Abstract
Abstract. CMAM30 is a 30-year data set extending from 1979 to 2010 that is generated using a version of the Canadian Middle Atmosphere Model (CMAM) in which the winds and temperatures are relaxed to the Interim Reanalysis product from the European Centre for Medium-Range Weather Forecasts (ERA-Interim). The data set has dynamical fields that are very close to the reanalysis below 1 hPa and chemical tracers that are self-consistent with respect to the model winds and temperature. The chemical tracers are expected to be close to actual observations. The data set is here compared to two satellite records – the Atmospheric Chemistry Experiment Fourier transform spectrometer and the Odin Optical Spectrograph and Infrared Imaging System – for the purpose of validating the temperature, ozone, water vapour and methane fields. Data from the Aura microwave limb sounder are also used for validation of the chemical processing in the polar vortex. It is found that the CMAM30 temperature is warmer by up to 5 K in the stratosphere, with a low bias in the mesosphere of ~ 5–15 K. Ozone is reasonable (±15 %), except near the tropopause globally and in the Southern Hemisphere winter polar vortex. Water vapour is consistently low by 10–20 %, with corresponding high methane of 10–20 %, except in the Southern Hemisphere polar vortex. Discrepancies in this region are shown to stem from the treatment of polar stratospheric cloud formation in the model.
Highlights
Reanalysis data sets such as those used in this study (the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis Interim product, or ERA-Interim) are the result of high-resolution models that assimilate past measurements to produce a consistent product that is a reliable representation of the atmospheric state over a given time period
Beta angles for Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) are typically less than 50◦ from the zenith, with 13 % of measurements taken at beta angles between 50◦ and 65◦
All observational data are interpolated onto the CMAM30 pressure levels except for the Optical Spectrograph and Infrared Imaging System (OSIRIS) temperatures derived from the O2 A-band
Summary
Reanalysis data sets such as those used in this study (the European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis Interim product, or ERA-Interim) are the result of high-resolution models that assimilate past measurements to produce a consistent product that is a reliable representation of the atmospheric state over a given time period. Other differences between the CMAM30 data set and observations may arise because while the large-scale dynamical fields are constrained to be close to ERA-Interim winds and temperatures, the chemical fields evolve according to the model chemistry, and small-scale dynamics and the physical parameterizations that mimic the subscale behaviour can affect even the large-scale dynamical fields. It is necessary to provide a more complete validation of the chemical and dynamical fields from the CMAM30 data set To accomplish this task, data from the Atmospheric Chemistry Experiment Fourier transform spectrometer (ACE-FTS) instrument on-board the ACE satellite, the Optical Spectrograph and Infrared Imaging System (OSIRIS) on-board the Odin satellite, and the microwave limb sounder instrument on-board the Aura satellite (Aura-MLS) are used. To avoid introducing spurious trends into the CMAM simulation, the global-average temperatures in the ERA-Interim data for levels at 5 hPa and above were modified before being used in the nudging following the method described in McLandress et al (2014). Denitrification or dehydration of the polar vortex over the winter season does not occur, with HNO3 and water vapour returning to the gas phase based on thermodynamic equilibrium
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
