements.…”

“…The model output was sampled to match the times and locations of ACE-FTS measurements. We used an updated version of the advanced method in Kolonjari et al (2018). Instead of taking the model output at the closest time to the ACE-FTS measurement time, the model output was linearly interpolated onto the ACE-FTS time.…”

“…This reduces the bias introduced by diurnal cycles, which can cause certain volume mixing ratios (VMRs; e.g., that of NO and NO 2 ) to vary significantly between model output times. As in Kolonjari et al (2018), the model output is also interpolated vertically in log pressure space and bilinearly in latitude and longitude to account for spatial variation between model grid points.…”

Water vapour and ozone in the upper troposphere – lower stratosphere: Global climatologies from three Canadian limb-viewing instruments

“…These climatologies provide information on the atmospheric environment and permit investigations into the distribution of trace gases and the patterns resulting from circulation and transport processes (e.g., Randel et al, 1998;Jones et al, 2012;Koo et al, 2017). Additional uses of climatologies include evaluating systematic differences between model or observational datasets (e.g., Eckstein et al, 2017;Kolonjari et al, 2018), evaluating trends (e.g., Deeter et al, 2018), and acting as a priori information for the retrieval of trace gas profiles from measurements (e.g., Vigouroux et al, 2008;Sofieva et al, 2014). In recent years, there has been a push to expand the database of climatologies focused on one of the most challenging regions of the atmosphere to study, the upper tropospherelower stratosphere (UTLS), in order to better constrain the role the UTLS plays in climate processes through the detailed characterization of the constituents of the region (SPARC-CCMVal, 2010;SPARC, 2017;Kunkel et al, 2018).…”

“…However, satellite instruments can still encounter difficulties making measurements in the UTLS because of, for example, the coarse vertical sensitivity of nadir-viewing instruments, which can prevent vertical UTLS features from being well resolved, or because of the long path lengths of limb-viewing instruments, which can smear out finer structures in UTLS gas distributions. Chemistry-climate models can aid investigations into climate forcers, such as greenhouse gases, by providing detailed simulations of chemical and transport processes; however, these must be evaluated against measurements to ensure their veracity (e.g., Pendlebury et al, 2015;Kolonjari et al, 2018).…”