Comparison of the CMAM30 data set with ACE-FTS and OSIRIS: polar regions

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.